Superfund Research Program
Remediation Product Toxicity Evaluation Core
Project Leader: Stephen A. Boyd
Grant Number: P42ES004911
Funding Period: 1995 - 2006
Year: 2005 2004
An overall goal of this core is to evaluate the biological activities of intermediate and terminal remediation products. For PCBs, a two stage anaerobic/aerobic biotreatment process has been proposed. The anaerobic step removes chorines from more heavily chlorinated congeners, resulting in a mixture of lesser chlorinated PCBs that are more amenable to aerobic biodegradation. Anaerobic dechlorination of PCBs in also a naturally occurring process in sediments. Thus defining the biological activities of microbially dechlorinated PCB mixtures is important whether or not they are generated by remediation activities.
PCB dechlorination generally results in a less toxic mixture, especially for biological endpoints involving the Ah receptor. However, the Core has previously demonstrated that PCB dechlorination can in some cases affect uterine muscle activity. During the past year, microbially dechlorinated Aroclor 1260 and Aroclor 1260 were compared with regard to their stimulatory effect on uterine muscle contraction using a muscle perfusion assay. The microbially dechlorinated mixture increased uterine contraction frequency seven-fold, while the parent Aroclor 1260 had no significant effect. The most prominent congeners in the dechlorinated mixture were 2,2’,4,4’-tetrachlorbiphenyl and one or more of four congeners (2,3,3',5-tetrachlorobiphenyl, 2,3',4,5-tetrachlorobiphenyl, 2,2',4,4',6-pentachlorobiphenyl and 2,2',4,5',6-pentachlorobiphenyl) that coelute chromatographically. When tested individually, however, these congeners exerted only modest effects. Thus they can not fully account of the much greater activity of the dechlorinated Aroclor 1260 mixture on the frequency of uterine muscle contractions.
A second task of the core is to assess the bioavailability of aged residues in soil and sediment. To that end, they have been surveying old and former apple orchards in Michigan for DDT and its metabolites DDD and DDE (collectively DDx), and assessing the oral availability of these residues. Many such sites are being developed for housing, and the oral ingestion of soil is a common route of exposure for young children. To assess bioavailability, the Core is using a model designed to mimic the digestive process, essentially extracting the soil with synthetic stomach and small intestinal fluids. They have found mean total DDx concentrations ranging from 0.01 to 18.7 µg/g soil, depending on the history of DDT use and changes in land use since DDT application. In all cases evaluated, 79 to 88 % is bioavailable, should the soil be ingested.