Influence of Salinity and Sulfate on the Toxicity of Chromium(vi) to the Estuarine Diatom Thalassiosira Pseudonana¹

The acute toxicity of Cr(VI) to the diatom Thalassiosira pseudonana (Hasle and Heimdal) clone 3H was determined in artificial media of 3.2 and 0.32 ppt salinity and with variations of sulfate concentration in the media independent of salinity. Inhibitory concentrations of Cr(VI) ranged from 6.6 μM for growth rate and 4.9 μM for cell yield at 3.2 ppt salinity and 2.8 μM sulfate to 0.04 μM for growth rate and 0.02 μM for cell yield at 0.32 ppt salinity and 0.019 mM sulfate. The inhibition by Cr(VI) was a function of the ratio of Cr(VI) to sulfate. Inhibition occurred when‐this ratio exceeded about 500:1. It is suggested that the mechanism for the toxicity of Cr(VI) to diatoms and perhaps other aquatic organisms involves a site at which sulfate and chromate compete.