Evaluation of the water‐effect ratio procedure for metals in a riverine system

Abstract

AbstractSite‐specific metal standards were determined for a part of the lower Lehigh River using the U.S. Environmental Protection Agency's water‐effect ratio (WER) procedure. The WERs were based on laboratory and site water (collected downstream of the City of Allentown Publicly Owned Treatment Works) testing of the species Ceriodaphnia dubia and Pimephales promelas (fathead minnow) and five metals (copper, cadmium, lead, silver, and zinc) during four different months. Both species generally exhibited similar patterns in WERs. The greatest variability between the two species was observed for copper, silver, and lead. Ceriodaphnia yielded a lower mean WER than the fathead minnow for lead and zinc and WERs similar to those of the fathead minnow for copper, cadmium, and silver. The species more sensitive to a given metal did not always exhibit a higher WER, as had been previously assumed. A comparison of final WER calculations indicated that the geometric mean WER (1983 method) was typically higher than the final WER obtained using the 1994 guidance. For most metals, site water toxicity was reduced due to nonacutely toxic dissolved metal. Copper yielded the highest final WER regardless of the calculation method used. Regression analyses indicated that the copper WER was directly related, and the cadmium WER inversely related, to effluent concentration. Copper, lead, and silver WERs were related to site water pH. Cadmium and lead WERs were related to pH and dissolved solids. Zinc WERs were unrelated to any of the water quality variables measured and were similar among site water samples. Our results suggest it is prudent to use two species in WER testing and different site water samples to derive a final WER, particularly at sites that are not effluent dominated.