M11 AM Using Stable Isotopes in Ecotoxicology
Monday, 14 November 2005: 8:00 AM - 11:40 AM in 343-344

(WAL-1117-810307) Using stable isotopes to track biomagnification of polychlorinated biphenyls (PCBs) through stream food webs.

Walters, D¹, Fritz, K¹, Johnson, B¹, Lazorchak, J¹, ¹ US EPA, Office of Research and Development, Cincinnati, Ohio, USA

ABSTRACT- Biomagnification studies in streams are rare. This is surprising because PCBs and other persistent organic pollutants are known to biomagnify in aquatic ecosystems, and contaminated sediments are pervasive in stream ecosystems. Most studies of biomagnification are from lentic systems, which are characterized by organic matter and sediment retention. It is unclear of PCBs biomagnify and persist in streams, which are characterized by sediment and organic matter export. We investigated PCB contamination in Twelvemile Creek (Clemson, SC, USA), a stream that received > 400,000 lbs of PCBs from 1955-1978. Our goals were to determine if PCBs biomagnify in streams and to measure the relative importance of heterotrophic and autotrophic pathways for biomagnification. Sites were sampled during spring (n=6) and fall (n=4) 2003-04. Major components of the foodweb were analyzed for total PCBs (n = 525), ¹³C and ¹⁵N (n = 1325). Biomagnification was apparent as mean ¹⁵N strongly predicted PCBs (r² = 0.58), and PCBs consistently increased with trophic level. We found no consistent patterns related to carbon pathways when the entire foodweb was considered. ¹³C and PCBs were uncorrelated, suggesting that carbon source was unrelated to biomagnification. However, analysis of individual trophic groups indicated that carbon source effects PCB concentrations. PCBs in grazing insects (970 ng g^-1) were more than double those in leaf shredding insects (370 ng g^-1) even though PCB concentrations were similar for periphyton and leaves. Periphyton ¹³C was significantly related to grazer ¹³C (r² = 0.34) but not to shredders. These results suggest that greater reliance on algal resources contributes to higher PCB concentrations within trophic levels. Our results show that PCBs biomagnify and persist in streams, but the importance of autotrophic and heterotrophic pathways is unclear. Although this work was reviewed by EPA and approved for publication, it may not reflect official Agency policy.

Key words: trophic transfer, organic pollution, river sediment, Superfund