Effects of tributyltin on a coastal North Sea plankton community in enclosures

The toxicity of tributyltin (TBT) to a neritic North Sea plankton community was studied in experiments using outdoor enclosures with a volume 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 decrease 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 exposure time. At high TBT concentrations, enhanced pH levels and oxygen concentrations were observed, indicating high algal production levels, which would result from reduced grazing by zooplankton. Depending on exposure time, EC50 values for the indirect effect of TBT on pH varied between 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 that testing chemicals in outdoor enclosures can provide data complementary to that obtained from laboratory toxicity tests.