the Toxicity of Cadmium and Zinc to the Mysid Shrimp, \u3cem\u3eNeomysis americana\u3c/em\u3e Smith (Crustacea: Mysidacea)

Mysid shrimp, Neomysis americana Smith, were subjected to long term exposure of low concentrations of cadmium under dynamic conditions to determine changes in tissue cadmium or zinc concentrations. No appreciable accumulation was detected. However, this may be a reflection of the limitations of the analytical method used to determine cadmium and zinc concentration levels. Other groups of mysids were exposed to cadmium and zinc under static conditions to evaluate the extent of relative toxicity of each metal. Comparative 24 hour LC50 (concentration lethal to 50% of the population within 24 hours) values derived by multiple regression indicated relative toxicity of cadmium to zinc to be at an approximately 10:1 ratio (cadmium 24-hour LC50 = 82.30 ug/L; zinc 24-hour LC50 = 872.93 ug/L). The cadmium LC50 line exhibited a greated negative slope than the zinc LC50line, indicating a greater toxicity of cadmium. Also, curvalinearity of the regression lines indicated factors more complex than simple replacement or competition for sites on a specific protein effect the bioassays at higher concentration levels, the result being a greater toxicity of cadmium. Metal bioassays of both the dynamic and the static types of marine systems may be unsuitable for precise quantitative determinations of LC50 values due, at least in part, to the highly ionic environment