Molybdenum trioxide

Repeated dose toxicity: oral

Administrative data

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2010-10-07 to 2011-10-19

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

Guideline study (OECD 408), conducted and reported in accordance with GLP principles. The study includes additional parameters, such as analysis of oestrous cycles and sperm, as per guideline OECD 416.

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

reference to other study

Reference

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2010-07-29 to 2010-08-26

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Remarks:

This study was conducted as a dose-range-finding- and toxicokinetic study for a subsequent repeat-dose 90-day study. Although there were no specific testing guidelines stated for this study, the study design in accordance with general regulatory guidelines for toxicity studies.

Reason / purpose for cross-reference:

reference to other study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

no guideline required

Principles of method if other than guideline:

This study was conducted as a dose-range-finding- and toxicokinetic study for a subsequent repeat-dose 90-day study. Although there were no specific testing guidelines stated for this study, the study design was in accordance with general regulatory guidelines for toxicity studies. To investigate possible differences in uptake and to select an appropriate type of administration for the 90-day study (via gavage or via food), both types were used in separate groups in this 28-day dose-range-finding study. For technical reasons (IUCLID), there are two separate study records for administration via gavage and via food.

GLP compliance:

no

Remarks:

Basic GLP rules were followed without Quality Control and Auditing Procedures

Limit test:

no

Species:

rat

Strain:

other: Crl: CD(SD)

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: approximately 9 weeks old
- Weight at study initiation (mean weight): males: 319 g (range 280 to 360 g); females: 208 g (range: 184 to 233 g)
- Housing: animals were individually housed in elevated, stainless steel, wire mesh cages during the study. An enrichment device (e.g., a Nylabone®) was provided in each animal’s cage at all times. Analysis undertaken showed that the enrichment device Nylabone®contain less than 1 ng Mo/g.
- Diet (ad libitum): Certified Rodent Diet, No. 2016C (pellets) (Harlan Teklad, Madison, WI)
- Water (ad libitum): water (New Jersey-American Water Company, Cherry Hill, New Jersey) was available via an automated watering system.
- Acclimation period: 2 weeks; all animals were examined during the stabilisation period to confirm suitability for study

Currently acceptable practices of good animal husbandry were followed e.g., Guide for the Care and Use of Laboratory Animals; National Academy Press, 1996.

ENVIRONMENTAL CONDITIONS
- Temperature: 20 to 25°C
- Relative humidity: 42 to 63%
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

oral: gavage

Vehicle:

water

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:
- Group 1: an appropriate amount of distilled water (vehicle) was measured into a graduated cylinder from which the necessary daily aliquots were then removed and transferred to appropriately labelled dosing containers.
- Groups 2 to 4: the appropriate amount of sodium molybdate dihydrate was weighed and transferred to an appropriately sized graduated cylinder. The final volume was reached with the addition of distilled water (vehicle). The cylinder was capped and inverted several times to mix. Once a clear solution was obtained, the appropriate aliquots were transferred to appropriately labeled dosing containers.
Fresh dose formulations were prepared once, at least one week prior to the first day of dosing. Aliquots and storage containers were stored refrigerated when not in use.

VEHICLE
Tap water supplied by New Jersey-American Water Company, Cherry Hill, New Jersey, was distilled at the Testing Facility.
- Lot No.: DDW 0008 and DDW 0009
- Storage: room temperature

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analyses to determine homogeneity and concentration of the test substance with carriers under the conditions of this study were conducted.
All dose formulation samples were analysed using an appropriate validated method for molybdenum, copper, zinc and manganese.

- HOMOGENEITY AND DOSE CONFIRMATION ANALYSIS
Samples of water formulations (~15 mL in duplicate) for Groups 1 to 4 were collected from each prepared batch after preparation. Samples of water formulations (~15 mL in duplicate) for Groups 1 to 4 were collected from each prepared batch at weekly intervals during the 4 weeks of dosing. Dose formulation samples were stored refrigerated.

- STABILITY
It was confirmed that the dose formulations were stable for at least 5 weeks when prepared and stored at room temperature in low humidity.

Results:
Analysis of dose formulatios prior to initiating of dosing confirmed that the preparation procedures used for this study produced dose formulations of appropriate concentration of molybdenum (Mo).Mean analytical concentrations, expressed as concentration and percent of nominal (desired) concentrations were as follows:

Nominal Mo concentration:
Group 1: 0 mg/mL
Group 2: 0.8 mg/mL
Group 3: 4.0 mg/mL
Group 4: 4.0 mg/mL

Analytical Mo. concentration:
Group 1: <0.0001 mg/mL
Group 2: 0.79 mg/mL
Group 3: 3.91 mg/mL
Group 4: 3.86 mg/mL

Analytical Mo concentration (% of nominal):
Group 1: not applicable
Group 2: 99%
Group 3: 98%
Group 4: 97%

Similar acceptable results were found with the dose formulations samples collected weekly during the conduct of the study and assayed after the completion of the dosing.

Duration of treatment / exposure:

28 days

Frequency of treatment:

Groups 1 to 3: once daily; Group 4: twice daily with the second dose 7-8 hours after the first dose (except on Day 28 when the second dose was after the 8 hours post-dose blood sample) and each dose was 2.5 mL/kg of the 4 mg Mo/mL dose solution.

Dose / conc.:

10 mg/kg bw/day (nominal)

Remarks:

equivalent to 4 mg Mo/kg bw/day

Dose / conc.:

50 mg/kg bw/day (nominal)

Remarks:

equivalent to 20 mg Mo/kg bw/day

Dose / conc.:

50 other: mg/kgbw/day, given as two doses per day of 25 mg/kgbw, each

Remarks:

Equivalent to 20 mg Mo/kg bw/day. Given as 2 doses per day (2 x 25 mg/kgbw of the test item, equivalent to 2x10 mg Mo/kg bw).

No. of animals per sex per dose:

Group 1 (0 mg Mo/kg bw/day): 5 males / 5 females
Group 2 (4 mg Mo/kg bw/day): 5 males / 5 females
Group 3 (20 mg Mo/kg bw/day): 5 males / 5 females
Group 4 (2 x 10 mg Mo/kg bw/day): 5 males / 5 females

Control animals:

yes, concurrent vehicle

Details on study design:

Dose selection rationale:
- In a study by Pandey and Singh, 2002*, 50 mg/kg bw sodium molybdate was possibly toxic to the testes and body weight when given as an oral bolus dose (probably gavage), 5 days/week for 60 days. In the same study, 30 mg/kg was a LOAEL and 10 mg/kg bw was possibly a NOAEL or might be a LOAEL.
- In a study by Cox, et al, (1960)*, molybdenum was given as sodium molybdate in two synthetic diets at 500 ppm (about 50 mg/kg bw) for 5 to 8 weeks. This proved to be toxic with diarrhoea and decreased weight gain, and with high liver molybdenum levels and no effect on liver copper stores.

Thus, a dose of 50 mg/kg thus seemed to be a dose level which should be toxic but might be too high if there is excessive weight loss. A dose of 10 mg/kg was considered to be a NOAEL but may be toxic to the testes.

*References:
- Pandey, R. and Singh, S.P. 2002. Effects of molybdenum on fertility of male rats. BioMetals Mar.15 (1): 65-72.
- Cox, D.H., Davis, G.K., Shriley, R.L. and Jack, F.H. 1960. Influence of excess dietary molybdenum on rat and calf liver and heart enzymes. J. Nutrition 70: 63-68.

Positive control:

None

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily (once in the morning and once in the afternoon)
- Cage side observations checked: mortality and signs of severe toxic or pharmacologic effects.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: once pretest and twice weekly during the study period; examinations included observations of general condition, skin and fur, eyes, nose, oral cavity, abdomen and external genitalia as well as evaluations of respiration.

BODY WEIGHT: Yes
- Time schedule for examinations: twice pretest, twice weekly during treatment and terminally (after fasting). Terminal, fasted body weights were obtained just prior to necropsy.

FOOD CONSUMPTION: Yes
Feed was available without restriction 7 days/week. Animals were presented with full feeders of known weight. After 2, 3, 4 or 5 days, feeders were reweighed and the resulting weight was subtracted from the full feeder weight to obtain the grams consumed per animal over the 2, 3, 4 or 5-day period. Food consumption was measured (weighed) once pretest and twice weekly during treatment.
Calculation: Food consumption (g/day) = grams of food consumed ÷ 2, 3, 4 or 5 days

TEST SUBSTANCE INTAKE: Not applicable

FOOD CONVERSION EFFICIENCY: Yes
Calculated from weekly body weight and food consumption data:
Feed Efficiency = (body weight gain (g)/food consumption (g/interval)) x 100

WATER CONSUMPTION AND COMPOUND INTAKE: No

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: No

CLINICAL CHEMISTRY: No

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

TOXICOKINETICS: Yes
Blood samples were obtained for the determination of serum concentrations of molybdenum.
- Collection times and number of animals: on Day 28, blood samples for molybdenum determinations were obtained from 5 animals/sex/group/time point from each group predose and 1, 2, 4 and 8 hours post-dose for Groups 1 to 3; predose and 1, 2, 4 and 8 hours post-dose the first dose of the day for Group 4.
- Collection procedures: approximately 0.5 mL (males) and 0.4 mL (females) of whole blood was obtained from each unanaesthetized animal via the
jugular vein. Animals were not fasted prior to blood collection. Blood was collected into tubes containing no additive, in an upright position and allowed to clot for at least 30 minutes for serum separation. Serum was harvested within 2 hours after collection of each blood sample.
- Storage and disposition of samples: serum was separated by centrifugation (for 10 minutes at approximately 3000 rpm, at approximately 2 to 8°C).
Approximately 0.2 mL of serum was transferred into a single cryotube. All sample tubes were stored frozen at nominal -80°C (±10°C) until analysed or for at least 2 months after the issuance of the final bioanalytical report.
- Analysis/Reporting: serum samples were analyzed with a validated inductively coupled plasma mass spectrometry (ICP-MS) method.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
Necropsy was performed on 5 animals/sex/group after animals had been treated for 28 days. Animals were fasted overnight prior to necropsy.
Exsanguination following carbon dioxide inhalation.
Complete macroscopic examinations were performed on all animals. The macroscopic examination included examination of the external surface and all orifices; the external surfaces of the brain and spinal cord; the organs and tissues of the cranial, thoracic, abdominal and pelvic cavities and neck; and the remainder of the carcass for the presence of macroscopic morphologic abnormalities.

ORGAN WEIGHTS:
The following organs were weighed for all animals at the scheduled sacrifice interval: brain, epididymides, kidneys, liver, spleen and testes.
Prior to weighing, the organs were carefully dissected and properly trimmed to remove adipose and other contiguous tissues in a uniform manner.
Organs were weighed as soon as possible after dissection in order to avoid drying. Paired organs were weighed together.

HISTOPATHOLOGY: Yes
The following tissues were obtained at the scheduled sacrifice interval and preserved for all animals: adrenal glands, aorta (thoracic), bone marrow smear (femur), bone (sternum, distal femur), bone marrow (sternum, distal femur), brain, cecum, colon, epididymides, oesophagus, eyes, Harderian gland, heart, kidneys, lacrimal glands, liver, lungs (with mainstem bronchi), lymph nodes (mesenteric, mediastinal), mammary gland, nerve (sciatic), optic nerve, ovaries, pancreas, pituitary gland, prostate gland, rectum, salivary glands (submandibular), seminal vesicles, skeletal muscle (rectus femoris), skin (dorsal – base of tail), small intestine (duodenum, ileum, jejunum and Peyer’s patches/GALT), spinal cord (cervical), spleen, stomach, testes, thymus, thyroid (with parathyroid), trachea, urinary bladder, uterus (body/horns) with cervix, vagina and tissues with macroscopic findings including tissue masses

In addition, slides of the following tissues were prepared and examined microscopically for all animals: epididymides, kidneys, testes and tissues with macroscopic findings including tissue masses. The tissues were selected on the basis of the results of previous studies of molybdenum in the scientific literature. Any abnormalities not noted during macroscopic examinations which were seen during histology processing were recorded.

Statistics:

The following parameters were analysed statistically: body weight, body weight change from interval to interval, cumulative body weight change from baseline, food consumption and organ weights.
Test substance-treated groups were compared to the control using the following procedures: Bartlett's test for variance homogeneity, F1 approximate test
for monotonicity, Williams' test, Dunnett's test, H1 approximate test for monotonicity, Shirley's test and Steel's test.
For all parameters, significant differences between control and test substance-treated groups were expressed at the 5% (p<0.05), 1% (p<0.01) or the 0.1% (p<0.001) level.
The following major computer/software systems were utilized at Huntingdon Life Sciences, East Millstone, New Jersey: Liberate Reporting System, Microsoft Word and/or Excel, Quasar, REES Scientific Environmental Monitoring System, WinNonlin Professional and Xybion Path/Tox System.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

effects observed, treatment-related

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
All animals survived until their scheduled sacrifice.
There were no test substance-related clinical signs in any of the test animals.

BODY WEIGHT AND WEIGHT GAIN
There were no test substance-related effects on body weights in any of the orally gavaged test groups of animals.

FOOD CONSUMPTION AND FOOD CONVERSION EFFICIENCY:
There were no test substance-related effects on food consumption in any of the orally gavaged test groups of animals (although there were occasionally seen decreases in food conversion efficiency). There was a statistically significant increase in food consumption at 2 intervals in the 2 x 10 mg Mo/kg/day gavage dosed females but this difference was not considered treatment-related.

ORGAN WEIGHTS
There were no test substance-related effects on organ weights in any of the orally gavaged test groups of animals.

GROSS PATHOLOGY
There were no test article related macroscopic findings.

HISTOPATHOLOGY: NON-NEOPLASTIC
There were no microscopic findings related to administration of sodium molybdate dIhydrate by gavage dosing:

TOXICOKINETICS:
Serum concentrations of molybdenum were quantifiable in all collected serum samples following gavage administrations of vehicle and sodium molybdate dihydrate for 28 consecutive days.
Values of the selected toxicokinetic parameters for molybdenum are summarized in Table 1 (see "Any other information on results incl. tables" below).
- AUC0-8h and Cmax values of molybdenum for male and female rats increased proportionately with increasing oral gavage doses of molybdenum.
- results demonstrate a linear relationship between the administered dose of molybdenum and these two toxicokinetic parameters.
- slight gender differences in exposure to molybdenum were observed after oral gavage administration of sodium molybdate dihydrate at the examined dose levels. The gender ratios (males/females) for molybdenum ranged from 1.15 to 1.95 for AUC0-8h values and 1.16 to 1.59 for Cmax
values.
- molybdenum systemic exposures (assessed by extrapolated AUC0-24h) at 4 and 20 mg Mo/kg bw/day after dietary administration (please refer to Section 7.5.1 Repeated dose toxicity: oral: s_Hoffman_2011_28 d_dietary administration) were approximately comparable to those after gavage administrations. The dietary/gavage ratios of the AUC0-24h values for males were 0.67 and 0.57, and for females were 1.02 and 1.26 after administration of sodium molybdate dihydrate at 4 and 20 mg Mo/kg bw/day, respectively.

Dose descriptor:

NOAEL

Effect level:

50 mg/kg bw/day (actual dose received)

Based on:

test mat.

Remarks:

equivalent to 20 mg Mo/kg bw/day

Sex:

male/female

Basis for effect level:

other: see 'Remark'

Remarks on result:

other: see 'Remarks'

Remarks:

Oral dosing of rats with 4 or 20 mg/kg/day of Mo (molybdenum in sodium molybdate dihydrate) via gavage for 28 days of doses resulted in no systemic effects and in particular, no adverse effects observed at postmortem examination or in the histopathology of the kidneys, testes or epididymides.

Remarks on result:

other: see 'Remarks'

Remarks:

Molybdenum systemic exposures at 4 and 20 mg Mo/kg bw/day via gavage were approximately comparable to those after dietary administrations (please refer to Section 7.5.1 Repeated dose toxicity: oral: s_Hoffman_2011_28 d_dietary_administration) in male and female rats.The high dose of 20 mg/kg/day of Mo, when dosed for 28 consecutive days, was very well tolerated and was considered to be a no observed adverse effect level (NOAEL).

Critical effects observed:

not specified

Table 1: Values of Serum Toxicokinetic Parameters of Molybdenum in Male and Female Rats following Oral Gavage of Sodium Molybdate Dihydrate

Route of Administration	Sex	Group	Molybdenum Dose (mg Mo/kg/day)	AUC0-8h (ng * h/mL)	AUC0-24h (ng * h/mL)^c	Cmax (ng/mL)
Oral gavage	Male	1	0^a	203	587	28.7
		2	4	31400	47100	7020
		3	20	172000	288000	30300
		4	2 x 10^b	110000	184000	20400
	Female	1	0^a	177	509	24.8
		2	4	19000	25500	5290
		3	20	88400	127000	22900
		4	2 x 10^b	62800	98800	12800

a: Group 1 animals were orally (gavage) administered vehicle (distilled water) but received approximately 0.08mg Mo/kg bw/day from the diet.

b: Group 4 animals were orally (gavage) administered twice per day of sodium molybdate dihydrate with the second dose 7-8 hours after the first dose, except on Day 28 (blood collection day) when the second dose was administered after the 8 hours post-dose blood sample.

c:  AUC_0-24h values were assigned 5-folds of AUC0-8h

Conclusions:

NOAEL = 20 mg/kg/day of Mo

Oral dosing of rats with 4 or 20 mg/kg/day of Mo (molybdenum in sodium molybdate dihydrate) via the oral gavage (once per day or twice a day (2x 10 mg/kg)) for 28 days of doses resulted in no systemic effects and in particular, no adverse effects observed at postmortem examination or in the histopathology of the kidneys, testes or epididymides. There were quantifiable and dose-related levels of serum Mo in animals dosed via gavage.
Molybdenum systemic exposures at 4 and 20 mg Mo/kg bw/day after dietary administration (please refer to Section 7.5.1 Repeated dose toxicity: oral: s_Hoffman_2011_28 d_dietary administration) were approximately comparable to those after gavage administrations in male and female rats.
The high dose of 20 mg/kg/day of Mo, when dosed for 28 consecutive days, was very well tolerated and was considered to be a no observed adverse effect level (NOAEL).

Cross-reference 2

Reason / purpose for cross-reference:

reference to other study

Reference

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2010-07-29 to 2010-08-26

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

This study was conducted as a dose-range-finding- and toxicokinetic study for a subsequent repeat-dose 90-day study. Although there were no specific testing guidelines stated for this study, the study design was in accordance with general regulatory guidelines for toxicity studies.

Reason / purpose for cross-reference:

reference to other study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

no guideline required

Principles of method if other than guideline:

This study was conducted as a dose-range-finding- and toxicokinetic study for a subsequent repeat-dose 90-day study. Although there were no specific testing guidelines stated for this study, the study design was in accordance with general regulatory guidelines for toxicity studies. To investigate possible differences in uptake and to select an appropriate type of administration for the 90-day study (via gavage or via food), both types were used in separate groups in this 28-day dose-range-finding study. For technical reasons (IUCLID), there are two separate study records for administration via gavage and via food.

GLP compliance:

no

Remarks:

Basic GLP rules were followed without Quality Control and Auditing Procedures

Limit test:

no

Species:

rat

Strain:

other: Crl: CD(SD)

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: approximately 9 weeks old
- Weight at study initiation (mean weight): males: 319 g (range 280 to 360 g); females: 208 g (range: 184 to 233 g)
- Housing: animals were individually housed in elevated, stainless steel, wire mesh cages during the study. An enrichment device (e.g., a Nylabone®) was provided in each animal’s cage at all times. Analysis undertaken showed that the enrichment device Nylabone®contain less than 1 ng Mo/g.
- Diet (ad libitum): Certified Rodent Diet, No. 2016C (pellets) (Harlan Teklad, Madison, WI)
- Water (ad libitum): water (New Jersey-American Water Company, Cherry Hill, New Jersey) was available via an automated watering system.
- Acclimation period: 2 weeks; all animals were examined during the stabilisation period to confirm suitability for study

Currently acceptable practices of good animal husbandry were followed e.g., Guide for the Care and Use of Laboratory Animals; National Academy Press, 1996.

ENVIRONMENTAL CONDITIONS
- Temperature: 20 to 25°C
- Relative humidity: 42 to 63%
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

oral: feed

Vehicle:

other: Certified Rodent diet, No. 2016C

Details on oral exposure:

DIET PREPARATION
- Mixing appropriate amounts with Certified Rodent Diet, No. 2016C (Harlan Teklad, Madison, Wisconsin)
- Lot/batch no.: 061410 MA, 050310 MB and 050310 MA
- Storage: room temperature
The background concentration of Mo in the diet was negligible compared to the amounts intentionally added to the diets in the treatment groups.
- Preparation:
Group 1: None required. Certified Rodent Diet No. 2016C (meal) was used as needed.
Groups 2 to 3: the specified amount of sodium molybdate dihydrate was weighed in the specific (previously tared and labelled) transfer container for each dose group.
Diets were mixed in ascending order of concentrations as follows:
Preliminary Diet Preparation: the corresponding amount of Certified Rodent Diet No. 2016C (meal) was weighed into an appropriately labelled dose group bucket.
Premix: approximately 1.0 kg of the untreated diet from the dose group bucket being prepared was removed and placed into the bowl of a Hobart mixer. The test substance was poured onto the layer of feed in the mixer bowl. The test substance container was rinsed with several grams of diet and added to the mixer bowl. Approximately 100-400 g of untreated diet was added to the mixer bowl. Using a paddle blade, the mixer was run on speed 1 for approximately 15 minutes.
General Mix: approximately one half of the remaining diet from the dose group bucket being prepared was poured into the PKTwinshell mixer. The premix from the Hobart mixer was added to the PK-Twinshell and the Hobart bowl and paddle blade were rinsed with several grams of untreated diet. All remaining diet was poured into the PK-Twinshell mixer and the mixer was run for approximately 30 minutes.
The mixture was prepared once, at least one week prior to the first day of dosing, and stored at room temperature in low humidity when not in use.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analyses to determine homogeneity and concentration of the test substance with carriers under the conditions of this study were conducted.
All dose formulation samples were analysed using an appropriate validated method for molybdenum, copper, zinc and manganese.

- HOMOGENEITY AND DOSE CONFIRMATION ANALYSIS
Samples of diet formulations (~50 g in duplicate from top, middle and bottom) for Groups 1 to 3 were collected from each prepared batch after preparation.
Samples of diet formulations (~50 g in duplicate) for Groups 1 to 3 were collected from each prepared batch at weekly intervals during the 4 weeks of dosing.
Dose formulation samples were stored at room temperature in low humidity.

- STABILITY
It was confirmed that the dose formulations were stable for at least 5 weeks when prepared and stored at room temperature in low humidity.

Results:
Analysis of mixes, prepared and assayed prior to initiating of dosing, confirmed that the preparation procedures used for this study produced diets of appropriate concentration of molybdenum (Mo) and that homogeneous dietary mixtures were administered. Mean analytical concentrations, expressed as concentration and percent of nominal (desired) concentrations were as follows:

Nominal Mo concentration:
Group 1: 0 ppm
Group 2: 50 ppm
Group 3: 250 ppm

Analytical Mo. concentration:
Group 1: 0.86 ppm
Group 2: 49 ppm
Group 3: 253 ppm

Analytical Mo concentration (% of nominal):
Group 1: not applicable
Group 2: 98%
Group 3: 101%

Similar acceptable results were found with the diet preparations samples collected weekly during the conduct of the study and assayed after the completion of the dosing.

Duration of treatment / exposure:

28 days

Frequency of treatment:

ad libitum

Dose / conc.:

10 mg/kg bw/day (nominal)

Remarks:

Equivalent to 4 mg Mo/kg bw/day. Actual intake was generally comparable to target dose levels throughout the study, with some deviation towards the end as a result of increasing bodyweight without proportional increases in food consumption (normal for young/growing rats).

Dose / conc.:

50 mg/kg bw/day (nominal)

Remarks:

Equivalent to 20 mg Mo/kg bw/day. Actual intake was generally comparable to target dose levels throughout the study, with some deviation towards the end as a result of increasing bodyweight without proportional increases in food consumption (normal for young/growing rats).

No. of animals per sex per dose:

Group 5 (0 mg Mo/kg bw): 5 males / 5 females
Group 6 (4 mg Mo/kg bw): 5 males / 5 females
Group 7 (20 mg Mo/kg bw): 5 males / 5 females

Control animals:

yes, plain diet

Details on study design:

Dose selection rationale:
- In a study by Pandey and Singh, 2002*, 50 mg/kg bw sodium molybdate was possibly toxic to the testes and body weight when given as an oral bolus dose (probably gavage), 5 days/week for 60 days. In the same study, 30 mg/kg was a LOAEL and 10 mg/kg bw was possibly a NOAEL or might be a LOAEL.
- In a study by Cox, et al, (1960)*, molybdenum was given as sodium molybdate in two synthetic diets at 500 ppm (about 50 mg/kg bw) for 5 to 8 weeks. This proved to be toxic with diarrhoea and decreased weight gain, and with high liver molybdenum levels and no effect on liver copper stores.

Thus, a dose of 50 mg/kg thus seemed to be a dose level which should be toxic but might be too high if there is excessive weight loss. A dose of 10 mg/kg was considered to be a NOAEL but may be toxic to the testes.


*References:
- Pandey, R. and Singh, S.P. 2002. Effects of molybdenum on fertility of male rats. BioMetals Mar.15 (1): 65-72.
- Cox, D.H., Davis, G.K., Shriley, R.L. and Jack, F.H. 1960. Influence of excess dietary molybdenum on rat and calf liver and heart enzymes. J. Nutrition 70: 63-68.

Positive control:

None

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily (once in the morning and once in the afternoon)
- Cage side observations checked: mortality and signs of severe toxic or pharmacologic effects.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: once pretest and twice weekly during the study period; examinations included observations of general condition, skin and fur, eyes, nose, oral cavity, abdomen and external genitalia as well as evaluations of respiration.

BODY WEIGHT: Yes
- Time schedule for examinations: twice pretest, twice weekly during treatment and terminally (after fasting). Terminal, fasted body weights were obtained just prior to necropsy.

FOOD CONSUMPTION: Yes
Feed was available without restriction 7 days/week. Animals were presented with full feeders of known weight. After 2, 3, 4 or 5 days, feeders were reweighed and the resulting weight was subtracted from the full feeder weight to obtain the grams consumed per animal over the 2, 3, 4 or 5-day period. Food consumption was measured (weighed) once pretest and twice weekly during treatment.
Calculation: Food consumption (g/day) = grams of food consumed ÷ 2, 3, 4 or 5 days

TEST SUBSTANCE INTAKE: Yes
Calculated from food consumption data and based on nominal dietary concentrations:
Test substance intake (mg Mo/kg/day) = food consumption/body weight (g/kg/day) x dietary concentration (mg Mo/g of diet)
The current body weight was used in the calculation

FOOD CONVERSION EFFICIENCY: Yes
Calculated from weekly body weight and food consumption data:
Feed Efficiency = (body weight gain (g)/food consumption (g/interval)) x 100

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: No

CLINICAL CHEMISTRY: No

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

TOXICOKINETICS: Yes
Blood samples were obtained for the determination of serum concentrations of molybdenum.
- Collection times and number of animals: on Day 27, blood samples for molybdenum determinations were obtained from 5 animals/sex/group/time point from each group at approximately (± 75 minutes) 0900, 1100, 1300, 1500 and 1700 hours.
- Collection procedures: approximately 0.5 mL (males) and 0.4 mL (females) of whole blood was obtained from each unanaesthetized animal via the jugular vein. Animals were not fasted prior to blood collection. Blood was collected into tubes containing no additive, in an upright position and allowed to clot for at least 30 minutes for serum separation. Serum was harvested within 2 hours after collection of each blood sample.
- Storage and disposition of samples: serum was separated by centrifugation (for 10 minutes at approximately 3000 rpm, at approximately 2 to 8°C).
Approximately 0.2 mL of serum was transferred into a single cryotube. All sample tubes were stored frozen at nominal -80°C (±10°C) until analysed or for at least 2 months after the issuance of the final bioanalytical report.
- Analysis/Reporting: serum samples were analysed with a validated inductively coupled plasma mass spectrometry (ICP-MS) method.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
Necropsy was performed on 5 animals/sex/group after animals had been treated for 28 days. Animals were fasted overnight prior to necropsy.
Exsanguination following carbon dioxide inhalation.
Complete macroscopic examinations were performed on all animals. The macroscopic examination included examination of the external surface and all orifices; the external surfaces of the brain and spinal cord; the organs and tissues of the cranial, thoracic, abdominal and pelvic cavities and neck; and the remainder of the carcass for the presence of macroscopic morphologic abnormalities.

ORGAN WEIGHTS:
The following organs were weighed for all animals at the scheduled sacrifice interval: brain, epididymides, kidneys, liver, spleen and testes.
Prior to weighing, the organs were carefully dissected and properly trimmed to remove adipose and other contiguous tissues in a uniform manner. Organs were weighed as soon as possible after dissection in order to avoid drying. Paired organs were weighed together.

HISTOPATHOLOGY: Yes
The following tissues were obtained at the scheduled sacrifice interval and preserved for all animals: adrenal glands, aorta (thoracic), bone marrow smear (femur), bone (sternum, distal femur), bone marrow (sternum, distal femur), brain, cecum, colon, epididymides, esophagus, eyes, Harderian gland, heart, kidneys, lacrimal glands, liver, lungs (with mainstem bronchi), lymph nodes (mesenteric, mediastinal), mammary gland, nerve (sciatic), optic nerve, ovaries, pancreas, pituitary gland, prostate gland, rectum, salivary glands (submandibular), seminal vesicles, skeletal muscle (rectus femoris), skin (dorsal – base of tail), small intestine (duodenum, ileum, jejunum and Peyer’s patches/GALT), spinal cord (cervical), spleen, stomach, testes, thymus, thyroid (with parathyroid), trachea, urinary bladder, uterus (body/horns) with cervix, vagina and tissues with macroscopic findings including tissue masses

In addition, slides of the following tissues were prepared and examined microscopically for all animals: epididymides, kidneys, testes and tissues with macroscopic findings including tissue masses. The tissues were selected on the basis of the results of previous studies of molybdenum in the scientific literature. Any abnormalities not noted during macroscopic examinations which were seen during histology processing were recorded.

Statistics:

The following parameters were analysed statistically: body weight, body weight change from interval to interval, cumulative body weight change from baseline, food consumption and organ weights.
Test substance-treated groups were compared to the control using the following procedures: Bartlett's test for variance homogeneity, F1 approximate test
for monotonicity, Williams' test, Dunnett's test, H1 approximate test for monotonicity, Shirley's test and Steel's test.
For all parameters, significant differences between control and test substance-treated groups were expressed at the 5% (p<0.05), 1% (p<0.01) or the 0.1% (p<0.001) level.
The following major computer/software systems were utilized at Huntingdon Life Sciences, East Millstone, New Jersey: Liberate Reporting System, Microsoft Word and/or Excel, Quasar, REES Scientific Environmental Monitoring System, WinNonlin Professional and Xybion Path/Tox System.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

not adverse

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

effects observed, treatment-related

Description (incidence and severity):

due to palatability

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
All animals survived until their scheduled sacrifice.
There were no test substance-related clinical signs in any of the test animals.

BODY WEIGHT AND WEIGHT GAIN
There was a statistically significant and dose-related decrease in body weight gains in the dietary dosed males from Day 12 onwards (and this was reflected in occasionally decreased food conversion efficiency and also a small decrease in daily food intake in the dosed male animals which suggested an effect on palatability). This was not observed in the females. On the last day of the study, a decrease in body weight or body weight gain was observed among most groups that was not considered to be treatment related; this decrease is believed to be due, at least in part, to the fasting for 8 hours prior to necropsy.

FOOD CONSUMPTION AND FOOD CONVERSION EFFICIENCY:
There were no test substance-related effects on food consumption in any of the dietary dosed test groups of animals (although there were occasionally decreases in food conversion efficiency and a probable palatability effect during this period of dosing).

TEST SUBSTANCE INTAKE:
Test substance (molybdenum) intake for the dietary dosed animals was generally comparable to the targeted dose levels, especially at the beginning of the study. However, generally more deviation (lower than target intake) at the end of the study was seen as a result of increasing body weights of the test animals without proportional increases in food consumption, as is the norm for young and growing rats: On Test Days 5-26, the intake in males in the 4 mg Mo/kg/day group was 4.3 to 3.2 mg Mo/kg/day (mean=3.61 mg Mo/kg/day). In males in the 20 mg Mo/kg/day group the intake was 19.3-15.8 mg Mo/kg/day (mean=17.1 mg Mo/kg/day). In the females the intake in the 4 mg Mo/kg/day group was 4.5-4.0 mg Mo/kg/day (mean = 4.17 mg Mo/kg/day). In females in the 20 mg Mo/kg/day group intake was 29.0-20.9 mg Mo/kg/day (mean=22.7 mg Mo/kg/day).

ORGAN WEIGHTS
There were no test substance-related effects on organ weights in any of the dietary dosed test groups of animals.

GROSS PATHOLOGY
There were no test article related macroscopic findings.

HISTOPATHOLOGY: NON-NEOPLASTIC
There were no microscopic findings related to administration of sodium molybdate dihydrate by dietary administration.

TOXICOKINETICS:
Serum concentrations of molybdenum were quantifiable in all collected serum samples following dietary administrations of vehicle and sodium molybdate dihydrate for 28 consecutive days.
Values of the selected toxicokinetic parameters for molybdenum are summarized in Table 1 (see "Any other information on results incl. tables" below).
- AUC0-8h values of molybdenum for male and female rats increased proportionately with increasing dietary doses of molybdenum.
- no gender differences in exposure to molybdenum were observed after dietary administration of sodium molybdate dihydrate at the examined dose levels.
- molybdenum systemic exposures (assessed by extrapolated AUC0-24h) at 4 and 20 mg Mo/kg bw/day after dietary administration were approximately comparable to those after gavage administrations (please refer to Section 7.5.1 Repeated dose toxicity: oral: s_Hoffman_2011_28 d_gavage). The dietary/gavage ratios of the AUC0-24h values for males were 0.67 and 0.57, and for females were 1.02 and 1.26 after administration of sodium molybdate dihydrate at 4 and 20 mg Mo/kg bw/day, respectively.

Dose descriptor:

NOAEL

Effect level:

50 mg/kg bw/day (nominal)

Based on:

test mat.

Remarks:

equivalent to 20 mg Mo/kg bw/day

Sex:

male/female

Basis for effect level:

other: see 'Remark'

Remarks on result:

other: see 'Remarks'

Remarks:

Molybdenum systemic exposures at 4 and 20 mg Mo/kg bw/day after dietary administration were approximately comparable to those after gavage administrations (please refer to Section 7.5.1 Repeated dose toxicity: oral: s_Hoffman_2011_28 d_gavage) in male and female rats. The high dose of 20 mg/kg/day of Mo, when dosed for 28 consecutive days, was very well tolerated and was considered to be a no observed adverse effect level (NOAEL).

Critical effects observed:

not specified

Table 1: Values of Serum Toxicokinetic Parameters of Molybdenum in Male and Female Rats following Dietary Administration of Sodium Molybdate Dihydrate

Route of Administration	Sex	Group	Molybdenum Dose (mg Mo/kg/day)	AUC0-8h (ng * h/mL)	AUC0-24h (ng * h/mL)^b	Cmax (ng/mL)
Dietary	Male	1	0^a	153	765	N.A.
		2	4	6330	31650	N.A.
		3	20	32900	164500	N.A.
	Female	1	0^a	154	770	N.A.
		2	4	5200	26000	N.A.
		3	20	31900	159500	N.A.

a: Group 1 animals were administered vehicle diet [Certified Rodent Diet, No. 2016C (meal) (Harlan Teklad, Madison, WI)] and received approximately 0.08mg Mo/kg bw/day from the diet.

b: AUC_0-24hvalues were assigned 5-folds of AUC0-8h

N.A. : not applicable

Conclusions:

NOAEL = 20 mg/kg/day of Mo

Oral dosing of rats with 4 or 20 mg/kg/day of Mo (molybdenum in sodium molybdate dihydrate) via the dietary route for 28 days of doses resulted in no systemic effects and in particular, no adverse effects observed at postmortem examination or in the histopathology of the kidneys, testes or epididymides. A dose related reduction in bodyweight gain was noted in males treated via their diet. This may have been due in part to slightly reduced food intake in these animals due to reduced palatability of the diet. There were quantifiable and dose-related levels of serum Mo in animals dosed via the dietary route. Molybdenum systemic exposures at 4 and 20 mg Mo/kg bw/day after dietary administration were approximately comparable to those after gavage administrations (please refer to Section 7.5.1 Repeated dose toxicity: oral: s_Hoffman_2011_28 d_gavage) in male and female rats.
The high dose of 20 mg/kg/day of Mo, when dosed for 28 consecutive days, was very well tolerated and was considered to be a no observed adverse effect level (NOAEL).

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2011

Report date:

2011

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity Study in Rodents)

Version / remarks:

modified to include oestrous cycle and sperm analyses as specified in OECD 416.

GLP compliance:

yes

Remarks:

Only analysis of dose formulations,blood & tissues were non-GLP (the lab Michigan State University is non-GLP).However,the laboratory is fully certified under the American Association of Veterinary Laboratory DDiagnosticians (AA VLD) and has a QC program.

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

10102-40-6

Cas Number:

10102-40-6

IUPAC Name:

10102-40-6

Constituent 2

Reference substance name:

sodium molybdate dihydrate

IUPAC Name:

sodium molybdate dihydrate

Test material form:

solid: particulate/powder

Details on test material:

- Name of test material (as cited in study report): Sodium molybdate dihydrate
- Molecular formula: Na2MoO4.2H2O
- Molecular weight: 241.95
- Physical state: white crystalline powder
- Analytical concentration: 39.5 ± 0.8% Mo (theoretical content is 39.65, so material is > 99% pure)
- Expiration date of the batch: 04-05-2011 (last dosing of animals: 25-01-2011)
- Storage condition of test material: room temperature

Test animals

Species:

rat

Strain:

Sprague-Dawley

Remarks:

Crl: CD(SD)

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: approximately 7 weeks
- Weight at study initiation (mean weight): males: 338.4 g (range: 309.8 - 377.6 g); females: 229.6 g (range: 187.9 - 263.5 g)
- Housing: animals were individually housed in elevated, stainless steel, wire mesh cages. An enrichment device (e.g., a Nylabone®) was provided in each animal’s cage at all times. Previous analysis of Nylabone in the range finder study (please refer to Section 7.5.1 Repeated dose toxicity: oral: s_Hoffman_2011_28 d_gavage and Section 7.5.1 Repeated dose toxicity: oral: s_Hoffman_2011_28 d_dietary administration) showed that it contained no significant amount of molybdenum (<1ng Mo/g).
- Diet (ad libitum): Certified Rodent Diet, No. 2016C (meal) (Harlan Teklad, Madison, Wisconsin); fresh feed was presented weekly during the study except during Week 1 when fresh feed was presented 3 times.
- Water (ad libitum): water (New Jersey-American Water Company, Cherry Hill, New Jersey) via an automated watering system.
- Acclimation period: approximately 2.5 weeks; all animals were examined during the stabilization period to confirm suitability for study.

Currently acceptable practices of good animal husbandry were followed e.g., Guide for the Care and Use of Laboratory Animals; National Academy Press, 1996.

ENVIRONMENTAL CONDITIONS
- Temperature: 19 to 23°C (daily average range)
- Relative humidity: 34 to 49% (daily average range)
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

oral: feed

Vehicle:

other: Certified Rodent diet, No. 2016C

Details on oral exposure:

DIET PREPARATION
- Rate of preparation of diet (frequency): fresh dose formulations were prepared once weekly for the first 4 weeks of the study and then every other week for the rest of the treatment period to approximate as closely as possible the target dose levels in mg/kg bodyweight. Dose formulations were prepared as averaged mixtures for the males and females (based on body weight and feed consumption data from the preceding interval and the molecular weight ratio of the test substance) in each group
- Mixing appropriate amounts with Certified Rodent diet, No. 2016C
- Storage temperature of food: stored at room temperature in tightly sealed bags when not in use. It was confirmed in a range finder study (please refer to Section 7.5.1 Repeated dose toxicity: oral: s_Hoffman_2011_28 d_gavage and Section 7.5.1 Repeated dose toxicity: oral: s_Hoffman_2011_28 d_dietary administration) that dose formulations are stable for at least 5 weeks when prepared and stored at room temperature.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analyses to determine homogeneity and concentration of the test substance with carriers were performed. A validated method for molybdenum, copper, zinc and manganese was used.
- Homogeneity and confirmation analysis:
Samples of diet formulations (approximately 50 g in duplicate from the top, middle and bottom from the 1st week’s preparation, and approximately 50 g in duplicate from the middle from each subsequent preparation) for Groups 1 to 4 were collected from each prepared batch after preparation. Dose formulation samples were stored at room temperature in tightly sealed bags. Due to questionable analytical results, the back-up samples from the Week 1 formulations were blind labelled and shipped for analysis. These confirmed the original results.
-Stability: stability for at least 5 weeks of storage was determined for samples generated in a range finder study (please refer to Section 7.5.1 Repeated dose toxicity: oral: s_Hoffman_2011_28 d_gavage and Section 7.5.1 Repeated dose toxicity: oral: s_Hoffman_2011_28 d_dietary administration)

- Method of analysis:
Molybdenum analysis was performed by inductively coupled plasma - mass spectroscopy (ICP-MS).

Feed samples were dried overnight in a 75 degree Celsius oven, and a dry matter ratio was obtained by measuring the moisture lost in drying. Dry feeds were weighed out and digested overnight in a 95 degree Celsius oven in individual sealed vessels with 1 mL nitric acid: 100 mg feed ratio. The resulting solution was diluted with 18 MΩ water to a final mass of 25 g. The concentrated solutions and salts were further diluted with 18 MΩ water to lower the concentration of the analytes in the diluted samples into the calibration range.
Three modes were used to minimize the spectral interferences for the analysis, copper (mass 65), zinc (mass 66) and cobalt (mass 59) were analysed in helium mode. Selenium (mass 78) and iron (mass 56) were analysed in hydrogen mode. Lastly, manganese (mass 55) , and molybdenum (mass 95) were analysed in non-gas mode.

Results:
Analysis confirmed that the preparation procedure used for this study produced homogeneous mixtures under storage conditions used in this study. Analyses conducted during the treatment period confirmed that dose formulations of appropriate concentration were administered. The initial results from the Week 1 preparations were suspect (they varied between 83-121% of the expected results) but analysis of secondary (and blinded samples) showed similar results and thus the initial results were accepted for summary calculations below.
Mean nominal and analytical Mo results, expressed as concentration and percent of nominal (desired) concentrations were as follows:

Nominal Mo concentration:
Group 1 (control group): 0 ppm
Group 2 (5 mg Mo/kg bw/day): 75 ppm
Group 3 (17 mg Mo/kg bw/day): 263 ppm
Group 4 (60 mg Mo/kg bw/day): 896 ppm

Analytical Mo concentration:
Group 1 (control group): 0.9 ppm
Group 2 (5 mg Mo/kg bw/day): 68 ppm
Group 3 (17 mg Mo/kg bw/day): 268 ppm
Group 4 (60 mg Mo/kg bw/day): 907 ppm

Analytical Mo concentration (% of nominal):
Group 1 (control group): not applicable
Group 2 (5 mg Mo/kg bw/day): 91
Group 3 (17 mg Mo/kg bw/day): 102
Group 4 (60 mg Mo/kg bw/day): 101

The Mo concentration in Group 1 samples was considered typical and expected background.

Duration of treatment / exposure:

Test and control groups: 91 (males) or 92 (females) days

Frequency of treatment:

Test and control groups: ad libitum feed presentation.

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

12.5 mg/kg bw/day (nominal)

Remarks:

equivalent to 5 mg Mo/kg bw/day

Doses / concentrations 2

Dose / conc.:

42.5 mg/kg bw/day (nominal)

Remarks:

equivalent to 17 mg Mo/kg bw/day

Doses / concentrations 3

Dose / conc.:

150 mg/kg bw/day (nominal)

Remarks:

equivalent to 60 mg Mo/kg bw/day

No. of animals per sex per dose:

Group 1 (control group): 10 males / 10 females (for sacrifice/necropsy after 90 days) PLUS an extra 10 males and 10 females for a 60 day recovery period.
Group 2 (5 mg Mo/kg bw/day): 10 males / 10 females
Group 3 (17 mg Mo/kg bw/day): 10 males / 10 females
Group 4 (60 mg Mo/kg bw/day): 10 males / 10 females (for sacrifice/necropsy after 90 days) PLUS an extra 10 males and 10 females for a 60 day recovery period.

Control animals:

yes, plain diet

Details on study design:

Dose selection rationale:
- In a study by Pandey and Singh (Pandey and Singh, 2002)*, 50 mg/kg bw sodium molybdate was possibly toxic to the testes and bodyweight when given as an oral bolus dose (probably gavage), 5 days/week for 60 days. In the same study, 30 mg/kg was a LOAEL and 10 mg/kg bw was possibly a NOAEL or might be a LOAEL.
- In a study by Cox et. al. (1960)*, Mo was given as sodium molybdate in two synthetic diets at 500 ppm (about 50 mg/kg bw) for 5-8 weeks. This proved to be toxic with diarrhea and decreased weight gain, and with high liver molybdenum levels and no effect on liver copper stores.
- All the rats died during the first week of a study where they were given 400 mg Mo/kg bw/day in the diet (Nielands et al., 1948)*.
- In a range-finding study (please refer to Section 7.5.1 Repeated dose toxicity: oral: s_Hoffman_2011_28 d_gavage and Section 7.5.1 Repeated dose toxicity: oral: s_Hoffman_2011_28 d_dietary administration), there were no remarkable treatment effects, including no effects on the testes, from oral gavage or dietary dosing at 4 and 20 mg Mo/kg bw/day for 28 days (equivalent to 10 and 50 mg/kg bw/day of sodium molybdate dihydrate).

Therefore, for this study, it was estimated that the low dose (5 mg Mo/kg bw/day) should have been without effect based on the results of a range-finding study (please refer to Section 7.5.1 Repeated dose toxicity: oral: s_Hoffman_2011_28 d_gavage and Section 7.5.1 Repeated dose toxicity: oral: s_Hoffman_2011_28 d_dietary administration) and previous published studies. The selection for the middle dose (17 mg Mo/kg bw/day) was based on the fact that it is logarithmically between the high and low dose. It was expected that some effects at the high dose (60 mg Mo/kg bw/day) would be seen, based on other published studies. In addition, palatability was not expected to be a problem since Arrington et. al. (1965)* did not see a decrease in food consumption in rats given up to 80 mg Mo/kg bw/day in the diet (as sodium molybdate dihydrate) for 6 weeks. Also, 60 mg Mo/kg bw/day represents a dose level which is about 20,000 times higher than typical human dietary intake (205 mcg Mo/day or 3 mcg Mo/kg bw/day) and it was estimated that much higher doses than 60 mg Mo/kg bw/day would result in undesired mortality.

* References:
- Arrington, L.R. et. al. 1965. Molybdenum toxicity in rats and rabbits. Journal of the Florida Academy of Science 28: 129-136.
- Cox, D., et al. 1960. Influence of excess dietary molybdenum on rat and calf liver and heart enzymes. Journal of nutrition. 70: 63-68.
- Neilands. J.B., Strong. F.M., Elvehjem. C.A. 1948. Molybdenum in the nutrition of the rat. J. Biol. Chem. 2: 431-439.
- Pandey R. and Singh S.P. 2002. Effects of molybdenum on fertility of male rats. Department of Zoology, University of Lucknow, UP Biometals. 1: 65-72.

- Post-exposure recovery period in satellite groups: recovery groups were kept on normal untreated diet for 59 days (females) and 60 days (males) prior to termination.

Positive control:

None.

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily for mortality and general condition; during the treatment period, all animals were observed for signs of toxic or pharmacologic effects at least twice daily. These observations were made concurrently with the viability checks.

DETAILED CLINICAL OBSERVATIONS AND NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule: animals were removed from their cages and examined once pretest and weekly during the study period (except examinations were
performed twice during the first week of the recovery period).
- Examinations included observations of skin and fur, eyes and mucous membranes, respiratory and circulatory effects, autonomic effects such as salivation, central nervous system effects, including tremors and convulsions, changes in the level of motor activity, gait and posture, reactivity to handling or sensory stimuli, grip strength, and stereotypies or bizarre behaviour (e.g., self-mutilation, walking backwards) according the Testing Facility SOPs describing detailed physical and behavioural examination.
- Grip strength was measured by allowing the animal to grip an inverted cage and then applying a gentle, horizontal pull on the tail, slowly drawing the animal backward. The grip strength was determined in terms of gripping resistance of the animal to this action.

BODY WEIGHT: Yes
- Time schedule for examinations: animals were weighed twice pretest, weekly during the study and terminally (after fasting). Terminal, fasted body weights were obtained just prior to necropsy.

FOOD CONSUMPTION: Yes
- Feed was available without restriction 7 days/week. Animals were presented with full feeders of known weight. After up to 6 days, feeders were reweighed and the resulting weight was subtracted from the full feeder weight to obtain the grams consumed per animal over the up to 6-day period.
- Food consumption was measured (weighed) during the week prior to treatment initiation (over a 6-day period), at Days 2 and 4 and 7 in the first week of
dosing.
- The amount of food consumed over a 6-day period was used to determine feed concentration calculations for Week 2 and weekly (over a 6-day period) for the first 4 weeks and every other week during the rest of the study.

TEST SUBSTANCE INTAKE: Yes
Calculated from food consumption data and based on nominal dietary concentrations:
Test Substance Intake (mg Mo/kg bw/day) = Food consumed (g/kg bw/day) x concentration of molybdenum in diet (mg Mo/g diet)
The current body weight was used in the calculation.

FOOD CONVERSION EFFICIENCY: Yes
Calculated from weekly body weight and food consumption data:
Food Conversion Efficiency = (body weight gain (g)/ food consumption (g/interval)) x 100

WATER CONSUMPTION AND COMPOUND INTAKE: No

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: animals were examined pretest and at termination of the treatment period. Lids, lacrimal apparatus and conjunctiva were examined visually. The cornea, anterior chamber, lens, iris, vitreous humor, retina and optic disc were examined by indirect ophthalmoscopy.
Mydriacyl 1% was used to induce mydriasis.
- Dose groups that were examined: all animals

HAEMATOLOGY: Yes
- Time schedule for collection of blood and anaesthetic used: blood obtained via the jugular vein (unanaesthetized or when necessary lightly anaesthetized with isofluorane) or the orbital sinus (lightly anaesthetized with isofluorane) was used to analyse hematology and coagulation parameters at termination of the treatment period.
- Animals fasted: Yes, prior to blood collection
- How many animals: 10 animals/sex/group
- Parameters checked: haemoglobin concentration, haematocrit, erythrocyte count, platelet count, mean corpuscular volume, mean corpuscular haemoglobin, mean corpuscular haemoglobin concentration, red cell distribution width, total leukocyte count, reticulocyte count, differential leukocyte count1, prothrombin time and activated partial thromboplastin time

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood and anaesthetic used: blood obtained via the jugular vein (unanaesthetized or when necessary lightly anaesthetized with isofluorane) or the orbital sinus (lightly anaesthetized with isofluorane) was used to analyse clinical chemistry parameters at termination of the treatment period.
- Animals fasted: Yes, prior to blood collection
- How many animals: 10 animals/sex/group
- Parameters checked: aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, blood urea nitrogen, creatinine, glucose, cholesterol, triglycerides, total protein, albumin, uric acid, total bilirubin, sodium, potassium, chloride, calcium, inorganic phosphorus, globulin and albumin/globulin ratio (calculated value; albumin ÷ globulin)

URINALYSIS: No

BLOOD MOLYBDENUM:
Blood samples were obtained for the determination of serum concentrations of molybdenum (and copper, zinc and manganese).
- Collection intervals: during Week 4 (Days 22 to 25), Week 12 (Days 78 to 81) and during the 1st week of the recovery period (2 days and 7 days after
termination of the treatment period);
- No. of annimals: blood samples were obtained for molybdenum determinations from all surviving animals at each interval. During Weeks 4 and 12, approximately equal numbers of animals per sex per group per day were sampled. Samples were collected at approximately 0900 (±75 minutes) on each day.
- Collection procedures: approximately 0.5 mL of whole blood was obtained from each unanaesthetized animal via the jugular vein. When necessary, animals were lightly anesthetized with isofluorane. Animals were not fasted prior to blood collection. Blood was collected into plastic silicone coated interior (Royal Blue Top) tubes, containing no additive and placed at room temperature in an upright position and allowed to clot for at least 30 minutes.
In Week 12 for all animals scheduled for terminal sacrifice, blood (approximately 0.25 mL) was also collected into lithium heparin tubes and inverted and placed into wet ice.
- Processing, storage and disposition of samples: blood samples collected into plastic silicone coated interior tubes were processed to obtain serum. Serum was separated by centrifugation (for 10 minutes at approximately 3000 rpm, at approximately 2–8°C). Serum (approximately 0.2 mL) was transferred into a cryotube. Tubes were stored frozen at approximately -80°C (±10°C) (within 2 hours after collection of each blood sample).
Blood samples collected into tubes containing lithium heparin were transferred into cryotubes and stored refrigerated at approximately 2 to 8 °C (within 2 hours after collection of each blood sample).
- Sample analysis and reporting: serum samples were analysed with a validated inductively coupled plasma mass spectrometry (ICP-MS) method under non-GLP conditions.
200 µL of each digest, and serum/blood samples, were pipetted and diluted with 5 mL of a solution containing 0.5% EDTA and Triton X-100, 1% ammonia hydroxide, 2% propanol and 20 ppb of scandium, rhodium, indium and bismuth as internal standards. An Agilent 7500ce Inductively Coupled Plasma - Mass Spectrometer (ICP-MS) was used for the analysis. The ICP-MS was tuned to yield a minimum of 5000 cps sensitivity for 1 ppb yttrium (mass 89), less than 1.0% oxide level as determined by the 156/140 mass ratio and less than 2.0% double charged ions as determined by the 70/140 mass ratio. Each element was calibrated using a 4 point linear curve of the analyte: internal standard response ratio.
Three modes were used to minimize the spectral interferences for the analysis, copper (mass 65), zinc (mass 66) and cobalt (mass 59) were analysed in helium mode. Selenium (mass 78) and iron (mass 56) were analysed in hydrogen mode. Lastly, manganese (mass 55) , and molybdenum (mass 95) were analysed in non-gas mode.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
- Necropsy was performed on up to 10 animals/sex/group after animals had been treated for up to 92 days. Animals were fasted overnight prior to necropsy. Necropsy of the remaining 10 animals/sex/group from Groups 1 and 4 occurred after the animals had been allowed to recover for up to 60 days after termination of the treatment period.
- A necropsy schedule was established to ensure that approximately equal numbers of males and females were examined on each day of necropsy and that examination of animals of both sexes were performed at similar times of the day throughout the necropsy period.
- Exsanguination following carbon dioxide inhalation.
- Complete macroscopic examinations were performed on all animals including examination of the external surface and all orifices; the external surfaces of the brain and spinal cord; the organs and tissues of the cranial, thoracic, abdominal and pelvic cavities and neck; and the remainder of the carcass for the presence of macroscopic morphologic abnormalities.

ORGAN WEIGHTS:
- The following organs were weighed for all animals at the scheduled sacrifice intervals: adrenal glands, brain (medulla, pons, cerebrum and cerebellum), epididymides, heart, kidneys, liver, ovaries, pituitary gland (weighed post-fixation), prostate gland, seminal vesicles, spleen, testes, thymus, thyroid/parathyroid glands (weighed post-fixation), and uterus (body/horns) with cervix.
- Prostate and seminal vesicles were weighed together.
- Prior to weighing, the organs were carefully dissected and properly trimmed to remove adipose and other contiguous tissues in a uniform manner. Organs were weighed as soon as possible after dissection in order to avoid drying. Paired organs were weighed together.

HISTOPATHOLOGY: Yes
- The following tissues were obtained during the necropsies and preserved for all animals: adrenal glands, aorta (thoracic), bone (sternum, distal femur), bone marrow (sternum, distal femur; qualitative examination (no differential count)), brain (medulla, pons, cerebrum and cerebellum), epididymides, esophagus, eyes, Harderian gland, heart, kidneys, lacrimal glands, large intestine (cecum, colon, rectum; cecum and colon were examined microscopically; however, the rectum was not examined microscopically), liver, lungs (with mainstem bronchi), lymph nodes (mesenteric, mediastinal), mammary gland (inguinal), nerve (sciatic), ovaries, pancreas, pituitary gland, prostate gland, salivary glands (submandibular), seminal vesicles, skeletal muscle (rectus femoris), skin (doral – base of tail), small intestine (duodenum, ileum, jejunum, Peyer’s patches/GALT), spinal cord (cervical, mid-thoracic, lumbar), spleen, stomach, testes, thymus, thyroid/parathyroid glands, trachea, urinary bladder, uterus (body/horns) with cervix, vagina and tissues with macroscopic findings including tissue masses
- In addition, slides of the indicated tissues were prepared and examined microscopically for all animals sacrificed at termination of the treatment period as well as the animal which died an unscheduled death. Any abnormalities not noted during macroscopic examinations which were seen during histology processing were recorded. In addition, the adrenal glands from males and the kidneys from females in Groups 2 and 3, sacrificed at termination of the treatment period and from animals in Groups 1 and 4 sacrificed at the end of the recovery period were examined microscopically.

LIVER AND KIDNEY TISSUE CONCENTRATIONS:
- Liver (left lobe) and kidney (a longitudinal section of the left kidney) samples (at least 0.5 grams) were collected and were analysed for molybdenum, copper, zinc and manganese under non-GLP conditions using a validated inductively coupled plasma mass spectrometry (ICP-MS) method.
- Tissues were dried in a 75°C oven in preparation for the acid digest and analysis.

Other examinations:

VAGINAL CYTOLOGY/ESTROUS CYCLING
- Daily vaginal smears were taken from each female at approximately the same time each day and the stage of oestrous determined, commencing after completing 6 weeks of dosing for 3 weeks (Weeks 7-9).
- At the end of the study, the overall pattern of each female was characterized as regularly cycling (having recurring 4 to 5 day cycles), irregularly cycling (having cycles with a period of diestrus longer than 3 days or a period of cornification longer than 2 days), or not cycling (having prolonged periods of either vaginal cornification or leukocytic smears).
- An animal was considered to be "not cycling" if she showed three or more consecutive days of oestrus or five or more consecutive days of dioestrus.
- Cycle length may be defined as the number of days from one oestrus to the next oestrus. Incomplete cycles are not counted in calculating mean cycle length. Mean cycle length for each animal is calculated first, and the mean of these means is then calculated to represent the group.

SPERM AASSESSMENT
Sperm evaluations were performed as outlined in OECD 416 (adopted 22 Jan 2001).
- Sperm counts: the right testis and cauda epididymis of all surviving animals at the terminal sacrifice and at the recovery sacrifice were removed intact, weighed fresh, and then frozen at approximately –80ºC (± 10°C) until evaluation for sperm count (spermatids in the testis).
- All surviving males (all groups at terminal sacrifice and at the recovery sacrifice) were processed for sperm counts. For each of these animals, homogenized samples of the caudal epididymis and the testis were stained and examined. For each stained preparation, 10 fields were counted. The total number of sperm in the caudal epididymis, or spermatids in the testis, was calculated and reported adjusted for organ weight.
- Sperm morphology: sperm morphology slides were prepared for each of the surviving males (all groups at terminal sacrifice and at the recovery sacrifice). The slides of all males at the terminal sacrifice and at the recovery sacrifice were evaluated for morphological development (approximately 200 sperm per animal within the 2 slides were assessed).
- Sperm motility: from all males (all groups at the terminal sacrifice and at the recovery sacrifice), the right vas deferens were excised. After a “swim-out” period, a sample was placed in an analyser and at least 200 sperm and/or five microscope field images were stored electronically.
- The stored fields belonging to the all males chosen for sperm counts were reported for percent motility.

Statistics:

The following parameters were analysed statistically: body weight, body weight change from interval to interval, cumulative body weight change from baseline, food consumption, food conversion efficiency, haematology, coagulation, clinical chemistry, organ weights, estrous cycles and sperm evaluations
The parameters to analyze were identified as continuous, discrete or binary. Test-substance treated groups were then compared to the control using the following procedures.
For all parameters, significant differences between control and test substance-treated groups were expressed at the 5% (p<0.05), 1% (p<0.01) or the 0.1% (p<0.001) level.
- Continuous parameters: Bartlett's test for variance homogeneity, Williams' test, Dunnett's test, Shirley's test for a monotonic trend, Steel's test, F1 test, H1 test, t-tests and Wilcoxon rank sum tests
- Discrete parameters: Jonckheere-Terpstra test, Kruskal-Wallis test, and exact Wilcoxon rank sum tests
- Binary parameters: Cochran-Armitage test, א2 test and Fisher's Exact tests
The following major computer/software systems were utilized at the laboratory: ClinAxys II, Hamilton – Thorne Sperm analyzer, Liberate Reporting System, Microsoft Word and/or Excel, Pristima System, Quasar, REES Scientific Environmental Monitoring System and Xybion Path/Tox System

Results and discussion

Results of examinations

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Food efficiency:

effects observed, treatment-related

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

no effects observed

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

not examined

Behaviour (functional findings):

no effects observed

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
There were no test substance-related unscheduled decedents.
There were no test substance-related clinical signs.

BODY WEIGHT AND WEIGHT GAIN
Dosing phase:
Males:
- 60 mg Mo/kg bw/day: statistically significant decreases in body weight gains were observed almost weekly from Week 1 through Week 13 as measured from the pretest baseline and as measured from interval-to-interval. By the end of the dosing phase, absolute body weight were 15.1% less than controls.
- 5 and 17 mg Mo/kg bw/day: no test substance-related effects on the body weights

Females:
- 60 mg Mo/kg bw/day: statistically significant decreases in body weight gains weekly starting at Week 6 as measured from the pretest baseline. These differences were only occasionally seen in the interval-to-interval measures. By the end of the dosing phase, absolute body weight in the 60 mg Mo/kg bw/day females was 5.6% lower than controls (the value was not statistically significant).
- 5 and 17 mg Mo/kg bw/day: no test substance-related effects on the body weights

Recovery phase:
Males:
- 60 mg Mo/kg bw/day: statistically significant increases in body weight gains were noted at each weekly intervals but the absolute body weight was still 9.5% less than controls by the end of the study.
Females:
- 60 mg Mo/kg bw/day: weekly increases in body weight gains but only a few values were statistically significant. The absolute body weights in these females were considered to have recovered by the end of the study.

FOOD CONSUMPTION:
Dosing phase:
- 60 mg Mo/kg bw/day males had statistically significant decreases in food consumption on numerous occasions throughout the dosing phase.
- The weekly food consumption in test substance-treated females was generally considered to be comparable to control values.

Recovery phase:
- weekly food consumption in the 60 mg/kg bw/day males and females was considered to be comparable to their concurrent controls.

TEST SUBSTANCE INTAKE
- Test substance intake was on average close to the intended values with the males consistently less than intended and the females consistently greater than intended as a result of using averaged body weight and food consumption data for the calculations of dose concentration during the study.
- The averaged results for the study are summarized in Table 3 (please refer to "Any other information on results incl. tables" below.)

FOOD CONVERSION EFFICIENCY
Dosing phase:
- Food conversion efficiency showed that the 60 mg Mo/kg bw/day males and females generally had lesser values than the concurrent control animals during the dosing phase. This suggests that the reduced bodyweight gain was not only due to reduced food intake as a possible consequence of a palatability problem, but may suggest some interference with nutrition.
- No such effects were observed in the mid and low dose groups of animals.

Recovery phase:
- Food conversion efficiency showed that the 60 mg Mo/kg bw/day males and females generally had greater values than the concurrent control animals during the initial intervals indicating a recovery from the dosing phase.

OPHTHALMOSCOPIC EXAMINATION
There were no test substance-related ocular abnormalities.

HAEMATOLOGY
No test substance-related haematologic findings.
No test substance-related findings for coagulation.

CLINICAL CHEMISTRY
No test article-related clinical chemistry changes.

ORGAN WEIGHTS
Dosing phase and recovery phase:
No test substance-related findings.

GROSS PATHOLOGY
No test substance-related macroscopic findings.

HISTOPATHOLOGY: NON-NEOPLASTIC
Dosing phase:
- Microscopic findings considered to be related to test-substance administration were present in the kidneys of females administered 60 mg Mo/kg bw/day. Two females from the 60 mg Mo/kg bw/day dose group showed slight diffuse hyperplasia of the proximal tubules in the kidney. Although the finding was only present in two test substance treated rats, it is uncommon as a background finding in this age of animal and is therefore considered test-substance related. It is possible that the elevated concentrations of copper in the kidneys may play some role in the histopathological changes in the kidneys among the high dose females.

Recovery phase:
- The finding of proximal tubule hyperplasia in the kidneys of females administered 60 mg Mo/kg bw/day was not observed in any of the animals following a 60 day recovery period.

BLOOD MOLYBDENUM:
Mean serum and whole blood molybdenum results from the Weeks 4 and 12 during dosing and the Days 2 and 7 during recovery can be seen In Table 1 and Table 2 (please refer to "Any other information on results incl. tables" below.)
The results showed:
- Males had higher serum and/or whole-blood exposure to Mo than the females (~23% on average for Groups 2-4) at all dose levels at both weeks 4 and 12 of dosing. This is the opposite of expected based on the test substance intake results where the females had higher Mo intake.
- No or only slight accumulation of Mo in the serum (week 12 serum results were only slightly greater (~14% on average for Groups 2-4 both sexes) than week 4 serum results).
- Whole blood results in week 12 were consistently lower (~55% on average for Groups 2-4 both sexes) than the serum results in Week 12.
- A rapid recovery at days 2 and 7 after completion of dosing as expressed by substantially and progressively lower serum results at both intervals of measurement in the Group 4 animals.
- Serum copper levels were increased in the high dose Group 4 animals compared with the control Group 1 animals. The mean copper levels at 4 weeks in the control males was 1.266 μg/mL and in the females was 1.767 μg/mL. In the Group 4 males the level was 4.512 μg/mL and in females was 4.513 μg/mL . At 12 weeks, the levels were still high with serum copper levels in Group 4 males of 5.786 μg/mL and in females of 6.627 μg/mL.

VAGINAL CYTOLOGY7ESTROUS CYCLE.
No test substance-related effects on vaginal cytology and oestrous cycles during weeks 7-9 of the dosing phase.

SPERM EVALUATIONS:
No effect of treatment was observed on testes or secondary sex organ weights, and no effects on spermatid or sperm counts, motility or morphology were observed.

ORGAN ANALYSIS - LIVER AND KIDNEY:
Mean organ molybdenum concentrations (dry weight basis) from the terminal and recovery sacrifice intervals are shown in Table 4 and Table 5 (please refer to "Any other information on results incl. tables" below).

The results showed:
- Group 2 liver concentrations at termination were only slightly higher than Group 1 liver concentrations suggesting close to background levels at the low dose level.
- Groups 3 and 4 liver concentrations at termination were elevated above Groups 1-2 concentrations, but not in a fully dose proportional manner.
- Group 4 liver concentrations at end of recovery were substantially lower than at termination suggesting a nearly complete recovery (especially in the males) towards background levels.
- Groups 2-4 kidney concentrations at termination were elevated above Group 1 concentrations and in a nearly dose proportional manner.
- Group 4 kidney concentrations at end of recovery were substantially lower than at termination suggesting incomplete recovery towards background levels.

In addition the following results were found:
- Liver and kidney copper levels were increased in the high dose Group 4 animals compared with the control Group 1 animals.
- Mean liver copper level in Group 1 males was 16.97 μg/g and in females was 19.22 μg/g. In Group 4 males it was 25.06 μg/g, and in females was 36.33 μg/g.
- Kidney copper levels in Group 1 males was 30.191 μg/g and in females was 43.538 μg/g. In Group 4 males it was 81.70 μg/g and in the females was 138.72 μg/g.
- In the recovery Group 4 animals, copper levels in liver and kidney were reduced but still higher than in the Group 1 controls. This may be important since some of the kidney toxicity may be related to the high copper levels in the tissues.

Effect levels

1

Dose descriptor:

NOAEL

Effect level:

42.5 mg/kg bw/day (nominal)

Based on:

test mat.

Remarks:

equivalent to 17 mg Mo/kg bw/day

Sex:

male/female

Basis for effect level:

other: NOAEL is based on the effects on body weights and kidneys seen at 60 mg Mo/kg bw/day.

2

Dose descriptor:

NOAEL

Effect level:

>= 150 mg/kg bw/day (nominal)

Based on:

test mat.

Remarks:

equivalent to 60 mg Mo/kg bw/day

Sex:

male/female

Basis for effect level:

other: NOAEL based on no effects on testicular (or gonadal) and sperm and oestrous cycle effects at the highest dose tested (60 mg/kg bw/d).

Target system / organ toxicity

Critical effects observed:

not specified

Any other information on results incl. tables

Table 1: Serum and Whole Blood Molybdenum Results - males

GROUP	Serum Week 4	Serum Week 12	Whole Blood Week 12	Serum Day 2 Recovery	Serum Day 7 Recovery
	(ng/mL)	(ng/mL)	(ng/mL)	(ng/g)	(ng/g)
1	18.7	19.4	11.9	19.0	20.6
2	1332	1309	912	NA	NA
3	4687	4674	2930	NA	NA
4	16277	18497	9903	4382	2425

NA = not applicable

Table 2: Serum and Whole Blood Molybdenum Results - females

GROUP	Serum Week 4	Serum Week 12	Whole Blood Week 12	Serum Day 2 Recovery	Serum Day 7 Recovery
	(ng/mL)	(ng/mL)	(ng/mL)	(ng/g)	(ng/g)
1	19.8	17.9	11.1	15.1	33.3
2	991	1121	720	NA	NA
3	3370	4311	2628	NA	NA
4	13176	15531	7736	6447	2841

NA = not applicable

Table 3: Test Substance Intake Results – mg Mo/kg bw/day

Group – target dose	Males	Females	Mean
2 – 5 mg Mo/kg bw/day	4.5	5.4	5.0
3 – 17 mg Mo/kg bw/day	15.1	19.0	17.1
4 – 60 mg Mo/kg bw/day	54.8	65.2	60.0

Table 4: Molybdenum in Organs Results - Terminal

GROUP	Liver Conc - males	Kidneys Conc. - males	Liver Conc - females	Kidneys Conc - females
	(ug/g)	(ug/g)	(ug/g)	(ug/g)
1	2.22	0.93	2.45	0.94
2	2.54	2.30	3.41	3.83
3	4.00	9.52	4.92	10.94
4	12.02	43.18	12.99	55.04

Table 5: Molybdenum in Organs Results - Recovery

GROUP	Liver Conc - males	Kidneys Conc. - males	Liver Conc - females	Kidneys Conc - females
	(ug/g)	(ug/g)	(ug/g)	(ug/g)
1	1.88	0.91	2.71	0.97
4	2.30	7.04	4.58	16.86

Applicant's summary and conclusion

Conclusions:

The dietary administration of 5, 17 or 60 mg/kg bw/day of Mo (molybdenum in sodium molybdate dihydrate) to rats for at least 90 days resulted in reduced bodyweight gain in the 60 mg Mo/kg bw/day animals. The effect was more severe in males. In males, this may have been due in part to slightly reduced food intake. Light microscopy evaluation of control and 60 mg Mo/kg bw/day animals identified test substance-related findings in the kidneys (slight diffuse hyperplasia of the proximal tubules) of two 60 mg Mo/kg bw/day females which recovered following up to 60 days after completion of dosing. No adverse effects were observed on the gonads, oestrous cycles or sperm analyses in any of the treated animals.
A NOAEL was determined to be 17 mg Mo/kg bw/day based on the effects on body weights and kidneys seen at 60 mg Mo/kg bw/day.
The NOAEL for testicular (or gonadal) and sperm and oestrous cycle effects is > 60mg Mo/kg bw/day.