Effects of three chemicals on the survival and reproduction of the oligochaete worm Enchytraeus coronatus in chronic toxicity tests

Abstract

Using Enchytraeus coronatus as a test organism, we have measured the effects of Derosal (carbendazim as active ingredient), 4-nitrophenol and potassium dichromate on survival (Lethal Concentration: LC50) and on several sublethal variables (Effective Concentrations: EC10, EC50 and the No Observed Effective Concentration: NOEC), in chronic agar tests. Worms were also exposed to carbendazim and potassium dichromate in a soil toxicity test (Enchytraeid Reproduction Test, ERT). Sublethal variables measured in agar tests (number of juveniles and cocoons per adult, number of eggs per cocoon, percent of hatching and adult biomass) were used to facilitate interpretation of the causes of reproductive inhibition of the number of juveniles in the ERT soil toxicity test. Effective concentrations (EC) were estimated using Probit and logistic models. The later provided a better fit for the response of the worms exposed to carbendazim in agar test, in which an increase of the number of juveniles with respect to control was found at low doses. The number of juveniles per adult was the most sensitive variable measured for the three substances in the agar toxicity tests. The reduction in the number of juveniles could be explained mainly by a negative effect on cocoon hatching due to carbendazim (4-week NOEC juveniles/adult = 0.32 mg l—1, 4-week EC10 Reproductive inhibition (RI) = 0.37mg l—1), a result probably related to failure of embryonic development. The effect of 4-nitrophenol on the number of juveniles (4-week NOEC = 0.32mg l—1, 4-week EC10 (RI) = 0.25 mg l—1) was interpreted as a consequence of a reduction in the number of eggs per cocoon, associated with a reduction in parental biomass. Reproductive inhibition (RI) in worms exposed to potassium dichromate (4-week NOEC juveniles/adult = 0.32mg l—1, 4-week EC10 (RI) = 0.40 mg l—1) was explained by a reduction in cocoon production, which apparently was not related to the loss of parental biomass but rather to a failure of worm reproductive physiology. The results of this study provide useful information regarding the effects of carbendazim, 4-nitrophenol and potassium dichromate on worm reproduction biology and contribute to our understanding of the effects of these substances measured in ERT soil toxicity tests.