Assessment of the impact of a bleached kraft mill effluent on a south-central USA river

We initiated a multifaceted, integrated investigation of the general health of the aquatic environment near a bleached kraft pulp and paper mill. This southcentral U.S. mill discharges about 125,000 cubic meters of treated ef fluent per day into an adjacent river. The sampling sites for this study we re 1.8 km upstream from the mill's discharge, 0.25 km below the mill's outl et, and 5 km downstream from the discharge area. No toxicity was observed u sing Ceriodaphnia dubia and Pimephales promelas in aqueous phase tests or w ith Hyalella azteca and Chironomus tentans in sediment phase tests. Field e xaminations of two small fish species and sediment macroinvertebrate commun ities from each sampling site revealed no significant adverse effects. Blue gill sunfish (Lepomis macrochirus) were exposed for 35 days to site sedimen ts and were evaluated for ethoxyresorufin O-dethylase (EROD) activity, cyto chrome P4501A (CYP1A) content, DNA strand breaks, condition index, organ in dices, gross pathology, and immune responses. No significant adverse effect s were observed in sediments immediately below the mill's effluent outlet, though detoxification enzyme activity was elevated in liver tissue of blueg ill sunfish exposed to site 3 sediment. Embryos of mosquitofish (Gambusia a ffinis) were evaluated for developmental and reproductive abnormalities fol lowing a static laboratory exposure of gravid females to sediments from the three study sites for 56 clays. The embryos showed no significant effects on a suite of reproductive parameters among the three sites. We concluded t hat there was no significant evidence of adverse impacts on the receiving r iver or its biota attributable to treated bleached kraft mill effluent base d on a comprehensive suite of bioindicators of exposure and effects. (C) 20 00 by John Wiley & Sons, Inc.