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CHIRAL CHLORDANE SIGNATURES IN USGS NATIONAL WATER-QUALITY ASSESSMENT PROGRAM SEDIMENT SAMPLES
Citation:
Ulrich, E. M., C S. Wong, S. A. Rounds, P. C. Van Metre, J. T. Wilson, A W. Garrison, AND W. T. Foreman. CHIRAL CHLORDANE SIGNATURES IN USGS NATIONAL WATER-QUALITY ASSESSMENT PROGRAM SEDIMENT SAMPLES. Presented at 23rd Annual Society of Environmental Toxicology and Chemistry Meeting, Salt Lake City, UT, November 16-20, 2002.
Impact/Purpose:
Extend existing model technologies to accommodate the full range of transport, fate and food chain contamination pathways, and their biogeographical variants, present in agricultural landscapes and watersheds. Assemble the range of datasets needed to execute risk assessments with appropriate geographic specificity in support of pesticide safety evaluations. Develop software integration technologies, user interfaces, and reporting capabilities for direct application to the EPA risk assessment paradigm in a statistical and probabilistic decision framework.
Description:
More than 260 important environmental contaminants are chiral (having structures that are nonsuperimposible mirror images). Although enantiomer pairs have identical physical-chemical properties, their toxicity, biodegradation, and environmental fate often are different. Cyclodextrin gas chromatography combined with electron-capture, negative ionization mass spectrometry was used to determine the chiral characteristics of chlordane components in sediment. Enantiomer fractions [EF = area (+) enantiomer / sum of (+) and (-) areas] were used to determine if biological degradation had occurred in surficial and suspended-sediment samples, and if there was a trend with depth in sediment cores. Suspended-sediment samples showed the most change from a racemic signature, possibly indicating greater bioavailability of chlordane associated with the suspended fraction. Surficial sediments contained evidence of biodegradation because of the presence of nonracemic EFs [not equal to 0.50; cis-chlordane (CC) = 0.502 - 0.62; trans-chlordane (TC) = 0.473 - 0.54; exo-heptachlor epoxide (HEPX) = 0.60 - 0.682]. The EF of HEPX in surficial sediment agrees with those found in soil, indicating agricultural soil as a likely source. At four core sites, EFs were close to racemic for TC and CC, with the greatest deviations from racemic observed in the top (recently deposited) core segment. In general, TC EFs were less than 0.5 and tend to increase slightly with depth, while the opposite was true for CC. These results suggest that little biodegradation has occurred in the sediment core, and that historical concentration profiles should be unaltered by biological degradation processes.