Date of Award

12-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Environmental Toxicology

Advisor

Lee, Cindy M

Committee Member

Walters , David M

Committee Member

van den Hurk , Peter

Committee Member

Coates , John T

Abstract

Polychlorinated biphenyls (PCBs) contaminate the sediment of the Twelvemile Creek / Lake Hartwell Superfund Site, and are known to be transported throughout the resident biota via trophic transport. Riparian spiders have recently become of interest because they are terrestrial organisms that have significant PCB exposures derived from aquatic sources. Many riparian spiders primarily consume insects emerging from contaminated aquatic systems, and these spiders can have a body burden as high as 2900 ng/g lipid. These emergent insects carry contaminants out of the river and into the riparian zone where they are captured by spiders, which effectively directs the contamination towards arachnivorous predators such as lizards, frogs, and birds.
The enantiomeric fraction (EF) was measured for chiral congeners to investigate the role of biological systems on transport of PCBs between trophic levels. The EF values varied between spider species, and indicate that foraging behavior may influence those parameters. Tetragnathid and basilica spiders were most similar, whereas both were different from araneid spiders despite all three spiders belonging to the same order of spiders. All spider taxa were significantly different from the aquatic prey source Chironomidae.
Two approaches were used to confirm that spiders have the capacity to metabolize their PCB body burdens. Tetragnathidae spiders were collected along Twelvemile Creek, their enzymes isolated, and exposed to individual non-planar and co-planar congeners. PCBs 88 and 149 were incubated with S9 fractions (extracts containing microsomal and cytosolic enzymes) from the spiders and qualitatively assessed for evidence of biotransformation. Tandem mass spectroscopy provided evidence to support the hypothesis that spiders have the capacity to biotransform PCBs. Additionally, PCB 61 was incubated with S9 fractions for quantitative analysis of a planar congener. Numerous compounds were detected after exposure, but OH-PCB 61 was measured at 1.63 (±0.35 SD) ng/g lipid at the Reese Mill sampling site for enzymes obtained with liquid nitrogen, thus indicating that spiders have the capacity to metabolize their PCB body burden. In the second approach mass spectroscopy of whole spider extracts of spiders obtained along the Twelvemile Creek arm of Lake Hartwell provided structural evidence that spiders can transform their body burden of PCBs to OH-PCBs for congeners with six or fewer chlorines.
Lastly, webs are hypothesized to play a protective role in spider ecotoxicology. Tetragnathid spiders are able to recycle approximately 90% of their web material without metabolizing it, thus creating an opportunity for web material to act as a storage location external to the body. Concentrations in webs ranged between 154 and 356 ppm, whereas concentrations for spiders at the same sampling locations ranged from 284 ng/g lipid to 2900 ng/g lipid. The enantiomeric fraction was also utilized to determine if storage in webs is an enantioselective process. Results indicate that web storage is enantioselective for PCB 149, with the (−) enantiomer being preferentially retained in web materials, which differs from that seen in spider samples, where the EF is approximately racemic.
These investigations examined the exposure and toxicological model for spiders, with the intent of aiding understanding the role spiders play in mediating transport and transformation across riparian ecotones. Results indicate that spiders may use a variety of strategies to manage their PCB body burdens ranging from enantioselective uptake of parent compounds, metabolism to hydroxylated metabolites, and transfer to web material. Understanding spider mediation of PCB transport and transformation can help development of strategies that both manage and mitigate the risks posed to the environment by PCBs at Twelvemile Creek and Lake Hartwell.

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