Potential underestimation of chlorinated hydrocarbon concentrations in fresh water

Abstract

Significant concentrations of PCBs and other chlorinated hydrocarbons have been found in dichloromethane extracts of filtered Niagara River, Canada, water at pH 12 after the water had been thoroughly extracted at pH 1. In samples from 43 dates in 1985-86, the contribution of the basic extract to the total concentration derived from acidic, basic and suspended solids extracts ranged from 0% for 31 of these chemicals to 100% for PCBs 15, 114 and 201, aldrin and p,p′-DDT. When the sums of concentrations of each chemical found in Niagara River water in the acidic, basic and suspended solids extracts over the 43 sampling dates were themselves summed, the basic fraction contributed 40% to the total concentrations of all chemicals, and 48% if only PCBs were considered. Experiments with water from another source showed that some PCBs were recovered in dichloromethane extracts of basic filtered water which had previously been thoroughly extracted under either acidic or neutral conditions. These results indicate that concentrations of chlorinated hydrocarbons in Niagara River water determined by extraction solely at neutral pH, the usual technique, may be underestimated. This finding, which may have general applicability to fresh waters, may be the result of a strong association between a fraction of the dissolved lipophilic chemicals and dissolved organic matter in fresh water, an association that is resistant to organic solvent extraction at acidic or neutral pH, but which is at least partially disrupted by extraction at high pH.