Toxicokinetic model assessment on the dechlorination of dietary toxaphene CHB-62 into CHB-44 in Atlantic salmon (Salmo salar L.).

European Union legislation on the upper limits of toxaphene in feed and food include the congeners CHB-26, CHB-62 and CHB-50 and is set at 50 µg kg⁻¹ feed for the sum of these three congeners. However, due to their elevated presence in fish, the congeners CHB-40 and CHB-41, CHB-44, and CHB-42 should also be included according to the European Food Safety Authority (EFSA) in 2005. Earlier trials with model zebra fish have shown in vivo dechlorination of dietary CHB-62 to CHB-44 and, to a lesser degree, of CHB-50 to CHB-40. Biomagnification patterns of Atlantic salmon, fed with technical toxaphene-enriched feeds, indicated that Atlantic salmon have a similar dechlorination. In the present study, a serial one-compartment physiological kinetic model, which includes differentiated growth of body components, is used to quantify the contribution of dechlorination to the congener-specific fillet accumulation of a mixture of dietary toxaphene congeners in Atlantic salmon. The model is assessed from experimental uptake and elimination kinetics of Atlantic salmon smolt fed with technical toxaphene for 122 days followed by a depuration period of 75 days in which the fish were fed toxaphene-free control feed. The serial one-compartment model shows that about 31% of CHB-44 that accumulated in the fillet originated from dietary CHB-62. In contrast, dechlorination of CHB-50 into CHB-40 is not significant. The results show that previously demonstrated in vivo dechlorination of CHB-62 into CHB-44 in zebra fish also occurs in the farmed fish species Atlantic salmon. This dechlorination can at least partly explain the relatively elevated CHB-44 observed in toxaphene fish surveys.