Environmental risk associated with the phytoextraction of persistent organic pollutants (POPs) from contaminated brownfield sites.

摘要

Polychlorinated biphenyl's (PCBs) are persistent organic pollutants known to cause adverse effects in both humans and animals. Uptake and bioaccumulation of PCB Aroclors in plants, as well as the congener contribution in invertebrates, was studied at two historically-contaminated field sites. Soil at Site 1 was contaminated with Aroclor 1248 at concentrations of 4.8 +/- 1.6 and 8.2 +/- 4.0 mug·g-1, respectively. Soil from site 2 was used in greenhouse experiments and is a mixture of Aroclors 1254 and 1260 at three concentration levels; low (2.5 +/- 0.1 mug·g -1), medium (36.6 +/- 6.0 mug·g-1) and high (70.0 +/- 0.3 mug·g-1). Study species included Cucurbita pepo spp pepo cv. Howden (pumpkin), Lumbricus terrestris (earthworm), Eisenia fetida (redworm) and Succinea putris (snail). Samples were analyzed via gas chromatography-electron capture detection (GC-ECD) for total PCB concentration and by gas chromatography-mass spectrometry (GC-MS) for individual congener concentrations.;For pumpkins, total PCB extraction (the average amount of PCBs removed by the whole plant) was on average 2.8-fold higher in the shoot when grown in soil amended with fertilizer. The increase in total extraction was likely a result of an increase in overall plant biomass as PCB concentrations within the shoot tissue did not change significantly between treatments. The addition of fertilizer was also found to increase PCB bioaccumulation in earthworms, with an average increase of 2.8 +/- 0.1 times the PCB concentration of earthworms living in soil without fertilizer. PCB bioaccumulation in worms indicates a potential for ecological risk to higher trophic organisms that feed on them, especially in fertilized phytoextraction plots, and thus requires further investigation.;During the development of a deterministic ecological risk assessment (ERA) invertebrate PCB tissue concentrations (from field and greenhouse studies) were used to model uptake of PCBs in higher trophic organisms. The values were included in allometric equations for the development of a total daily intake estimate (DI) and were combined with a literature review of species-specific toxicity reference values (TRV) which gave an indication of risk based on a hazard quotient (HQ) for three selected species (raccoon, shrew and robin). Results indicated that risk of PCB exposure at a variety of phytoextraction plot sizes was greatest for small mammals such as the short-tailed shrew and avian species such as the American robin, but was minimal for medium-sized mammals such as the raccoon. Hyper-conservative estimates included both Aroclor-and congener-based derivations of the DI for the selected species. Research to reduce or eliminate specific routes of exposure for PCBs entering into the food chain is an important area for future study as full-scale remediation has the potential to cause adverse effects in each of the selected representative species.;Results of a congener based analysis of soil from both field sites indicated that a change in the original technical standard congener contribution had occurred due to a process of contaminant weathering. Lower chlorinated congener contributions decreased, confirming that higher chlorinated congeners, which were more tightly bound to the soil are likely those which are more stable in the environment and thus contribute a greater percentage to the total PCB concentration over time. Analysis of three separate invertebrate test species, one earthworm (L. terretris), one redworm (E. fetida ) and one snail (S. pubis) showed that invertebrate species living within phytoextraction plots take on the same congener profile as the soil. The most prevalent dioxin-like congeners across all samples at both sites were congeners 105 and 118 although these congeners contributed a small amount to the overall concentration of the Aroclor mixture. This suggests that while important information is gained by the comparison of the congener contribution between weathered soil and original technical standards, an Aroclor-based analysis for total PCB concentrations of soil dwelling invertebrates may be sufficient for the derivation of a hazard quotient when the soil congener profile is known.