THE INFLUENCE OF SALINITY ON THE TOXICITY OF VARIOUS CLASSES OF CHEMICALS TO AQUATIC BIOTA

The objective of this study was to review all available aquatic toxici ty literature regarding the effects of salinity on the toxicity of var ious classes of inorganic and organic chemicals. Toxicity data for stu dies in which toxicity was assessed at various salinities were organiz ed by chemical classes and trophic groups. Seventy percent of the stud ies were conducted with either crustaceans or fish. The other 30% were with mollusks, annelids, zooplankton, bacteria, phytoplankton, or fun gi. Results from 173 data entries showed that negative correlations (t oxicity increasing with decreasing salinity) were reported most freque ntly (55%), followed by no correlations (27%) and positive correlation s (18%). The toxicity of most metals such as cadmium, chromium, copper , mercury, nickel, and zinc was reported to increase with decreasing s alinity. This finding is likely related to the greater bioavailability of the free metal ion (toxic form) at lower salinity conditions. Ther e was generally no consistent trend for the toxicity of most organic c hemicals with salinity. The one exception to this was reported with or ganophosphate insecticides, the toxicity of which appeared to increase with increasing salinity. Physiological characteristics of the variou s test species were important in determining the toxicity of the vario us classes of chemicals at a range of salinities. Results from various studies showed that euryhaline species were more resistant to toxic c onditions at isosmotic salinities due to minimization of osmotic stres s. Specific examples showed that fish were more resistant to toxic che micals at middle salinities when compared with either lower or higher extremes. Life history and ecology of test species were important fact ors to consider when interpreting salinity/contaminant interaction dat a.