Sublethal responses of the indicator Unio species (mussel) to selected phthalate esters

Sublethal effects of low and high molecular weight phthalates were assessed in Unio with a biomarker approach using gills and digestive gland as the main targets of xenobiotic uptake. Diisononyl phthalate, diisodecyl phthalate and dimethyl phthalate were studied for aquatic toxicity to nontarget freshwater mussels. Adult Unio sp. were exposed to sublethal concentrations. After 96 h exposure, total hemocyte counts in hemolymph and malondialdehyde, glutathione, superoxide dismutase, advanced oxidation protein product and protein yields in gill and digestive gland were determined. Total hemocyte counts increased significantly in the dimethyl phthalate and diisodecyl phthalate exposure groups, but decreased in diisononyl phthalate group. Malondialdehyde levels were higher in dimethyl phthalate in both tissues; whereas diisodecyl phthalate caused increase only in gills. Gill glutathione levels were lower in the diisodecyl phthalate while higher in the dimethyl phthalate in both tissues. Superoxide dismutase activities of both tissues decreased in test groups. Advanced oxidation protein product levels were higher in digestive gland than gill and in test groups compared to control. Differences in xenobiotic bioavailability may cause dissimilar responses even though these phthalates have low solubility. Changes in the biomarkers of lipid peroxidation indicate possible initial physical absorption by the mussel.