1-[2-(2-chloroethoxy)phenylsulfonyl]-3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)urea;triasulfuron (ISO)

Carcinogenicity

Description of key information

- Oral: NOAEL for systemic toxicity is 10 ppm (0.3 - 1.1 and 0.4 - 1.1 mg/kg bw/day for males and females, respectively); NOAEL for carcinogenicity is >6000 ppm (equivalent to 208.3 - 588.9 and 274.4 - 621.9 mg/kg bw/day for males and females, respectively); male/female, rat, 2 years, EPA OPP 83-5, GLP, Morrow 1987

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records

Reference

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

14 Nov 1984 to 25 Nov 1986

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EPA OPP 83-5 (Combined Chronic Toxicity / Carcinogenicity)

GLP compliance:

yes (incl. QA statement)

Species:

rat

Strain:

Sprague-Dawley

Remarks:

Crl:COBS CD (SD)BR

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Sex: Males/females
- Females nulliparous and non-pregnant: yes
- Age at study initiation: 43 days old
- Weight at study initiation: 202 and 146 g for males and females, respectively
- Housing: Animals were housed in individual, suspended, stainless steel, wire-bottomed cages during the quarantine and study periods.
- Diet: Ad libitum
- Water: Filtered tap water. Ad libitum
- Acclimatisation period: 14 days

ENVIRONMENTAL CONDITIONS
- Temperature (°F): 68 - 78
- Humidity (%): 30 - 70
- Air conditions: Well ventilated and air-conditioned
- Photoperiod: 12-hour light/ dark cycle

- IN-LIFE DATES: From: 14 Nov 1984 To: 25 Nov 1986

Route of administration:

oral: feed

Vehicle:

unchanged (no vehicle)

Details on exposure:

DIET PREPARATION
- The test substance was mixed at weekly intervals with basal diet in varying concentrations to prepare 3 treatment dietary levels. A premix of test article was prepared in basal diet (5.0 % w/w) and mixed for 2 minutes. Appropriate weights of the prepared premix were added to basal diet and mixed to prepare the 1000 ppm (Treatment II) and 6000 ppm (Treatment III) diets. Weighed portions of 1000 ppm diet were mixed with basal diet to prepare the 10 ppm (Treatment I) diet. All treatment diets were mixed for 15 minutes.
- Test diets were placed in glass feeding jars, covered, and stored at room temperature until presented to study animals. Test diets not used for filling jars were stored at room temperature in covered plastic containers for use in refilling emptied feeders. At no more than 2 days after preparation, fresh test diets were offered for weekly feeding.
- The test substance/basal diet mixtures were established to be stable for up to 14 days at room temperature.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Samples of treatment diets and basal diet were obtained after each weekly preparation.

Samples for homogeneity analysis were obtained from the top, middle, and bottom of each mixing vessel. Duplicate samples were taken and stored frozen.

Chemical analyses were performed to determine if test substance in the prepared diets was within acceptable limits of the target concentrations and if the diets were homogeneously blended.

Concentration analyses were done at monthly intervals through study month 24.

Homogeneity analyses was done prior to study start and again when batch sizes were changed.

Basal diet samples were analysed at the same time as test diets.

Duration of treatment / exposure:

104 weeks, with animals designated for the interim kill were exposed for 52 weeks.

Frequency of treatment:

Continuously

Post exposure period:

30 days (recovery period)

Dose / conc.:

10 ppm

Remarks:

Treatment I. Dietary equivalent to 0.3 - 1.1 and 0.4 - 1.1 mg/kg bw/day for males and females, respectively

Dose / conc.:

1 000 ppm

Remarks:

Treatment II. Dietary equivalent to 32.1 - 105.1 and 41.4 - 107.8 mg/kg bw/day for males and females, respectively

Dose / conc.:

6 000 ppm

Remarks:

Treatment III. Dietary equivalent to 208.3 - 588.9 and 274.4 - 621.9 mg/kg bw/day for males and females, respectively

No. of animals per sex per dose:

Treatment groups: 80, Recovery groups control and high dose: 10

Control animals:

yes, plain diet

Observations and examinations performed and frequency:

OBSERVATIONS
- Time schedule: Twice daily during the study in the early morning and late afternoon. Once each week during the study, all animals were individually removed from their cages and examined for physical changes and palpated for tissue masses. Prior to the start of the study, all rats were examined to ensure that they were normal. Cage-side observations included recording any changes in clinical condition or behaviour.

OPHTHALMOLOGY
- Time schedule: At study initiation, 12 months, 13 month sacrifice following the recovery stage.

BODY WEIGHT
- Time schedule for examinations: The body weight of each rat was recorded on receipt and one week after receipt. Body weights were recorded one day before feeding of the experimental diets commenced and then weekly through study week 103. Recovery animals were weighed weekly during the 4-week recovery period. Body weights were also determined before necropsy.

FOOD CONSUMPTION AND COMPOUND INTAKE
- Time schedule: Individual food consumption was measured weekly for 13 weeks and once every other week thereafter through to week 103. Food consumption was measured over a 7-day period except for 5-day measurement intervals at study weeks 5 and 10 to accommodate urine collection.
- Average daily test substance intake was calculated on a mg/kg bw basis for each food
consumption interval. These calculations were performed using extrapolated body weights based on individual animal growth.

WATER CONSUMPTION
- Time schedule: Individual water consumption values were determined for 10 randomly selected animals/sex/group for 5-day intervals during study weeks 1 and 2, for 6- and 4-day intervals during study weeks 51 and 52, respectively, and for 5 and 4 day interval during study weeks 103 and 104, respectively.

HAEMATOLOGY
- Time schedule: Haematology and clinical chemistry parameters were evaluated using blood samples obtained from 10 males and 10 females from each group at month 6 and from animals selected for the 12 month interim and 13 month recovery sacrifices. Ten animals/sex/group from the chronic subgroup were bled at 18 months and all surviving chronic animals were bled pre-terminally at 24 months.
- Individual blood samples were obtained by orbital sinus puncture during light ether inhalation anesthesia after overnight fasting.
- Haematology parameters evaluated: Haemoglobin, haematocrit, erythrocyte count, total leukocyte counts, differential leukocyte counts, reticulocyte count, platelet count, methaemoglobin, cell indices (MCV, MCH, and MCHC).

CLINICAL CHEMISTRY
- parameters evaluated: Calcium, chloride, potassium, sodium, inorganic phosphorus, serum alanine amino- transferase (SGPT), serum aspartate amino­ transferase (SGOT), glucose, creatinine, creatine phosphokinase, urea nitrogen, total cholesterol, albumin, globulin (calculated), A/G ratio (calculated), total protein, alkaline phosphatase, lactate dehydrogenase, bilirubin (total).

URINALYSIS
- Time schedule: Evaluated using samples collected during an overnight fast of 10 male and 10 female rats from each treatment group at 6 and 18 months and from animals selected for the 12-month interim and 13-month recovery sacrifices. Urinalysis was also perform on all surviving chronic animals pre-terminally at 24 months.
- Parameters evaluated: appearance, volume (overnight), specific gravity, pH, protein, glucose, ketones, occult blood, bilirubin, urobilinogen, microscopic examination.

Sacrifice and pathology:

GROSS PATHOLOGY
- All animals (found dead, accidentally killed, sacrificed moribund, or sacrificed on schedule) were necropsied.
- Necropsy included an examination of all external body surfaces, orifices and organs; the cranial cavity; carcass; the external and cut surfaces of the brain and spinal cord; the abdominal, thoracic, and pelvic cavities and their viscera; and cervical tissues and organs.

ORGAN WEIGHTS
- At necropsy the following organs were weighed: adrenals, brain, gonads (testes with epididymides or ovaries), heart, kidneys, liver, lung, spleen, thyroid/parathyroids (after fixation).
- Organ to final body weight ratios and organ to brain weight ratios were calculated.

HISTOPATHOLOGY
- At necropsy the following histopathology examinations were made: adrenals, aorta, bone and bone marrow (sternum), brain (cerebrum, cerebellum, and brain stem), oesophagus, eyes, gonads (testes with epididymides or ovaries), heart, intestine (sections of cecum, colon, duodenum, ileum, jejunum, and rectum), kidneys, liver, lung and mainstem bronchi, lymph nodes (mandibular and mesenteric nodes), mammary gland (female), muscle (skeletal), nerve (sciatic), pancreas, pituitary, prostate, salivary glands (mandibular), seminal vesicles, skin, spinal cord (cervical, midthoracic, and lumbar sections), spleen, stomach (cardiac, fundic, and pyloric areas), thymus, thyroid and parathyroid, trachea, urinary bladder, uterus/cervix, vagina, gross lesions and tissue masses with adjacent tissue.

Statistics:

- Parameters were analysed by an analysis of variance with any significant differences examined further by either Tukey's (equal populations) or Scheffe's (unequal populations) Test of Multiple Comparisons.
- Nonparametric data were analysed by Kruskal-Wallis' Test with any significant differences examined further by Kruskal-Wallis' Multiple Comparison Test.
- Statistically significant differences between the untreated control and any test group(s), as
determined by the multiple comparison test are reported.
- The 0.05 and 0.01 levels of significance were selected.

Clinical signs:

effects observed, non-treatment-related

Description (incidence and severity):

Clinical signs that appeared with the highest incidence in the treated and control groups alike included crusty eyes; malaligned incisors; enlargements of appendages, foot pads or ears; tissue masses that often became scabbed or abraided; poor coat quality, thin hair, or alopecia and staining of the fur; various eye abnormalities that were most likely due to the orbital sinus bleeding technique; and a deteriorating general condition of moribund animals. All of these abnormalities and others that occurred less frequently were considered incidental and unrelated to treatment.

Dermal irritation (if dermal study):

not examined

Mortality:

mortality observed, non-treatment-related

Description (incidence):

One untreated control female was accidentally killed. One of the animals assigned to the recovery subgroup died during the 4-week recovery period. Of the remaining animals found dead or sacrificed moribund, none of these deaths was directly attributed to treatment. The mortality incidence of high-dose males at week 104, however, was reduced when compared to the control group.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Treatment-related body weight depressions were noted in the 6000 ppm males and females at study week 1 and to the end of the study. Total body weight change for the high-dose groups was 25 and 39 % less than the control group for males and females, respectively.
Average body weights of the 1000 ppm males were significantly less than control means from week 1 to week 53 but not thereafter. Average weight gain of the 1000 ppm males surviving to week 103 was comparable to the control group. Body weights of the 1000 ppm female group were statistically lower than the control group from weeks 2 to 12 and during weeks 15, 17, 33, 61, 63 and weeks 81 to 91. Average weight gain of the 1000 ppm females surviving until week 103, however, was statistically comparable to the control group.
Body weights and body weight changes in the 10 ppm males and females were statistically comparable to control means through week 103.
On the initial day of the recovery study, body weights of the 6000 ppm treated males and females were statistically lower than control values. During recovery, the 6000 ppm treated animals body weight values were statistically lower than control values during recovery weeks 1 to 4 for males
and weeks 1 and 2 for females. However, total body weight changes were statistically greater than control values during the 4-week recovery period.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Average food consumption of the 6000 ppm males was significantly less than control means during weeks 1 to 4, 6 to 49, 53 to 61, 67 and 95. For the 6000 ppm females, mean food consumption was significantly reduced below control levels during weeks 1 to 4, 6 to 9, 12, 61 and 75. In all these instances, the differences were small and of no biological significance.
A few sporadic, statistically significant differences in food consumption were seen in the 10 ppm and the 1000 ppm groups when compared to controls. These differences were considered unrelated to treatment.
Food consumption values of the 6000 ppm recovery animals were consistently greater than control values during the 4-week recovery period with statistically significant differences being noted during weeks 1 to 3 for males and during week 1 for females.

Food efficiency:

not examined

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

no effects observed

Description (incidence and severity):

There were no differences between the treated and the control groups on any of these assessment occasions.

Ophthalmological findings:

effects observed, non-treatment-related

Description (incidence and severity):

No treatment-related differences were seen between test and control groups.

Haematological findings:

effects observed, non-treatment-related

Description (incidence and severity):

Haematological parameters assessed in treated males at 6, 12, 18 and 24 months and after a 4-week recovery period (6000 ppm only) were comparable to the corresponding control means. The statistically significant decrease in reticulocyte counts in the 6000 ppm group at 12 months and the increase in percent monocytes noted in the 6000 ppm recovery males were considered incidental and unrelated to treatment.
In females, sporadic, statistically significant differences between the treated and the untreated control groups were noted and included decreased RBC counts in the 1000 ppm group at 6 months, increased WBC counts in the 10 and 6000 ppm group at 12 months, and slightly increased haemoglobin levels in the 6000 ppm recovery subgroup. These differences were considered incidental and unrelated to treatment.

Clinical biochemistry findings:

effects observed, non-treatment-related

Description (incidence and severity):

There were no treatment-related changes in males or females for any of the clinical chemistry parameters examined at 6, 12, 18 or 24 months. The statistically significant decreased glucose levels in 6000 ppm females at 6 months, the increased average glucose level for 1000 ppm males at 6 months, the decreased total bilirubin and LDH levels in 6000 ppm females at 18 months, and the increased alkaline phosphatase levels in the 6000 ppm recovery males were considered incidental and unrelated to treatment.

Endocrine findings:

not examined

Urinalysis findings:

effects observed, non-treatment-related

Description (incidence and severity):

There were no effects of treatment on any of the urinary parameters evaluated at 6, 12, 18 or 24 months. The significant increase in urine volume noted in the 6000 ppm males at 6 months was considered incidental. Recovery animal urinalysis data was unremarkable.

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Statistically significant increases in organ-to-body weight ratios were observed in the 6000 ppm group at the 12-month sacrifice (adrenals, kidneys, and testes/epididymides in males and brain in females) and at the recovery sacrifice (kidneys, liver, spleen, and testes/epididymides in males). In addition, the average absolute liver weight of the 6000 ppm recovery females was significantly less than the untreated control mean. These differences were considered to be the result of significantly decreased final body weights.
At 24 months, organ-to-body weight ratios were significantly increased in the 6000 ppm males for brain, lung, and testes and in females for brain, heart, kidneys, liver (accompanied by a
significant decrease in relative brain weight ratio), lung, spleen and thyroid. These differences
were attributed to significantly decreased final body weights of the 6000 ppm group. In the case of the testes, however, a significantly increased absolute testes weight contributed to the
observed decrease in organ-to-body weight and organ-to-brain weight ratios. Additionally, absolute heart weight was significantly reduced in the 6000 ppm males and the lung weight-to-body weight ratio for the 10 ppm males was statistically greater than the control group. This latter finding was considered incidental and unrelated to treatment.

Gross pathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

Gross findings seen at necropsy varied greatly among the groups and were generally associated with spontaneous diseases commonly observed in aging Sprague-Dawley albino rats. No effects of treatment or dose­ response relationships were apparent at feeding levels of up to 6000 ppm.
The following findings were frequently seen in animals of both sexes in the control and treated
groups: liver - discoloration or mottled; pituitary - discoloration, enlarged, or soft; external
body regions and structures: foot pad(s) - scab(s), scabbed, thickened, ulcerated, swollen,
enlarged, crusted, or discolored red or tan; ears - thickened or thickened and firm; external surface - exudate, crusty material, discharge or discoloration, crusted, and stained fur or discoloration; tail - crusted or crusted and ulcerated; eyes - opacity; kidney(s) - cyst(s) - dilated pelvis(es), and discoloration or mottled; lungs - discoloration; lymph node(s) - discoloration or enlarged; stomach - abnormal contents, black, dark, dark material, or dark fluid, discoloration, and thick or thickened; tissue mass locations - pancreas and pituitary; and oral cavity - incisors malaligned or missing or not present.
Frequently observed findings in males included: testis(es) - discoloration or mottled, and soft or
flaccid; kidney - enlarged and granular, rough or roughened, irregular or pitted surface.
Frequent findings in females included: ovary(ies) - cystic or cyst(s); uterus/cervix - cyst(s) or
cyst(s) clear or black; vagina - abnormal contents. Additional kidney observations were gritty or
granular material, stone(s}, calculi or microcalculi. Female rats also had the following findings: adrenals - discoloration or mottled and enlarged; carcass - depletion of, lack of, little, or no body fat or emaciated, and additional tissue mass locations of abdominal region/abdomen/abdominal
cavity/abdominal wall/omentum; axillary region/chest/thorax or thoracic region; perineum/perianal/perineal region and side.
Although these incidences were often numerically greater in one or more treated groups when compared to the control group, these differences were spontaneous or incidental in nature since no dose-related pattern was apparent.

Neuropathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

Degenerative changes of the myelin and atrophy were observed in the sciatic nerves, spinal nerve roots, spinal nerves, cauda equina, and to a lesser extent in the spinal tracts of the many animals in no specific group. These neural findings, which were unrelated to treatment, were recorded as myelinopathy, atrophy, or neuropathy.

Histopathological findings: non-neoplastic:

effects observed, non-treatment-related

Description (incidence and severity):

12-month Interim Sacrifice and Death: No definitive compound-related microscopic changes were observed in the tissues of either sex at dietary concentrations of up to 6000 ppm. Incidental findings included: chronic progressive nephropathy, pelvic subepithelial mineralisation, pelvic calculi, suppurative pyelitis, suppurative nephritis, ureteritis, periureteritis, urethritis, and cystitis. These findings were present in both untreated and treated rats with comparable incidence and severity.
13-month Sacrifice (Recovery): The principal findings in recovery rats were incidental kidney lesions similar to those observed in the 12-month sacrifice groups; chronic progressive nephropathy, pelvic calculi, and pelvic subepithelial mineralisation. No ureteritis or urethritis were observed. Multifocal non-suppurative hepatitis and hepatocytic vacuolation were observed in the liver. These lesions, which occurred sporadically in both control and treated rats, were of the usual type and number observed in rats of this age and strain.
24-month Sacrifice and Death: Non-neoplastic lesions, which were observed in rats in the treated and control groups, were of the type and incidence commonly noted in aged laboratory rats. The most prevalent of these findings was chronic progressive nephropathy. Additional renal changes, which were noted more frequently in females, included pelvic concretions and pelvic sub-epithelial mineralisation; suppurative nephritis (observed more frequently in males); prostatitis (observed more frequently in males). Chronic and sub-chronic myocarditis occurred incidentally in a large number of rats, especially males. Chronic and sub-chronic pancreatitis occurred less frequently. Ulcerative dermatitis and suppurative dermatitis usually affecting the feet were the most frequent skin lesions. Squamous cell hyperplasia usually accompanied the dermatitis. Epidermal inclusion and keratin cysts occurred less frequently than dermatitis. The prevalent vascular change was angiectasis which was more frequently observed in female groups
and primarily affected the pituitary, adrenal, and liver. In adrenals from female rats, the
angiectasis was often accompanied by thrombosis. Additional findings in adrenals of females were cortical vacuolation and hypertrophy. Degenerative changes observed in the liver, which were characterised by vacuolation and hepatocytic cystic changes, tended to occur less frequently in 6000 ppm treated animals. Other incidental findings included dilated glands in
the mucosa of the stomach, pelvic dilation in the kidneys, chondrodysplasia and osseous metaplasia of ears, ovarian cysts, suppurative vaginitis, dilated lumens of uteri, hypospermia in epididymides and testes, atrophy of testes, and periarteritis in testes. Enlarged pituitaries resulted secondarily in hydrocephalus and ventral compression of the brain. The predominant lung lesions observed with approximated equal frequency in treated and control groups were the accumulation of foamy macrophages. A few rats had nematode parasites in the large intestine.
A statistical evaluation of the incidence of non-neoplastic lesions observed in all animals
combined, failed to reveal any effects of test substance treatment.
Non-neoplastic, proliferative lesions were observed in several tissues at comparable frequencies in both the control and treated groups. No treatment-related effects were evident. Acinar hyperplasia occurred at high frequency in mammary gland of treated and control males and
females. This lesion, which was accompanied by various amounts of proteinaceous secretions and glandular distention, was termed galactocele. Squamous cell hyperplasia, as previously noted, occurred at approximately the same frequency in treated and control animals of both sexes and usually accompanied ulcerative or suppurative dermatitis. Pituitary hyperplasia was frequently observed in both male and female rats and was often accompanied by angiectasis. Adrenal medullary hyperplasia, which was frequently observed in males, showed a statistically significant negative trend in females. Bile duct hyperplasia, which also occurred more frequently in males, was incidental and unrelated to treatment. In males, a higher incidence of interstitial cell hyperplasia was observed in the 6000 ppm group. This difference was not statistically significant and was not attributed to treatment.

Histopathological findings: neoplastic:

effects observed, non-treatment-related

Description (incidence and severity):

A high incidence of neoplastic lesions were observed in animals from all groups including the controls. Frequently occurring tumors were observed in the endocrine tissues of both sexes and in the mammary gland of female rats. These tumors are known to have a high spontaneous rate
of occurrence in Sprague-Dawley rats. The incidence of adenomas, fibroadenomas, fibromas, adenocarcinomas, and all mammary tumors combined in treated females was statistically comparable to the control group.
A slightly greater incidence of interstitial cell tumors was noted in 6000 ppm males. This
difference was not statistically significant and these results are attributed to spontaneous
variations in tumor incidence.
Endocrine tumors of the pituitary, adrenal, pancreas, and thyroid were present in various
incidences and had no relationship to test substance exposure. High incidences of pituitary
tumors, both adenomas and carcinomas, were observed in males and females from all groups. Many of these tumors were large and several carcinomas had invaded adjacent portions of the brain. Pheochromocytomas and less frequently, malignant pheochromocytomas, were observed in male adrenal gland. Adrenal cortical tumors were seen infrequently and predominated in females. Pancreatic islet cell tumors occurred in both sexes with decreased numbers in Group
treatment II and III females and increased numbers in Group treatment II and III males. The variation in numbers of pancreatic islet cell tumors in males were not considered treatment related. Thyroid C-cell tumors occurred in similar numbers in both males and females.
A variety of other neoplasms occurred in all groups, in small numbers, or in individual animals
with no apparent relationship to treatment with the test substance.

Key result

Dose descriptor:

NOAEL

Remarks:

General systemic toxicity

Effect level:

10 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

food consumption and compound intake

organ weights and organ / body weight ratios

Remarks on result:

other: Dietary equivalent to 0.3 - 1.1 and 0.4 - 1.1 mg/kg bw/day for males and females, respectively

Key result

Dose descriptor:

NOAEL

Remarks:

Carcinogenicity

Effect level:

> 6 000 ppm

Based on:

test mat.

Sex:

male/female

Remarks on result:

other: Dietary equivalent to 208.3 - 588.9 and 274.4 - 621.9 mg/kg bw/day for males and females, respectively

Key result

Critical effects observed:

no

Verification of test diets
- Homogeneity analysis of diet samples taken from the top, middle, and bottom segments of the mixing vessel indicate that the test substance was uniformly distributed in the diet mixtures for batch sizes of 52 (Treatment III) and 58 (Treatment I and II) and 38 (Treatment I, II and III) kilograms.
- Monthly diet analyses through month 24 revealed that test substance concentrations were within acceptable limits of the target concentrations of 10, 1000 and 6000 ppm.

 

Table 1. Intergroup comparison of body weight (g): selected weeks

Week	Dietary Concentration of test substance (ppm)
	Males				Females
	0	10	1000	6000	0	10	1000	6000
Initial	202	202	202	203	146	146	146	146
1	243	243	237*	227**	166	163	161	157**
2	289	292	282*	267**	189	186	183**	174**
13	517	529	492**	430**	296	289	286	253**
27	621	636	594**	517**	345	343	331	284**
33	652	666	622**	541**	364	347	339**	294**
39	675	689	637**	551**	380	376	362	303**
53	720	734	681*	593**	419	407	397	331**
77	752	780	733	626**	481	455	441	364**
79	747	788	731	623**	487	451	447	365**
103	746	763	707	609**	502	483	475	362**

* Statistically significant difference from control group mean, p<0.05 (Student’s t-test, 2-sided)

** Statistically significant difference from control group mean, p<0.01 (Student’s t-test, 2-sided

 

Table 2. Intergroup comparison of body weight change (g)

Initial vs week 103	Dietary Concentration of test substance (ppm)
	Males				Females
	0	10	1000	6000	0	10	1000	6000
	543	562	505	407**	356	338	328	216**

** Statistically significant difference from control group mean, p<0.01 (Student’s t-test, 2-sided)

 

Table 3. Intergroup comparison of male organ weights adjusted for body weight (g)

Organ	Dietary Concentration of test substance (ppm)
	0	10	1000	6000
12-month interim
Adrenals	0.0075	0.0088	0.0085	0.0094*
Kidney	0.5558	0.6115	0.6276	0.6476*
Testes (with epididimides)	0.7880	0.7786	0.9277	0.9839*
24-month interim
Brain	0.3538	0.3349	0.3722	0.4104**
Lung	0.3542	0.3283	0.3649	0.4398**
Testes (with epididimides)	0.6650	0.6473	0.7103	0.9820**

* Statistically significant difference from control group mean, p<0.05 (Student’s t-test, 2-sided)

** Statistically significant difference from control group mean, p<0.01 (Student’s t-test, 2-sided)

 

Table 4. Intergroup comparison of female organ weights adjusted for body weight (g)

Organ	Dietary Concentration of test substance (ppm)
	0	10	1000	6000
12-month interim
Brain	0.5192	0.5072	0.5367	0.6473**
24-month interim
Brain	0.4883	0.4854	0.4962	0.6633**
Heart	0.3334	0.3461	0.3503	0.4241**
Kidneys	0.7148	0.7872	0.7498	0.8935**
Liver	2.6458	2.7041	2.7592	3.0487*
Lung	0.3940	0.4254	0.4137	0.5741**
Spleen	0.1650	0.1748	0.1769	0.1984*
Thyroid	0.0066	0.0069	0.0076	0.0094*

* Statistically significant difference from control group mean, p<0.05 (Student’s t-test, 2-sided)

Conclusions:

Based on these results, it is concluded that the test substance is not oncogenic in the rat when administered in the feed for 104 weeks at the maximum tolerated dose of 6000 ppm. Thus the no observed adverse effect level (NOAEL) for carcinogenicity was estimated to be 6000 ppm, equivalent to 208.3 - 588.9 and 274.4 - 621.9 mg/kg bw/day for males and females, respectively. Additionally, the NOAEL for systemic toxicity was 10 ppm, equivalent to 0.3 - 1.1 and 0.4 - 1.1 mg/kg bw/day for males and females, respectively.

Executive summary:

The test substance was administered in the diet to 80 male and 80 female Sprague-Dawley rats at feeding levels of 0, 10, 1000, or 6000 ppm for up to 104 weeks. This study was conducted according to EPA OPP 83-5 following GLP. Ten rats/ sex/ group were sacrificed after 53 weeks on test and an additional 10 rats/ sex in the control and 6000 ppm groups received the control or the 6000 ppm diet for 53 weeks and then were fed the control diet during a 4-week recovery period. Parameters evaluated during the in-life phase of the study included an assessment of mortality, clinical condition, ophthalmology, body weight, food consumption, water consumption, haematology, clinical chemistry, and urinalysis. Gross necropsies were performed and tissues were saved for histopathological examinations of all animals found dead, sacrificed moribund, or undergoing scheduled sacrifice. Organ weights were recorded for animals undergoing scheduled necropsies.

There were no treatment-related effects on clinical condition, ophthalmology, water consumption, or clinical laboratory parameters. Survival in the 6000 ppm males was slightly greater than controls at week 104. Dose-related reduction in body weight gain present at feeding levels of 1000 ppm were accompanied by decrease food consumption at 6000 ppm. Body weight change for the 1000 ppm group was comparable to controls at 103 weeks but was reduced by 25 and 39 % in the 6000 ppm males and females, respectively. Slightly elevated organ to body weight ratios noted in the 6000 ppm group were secondary to decreased body weight. No definitive evidence of an increased incidence of either neoplastic or non-neoplastic lesions was observed in this study.

Based on these results, the no observed adverse effect level (NOAEL) for systemic toxicity was estimated to be 10 ppm, equivalent to 0.3 - 1.1 and 0.4 - 1.1 mg/kg bw/day for males and females, respectively. Additionally, it was concluded that the test substance is not oncogenic in the rat when administered in the feed for 104 weeks at the maximum tolerated dose of 6000 ppm. Thus, the no NOAEL for carcinogenicity was estimated to be 6000 ppm, equivalent to 208.3 - 588.9 and 274.4 - 621.9 mg/kg bw/day for males and females, respectively.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

208.3 mg/kg bw/day

Study duration:

chronic

Species:

rat

Quality of whole database:

GLP compliant EPA OPP 83-2 study

Carcinogenicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Carcinogenicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Based on the available data classification for carcinogenicity is not warranted in accordance with EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation No. 1272/2008.

Additional information

Studies required in Annex VII and some other studies required for higher tonnage are available. All the studies available have been included in the dossier for this endpoint. Two studies are available assessing the carcinogenic potential of the test substance in rats (Morrow 1987a) and mice (Morrow 1987b). No definitive evidence of an increased incidence of either neoplastic or non-neoplastic lesions was observed in either of these studies. Therefore, it was concluded that the test substance has no carcinogenic potential.