BIOASSAYING THE TOXICITY OF TRIBUTYLTIN-(TBT)-POLLUTED SEDIMENT TO SPAT OF THE BIVALVE SCROBICULARIA-PLANA

A solid-phase sediment toxicity bioassay with small spat (2 to 3 mm in length) of the estuarine bivalve Scrobicularia plana (da Costa) was r un for 36 d in 1992: lethal and sublethal effects were investigated. W hile 2 negative control sediments allowed juvenile weight gain in exce ss of 140% of initial weight, a control sediment contaminated with non -tributyltin (TBT) compounds resulted in mortalities > 80% in 12 d. A TBT-polluted sediment (0.27 mug Sn g-1 dry wt) did not produce any mor tality or avoidance response, but both growth and burying activity of clams at the end of the trial were significantly reduced with respect to those of spat in control treatments. Although frozen storage of sed iment samples renders this experiment somewhat inconclusive, results c onfirm suspicion of field TBT-sediment deleterious effects at approxim ately 0.3 mug Sn g-1 dry wt. The environmental implications of finding s are discussed in relation to the disappearance of S. plana populatio ns throughout Atlantic Europe concurrent with TBT build-up in deposits ; in addition, arguments are presented to emphasize the ecological rel evance of sublethal stress affecting parameters such as the differenti al capability of benthic bivalves to avoid predation. Finally, the sui tability of S. plana spat for widespread sediment toxicity bioassays i s assessed.