Lethal body residue of chlorophenols and mixtures of chlorophenols in benthic organisms

The lethal body residue (LBR) of a few chlorophenol congeners were measured in the oligochaete worm Lumbriculus variegatus, and the LBR of pentachlorophenol was measured also in a midge, Chironomus riparius larvae. LBR is defined as the concentration of the compound in the organism, on molar basis, to cause death, and the LBR(50) is defined as the calculated LBR value to cause a 50% mortality in population after a given time. Groups of 30 or 40 organisms were exposed to different chlorophenol concentrations in artificial soft fresh water to achieve differential mortality. Exposure times were either 24 h or 48 h. In addition to exposures with individual congeners, mixtures of chlorophenols were also tested. After each exposure, the surviving organisms were collected and the body burden of chlorophenols was measured by gas chromatography with electron capture detection. The measured body burden was related to the percent mortality in the group. The trichlorophenols and pentachlorophenol have a 48-h LBR(50) of 0.45-0.66 micromol/g wet weight in L. variegatus. The 48-h LBR(50) of pentachlorophenol for C. riparius was 0.15 micromol/g wet weight, indicating a slight difference in the sensitivity of these two species. The 48-h LBR(50) of 2,3,4,6-tetrachlorophenol is 0.91 micromol/g wet weight, and the value for 2,6-dichlorophenol is 1.2 micromol/g wet weight in L. variegatus. The 48-h LBR(50)s of the chlorophenol mixtures ranged from 0.50 to 0.83 micromol/g wet weight, demonstrating an additive toxicity.