Profiles of environmental and endogenous estrogens in the zebra mussel Dreissena polymorpha

Contamination of freshwater environments by estrogenic compounds has led to concern over potential impacts on invertebrate species. The uptake of the environmental estrogen 17beta-estradiol (E2) by the freshwater bivalve Dreissena polymorpha and the nature of estrogenic substances in tissues of D. polymorpha mussels collected from four freshwater sites were investigated. Exposure of mussels to [(14)C]-E2 (7.5 ngl(-1), 13 days) revealed that the estrogen bioconcentrated 840+/-58 (males) and 580+/-77 (females) fold (mean+/-95% confidence limits) and was metabolised in tissues to a persistent lipophilic ester. Estrogenic activity, measured using a recombinant human estrogen receptor transcription screen (YES), was detected in tissue extracts of all mussels sampled from freshwater sites. At two reference sites the estrogenic activities of mussel tissues were <1ng E2 equivalents g(-1) wet weight tissue (ng EEQ g(-1) ww) which increased to 7.4-45.7ng EEQg(-1) ww for both free and esterified estrogens extracted from hydrolysed tissue extracts. In mussels collected from two contaminated river sites, estrogenic activity was 0.2-6.7ng EEQ g(-1) ww (free estrogens) and 25.6-316.2ng EEQ g(-1) ww for total estrogens. Fractionation of the tissue extracts revealed that E2 (as the ester) was the predominant estrogen detected in both sexes of D. polymorpha, however, the xenoestrogen nonylphenol (NP) was also detected in mussels sampled from contaminated rivers. The detection of endogenous esterified E2 and the potential for accumulation of exogenous E2 and NP in D. polymorpha tissues suggests that this bivalve could be susceptible to exposure to estrogenic contaminants in the aquatic environment.