Chronic tributyltin toxicity experiments with the chesapeake bay copepod,Acartia tonsa

Abstract

Repeated chronic toxicity experiments were conducted with the Chesapeake Bay zooplankter Acartia tonsa to evaluate its sensitivity to tributyltin (TBT). Experiments were initiated with A. tonsa nauplii <48 h old. All tests were conducted with continuous-flow conditions and measured TBT concentrations. Results from a 9-d range finding experiment and two 6-d chronic experiments are presented. TBT test concentrations were maintained with minimal fluctuations over time and toxicity results were similar in the repeated chronic experiments. The range-finding experiment demonstrated severe reductions in survival of A. tonsa at the lowest measured concentration (0.029 μg TBT/L). In the 6-d experiments, 0.023 and 0.024 μg TBT/L were the lowest measured TBT concentrations to significantly reduce survival relative to the controls (i.e., lowest observed effect concentration [LOEC]). No observed effect concentrations (NOEC) measured at 0.012 and 0.010 μg TBT/L were used to calculate chronic values of 0.016 and 0.017 μg TBT/L for these two experiments. A. tonsa nauplii are very sensitive to TBT relative to other estuarine organisms. These toxicity data are environmentally relevant since TBT concentrations exceeding the chronic value for A. tonsa have been reported from numerous locations in Chesapeake Bay.