the weight loss and alteration in muscular function were the reasons behind the
coiling of earthworms in 100% of the cases treated with parathion. It has also been
reported that earthworms treated in organophosphate pesticides find difficulty in
locomotion after getting intoxicated and they become unable to feed themselves
which causes a considerable weight loss in them (Bustos-Obregón and Goicochea
2002).
A dose-dependent trend showing the decrease in earthworm biomass over a
14-day exposure period was further confirmed by the one-way ANOVA test. After
the 7-day exposure to MP, it was found that there was no significant difference in the
growth inhibition in low and medium dosage (25, 40 and 55 mg a.i./kg) (Tukey’s
test, P < 0.05) whereas, there was a significant (P < 0.05) difference from the
control at a dose of 70 mg a.i./kg. On the 14th day, there was positive growth
inhibition in all the reactors. In dosage of 55 and 70 mg a.i./kg, there was more than
80% biomass loss of earthworms as compared to the control. From Tukey’s test as a
post-hoc analysis, it was observed that the earthworm growth inhibition at 14th day
was significantly (P < 0.05) different from the control at higher doses of 55 and
70 mg a.i./kg. However, there was no significant difference compared to control
(P > 0.05) at a low concentration of MP of 25 and 40 mg a.i./kg.
20.3.3 Chronic Toxicity Test
20.3.3.1 Effect on Earthworm Growth Inhibition
The growth inhibition of earthworms at 28th day in the chronic toxicity test was
observed at different doses of MP 2% dust a.i. as presented in Fig. 20.4. A negative
growth inhibition was observed in the control as well for doses of 2.5 and 4.0 mg a.i./
kg. The earthworm growth rates observed as compared to control at MP doses of 2.5,
4.0, 6.4 and 10.2 mg a.i./kg were not significantly (P > 0.05) reduced with values
around 3.87%, 8.45%, 16.04% and 7.20%, respectively. However, the earthworm
growth rate was significantly (P < 0.05) reduced to 21% and 78% at MP doses of
16.3 and 23.0 mg a.i./kg, respectively. The negative growth inhibition at the lower
dose was plausibly due to the weekly addition of 5 g of dried septic tank sludge as
feeding material for 4 weeks. The high organic carbon content of the septic tank
sludge provided the earthworms with the necessary food required for their growth.
At lower doses, the earthworms were in the proper state but started to become stiff
and structural coiling beyond an MP dose of 6.4 mg a.i./kg. Coiling has been
regarded as a symptom of weight loss (Bustos-Obregón and Goicochea 2002).
From ANOVA Tukey’s test, it was observed that there was no statistically significant difference of lower and medium doses with control (P > 0.05) at 28 days
indicating that MP 2% dust a.i. has little effect on the growth of earthworms. A
statistically significant (P < 0.05) difference with the control was observed at the MP
doses of 16.3 and 25 mg a.i./kg.
20 Effect of Methyl Parathion on the Growth and Reproduction of Eisenia. . .
359
coiling of earthworms in 100% of the cases treated with parathion. It has also been
reported that earthworms treated in organophosphate pesticides find difficulty in
locomotion after getting intoxicated and they become unable to feed themselves
which causes a considerable weight loss in them (Bustos-Obregón and Goicochea
2002).
A dose-dependent trend showing the decrease in earthworm biomass over a
14-day exposure period was further confirmed by the one-way ANOVA test. After
the 7-day exposure to MP, it was found that there was no significant difference in the
growth inhibition in low and medium dosage (25, 40 and 55 mg a.i./kg) (Tukey’s
test, P < 0.05) whereas, there was a significant (P < 0.05) difference from the
control at a dose of 70 mg a.i./kg. On the 14th day, there was positive growth
inhibition in all the reactors. In dosage of 55 and 70 mg a.i./kg, there was more than
80% biomass loss of earthworms as compared to the control. From Tukey’s test as a
post-hoc analysis, it was observed that the earthworm growth inhibition at 14th day
was significantly (P < 0.05) different from the control at higher doses of 55 and
70 mg a.i./kg. However, there was no significant difference compared to control
(P > 0.05) at a low concentration of MP of 25 and 40 mg a.i./kg.
20.3.3 Chronic Toxicity Test
20.3.3.1 Effect on Earthworm Growth Inhibition
The growth inhibition of earthworms at 28th day in the chronic toxicity test was
observed at different doses of MP 2% dust a.i. as presented in Fig. 20.4. A negative
growth inhibition was observed in the control as well for doses of 2.5 and 4.0 mg a.i./
kg. The earthworm growth rates observed as compared to control at MP doses of 2.5,
4.0, 6.4 and 10.2 mg a.i./kg were not significantly (P > 0.05) reduced with values
around 3.87%, 8.45%, 16.04% and 7.20%, respectively. However, the earthworm
growth rate was significantly (P < 0.05) reduced to 21% and 78% at MP doses of
16.3 and 23.0 mg a.i./kg, respectively. The negative growth inhibition at the lower
dose was plausibly due to the weekly addition of 5 g of dried septic tank sludge as
feeding material for 4 weeks. The high organic carbon content of the septic tank
sludge provided the earthworms with the necessary food required for their growth.
At lower doses, the earthworms were in the proper state but started to become stiff
and structural coiling beyond an MP dose of 6.4 mg a.i./kg. Coiling has been
regarded as a symptom of weight loss (Bustos-Obregón and Goicochea 2002).
From ANOVA Tukey’s test, it was observed that there was no statistically significant difference of lower and medium doses with control (P > 0.05) at 28 days
indicating that MP 2% dust a.i. has little effect on the growth of earthworms. A
statistically significant (P < 0.05) difference with the control was observed at the MP
doses of 16.3 and 25 mg a.i./kg.
20 Effect of Methyl Parathion on the Growth and Reproduction of Eisenia. . .
359