RELATIONSHIP BETWEEN CHRONIC TOXICITY AND BIOACCUMULATION OF CADMIUM IN HYALELLA-AZTECA

The chronic toxicity of Cd to Hyalella in Burlington City tap (Lake Ontario) water with additions of complexing agents, distilled water, or sediments was much more constant if toxicity was expressed as a function of Cd bioaccumulated, rather than the Cd concentrations added or measured in the water. Additions of 20 mg humic acid/L or 0.5-mu-M EDTA increased the 6-wk EC50 from 0.53 to 4.6 and 19-mu-g/L, respectively. The EC50 based on bioaccumulated Cd, however, increased from 38 to only 44-mu-g/g (dry weight). Addition of sediments increased the 4-wk EC50 by > 1000-, 13-, or 2.3-fold for EC50s based on nominal Cd added, Cd concentrations measured in water, or Cd concentrations accumulated by Hyalella, respectively. A 10-fold reduction in hardness caused a twofold increase in the 6-wk EC50 based on Cd accumulation. The relationship between survival and Cd bioaccumulation by Hyalella was, therefore, affected less by complexing agents, hardness, and sediments than was survival compared with concentrations in water. Published Cd concentrations in Hyalella from a number of Ontario lakes are close to levels associated with toxicity in the laboratory.