Effects of estuarine organic matter biogeochemistry on the bioaccumulationof PAHs by two epibenthic species

Polycyclic aromatic hydrocarbon (PAH) biota-sediment accumulation factors ( BSAF) were quantified in sediments from two sites in southeastern Louisiana in a 14 d microcosm study using Palaemonetes pugio and Rangia cuneata and two radiolabeled PAHs, phenanthrene and benzo[a]pyrene (b[a]p). For both PA Hs studied, mean BSAFs were significantly higher (p < 0.0001) in both organ isms in sediments from Bayou Trepagnier (BSAF = 0.628 g OC g TLE-1), a brac kish swamp, compared to Pass Fourchon (0.065 g OC g TLE-1), a coastal salt marsh. In order to explain observed patterns in BSAFs, organic carbon-norma lized PAH distribution coefficients between the sediment and freely dissolv ed phases (K-OC)(OBS) were determined as well as the various geochemical va riables of particulate and dissolved organic matter (POM and DOM, respectiv ely). These included analyses of particle surface area, total organic carbo n (TOC), carbon to nitrogen ratios (C:N), and dissolved organic carbon (DOC ). Bayou Trepagnier was higher in surface area, TOC, C:N, as well as DOC su ggesting that the difference in BSAFs may be attributed to compositional di fferences in POM and DOM between sites. We can not exclude the possibility that other factors (such as differences in organism behavior resulting from contrasting sediment characteristics) were responsible for BSAFs varying b etween the two sites. Phenanthrene BSAFs were typically higher than b[a]p B SAFs, suggesting contaminants were limited in their desorption from sedimen t particles as a function of PAH molecular weight. Mean BSAFs for both PAHs were higher on Day 7 than on Day 14. The reason for this decrease is uncle ar, but did not appear to be due to organisms becoming increasingly stresse d in the microcosms. Visual observations indicated that animals remained fe eding while no decreases in organism total lipid levels were detected. The trends in BSAFs between sites and over the time course of this experiment s uggest that contaminant bioaccumulation in estuarine systems should not be considered to be an equilibrium process.