Screening Bioavailable Hydrophobic Toxicants in Surface Waters with Semipermeable Membrane Devices: Role of Inherent Oleic Acid in Toxicity Evaluations

Semipermeable membrane devices (SPMDs) were deployed for 4 weeks in two rivers in Lithuania. The SPMD dialysates were tested in the Microtox assay and, surprisingly, the sample from the relatively clean imagela River exhibited three times more toxicity than the sample from the Vilnia River receiving discharge from several industrial enterprises and municipal wastewater. The whole dialysates were subjected to bioassay-directed fractionation on silica gel columns. Toxicity testing of each fraction revealed that most of the toxicity was contained in fraction 10, which was eluted with 100% acetone. GC/FID, GC/ECD, and GC/FTIR/MS analysis of the fractions indicated that the major component of this fraction was oleic acid. The oleic acid was most likely the hydrolysis product of methyl oleate, the major impurity of the SPMD triolein. It can be inferred that oleic acid was responsible for the toxicity of this fraction in Microtox, as a threefold difference in the toxicity between the two samples was also marked by a threefold difference in their oleic acid content. Toxicity of unsaturated fatty acids in various tests, including Microtox, has been demonstrated elsewhere. Vilnia fraction 2, which was eluted with 100% hexane, exhibited the most toxicity of the remainder of silica gel fractions. The spectral analysis demonstrated that other toxic fractions contained a number of halogenated compounds and PAHs. In general, SPMDs have proved to be a useful way to screen for hydrophobic toxicants in water. However, sample clean-up procedures to remove oleic acid may be required prior to toxicity testing for the estimation of the true toxic potential of the accumulated pollutants.