AN EVALUATION OF THE TOXIC INFLUENCES ON ASELLUS-AQUATICUS (L) IN AN URBAN STREAM ENVIRONMENT

Individually caged asellids placed in urban receiving waters were subj ected to discharges from stormwater and combined sewer overflow outfal ls. In each field trial the volume of precipitation and the number of dry days were recorded on a weekly basis and the metal (copper, zinc, cadmium. lead) body concentrations of caged organisms were measured. U sing Principal Component Analysis (PCA), combinations of the measured parameters which explained much of the variation in organism mortality or changes in the weight of caged asellids were isolated. Three diffe rent sets of variable combinations were identified two of which explai ned significant independent sources of variation responsible for chang es in organism weight and one which explained a significant source of the variation in assellid mortality. Organism mortality and weight cha nge were selected as dependent variables and regressed against the pri ncipal components of the independent variable predictors to produce em pirical first order regression equations. Changes in the weight of cag ed organisms were found to result from the joint interaction of a numb er of identified variables. Copper was identified as being the most im portant metal toxicant with respect to mortality. Meteorological varia bles were found to have a greater influence on organism mortality than upon changes in organism weight.