The effects of parasites and temperature on the accumulation of xenobiotics in a freshwater clam

Freshwater invertebrates are exposed to many stress factors in their habita t. This study is the first attempt to assess the effects of digenean tremat ode infection on bioaccumulation of [H-3]bentzo(a)pyrene (BaP) and [C-14]2, 4,5-trichlorophenol (TCP) in the freshwater clam Pisidium amnicum. Static 2 4-h exposures were carried out in the laboratory both in July (at 20 degree s C) and in February (at 4 degrees C) to see the effect of seasonal tempera tures. Three species of digenean trematodes were found in the bivalves. Bun odera luciopercae was the most common parasite with prevalences of 52%. The other two species with prevalences from 2% to 23% were Palaeorchis crassus and Phyllodistomum elongatum. At 20 degrees C the bioconcentration factors (BCFs) of both compounds were higher in uninfected clams when compared to infected ones, but the differences were not significant. The BCFs of TCP we re significantly higher at 4 degrees C than at 20 degrees C for both infect ed and uninfected clams. The concentrations of BaP and TCP in the clam tiss ue were equal in both infected and uninfected clams, and higher than in the ir parasites. However, at 20 degrees C the TCP concentration in the tissues of Palaeorchis-infected clams was lower than in the uninfected clams or in the parasite tissue. The differences are explained by the parasites' life cycle and feeding behavior. Our results suggest that both parasite infectio n and temperature are important for accumulation of organic pollutants and should be considered in aquatic hazard assessment.