CHRONIC TOXICITY OF WATER TRIBUTYLTIN (TBT) AND COPPER TO SPAT OF THEBIVALVE SCROBICULARIA-PLANA - ECOLOGICAL IMPLICATIONS

Two 30 d long static toxicity tests were performed on small spat (2 to 3 mm in length) of the estuarine bivalve Scrobicularia plana (da Cost a): the effects of tributylin (TBT) and copper on the survival and bur ying activity in sand of juveniles were monitored in 1991, and growth and burying activity as affected by TBT were investigated on a sample of a different cohort in 1992. Results showed that an LC50 (concentrat ion killing 50% of the population considered) could be set for TBT at < 1.3 mug Sn l-1 (as analysed), while exposure to up to 80 mug Cu l-1 did not result in increased mortalities with respect to the controls. Every dose of TBT tested in 1991 (nominal 0.5, 1, 2 and 4 mug Sn l-1) impaired the burying activity of spat significantly from Day 6, and Cu concentrations at 20 mug l-1 and above also increased the burying tim e of juveniles by the end of the experiment; the no-observed-effect co ncentration (NOEC) for Cu was the lowest dose tested (i.e. 10 mug l-1) . In 1992 the effect of 4 lower TBT concentrations (nominal 50, 125, 2 50 and 500 ng Sn l-1) on the juvenile burying activity was somewhat in consistent; however, burying time of individuals exposed to 500 ng Sn l-1 was always higher than that estimated to be characteristic of spat at initiation of the test. In addition, juvenile growth (weight gain) was significantly reduced by all TBT concentrations (i.e. lowest rang e of 12 to 43 ng Sn l-1, as analysed). It is concluded that TBT has pr obably caused the disappearance of some S. plana populations in the UK ; similarly, organotin may have also caused the decline in S. plana ab undance in populations from elsewhere in Europe.