2% dust a.i. showed lower cocoon production. The difference in the cocoon production was significantly (P < 0.05) different in all the doses of MP as compared to
the control. Production of cocoons by the earthworms was found to be a sensitive
parameter with the exposure to pesticides like paraquat, fentin, benomyl,
phenmedipham, carbaryl, copper oxychloride and dieldrin (Cikutovic et al. 1993;
Gupta and Saxena 2003; Reinecke and Reinecke 2007; Van Gestel 1992).
At MP doses of 2.5, 4.0, 6.4, 10.2 and 16.3 mg a.i./kg, the average weight per
cocoon was not statistically (P > 0.05) different from the control. When the dose of
MP was 26.2 mg a.i./kg, there was a statistically significant (P < 0.05) difference as
compared to the control. The results obtained in this study were in good agreement
with other studies (Xiao et al. 2006) showing the effect of pesticides like acetochlor
on the reproduction ability of the earthworms.
20.4 Conclusions
The toxicological effects of organophosphate insecticide methyl parathion (MP) 2%
dust (active ingredient, a.i.) on epigeic earthworm Eisenia fetida at different lethal
and sub-lethal concentrations were assessed in this study. MP 2% dust a.i. was found
to be extremely toxic to the epigeic earthworm Eisenia fetida. The median lethal
concentration (LC 50 ) for E. fetida was found to be 36.63 mg a.i./kg, which confirms
the extremely toxic nature MP 2% dust. A lower dose of 25 mg a.i./kg of MP 2%
dust in acute toxicity test resulted in no mortality but showed a 24% loss in biomass
as compared to the initial weight of the earthworms following a dose-dependent
relationship. Septic tank sludge as an organic admixture was found to be a suitable
feeding material for earthworms as it was observed to lead to a negative growth
inhibition at a lower dose of MP 2% dust a.i. in the chronic toxicity test. This
negative growth inhibition was essentially due to the high organic carbon content of
septic tank sludge. In the chronic toxicity test, it was observed that the cocoon
production by the earthworms was very less at higher sub-lethal doses. This can be
attributed to the structural coiling of the earthworms as the earthworms plausibly find
it difficult to copulate in terms of their posture of mating. It can be concluded from
the study that the change in the earthworm biomass and the reproduction potential
are the sensitive endpoints than the lethal concentration (LC 50 ) as they provide an
early response to the sub-lethal doses of pesticides.
References
Abdullah AR, Bajet CM, Matin MA, Nhan DD, Sulaiman AH (1997) Ecotoxicology of pesticides
in the tropical paddy field ecosystem. Environ Toxicol Chem 16(1):59–70
Abhilash PC, Singh N (2009) Pesticide use and application: an Indian scenario. J Hazard Mater 165
(1–3):1–12
20 Effect of Methyl Parathion on the Growth and Reproduction of Eisenia. . .
361
the control. Production of cocoons by the earthworms was found to be a sensitive
parameter with the exposure to pesticides like paraquat, fentin, benomyl,
phenmedipham, carbaryl, copper oxychloride and dieldrin (Cikutovic et al. 1993;
Gupta and Saxena 2003; Reinecke and Reinecke 2007; Van Gestel 1992).
At MP doses of 2.5, 4.0, 6.4, 10.2 and 16.3 mg a.i./kg, the average weight per
cocoon was not statistically (P > 0.05) different from the control. When the dose of
MP was 26.2 mg a.i./kg, there was a statistically significant (P < 0.05) difference as
compared to the control. The results obtained in this study were in good agreement
with other studies (Xiao et al. 2006) showing the effect of pesticides like acetochlor
on the reproduction ability of the earthworms.
20.4 Conclusions
The toxicological effects of organophosphate insecticide methyl parathion (MP) 2%
dust (active ingredient, a.i.) on epigeic earthworm Eisenia fetida at different lethal
and sub-lethal concentrations were assessed in this study. MP 2% dust a.i. was found
to be extremely toxic to the epigeic earthworm Eisenia fetida. The median lethal
concentration (LC 50 ) for E. fetida was found to be 36.63 mg a.i./kg, which confirms
the extremely toxic nature MP 2% dust. A lower dose of 25 mg a.i./kg of MP 2%
dust in acute toxicity test resulted in no mortality but showed a 24% loss in biomass
as compared to the initial weight of the earthworms following a dose-dependent
relationship. Septic tank sludge as an organic admixture was found to be a suitable
feeding material for earthworms as it was observed to lead to a negative growth
inhibition at a lower dose of MP 2% dust a.i. in the chronic toxicity test. This
negative growth inhibition was essentially due to the high organic carbon content of
septic tank sludge. In the chronic toxicity test, it was observed that the cocoon
production by the earthworms was very less at higher sub-lethal doses. This can be
attributed to the structural coiling of the earthworms as the earthworms plausibly find
it difficult to copulate in terms of their posture of mating. It can be concluded from
the study that the change in the earthworm biomass and the reproduction potential
are the sensitive endpoints than the lethal concentration (LC 50 ) as they provide an
early response to the sub-lethal doses of pesticides.
References
Abdullah AR, Bajet CM, Matin MA, Nhan DD, Sulaiman AH (1997) Ecotoxicology of pesticides
in the tropical paddy field ecosystem. Environ Toxicol Chem 16(1):59–70
Abhilash PC, Singh N (2009) Pesticide use and application: an Indian scenario. J Hazard Mater 165
(1–3):1–12
20 Effect of Methyl Parathion on the Growth and Reproduction of Eisenia. . .
361