Fig. 20.1. In the range finding test, no mortality of earthworm was observed in the
control reactors on the 7th and 14th day. The reactors with a concentration of 15 and
23 mg a.i./kg of MP 2% dust also showed no mortality. When the dosage level of MP
was increased to 50 and 75 mg a.i./kg, a mortality of 65% and 70% was observed
respectively at the 14th day. The observed earthworm mortality at 14th day was very
high as compared to that of the 7th day on which no mortality was observed at 50 mg
a.i./kg. Thus, it can be inferred that the toxicity of the insecticide affects the
earthworms with an increase in time and results in their mortality. At the maximum
dose level of MP, i.e. 113 mg a.i./kg, 100% earthworm mortality was observed. The
range of concentration of MP which caused mortality between 0% and 100% as
determined from this preliminary test was between 23 and 113 mg a.i./kg.
20.3.2 Acute Toxicity Test
20.3.2.1 Effect on Earthworm Mortality
The doses to be used for acute toxicity test were determined on the basis of range
finding test. The doses chosen were between 0% and 100% mortality of range
finding test. The mortality effect of different concentrations of MP 2% dust
a.i. from the acute toxicity test is presented in Fig. 20.2. No mortality was found
in the control reactors. From the experiment, it was found that there was no mortality
Fig. 20.2 Mortality rate of Eisenia fetida from acute exposure to MP 2% dust a.i.
20 Effect of Methyl Parathion on the Growth and Reproduction of Eisenia. . .
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