REDUCTION OF THE EFFICIENCY OF EXTRACTION OF LIPOPHILIC CHEMICALS FROM WATER BY DISSOLVED ORGANIC-MATTER

A study was made of the efficiency of liquid-liquid extraction of eight chlorinated hydrocarbons of varying lipophilicity from filtered (1 mm) organic-free water, soil humic acid solution, lacustrine dissolved organic matter solution, and a natural water. The efficiency of hexane extraction of the spiked chemicals without pH adjustment (i.e., the conventional technique) was reduced with increasing concentration of dissolved organic matter (DOM) and increasing chemical lipophilicity. At the same time, increasing amounts of the more lipophilic chemicals were found in subsequent extracts of the water at pH 12, and after chromic acid oxidation of the DOM. The results indicated that conventional liquid-liquid extraction underestimates the concentrations of ''dissolved'' highly lipophilic chemicals in fresh water, the extent of the underestimation depending upon the nature of the DOM. Sixteen-day exposure experiments with filtered natural waters containing roughly 5 mg/L DOM indicated that 6 to 8% of the most lipophilic chemical tested, mirex, was not recovered by standard hexane extraction without pH adjustment; with 5 mg/L of a soil-derived humic acid, 49% of mirex was not recovered by standard hexane extraction without pH adjustment. For highly lipophilic chemicals that are not destroyed by chronic acid oxidation, it is recommended that total concentrations in filtered or centrifuged fresh waters be determined by the chromic acid oxidation, it is recommended that total concentrations in filtered or centrifuged fresh waters be determined by the chronic acid oxidation/extraction technique.