EFFECTS OF TRIBUTYLTIN ON A COASTAL NORTH-SEA PLANKTON COMMUNITY IN ENCLOSURES

The toxicity of tributyltin (TBT) to a neritic North Sea plankton comm unity was studied in experiments using outdoor enclosures with a volum e of 1.2 m(3). Nominal TBT concentrations of 0, 0.056, 0.1, 0.18, 0.32 , and 0.56 mu g/L were tested in duplicate for 28 d. A first-order dec rease of TBT in the water column was observed for the highest nominal concentration, with a rate constant of 0.12 per day (t(1/2) of 5.7 d). Median effective concentration (EC50) values were determined for the dominant zooplankton species, Temora longicornis (Copepoda). The EC50 values were lower when calculated for biomass than when calculated for density and ranged between 0.15 and 0.32 mu g/L, depending on exposur e time. At high TBT concentrations, enhanced pH levels and oxygen conc entrations were observed, indicating high algal production levels, whi ch would result from reduced grazing by zooplankton. Depending on expo sure time, EC50 values for the indirect effect of TBT on pH varied bet ween 0.10 and 0.22 mu g/L, indicating that the indirect effects of TBT are at least as sensitive as the direct effects. The study showed tha t testing chemicals in outdoor enclosures can provide data complementa ry to that obtained from laboratory toxicity tests.