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 eigh t chlorinated hydrocarbons of varying lipophilicity from filtered (1 m m) 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 c onventional technique) was reduced with increasing concentration of di ssolved organic matter (DOM) and increasing chemical lipophilicity. At the same time, increasing amounts of the more lipophilic chemicals we re found in subsequent extracts of the water at pH 12, and after chrom ic acid oxidation of the DOM. The results indicated that conventional liquid-liquid extraction underestimates the concentrations of ''dissol ved'' highly lipophilic chemicals in fresh water, the extent of the un derestimation depending upon the nature of the DOM. Sixteen-day exposu re experiments with filtered natural waters containing roughly 5 mg/L DOM indicated that 6 to 8% of the most lipophilic chemical tested, mir ex, was not recovered by standard hexane extraction without pH adjustm ent; with 5 mg/L of a soil-derived humic acid, 49% of mirex was not re covered by standard hexane extraction without pH adjustment. For highl y lipophilic chemicals that are not destroyed by chronic acid oxidatio n, it is recommended that total concentrations in filtered or centrifu ged fresh waters be determined by the chromic acid oxidation, it is re commended that total concentrations in filtered or centrifuged fresh w aters be determined by the chronic acid oxidation/extraction technique .