ECOLOGICAL RISK ASSESSMENT OF COPPER AND CADMIUM IN SURFACE WATERS OFCHESAPEAKE-BAY WATERSHED

This ecological risk assessment was designed to characterize risk of c opper and cadmium exposure in the Chesapeake Bay watershed by comparin g the probability distributions of environmental exposure concentratio ns with the probability distributions of species response data determi ned from laboratory studies. The overlap of these distributions was a measure of risk to aquatic life. Dissolved copper and cadmium exposure data were available from six primary data sources covering 102 statio ns in Is basins in the Chesapeake Bay watershed from 1985 through 1990 . Highest environmental concentrations of copper (based on 90th percen tiles) were reported in the Chesapeake and Delaware (C and D) Canal, C hoptank River, Middle River, and Potomac River, the lowest concentrati ons of copper were reported in the lower and middle mainstem Chesapeak e Bay and Nanticoke River. Based on the calculation of 90th percentile s, cadmium concentrations were highest in the C and D Canal, Potomac R iver, Upper Chesapeake Bay, and West Chesapeake watershed. Lowest envi ronmental concentrations of cadmium were reported in the lower and mid dle mainstem Chesapeake Bay and Susquehanna River. The ecological effe cts data used for this risk assessment were derived primarily from acu te copper and cadmium laboratory toxicity tests conducted in both fres h water and salt water, chronic data were much mon limited. The 10th p ercentile (concentration protecting 90% of the species) for all specie s derived from the freshwater acute copper toxicity database was 8.3 m u g/L. For acute saltwater copper data, the 10th percentile for all sp ecies was 6.3 mu g/L copper, The acute 10th percentile for all species in the freshwater cadmium database was 5.1 mu g/L cadmium. The acute 10th percentile for all saltwater species was 31.7 mu g/L cadmium. Hig hest potential ecological risk from copper exposures was reported in t he C and D Canal area of the northern Chesapeake Bay watershed. Relati vely high potential ecological risk from copper exposure was also repo rted in Middle River. Moderate potential ecological risk from copper e xposure was reported in selected locations in the Choptank and Potomac Rivers. Potential ecological risk from copper exposure was either low or data were insufficient to assess ecological risk in the other 14 b asins. Potential ecological risk from cadmium exposures was much lower than for copper. Highest potential ecological risk from cadmium expos ure was reported in the C and D Canal. Low to moderate potential ecolo gical risk: for the most sensitive trophic group (fish) was reported i n the Potomac River, upper mainstem bay, West Chesapeake watershed, Ch optank River. and Chester River. In the other 12 basins, ecological ri sk was either judged to be low or insufficient data were available for determining risk.