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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

BCF (parent; whole fish, wet weight) = 121
BCF (parent; whole fish, normalised to 5% lipid content) = 72

Key value for chemical safety assessment

Additional information

A guideline study according to OECD 305, EPA-FIFRA 72-6, EPA-FIFRA 165-4, and US EPA OCSPP 850.1730 was conducted by Bruns & Justus (2014) in order to measure uptake, depuration and metabolism of the test item by determining its uptake rate constant (Ku), depuration rate constant (Kd) and the bioconcentration factor (BCF), including the qualitative and quantitative characterization of the metabolites in fish and water. 70 young bluegill sunfish (Lepomis macrochirus) were exposed for the uptake part of the study (two treatment levels (B+C), one control (A)) for 28 days. Further, a total of 30 bluegill sunfish were exposed to the test item for 7 respectively 14 days (15 fish at a time) to investigate the biotransformation (one treatment group (D)) in fish and water. The test was perfomed under flow-through conditions. A dosing system was used to maintain mean water concentrations of 0.0300 mg and 0.300 mg test item / L for the bioconcentration part and 0.300 mg / L for the biotransformation part. After the exposure of 28 days remaining test fish of part 1 were placed in clean water for further 14 days in order to determine the depuration of the test item. Lipids were extracted from four additional fish (part 1) in order to quantify the mean lipid content in fish on days 0, 28 and 42. The test fish of part 2 (biotransformation) were sampled and divided into edible and viscera tissues after 7 and 14 days. Tissues were extracted with acetonitrile/water mixtures. Between 93.9 % and 95.9 % of the TRR were extracted by this procedure. Metabolic profiles of the extracts were measured with reversed phase HPLC. The parent compound and metabolites were identified in extracts of edibles and viscera by spectroscopic methods.

The fish showed no mortalities or abnormal behaviour throughout the test in all test vessels. Isotianil accumulates in bluegill sunfish with a total residue bioconcentration factor of about 233 to 244 for whole fish. The total residue bioconcentration factor is calculated as the mean accumulation factor observed during steady state (sum of radio-labelled compounds, isotianil parent, metabolites and unextractable radioactivity). In case of this study the mean accumulation factor for the measurement days 7 - 28 were used for calculation of the total residue bioconcentration factor. When exposure ceases, the residues are depurated with a half-life of 0.744 – 0.876 days for the 0.0300 and 0.300 mg/L exposure groups, respectively. After 14 days in uncontaminated water 97.5% (nominal concentration of 0.0300 mg/L) and 97.6% (nominal concentration of 0.300 mg/L) of the mean plateau radioactivity were depurated from whole fish. 95% of the mean plateau radioactivity has been depurated from whole fish after 3.22 (0.0300 mg/L) and 3.79 days (0.300 mg/L), respectively. The uptake rate constant (Ku), depuration rate constant (Kd), time for half clearance and the kinetic bioconcentration factors (based on TRR) for edible parts and for whole fish were determined. The parameter estimates were determined to be:

Origin Calculation Results

0.0300 mg [isothiazole-3-14C, carboxamide-14C]isotianil / L(based on TRR)

0.300 mg [isothiazole-3-14C, carboxamide-14C]isotianil / L(based on TRR)

Parameter

Edible parts

Viscera

Whole Fish

Edible parts

Viscera

Whole Fish

Kinetic Bioconcentration Factor (BCFTRR)

90.4

545

269

58.3

486

234

Time to Reach 95% of Steady-State (days)

1.79

3.62

3.22

2.99

3.89

3.79

t(1/2) for Clearance (days)

0.412

0.835

0.744

0.691

0.898

0.876

Uptake Rate Constant (Ku) (1/day)

152 (± 28.4)

452 (± 24.2)

251 (± 11.0)

58.5 (± 4.10)

375 (± 16.2)

186 (± 7.06)

Clearance Rate Constant (Kd) (1/day)

1.68(± 0.242)

0.830 (± 0.0432)

0.932 (± 0.0583)

1.00 (± 0.175)

0.772 (± 0.0364)

0.792 (± 0.0460)

The analysis of stock solutions of the test compound revealed that [isothiazole-3-14C, carboxamide-14C]isotianil was stable in stock solutions during the time of the experiments.

Water samples were analysed by HPLC with radiodetection after solid phase extraction (SPE). In the water samples collected during the exposure period, an amount of 91.6% to 99.5% of the TRR was identified. The parent compound Isotianil was by far the main component and accounted for 69.3% to 91.6% of the radioactivity (TRR). The metabolite DCIT-acid was found in a range of 2.7% to 8.4%. The metabolites sulfate and glucuronide of 4’-OH-isotianil were found at 8.2% to 19.0% of the TRR. The TRRs in the water corresponded to 214 to 308 µg/L. After one day of depuration, the parent compound Isotianil was still the major component, representing 42.3% of the TRR. The two conjugated metabolites sulfate and glucuronide of 4’-OH-isotianil were found at higher portions than during the exposure phase, i.e. at 34.8% of the TRR. However, the TRR in the water was at a much lower level of 18.5µg/L. The identification rate was 77.0% of the TRR. These results show that after termination of the exposure to radiolabelled isotianil, the concentration of total radioactivity was decreasing rapidly in the water. The metabolites in the water originated from excretion by the fish. To assesses biotransformation edible parts and viscera of fish sampled on day 7 and 14 were extracted with acetonitrile/water mixtures. Between 93.9% and 95.9% of the TRR was extracted. The TRRs in the edible parts were 11.7 mg/kg (day 7) and 20.7 mg/kg (day 14) and were much lower than in the viscera, where TRRs of 97.9 mg/kg (day 7) and 120.0 mg/kg (day 14) were observed. After purification by SPE and concentration the extracts represented 92.7% to 95.0% of the TRR and were analysed with HPLC. Parent compound and the metabolite DCIT-acid were identified by LC-MS/MS spectrometry. The metabolite 4’-OH-isotianil as well as two conjugates, the sulfate of 4’-OH-isotianil and the glucuronide of 4’-OH-isotianil, were identified by LC-MS/MS spectrometry and by NMR spectroscopy. Between 84.4% and 94.0% of the TRR in the edible parts and viscera of the fish was identified. Parent compound was by far the major component in the edible parts, representing 75.3% (day 7) and 67.2% (day 14) of the TRR. The sum of the sulfate and of the glucuronide of 4’-OH-isotianil represented 3.0% (day 7) and 17.3% of the TRR and the unconjugated metabolite represented 6.1% and 6.0% of the TRR. The metabolite DCIT-acid was found only in the samples of day 14, at 3.6% of the TRR. In the viscera samples of the fish, the major components were parent compound, the sum of the sulfate and of the glucuronide of 4’-OH-isotianil and the unconjugated 4’ OH-isotianil, occurring in a range of 20.3% to 39.8% of the TRR. The DCIT-acid was detected at 4.2% (day 7) and 3.5% of the TRR (day 14). Isotianil was moderately metabolised in fish after uptake from water. Two metabolic routes were observed: (a) hydroxylation at the 4-position of the anthranilonitrile ring, followed by conjugation with sulfuric and glucuronic acid and (b) cleavage of the molecule leading to the metabolite DCIT-acid. A mean lipid content (day 0-28) of 8.46 % for the used batch was found. Based on these results the steady-state-BCF parent (based on whole fish, wet weight) in the 0.300 mg / L test level is 121. The steady-state-BCF for parent (normalised to 5% lipid content in fish) is 72.