Accumulation and elimination kinetics of dietary endosulfan in Atlantic salmon (Salmo salar)

The carry-over of dietary endosulfan to the fillet of farmed Atlantic salmon was studied. The uptake and elimination rate constants of the α and β isoform of endosulfan were determined in seawater adapted Atlantic salmon (initial weigh 173 ± 25 g) fed on endosulfan enriched diets (724 and 315 μg kg^-1 for α- and β-endosulfan, respectively) for 92 days, followed by a 56 days depuration period with feeding on control diets (<0.3 μg kg^-1 endosulfan). The accumulation of the toxic metabolite endosulfan sulphate, which was not detected (<0.5 μg kg^-1) in the experimental feeds, was also determined. Dietary β-endosulfan was more persistent than α-endosulfan as demonstrated by a higher uptake (41 ± 8% vs. 21 ± 2%) and lower elimination (26 ± 2 × 10^-3 day^-1 vs. 40 ± 1 × 10^-3 day^-1) rate constants, and a higher biomagnification factor (0.10 ± 0.026 vs. 0.05 ± 0.003, p < 0.05). Based on the decrease in diastereometric factor over time, biotransformation was estimated to account for at least 50% of the endosulfan elimination. The formation of the metabolite endosulfan sulphate comprised a maximum 1.2% of the total accumulation of endosulfan. Using a simple one-compartmental model and the experimentally-determined rate constants, it was predicted that only dietary concentration higher than 7.5 mg kg^-1 would cause the estimated maximum residue level (MRL) in fillet of 0.47 mg kg^-1 to be exceeded. Model estimations also predict that current EU maximum permitted levels in fish feeds (0.005 mg kg^-1) would give fillet concentrations that are under the detection limit (0.3 μg kg^-1), which is in agreement with the general absence of endosulfan in monitored farmed Atlantic salmon.