The determination of the toxic influences to Gammarus pulex (amphipoda) caged in urban receiving waters.

: A statistical procedure comprising principal component analysis and multiple regression has been applied to the in situ mortality response data for Gammarus pulex caged downstream of a combined sewer overflow (CSO) and a surface water outfall (SWO). The mortality and heavy metal bioaccumulation responses of the species as well as seventeen different chemical and hydrological characteristics of the receiving watercourse were monitored continuously for 36 days. Flow rate, BOD5, suspended solids, total ammonia, total aqueous copper and lead concentrations and dissolved aqueous concentrations of zinc and copper influenced the mortality response of Gammarus pulex. The relationships between the mortality response and the selected independent variables are expressed in the form of stable quantitative equations by regressing the dependent variable (i.e. mortality) against the principal components of the independent parameters. This statistical approach represents an important tool for interpreting large intercorrelated sets of environmental data obtained in situ.