Ametryn

Bioaccumulation: aquatic / sediment

Description of key information

Three aquatic bioaccumulation studies, across two different species of freshwater fish, all returned whole body bioconcentration factors (BCF) of 62.7x to 83x.

Additional information

Three studies are available that describe the bioaccumulation of the substance.

The key study is a Klimisch-1, GLP-compliant study, sponsored by Ciba-Geigy and carried out in 1991 by Springborn Laboratories Inc. (Dionne E) according to EPA OPP 165-4 (Laboratory Studies of Pesticide Accumulation in Fish) [equivalent or similar to OECD 305 (Bioconcentration: Flow-through Fish Test), EC C.13], but with a 38-day uptake period instead of 28. The uptake of 85μg/L nominal (88±11μg/L measured) 14C-Ametryn from aquarium water by bluegill sunfish was studied for 38 days, followed by a 28-day depuration phase. The concentration of 14C-residues in both the edible (muscle) and the non-edible (viscera and carcass) tissues of the fish reached an apparent steady state by day 21. From the mean measured aqueous Ametryn concentration during the uptake phase, and the mean steady-state tissue concentrations, bioconcentration factors for bluegill were 61 X for edible tissue, 110 X for non-edible tissue, which correspond to 83 X for the whole fish. The half-life (50% elimination) of the accumulated 14C-residues occurred between days 14 and 21, days 3 and 7, and days 7 and 10 of the depuration phase for edible, non-edible and whole body tissues, respectively. By day 28 of depuration, 58%, 80% and 69% of the 14C-residues present on the last day of exposure had been eliminated from the edible, non-edible and whole body tissues, respectively. Tissues from a separate 28-day exposure of bluegill sunfish to 88μg/L Ametryn were used to identify metabolites. Metabolism of ametryn in bluegill sunfish appears to be via dealkylation followed by conjugation of the thiomethyl group to form a cysteine conjugate, which may further rearrange to form a cystine metabolite or undergo N-acetylation.

The first supporting bioaccumulation study was sponsored by Sipcam Agro S.A. and carried out in 1996 by Bioagri (Zaccaria CB) in accordance with IBAMA – Portaria No. 139/1994 [equivalent or similar to OECD 305B (Bioaccumulation: Semi-static Fish Test), no EC method]. The uptake of 9μg/L and 90μg/L nominal (9.2μg/L and 93μg/L measured) 14C-Ametryn from aquarium water by zebrafish was studied for 7 days, followed by a 28-day depuration phase. The test was run at 22-24°C and the concentration of 14C-residues in the whole fish were measured and toxicokinetic parameters for the uptake and depuration phases were calculated using a computer program (BIOCINE).  This method estimated uptake rate constants Ku = 0.3423 ± 0.1250 (low concentration) and Ku = 0.5685 ± 0.0846 (high concentration), and depuration rate constants Kd = 0.0111 ± 0.0017 (low concentration) and Kd = 0.0091 ± 0.0006 (high concentration), a half-life of 62.3256 ± 9.3853 hours (low concentration) and 76.5629 ± 5.4701 hours (high concentration), and the time to reach 90% of steady state = 207.0411 ± 31.17 hours (low concentration) and 254.3366 ± 18.1713 hours (high concentration). The BCF at steady state estimated by BIOCINE was 30.7 ± 6.6070 (low concentration) and 62.7 ± 4.8623 (high concentration). The study did not meet the validation criteria as the measured oxygen concentrations across all groups were below 60% saturation (which is 5 mg/L at 24°C).

The second supporting bioaccumulation study was sponsored by Ciba-Geigy and carried out in 1982 by ABC Labs (Boudreau, Forbis and Cranor) according to a method equivalent or similar to OECD 305 (Bioconcentration: Flow-through Fish Test), EC C.13. The uptake of 100μg/L nominal (94 to150μg/L measured, average 120μg/L) 14C-Ametryn from aquarium water by Lepomis macrochirus (bluegill sunfish) was studied for 28 days, followed by a 14-day depuration phase. Radioanalysis of edible and nonedible tissue sections throughout the exposure period indicated a rapid uptake of 14C-Ametryn. Tissue uptake concentrations ranged from 0.71 to 6.5 mg/kg for edible and 2.7 to 12 mg/kg for non-edible tissue. The maximum uptake concentrations for edible and non-edible tissues occurred on Days 28 and 21 of the study, respectively. These concentrations represent bioconcentration factors (BCF) of 56 and 110, respectively. The whole fish uptake concentration is interpolated to be 9.0 mg/kg with a BCF of 80. A biological steady-state appeared to be obtained by Day 10 of the study, as indicated by a linear regression analysis. To measure the elimination of 14C-Ametryn, the test fish were placed in clean water for 14 days. Radioanalysis throughout the depuration period indicated 49 and 79 percent clearance rates from edible and nonedible tissue, respectively. The edible levels decreased from 6.5 mg/kg on day 28 of uptake to 3.3 mg/kg by the end of the study; nonedible concentrations dropped from 11 mg/kg on day 28 to 2.3 mg/kg by Day 14 of depuration. The parent compound, Ametryn, was characterized as the major form of 14C-Ametryn residues in all three tissue types. The viscera tissue was the only tissue type investigated that contained 14C-Ametryn residues characterized as all of the known metabolites. Two additional unidentified forms of 14C-Ametryn residues were also characterized in the viscera tissue sample.