4-(5-(3,5-dichloro-4-fluorophenyl)-5-(trifluoromethyl)-4,5-dihydro-1,2-oxazol-3-yl)-N-(2-ethyl-3-oxo-1,2-oxazolidin-4-yl)-2-methylbenzamide

Bioaccumulation: aquatic / sediment

Link to relevant study record(s)

Reference

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1 Aug 2017 to 15 Sep 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 305 (Bioaccumulation in Fish: Aqueous and Dietary Exposure) -I: Aqueous Exposure Bioconcentration Fish Test

Version / remarks:

2012

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 850.1730 (Fish Bioconcentration Test)

Version / remarks:

2016

Deviations:

no

GLP compliance:

yes

Radiolabelling:

yes

Details on sampling:

- Toral radioactive residue (TRR): Samples (10 mL) of the solvent control and 1.3 µg/L exposure solutions were taken for LSC analysis on day -1, 0, 3, 7, 14, 21, and 28 of the uptake phase and on day 1, 3, 7, and 14 of the depuration phase. At each sampling interval, triplicate samples were taken for determination of TRR.

- TRR in fish tissue: To determine the concentration of total radioactive residue (TRR) in fish tissue, four fish from the exposure aquarium were taken on day 0, 1, 3, 7, 14, 21, and 28 of the uptake phase. Additionally, four fish were taken from the test vessel on day 1, 3, 7, and 14 of the depuration phase. Fish were also removed from the solvent control aquarium at the same intervals with the exception of test initiation (day 0).

- To determine the concentration of [methylphenyl-U-14C] labelled test substance in exposure solutions, duplicate 500 mL aqueous samples were collected from the 1.3 µg/L nominal exposure and solvent control aquaria on day -1, 0, 3, 7, 14, 21, and 28 of exposure. One of the solvent control samples was used to prepare a quality control sample at each interval.

-To determine the concentration of [methylphenyl-U-14C] labelled test substance in fish tissue, four fish from solvent control and treated aquaria were collected on days14 and at the end of exposure and cut into small pieces. Four whole fish were combined and extracted with 25 mL of 1/1 dichloromethane/methanol (v/v). These extracts were analyzed using HPLC-RAM.

- On each sampling occasion, the fish were selected at random and removed from each tank, euthanized using 1/2 tricane/sodium bicarbonate, and gently blotted dry. Each fish was weighed, total length was measured, and then each fish was filleted into edible and non-edible portions, which were weighed separately and then immediately analyzed. In addition, on day 14 and at the end of uptake, 10 whole fish were sampled and immediately stored in a freezer to be processed for future metabolite identification, as necessary.

- Lipid analysis: Lipid analysis was performed at the start of the uptake phase, at the end of the uptake phase and the end of the depuration phase.

Vehicle:

yes

Remarks:

acetone

Details on preparation of test solutions, spiked fish food or sediment:

PREPARATION OF TEST SOLUTION
The stock solution for the bioconcentration exposure (1.3 µg/L) was prepared by combining 68.74 mL of the 0.364 mg/mL primary radiolabeled stock solution with 25.00 mL of the 0.999 mg/mL primary non-radiolabeled stock solution and bringing to a final volume of 500 mL with acetone. Triplicate aliquots of the mixed stock solution were analyzed by LSC and the concentration was determined to be 0.100 mg/mL. The specific activity of this stock solution was calculated to be 70,408 dpm/µg.

Test organisms (species):

Lepomis macrochirus

Details on test organisms:

TEST ORGANISM
- Common name: Bluegill sunfish
- Size of the fish at test initiation: The smallest fish not being less than two-thirds the size of the largest fish.
- Feeding during test: The fish were fed the same commercial food as used during the acclimation period. The test fish were fed 1.5% body weight per day. The amount of food required was recalculated after each sampling interval based on the wet weights of the fish sampled. On fish tissue sampling days, fish were fed after analytical sampling. Uneaten food and fecal matter were removed (by siphon) from each aquarium within one hour after feeding.

ACCLIMATION
- Acclimation period: At least 14 days prior to testing
- Acclimation conditions: Same as test condition (flow-through condition)
- Type and amount of food: 1 to 2% of body weight per day with a commercial fish food
- Health during acclimation: The mortality rate of the stock batch of fish was 0.2% in the 7 days prior to the start of the test.

Route of exposure:

aqueous

Test type:

flow-through

Water / sediment media type:

natural water: freshwater

Remarks:

Well water drawn from a 100-meter bedrock well

Total exposure / uptake duration:

28 d

Total depuration duration:

14 d

Hardness:

72 mg/L as CaCO3

Test temperature:

23 ± 2 °C

pH:

- Acclimation phase: 7.1 - 7.6
- Uptake phase: 6.9 - 7.6
- Depuration phase: 7.1 - 7.5

Dissolved oxygen:

- Acclimation phase: 7.4 - 8.3 mg O2/L
- Uptake phase: 5.3 - 7.9 mg O2/L
- Depuration phase: 7.5 - 8.3 mg O2/L

TOC:

- Acclimation phase: 3.926 - 4.739 mg/L
- Uptake phase: 3.651 - 5.678 mg/L
- Depuration phase: 1.050 - 2.059 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: Clear glass aquaria constructed using silicone adhesive
- Size of vessel: 75 × 39 × 30 cm (length × width × height)
- Water level: Approximately 25 cm for a total solution volume of approximately 73 L per aquarium
- Type of flow-through: Continuous
- Flow rate: 420 mL/min of dilution water (turnover rate equivalent to 8 aquarium volumes per 24 hours and a 90% aquarium volume replacement every 7-hour period )
- No. of organisms per vessel:
- No. of vessels per concentration:1
- No. of vessels per control: 1
- Biomass loading rate: 0.28 g/L/aquarium/day of the 24-hour flow-through volume of the aquaria

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: The dilution water used for conducting the test was laboratory well water drawn from a 100-meter bedrock well, supplemented as needed with dechlorinated town of Wareham well water. Prior to use, dilution water was stored in a polyethylene tank where it was aerated to bring pH and dissolved gasses into equilibrium with the atmosphere.
- Intervals of water quality measurement: The temperature was monitored continuously in the solvent control vessel throughout the duration of
the test. The temperature, dissolved oxygen, and pH were measured daily in each vessel throughout the duration of the test.
- Total organic carbon (TOC): TOC was measured in all four aquaria one day prior to test initiation, at test initiation (day 0), and weekly during the uptake and depuration phases.
- Total hardness: Total hardness (expressed as CaCO3) was measured at test initiation in each aquarium.

OTHER TEST CONDITIONS
- Photoperiod: 16-hour light:8-hour dark period

RANGE-FINDING / PRELIMINARY STUDY
- Study design: 96-h acute toxicity test of the substance on rainbow trout (Oncorhynchus mykiss)
- Results used to determine the conditions for the definitive study: The 96-hour LC50 value was determined to be 0.13 mg/L. The definitive test exposure concentration was set to be 1/100th of the LC50, but still over 30 times higher than the detection limit for [methylphenyl-U-acetone, wa, thus 1.3 µg/L.

Nominal and measured concentrations:

- Nominal concentration: Solvent control, 1.30 µg/L
- Mean measured concentration: < LOQ, 1.21 µg/L, respectively. See Table 1 in 'Any other information on materials and methods incl. tables'

Reference substance (positive control):

no

Lipid content:

4.58 %

Time point:

other: Start of Uptake

Remarks on result:

other: Wet Weight Lipid Content

Lipid content:

5.5 %

Time point:

other: End of Uptake

Remarks on result:

other: Wet Weight Lipid Content

Lipid content:

5.07 %

Time point:

other: End of Depuration

Remarks on result:

other: Wet Weight Lipid Content

Key result

Conc. / dose:

1.24 µg/L

Temp.:

22 °C

Type:

BCF

Value:

820 dimensionless

Basis:

whole body w.w.

Time of plateau:

28 d

Calculation basis:

steady state

Remarks on result:

other: Whole Fish Confidence Intervals: 806 - 834

Conc. / dose:

1.24 µg/L

Temp.:

22 °C

Type:

BCF

Value:

812 dimensionless

Basis:

normalised lipid fraction

Remarks:

normalized to a 5% lipid content

Time of plateau:

28 d

Calculation basis:

steady state

Remarks on result:

other: Whole Fish Confidence Intervals: 798 - 826

Conc. / dose:

1.24 µg/L

Temp.:

22 °C

Type:

BCF

Value:

486 dimensionless

Basis:

edible fraction

Time of plateau:

28 d

Calculation basis:

steady state

Remarks on result:

other: Standard deviation: 36.39

Conc. / dose:

1.24 µg/L

Temp.:

22 °C

Type:

BCF

Value:

1 307 dimensionless

Basis:

non-edible fraction

Time of plateau:

28 d

Calculation basis:

steady state

Remarks on result:

other: Standard deviation: 88.62

Elimination:

yes

Parameter:

DT50

Depuration time (DT):

2.43 d

Elimination:

yes

Parameter:

DT50

Remarks:

growth-corrected half-life

Depuration time (DT):

2.57 d

Rate constant:

growth rate constant (d-1)

Value:

0.016

Rate constant:

growth-corrected depuration rate constant (d-1)

Value:

0.27

Rate constant:

overall uptake rate constant (L kg-1 d-1)

Value:

239.087

Remarks on result:

other: Standard error: 21.9384

Rate constant:

overall depuration rate constant (d-1)

Value:

0.285

Remarks on result:

other: Standard error: 0.0284

Details on kinetic parameters:

See 'Details on results'.

Details on results:

An overview of the results in provided in Table 3 to Table 10 in 'Any other information on results incl. tables'.

ANALYTICAL RESULTS
- Concentrations in the exposure solutions: All measured concentrations in the solvent control samples were below LOQ. Measured concentrations in the treated exposure solutions during the uptake phase ranged from 1.09 to 1.28 µg/L, representing 84 to 99% of the nominal concentration, respectively. The BCF values have been calculated using the time-weighted mean measured aqueous concentration, 1.24 µg/L. No measured concentrations above the limit of quantification (LOQ) were observed in the exposure solution throughout the depuration phase.
- Radioactivity characterization in extracted water samples: Throughout the uptake phase, 100% of the radioactivity present in the exposure tanks was confirmed to consist of [methylphenyl-U-14C]- labelled test substance. The percent recoveries of QC samples analyzed by HPLC during the exposure phase (N = 6) ranged from 95.4 to 107%.
- Concentrations in the fish: Mean measured concentrations in the edible fish tissue ranged from 441 to 645 µg/kg from day 3 through day 28 of the uptake phase. Steady state was considered to have been reached between day 14 and day 28. The mean concentration in the edible fish tissue at steady state was 601 µg/kg based on the concentrations on day 14, 21, and 28. Mean measured concentrations in the non-edible fish tissue ranged from 1112 to 1720 µg/kg from day 3 through day 28 of the uptake phase. The mean concentration in the non-edible fish tissue at steady state was 1618 µg/kg based on the concentrations on day 14, 21, and 28. Calculated concentrations in the whole body fish tissue ranged from 713 to 1035 µg/kg from day 3 through day 28 of the uptake phase. The mean concentration in the whole body fish tissue at steady state was 1015 µg/kg based on the concentrations on day 14, 21, and 28. On day 1 of the depuration phase, the mean measured concentration in the edible, non-edible, and whole body fish tissue was 466, 1109, and 730 µg/kg, respectively. These represented a 21 to 32% reduction in radioactive residues. On day 14 of the depuration phase, the mean measured concentration in the edible, non-edible, and whole body fish tissue was 29, 82, and 49 µg/kg, respectively. These represented a 95% reduction in radioactive residues.
- Radioactivity characterization in fish tissue samples: The majority of the radioactivity (98 to 99% of the TRR) was extractable from the whole body fish during the exposure phase. Characterization of [methylphenyl-U-14C]-labelled test substance was made by a comparison of HPLC sample retention times with the co-injected reference standard retention time. The calculated concentrations of [methylphenyl-U-14C]-labelled test substance in the fish tissue were 1155 µg/kg and 1280 µg/kg at day 14 and day 28, respectively.

BIOLOGICAL RESULTS
- Lipid analysis: Expressed as a percent of wet weight, the mean lipid content of the fish at the start of the uptake phase, end of the uptake phase, and the end of the depuration phase were 4.58, 5.50, and 5.07%, respectively. An overall mean lipid value of 5.05% was used in the calculation of lipid normalized BCF values.
- Bioconcentration factors: The BCF was determined for steady state (BCFSS) based on the mean of the concentrations in the fish on days 14, 21, and 28. The BCFSS was also normalized to a 5% lipid content (BCFSSL). The kinetic bioconcentration factor (BCFK) was determined following estimation of the uptake rate (K1) and depuration rate (K2) constants. The BCFK was normalized to a 5% lipid content (BCFKL). The BCFK was also corrected for growth by subtraction of the growth rate constant (Kg) from K2 (to give BCFKG), which was further normalized to a 5% lipid content (to give BCFKLG). The half-life (t½) and growth-corrected half-life (t½g) were also determined. Based on the time-weighted average measured concentration of [methylphenyl-U-14C]-labelled test substance in the aqueous exposure solution, the bioconcentration factors for whole fish tissue are summarized in the Table 10 in “Any other information on results incl. tables”. The depuration phase was conducted over a period of 14 days. After one day of depuration, 28% reduction in radioactive residues in the whole fish tissue was observed, which increased to > 95% after 14 days of depuration.

Table 3. Summary of Portion Fish Tissue Weights during the Test

Day	Tissue	Mean weight (g)
		Solvent control	1.3 µg/L
Uptake phase
0^a	Edible	1.0540	NA
	Non-Edible	0.7295	NA
	Whole Fish	1.7835	NA
3	Edible	0.8129	0.9549
	Non-Edible	0.5930	0.6462
	Whole Fish	1.4059	1.6011
7	Edible	0.9474	0.8826
	Non-Edible	0.6740	0.6784
	Whole Fish	1.6214	1.5610
14	Edible	1.0336	1.0155
	Non-Edible	0.7443	0.7768
	Whole Fish	1.7779	1.7923
21	Edible	1.3497	1.2566
	Non-Edible	0.9398	0.8507
	Whole Fish	2.2894	2.1072
28	Edible	1.2934	1.4344
	Non-Edible	0.9178	0.8997
	Whole Fish	2.2112	2.3341
Depuration Phase
1	Edible	1.0895	1.1730
	Non-Edible	0.7567	0.8124
	Whole Fish	1.8462	1.9854
3	Edible	1.2606	1.6535
	Non-Edible	0.8263	1.0880
	Whole Fish	2.0869	2.7415
7	Edible	1.6401	1.6030
	Non-Edible	1.1061	1.0398
	Whole Fish	2.7461	2.6428
14	Edible	2.0900	1.6133
	Non-Edible	1.3121	1.0225
	Whole Fish	3.4020	2.6358

a Fish used for weights on day 0 were sampled from the stock population.

NA = Not Applicable

NOTES: Portion weights are the average from the four fish sampled for solubilization at each interval. Whole fish weights are the average of the sum of the portions for each fish sampled

Table 4. Summary of Individual Fish Weight and Length during the Test

Test day	Solvent Control		1.3 µg/L
	Mean Weight (g)	Mean Length (mm)	Mean Weight (g)	Mean Length (mm)
Uptake Phase
0^a	1.8396	50.58	NA	NA
3	1.4473	46.435	1.6809	48.7525
7	1.6707	49.03	1.6158	49.335
14	1.8293	50.56	1.838	49.28
21	2.3568	54.3375	2.1647	50.5675
28	2.3095	53.2025	2.4472	52.1775
Depuration Phase
1	1.8842	49.67	2.0619	50.5075
3	2.144	52.415	2.8279	54.6825
7	2.8514	55.2425	2.727	53.9225
14	3.5115	60.7975	2.7194	55.545
Growth Rate (day-1)	0.01875	NA	0.01235	NA

a Fish used for lengths and weights on day 0 were sampled from the stock population.

NA = Not Applicable

Table 5. Determination of Parent [methylphenyl-U-14C]-labelled test substance Concentration in the Aqueous Extracts by HPLC

Day	Measured Concentration of total Radioactivity by LSC (µg/L)	% [methylphenyl-U-14C]-labelled test substance by HPLC	Measured Concentration of [methylphenyl-U-14C]-labelled test substance by HPLC (µg/L)a	Parent as % Nominal Concentrationb
Acclimation Phase
-1	1.1	100	1.10	84.9
	1.12	100	1.12	86.5
Mean	1.11	100	1.11	85.7
Uptake Phase		100
0	1.05	100	1.05	80.6
	1.05	100	1.05	81.1
Mean	1.05	100	1.05	80.8
3	1.22	100	1.22	93.9
	1.23	100	1.23	94.3
Mean	1.22	100	1.22	94.1
7	1.26	100	1.26	96.6
	1.26	100	1.26	96.7
Mean	1.26	100	1.26	96.7
14	1.26	100	1.26	96.6
	1.18	100	1.18	90.9
Mean	1.22	100	1.22	93.8
21	1.27	100	1.27	97.9
	1.26	100	1.26	96.8
Mean	1.27	100	1.27	97.4
28	1.25	100	1.25	96.2
	1.19	100	1.19	91.7
Mean	1.22	100	1.22	93.9

Table 6. Measured Concentrations of [methylphenyl-U-14C]-labelled test substance in Fish Tissue from the 1.3 µg/L Nominal Exposure Group during the Uptake Phase

 

Update phase day	Fish number	Edible Measured Concentration (µg/kg)	Non-Edible Measured Concentration (µg/kg)	Whole Fish Concentration (µg/kg)
0	1	<LOQ	<LOQ	<LOQ
	2	<LOQ	<LOQ	<LOQ
	3	<LOQ	<LOQ	<LOQ
	4	<LOQ	<LOQ	<LOQ
Mean (SD)		<LOQ (NA)	<LOQ (NA)	<LOQ (NA)
3	1	468.35	1267.85	805.10
	2	461.17	1111.16	720.50
	3	433.15	1125.50	716.25
	4	401.59	942.87	611.51
Mean (SD)		441.06 (30.39)	1111.85 (133.01)	713.34 (79.27)
7	1	458.70	1176.25	795.78
	2	523.09	1467.26	905.63
	3	567.57	1397.83	938.24
	4	580.47	1162.25	827.41
Mean (SD)		532.46 (54.97)	1300.90 (154.74)	866.77 (66.35)
14	1	551.61	1240.06	837.00
	2	785.01	1735.88	1182.52
	3	620.81	1648.81	1063.76
	4	624.35	1297.15	941.09
Mean (SD)		645.45 (98.88)	1480.48 (248.31)	1006.09 (149.74)
21	1	600.80	1836.35	1150.99
	2	558.63	2017.62	1125.24
	3	551.66	1819.41	1041.77
	4	563.95	1198.78	823.21
Mean (SD)		568.76 (21.95)	1718.04 (357.61)	1035.30 (148.88)
28	1	582.35	1563.44	971.17
	2	582.63	1631.70	1009.72
	3	567.50	1666.33	969.20
	4	626.54	1760.33	1060.90
Mean (SD)		589.76 (25.52)	1655.45 (81.95)	1002.74 (43.02)
Mean Steady State^a		601.32 (39.63)	1617.99 (123.13)	1014.71 (17.91)

a The mean steady state concentration for each tissue type is based on the average concentration from day 14, 21, and 28 and time-weighted average aqueous concentrations.

SD = Standard Deviation

LOQ = Limit of Quantification (edible tissue 2.83 µg/kg; non-edible tissue 3.02 µg/kg)

NA = Not Applicable

NOTE: All solvent control fish sampled resulted in concentration values <LOQ.

Table 7. Measured Concentrations of [methylphenyl-U-14C]-labelled test substance in Fish Tissue from the 1.3 µg/L Nominal Exposure Group during the Depuration Phase

Update phase day	Fish number	Edible Measured Concentration (µg/kg)	Non-Edible Measured Concentration (µg/kg)	Whole Fish Concentration (µg/kg)
1	1	487.90	1014.44	700.90
	2	513.85	1277.69	831.20
	3	436.17	1180.13	745.76
	4	426.80	963.53	643.63
Mean (SD) [% dep]		466.18 (41.62)	1108.95 (145.62)	730.37 (79.16)
				[28%]
3	1	284.61	1105.48	596.28
	2	280.29	749.82	458.65
	3	325.05	812.62	535.37
	4	306.98	896.13	554.33
Mean (SD) [% dep]		299.23 (20.81)	891.01 (155.03)	536.16 (57.60)
				[47%]
7	1	58.50	153.63	95.65
	2	78.03	234.14	147.53
	3	87.75	269.64	152.11
	4	106.40	264.06	171.18
Mean (SD) [% dep]		82.67 (19.95)	230.37 (53.48)	141.62 (32.31)
				[86%]
14	1	25.93	68.05	42.15
	2	24.04	73.16	43.45
	3	30.70	99.51	56.50
	4	34.68	85.69	55.16
Mean (SD) [% dep]		28.84 (4.80)	81.60 (14.05)	49.32 (7.56)
				[95%]

 SD = Standard Deviation

% dep = % depuration in whole fish from steady state value of 1015 µg/kg

Table 8. Distribution of Radioactivity in Whole Body Fish Tissue by Extraction/Combustion and HPLC-RAM Analysis during the Uptake Phase

Day	Sample Type	LSC		[methylphenyl-U-14C]-labelled test substance by HPLC-RAM
		Average Concentration of total Radioactivity (µg [14C]/kg tissue)	% TRR	% HPLC	Concentration (µg parent/kg tissue)	% TRR
1.3 µg/L
14	Extracts	1385	98.7	83.7	1155	83.7
	Non-extractable	17.9	1.3
	Total	1403	100
1.3 µg/L
28	Extracts	1442	99.1	88.7	1280	88.7
	Non-Extractable	13.2	0.91
	Total	1455	100

 

 

Table 9. Lipid Analysis during the Test

Wet Weight Lipid Content (%)
Identifier	Start of Uptake (Uptake Day 0)	End of Uptake^a(Uptake Day 29)	End of Depurationa (Depuration Day 15)
Fish 1	4.65	5.81	4.84
Fish 2	4.82	5.42	5.86
Fish 3	4.31	5.39	4.66
Fish 4	4.55	5.40	4.91
Mean	4.58	5.50	5.07
Standard Deviation	0.215	0.204	0.537
Overall mean		5.05

a. Samples taken once analytical results were determined and end of each phase was confirmed

Table 10. Bioconcentration Factors (BCF) during the Test

Uptake Phase	Edible Tissue	Non-Edible Tissue	Whole Fish	Whole Fish
Day	BCF	BCF	BCF	BCFL
3	359	904	580	574
7	436	1066	710	703
14	527	1209	822	813
21	457	1381	832	824
28	475	1332	807	799
Average at Steady State	486	1307	820	812
Standard Deviation	36.39	88.62	12.60	12.47
Whole Fish Confidence Intervals			806 - 834	798 - 826

 BCFL = Whole fish bioconcentration factor normalized to a 5% lipid content.

Validity criteria fulfilled:

yes

Remarks:

See Table 2 in 'Any other information on materials and methods incl. tables'

Conclusions:

[methylphenyl-U-14C] - labelled test substance was shown to have limited bioconcentration potential in fish over a 28 day exposure period, with all BCF values determined < 900. [methylphenyl-U-14C]-labelled test substance was rapidly eliminated from the fish with approximately 28% reduction in the fish body after one day of depuration, 86% reduction after seven days, and > 95% reduction after 14 days. The BCFss was determined to be 820.

Executive summary:

The objective of the study was to determine the uptake, bioconcentration, and elimination of [methylphenyl-U-14C]-labelled test substance in bluegill sunfish (Lepomis macrochirus) maintained under continuous renewal (flow-through) conditions. The study was conducted in accordance with the requirements of OSCPP Guideline 850.1730 Fish BCF (adopted April 1996) and OECD TG 305 (adopted October 2012). The study was compliant with GLP criteria. The exposure concentration for the bioconcentration test was selected based on the acute toxicity of the test substance to rainbow trout (Oncorhynchus mykiss) and its physical/chemical characterizations. The test concentration the exposure was set at 1.30 µg/L. The exposure concentration was 1/100th of the 96-hour LC50 value (0.13 mg/L) for the test substance to rainbow trout, but still over 30 times higher than the detection limit for [methylphenyl-U-14C]-labelled test substance in water (0.0348 µg/L). During the exposure (uptake) phase fish were continuously exposed to [methylphenyl-U-14C]-labelled test substance for a period of 29 days under continuous flow-through conditions. The final sample timing for the uptake phase was on day 28 of the exposure period; however, the fish remained in the exposure solutions until all results were available. A solvent control treatment, consisting of a test vessel treated with dilution water and acetone, was also included. Thereafter, the remaining fish were exposed to dilution water only for the post-exposure (depuration) phase of the test. Flow-through conditions were also employed for the depuration phase of the test which lasted 14 days.

 

Chemical analysis of the aqueous exposure solutions during the uptake phase resulted in measured concentrations ranging from 1.09 to 1.28 µg/L (84.1 to 98.7% of nominal concentrations). The measured concentrations met the requirement of being within 20% of the mean measured concentration. However, the bioconcentration factor (BCF) value was calculated using the time-weighted average aqueous concentration. The time-weighted average aqueous concentration is 1.24 µg/L, the average from uptake day 14, 21, and 28. A plateau in measured concentrations in whole body fish tissues (steady state) was considered to have been achieved between days 14 and 28 of the uptake phase. The mean concentration in whole body fish tissue at steady state during the uptake phase was 1.01 mg/kg. The BCF was determined for steady state (BCFSS) based on the mean of the concentrations in the fish on days 14, 21, and 28. The BCFSS was normalized to a 5% lipid content (BCFSSL). The kinetic bioconcentration factor (BCFK) was determined following estimation of the uptake rate (Ku or K1) and depuration rate (Kd or K2) constants. The BCFK was also normalized to a 5% lipid content (BCFKL). The BCFK was also corrected for growth by subtraction of the growth rate constant (Kg) from K2 (to give BCFKG), which was further normalized to a 5% lipid content (to give BCFKLG). The half-life (t½) and growth-corrected half-life (t½g) were also determined. The mean lipid content of the fish at the start of the uptake phase, end of the uptake phase, and end of the depuration phase were 4.58, 5.50, and 5.07%, respectively. An overall mean lipid value of 5.05% was used in the calculation of lipid normalized BCF values.

 

Based on the time-weighted average measured concentration of [methylphenyl-U-14C]-labelled test substance in the aqueous exposure solution, the BCFss was determined to be 820. And a half-life time of 2.43 days. Overall, the [methylphenyl-U-14C]-labelled test substance was shown to have limited bioconcentration potential in fish over a 28 day exposure period, with all BCF values determined < 900. [methylphenyl-U-14C]-labelled test substance was rapidly eliminated from the fish with approximately 28% reduction in the fish body after one day of depuration, 86% reduction after seven days, and > 95% reduction after 14 days.

Description of key information

BCF = 820 in whole fish (bluegill sunfish), OECD TG 305, Kang 2018

Key value for chemical safety assessment

BCF (aquatic species):

820 dimensionless

Additional information

The uptake, bioconcentration, and elimination of [methylphenyl-U-14C]-labelled test substance in bluegill sunfish (Lepomis macrochirus) was studied under GLP to OECD TG 305 (adopted October 2012). Test fish were exposed under flow-through conditions for a period of 29 days. The nominal test concentration for exposure was 1.30 µg/L, which is 1% of the 96-hour LC50 value (0.13 mg/L) for the test substance to rainbow trout, but still over 30 times higher than the detection limit for [methylphenyl-U-14C]-labelled test substance in water (0.0348 µg/L). Chemical analysis of the aqueous exposure solutions during the uptake phase resulted in measured concentrations ranging from 1.09 to 1.28 µg/L (84.1 to 98.7% of nominal concentrations), thus fulfilling the quality criteria of the test guideline. The bioconcentration factor (BCF) value was calculated using the time-weighted average aqueous concentration, which was 1.24 µg/L. The mean concentration in whole body fish tissue at steady state during the uptake phase was 1.01 mg/kg. The BCF was determined as 820 for steady state (BCFSS). All other BCF values, such as the lipid content normalised BCFSS, the kinetic bioconcentration factor (also normalised to lipid content, and/or growth rate) were also less than 900, indicating the limited bioconcentration potential of the substance. Flow-through conditions were also employed for the depuration phase of the test which lasted 14 days. The depuration half-life of the substance from fish tissue was determined as 2.43 days, and the substance was found to be rapidly eliminated from fish with about 28% reduction of tissue concentrations after one day of depuration, 86% reduction after seven days and more than 95% reduction after 14 days.