Transfer of benzo[a]pyrene and 2,2′,5,5′ tetrachlorobiphenyl from bacteria and algae to sediment-associated freshwater invertebrates

Feeding interactions between microorganisms and their grazers range from broad and general to very specific. Here we examined routes of transfer of [H-3]benzo[a]pyrene (BaP) and 2,2',5,5'[C-14]tetrachlorobiphenyl (PCB-52) from microorganisms in freshwater sediments to oligochaetes (Lumbriculus variegatus) and chironomid larvae (either Stictochironomus sp. or a mix of smaller taxa) when exposed to the compounds added either directly to sediments or to bacteria or diatoms previously labeled and then added to sediments. The appearance of radiolabel in animals after a gut clearing step to differentiate between ingested and absorbed compound was followed in time course experiments. Relative to the added radiolabel, BaP concentrations were greater than PCB concentrations in L. variegatus and were greater in animals fed radiolabeled sediments or bacteria than those offered diatoms. In contrast, the chironomids accumulated more PCB than BaP. The mix of small chironomids bioaccumulated more PCB when fed prelabeled algae than when fed sediment or bacteria. However, Stictochironomus sp. bioaccumulated more from sediments and/or bacteria. Food selection influences pathways of contaminant transfer, even to small animals at the base of the food web. We also tested whether the bioaccumulation of BaP and PCB would be predicted by the K-oc for the sediment (i.e., BCF/K-oc = 1). The quotients, averaged over experiments, were 1.08 and 1.53 for PCB-52 and BaP, respectively, hut error terms were large, with coefficients of variation being 83% and 135%, respectively.