Feeding selectivity and assimilation of PAH and PCB in Diporeia spp.

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Abstract
A series of experiments were conducted to estimate assimilation efficiencies of two hydrophobic organic contaminants and the influence of particle sizes on the selective sediment ingester, Diporeia spp. Florissant soil was divided into particle‐size fractions consisting of 0 to 63 μm, 0 to 20 μm, and 20 to 63 μm 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 exposure 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 comparable to previous studies. However, HCBP did not correlate with organic carbon over a range of particle sizes. Accumulation of both contaminants was greatest when animals were exposed to the 20‐ to 63‐μm size fraction, 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 associated with different particle‐size fractions possessing different amounts of organic carbon, with BaP having the greater tendency to associate with TOC.

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