FEEDING SELECTIVITY AND ASSIMILATION OF PAH AND PCB IN DIPOREIA SPP

A series of experiments were conducted to estimate assimilation effici encies of two hydrophobic organic contaminants and the influence of pa rticle sizes on the selective sediment ingester, Diporeia spp. Floriss ant soil was divided into particle-size fractions consisting of 0 to 6 3 mum, 0 to 20 mum, and 20 to 63 mum and dosed with radiolabeled 2,2,4 ,4,5,5'-hexachlorobiphenyl (HCBP) and/or benzo[a]pyrene (BaP) to which animals were exposed for individual assays. At the end of timed expos ure intervals, individual Diporeia and any fecal pellets they produced were removed from the sediment and analyzed for contaminant content. Assimilation efficiency was estimated via a selectivity index based on organic carbon. Assimilation efficiency of BaP (5.6-32.7%) was compar able to previous studies. However, HCBP did not correlate with organic carbon over a range of particle sizes. Accumulation of both contamina nts was greatest when animals were exposed to the 20- to 63-mum size f raction, suggesting that Diporeia selectively fed within this particle -size range. Accumulation of HCBP was consistently greater than BaP in all dual-labeled assays, suggesting a greater bioavailability of the PCB to Diporeia. Sediment analysis indicated that BaP and HCBP were as sociated with different particle-size fractions possessing different a mounts of organic carbon, with BaP having the greater tendency to asso ciate with TOC.