Toxicity tests of chlorinated hydrocarbons on the river mussel, Unio crassus (Bivalvia, Unionidae).

The toxicity of three highly volatile organic solvents - tetrachloroethane (Cl₂HC-CHCl₂), tetrachloroethylene (Cl₂C=CCl₂), trichloroethylene (ClHC=CCl₂) - was studied on Unio crassus specimens. The tested chlorinated hydrocarbons sink to the bottom of standing water bodies due to their high density; therefore they represent an increased risk for benthic organisms. For a start, all three compounds were applied in 100% saturation. In the case of tetrachloroethylene and trichloroethylene all specimens died within a few days. In the case of tetrachloroethane the intoxication process was much faster, all the specimens died within 4 hours. Tetrachloroethane proved to be the most toxic compound; its diluted solutions were further tested: in the 5% solution all U. crassus specimens died after 24 hours. The 1% solution had a strong disturbing effect on the behaviour of the bivalves, which was gradually moderated and eventually stopped on the 33^rd day. These results suggest that the examined chlorinated hydrocarbons are strongly toxic to living organisms even in aquatic medium and cause rapid death even in low concentrations. [ABSTRACT FROM AUTHOR]