Research report

The earthworms Pheretima posthuma were exposed to chromium (VI) levels varying from 0 to 100 ppm in three sets of experiments. In two sets the time required for 100 percent mortality was found to decrease with increase in chromium concentration but no trends were observed relating intermediate (< 100 percent) mortality to toxin concentration or time of exposure. The incidence of sexual reproduction and regeneration was higher in chromium‐treated media compared to controls. The results indicate that attempts to use tannery effluents for irrigation will be harmful to the soil environment even if the effluents are diluted seven times before use.