Testing Ambient Delaware River Water Using Short-Term Methods for Estimating Chronic Toxicity

A. Ronald MacGillivray and Thomas J. Fikslin

Delaware River Basin Commission (DRBC), West Trenton, New Jersey

Six chronic toxicity studies of ambient water in the tidal Delaware River (River Miles 63 to 115) were conducted to monitor cumulative chronic toxicity at twelve fixed sampling stations over an eleven year period (1990 through 2001). Freshwater and saltwater test species commonly used to assess toxicity of wastewater discharges from point sources and infrequently used to assess receiving (ambient) water were used. The tests methods used were Fathead Minnow, Pimephales promelas, larval survival and growth; Daphnid, Ceriodaphnia dubia, survival and reproduction; Green alga, Selenastrum capricornutum (Raphidocelis subcapitata), growth; Sheepshead minnow, Cyprinodon variegatus, larval survival and growth, and Mysid, Mysidopsis (Americamysis) bahia, survival and growth. Survival of all test organisms was not affected by exposure to the ambient water samples. Sublethal chronic toxicity was indicated at different sampling stations and in different species over the study period (e.g., adverse effect on Fathead Minnow growth at three sites in 1992 versus adverse effect on Ceriodaphnia dubia reproduction at one site in 2000). Biostimulation of Selenastrum capricornutum (Raphidocelis subcapitata) was observed corresponding with increased nitrate and total phosphorus concentrations in the water samples. Interpretation of the ambient Delaware River water chronic toxicity data is complicated by salinity differences at the sites. Alternative chronic toxicity studies are considered to assess attainment of aquatic life uses in estuarine waters.

Keywords: chronic toxicity, estuarine, ambient water, biostimulation