Concentrations of Some Lipophilic Chemicals in Fresh Water May Be Underestimated by Conventional Dichloromethane Extraction

A re-analysis of water samples collected to determine the occurrence of lipophilic organochlorine chemicals, total polychlorinated biphenyls (PCBs) and polynuclear aromatic hydrocarbons (PAHs) in six tributaries to Lake Ontario in 1997 to 1998 has shown relatively high concentrations of some of those chemicals in extracts of chromic acid-digested water after the water had been extracted at neutral pH. For organochlorine chemicals and PCBs the effect was dramatic-for some tributaries the sums of concentrations of the chemicals in the acidic extracts over all sampling dates were larger than the sums of concentrations of the chemicals in the (neutral) water plus suspended solids fraction that had been determined previously. In addition, some chemicals were found in the acidic extracts that were not found in the prior extracts of (neutral) water plus suspended solids. Although some individual PAHs were found at relatively high concentrations in the acidic extracts compared to extracts of (neutral) water plus suspended solids, in general the phenomenon was not significant for total PAHs. The implication of our finding is that conventional dichloromethane extraction of neutral (filtered) water and the suspended solids phases can significantly underestimate the concentrations of some lipophilic chemicals such as chlorinated hydrocarbons and PCBs in fresh water, leading to an underestimation of their loadings to aquatic ecosystems. However, it should be noted that the biological availability of chemicals that are only extractable after rigorous extraction of the water may be doubtful.