Effects of chlorinated benzenes on diatom fatty acid composition and quantitative morphology. IV. Pentachlorobenzene and comparison with trichlorobenzene isomers.

Cells of the diatom Cyclotella meneghiniana were exposed in a closed system to 0.095 ppm pentachlorobenzene over a period of 5 days. Changes in fatty acid and morphological percent composition were monitored to determine the effect of the toxicant. The greatest morphological change observed was an increase in lipid volume. Most morphological changes occurred in the 1 hour and 5 day sampling periods. Few changes in morphological characteristics or fatty acid percent composition were observed at eight hours, when the cells were in the dark. The C18:1 and C20:5 fatty acids were most variable with exposure to pentachlorobenzene. Results suggest that at sublethal doses, lipophilic toxicants exert effects that are biphasic. That is, immediately measurable effects are observed in the cells that include increases in storage products and changes in membranous organelles. Long-term effects are postulated to be the result of mobilization of lipophilic toxicants that have partitioned into lipid stores and are more available when lipids are metabolized. Although pentachlorobenzene has a higher octanol/water partition coefficient, it appears to exert fewer cellular changes than any trichlorobenzene isomer.