Sediments are increasingly recognized as both a carrier and a possible source of contaminants in aquatic systems, and these materials may also affect groundwater quality and agricultural products when disposed on land. Contaminants are not necessarily fixed permanently by the sediment, but may be recycled via biological and chemical agents both within the sedimentary compartment and the water column. Bioaccumulation and food chain transfer may be strongly affected by sediment-associated proportions of pollutants. Benthic organisms, in particular, have direct contact with sediment, and the contaminant level in the sediment may have greater impact on their survival than do aqueous concentrations. Following the findings of positive correlations between liver lesions in English Sole and concentrations of certain aromatic hydrocarbons in Puget Sound (Washington) sediment, it can be suspected that such substrates may also be responsible for a host of other serious and presently unrecognized changes at both the organismal and ecosystem levels.