| TOXIC CONCENTRATIONS IN FISH EARLY LIFE STAGES PEAK AT CRITICAL MOMENT |
| MURK, A.J., Wageningen University, PO Box 8000, NL 6700 EA Wageningen, The Netherlands, Tinka.Murk@WUR.NL; Foekema, E.M., IMARES, PO Box 57, 1780 AB Den Helder, the Netherlands, Edwin.Foekema@WUR.NL.
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| The effects of marine POPs including the dioxin-like PCB 126 on the early development of the marine flatfish sole (Solea solea) were tested in a prolonged early life stage (pELS) test including the metamorphosis of the symmetric larvae into an asymmetrical flatfish. ELSs of sole were exposed via seawater from 0 until 4, 8, 10 or 15 days post fertilisation (dpf) and the development of the larvae registered under further unexposed conditions. The LC50s at the start of the free-feeding stage (12 dpf) ranged between 39 and 83 ng PCB 126/l depending on exposure duration. Prolonged observation revealed that dose-related mortality strongly increased after the yolk sac stage and resulted in much lower LC50s ranging between 1.7 and 3.7 ng PCB 126/l for exposures during 15 to 4 dpf respectively. Exposure during the egg stage only caused adverse effects two weeks later. The internal LD50 of these larvae, determined with an in vitro gene reporter assay, was 1 ng was dioxin-equivalents (TEQ)/g lipid. This is within the same order of magnitude as in fish from polluted areas. As no physiological explanation for the delayed toxicity could be found, the developments of the internal POP concentrations in the larvae over time was modelled and measured for compounds with different Log Kow values. During development the fish larvae strongly change in physiology and behaviour which affects uptake and excretion of compounds. The study revealed peak tissue concentrations in developing sole at the end of the yolk sac stage for compounds with log Kow >6. The main exposure of fish eggs to POPs is through maternal transfer of POP-containing yolk lipids. As the lipid reserves are depleted just before the larvae become free feeding, the peak tissue POP-concentrations in the larvae even exceed those of the adult fish. This peak occurs shortly before the observed peak in (delayed) toxic effects. The results demonstrate that early life stage experiments terminated at the end of the yolk sac stage will underestimate the effects of lipophilic persistent toxic compounds. It also demonstrates that even when larvae hatch at relatively clean sites, the reproductive success of contaminated fish populations can be affected by persistent compounds that are accumulated by the female fish and passed on to their eggs. |
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