Very low levels of waterborne butyltins modulate hemocyte function in the blue mussel Mytilus edulis

Hemocyte functions were used to determine the effect of very low concentrations (1, 3 and 6 ng Sn l -1 ) of tributyltin (TBT) and dibutyltin (DBT) on the internal defense of adult blue mussel Mytilus edulis under flow-through conditions over 11 d.Hemolymph was sampled without harming mussels on Days 0, 1, 4 and 11 for measures of hemocyte count (HC), lysosome retention (LR) and phagocytic activity (PA).HC was increased from Day 1 by TBT at 6 ng l -1 and by DBT at 3 and 6 ng l -1 on Day 11.LR was increased by both butyltins at concentrations as low as 1 ng l -1 from Day 4. PA was increased by DBT at 6 ng l -1 from Day 4. No difference was detected between the impacts of TBT and DBT on LR but TBT had a greater impact on HC and DBT had a greater impact on PA.These results support the hypothesis that both TBT and DBT can cause modulations of the internal defense system of mussels at concentrations as low as 1 ng Sn l -1 after only a few days of continuous exposure.