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|Title:||Changing concepts and improved methods for evaluating the importance of PCBs as dredged sediment contaminants|
|Authors:||Long-Term Effects of Dredging Operations Program (U.S.)|
McFarland, Victor A.
Clarke, Joan U.
Gibson, Alfreda B.
|Publisher:||Environmental Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: Polychlorinated biphenyls (PCBs) are highly persistent and widespread contaminants frequently encountered by Corps of Engineers personnel involved with dredged material disposal activities. Interpretation of the potential ecological effects of disposing PCB-contaminated sediments in open water or using other methods is a persistent difficulty in the preparation of environmental impact statements and other documentation necessary for informed decisionmaking. However, the understanding of the nature and behavior of PCBs as environmental contaminants has progressed rapidly within the scientific community with the advances in analytical technology of the past few years. PCBs are a group of 209 congeners that have up to ten chlorine atoms on the biphenyl molecule and that differ from each other in the number and positions of the chlorines. About 100 of these congeners are found in the industrial PCB formulations marketed as Aroclors, released into the environment through disposal of transformer oils and other PCB-containing products, and are now widespread in sediments. Only some of these congeners are toxic, either directly through receptor binding or indirectly through microsomal enzyme induction. Most of the congeners that are toxic, or that are otherwise important due to their prevalence or persistence in the environment, belong to the isomer groups tetra-, penta-, and hexachlorobiphenyl (i.e. they have four to six chlorine atoms per molecule). Current evaluations of PCBs in environmental samples by quantitation as Aroclors or as total PCBs are of limited value due to degradation and differential affinities of congeners for various environmental compartments. PCBs that entered the environment as identifiable Aroclor mixtures are altered by these physical, chemical, and biological processes and cannot properly be identified by comparison with Aroclor analytical standards. Comparisons of PCB-contaminated Hudson River sediments, along with water and organism tissue samples exposed to those sediments, with Aroclor standards demonstrate the frequent lack of correspondence in PCB components between Aroclors and environmental samples. A more meaningful evaluation of PCBs in environmental samples can be accomplished by quantitation as totals in the isomer groups di- through decachlorobiphenyl (two to ten chlorines per molecule). This has the advantage of indicating the relative concentrations of the groups potentially containing the most toxic and bioaccumulating congeners. Furthermore, recent advancesdn analytical techniques are making the analysis of individual congeners more feasible., Thus, attention can be focused specifically on the PCB components that are important on the basis of toxicity, persistence, and prevalence, allowing a more accurate assessment of the environmental effects of various dredged material disposal options than is currently available. This paper summarizes the current understanding of the chemical nature of PCBs, the factors determining their persistence and potential to bioaccumulate, and the characteristics of individual PCB congeners that determine their widely differing potencies and modes of toxic effect.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||Miscellaneous Paper|