Relationship between metabolism and bioaccumulation of benzo[a]pyrene in benthic invertebrates.

The potential influence of polycyclic aromatic hydrocarbon (PAH) metabolism on bioaccumulation is well accepted, but rarely has been examined in many species of benthic invertebrates that commonly are found in contaminated sediments, or used in bioaccumulation or toxicity tests. In this study, the relative ability of 11 species of near-shore benthic invertebrates to metabolize and bioaccumulate a model PAH, benzo[a]pyrene (B[a]P), was evaluated. Species examined included six polychaetes (Clymenella torquata, Nereis virens, Nereis succinea, Nephtys incisa, Spio setosa and Cirriformia grandis), three bivalves, (Macoma balthica, Mya arenaria, and Mulinia lateralis), and two amphipods (Ampelisca abdita and Leptocheirus plumulosus). After 7 d of exposure to sediments spiked with radiolabeled B[a]P, metabolites comprised between 6.1% (Clymenella torquata) to 85.7% (Nereis succinea) of total accumulated B[a]P, with individual species from the same phylogenetic groups showing large differences in their ability to metabolize this PAH. Bioaccumulation factors (B[a]P in tissue/B[a]P in sediment) were inversely related to the species' ability to metabolize PAH, highlighting the importance of considering metabolism when interpreting bioaccumulation across several species. These data argue strongly against the continued use of the large polychaete Nereis virens, one of the species showing the greatest ability to metabolize B[a]P, for bioaccumulation testing when PAHs are being considered. Other commonly used test species had relatively low levels of metabolism (Ampelisca abdita, Leptocheirus plumulosus, and Macoma balthica), supporting their use in evaluation of potential PAH impact on the environment.

Role of source matrix in the bioavailability of polycyclic aromatic hydrocarbons to deposit-feeding benthic invertebrates.

The bioavailability of polycyclic aromatic hydrocarbons (PAHs) to benthic organisms is complicated by the variety of ways that they are introduced to coastal waters (dissolved, as nonaqueous phase liquids, and tightly bound to soot, coal, tire rubber, and eroded shale). In order to better understand the controlling variables that affect chemical and biological availability of PAHs, a study was conducted in which three deposit-feeding infaunal benthic invertebrate species (Cirriformia grandis, Clymenella torquata, and Macoma balthica) were exposed to sediments amended with PAH-rich materials (coal dust, tire rubber, diesel soot, creosote, crude oil, and fuel oil). Lipid and organic carbon normalized bioaccumulation factors (BAF(1oc)s) were calculated after 20 d of exposure and PAH bioavailability from the different treatments was assessed. Bioaccumulation of coal-derived PAHs usually was too low to be measured, though PAHs associated with soot and tire rubber showed significant accumulation in organism tissues. Polycyclic aromatic hydrocarbons from the fuel oil, creosote, and crude oil treatments were more bioavailable than PAHs bound in solid carbonaceous matrices (soot, coal, and tire rubber). Desorption of PAHs from the amended sediments into seawater also was measured using XAD resin. As was observed with bioaccumulation, PAHs in coal were desorbed the least; tire rubber and diesel soot were intermediate; and creosote, fuel oil, and crude oil desorbed to the greatest extent. In only one out of the three species evaluated was PAH bioaccumulation related to extent of desorption after 20 d. Decoupling between biological and chemical availability may be due to species-specific factors such as surfactant-mediated solubilization in the guts of some deposit-feeding organisms. A significant finding of this work was the demonstration that PAHs associated with soot and tire rubber in their native state (rather than experimentally added) are available to some benthic biota.

Influence of soot carbon on the bioaccumulation of sediment-bound polycyclic aromatic hydrocarbons by marine benthic invertebrates: an interspecies comparison.

The sorption of polycyclic aromatic hydrocarbons (PAHs) to soot carbon in marine sediments has been hypothesized to reduce PAH bioavailability. This hypothesis was tested for eight species of marine benthic invertebrates (four polychaete worms, Clymenella torquata, Nereis virens, Cirriformia grandis, and Pectinaria gouldii, and four bivalve mollusks, Macoma balthica, Mulinia lateralis, Yoldia limatula, and Mya arenaria) that span a wide range of feeding behavior, ability to metabolize PAHs, and gut chemistry. Organisms were exposed for 20 d to two PAH-spiked sediments, one with soot and one without soot. The soot treatment generally resulted in lower bioaccumulation than the no soot treatment, though the differences between treatments were not significant for all species. All but one species accumulated significant PAH concentrations in their tissues from the soot treatment, indicating that soot-bound PAH cannot be dismissed as unavailable to infaunal benthic biota. Bioaccumulation factors were correlated negatively to both the organisms' ability to metabolize PAHs and the gut fluid contact angle, supporting the hypotheses that high PAH metabolism results in lower bioaccumulation factors and bioavailability of PAHs may be limited partially by PAH solubilization in the gut lumen. The variability in bioaccumulation due to the soot treatment was much less than the variability between species and between PAH analytes. Comparatively low bioaccumulation was observed in Nereis virens, a species commonly used in bioaccumulation tests. These results suggest that more effort is needed in understanding the salient characteristics of species present in a threatened environment, rather than focusing solely on the sediment geochemistry (e.g., soot and organic carbon content) and contaminant characteristics when predicting ecological risk of PAH-contaminated sediments.