Date of Award

1999

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Environmental Sciences

First Advisor

Leslie C. Plhak

Abstract

The impact of pure azadirachtin (AZA) and neem-based insecticides (Neemix(TM) and Bioneem(TM)) on eight aquatic animals (crayfish, white shrimp, grass shrimp, blue crab, water fleas, oyster, freshwater snails, and mosquito) and two cells (hybridoma and oyster) were assessed by short term acute toxicity tests of 48 and 96 h. The LC50 (in vivo bioassays) and IC50 (in vitro bioassays) were determined for each species. Stability of (Neemix(TM) and Bioneem(TM)) was tested under light, air, and heat (24 and 37°C) for 1, 3, 6, and 9 days. Neemix(TM) and Bioneem(TM)) were fractionated into two fractions (volatiles and nonvolatiles) and toxicities of each were tested on water fleas. AZA showed less toxicity than Neemix(TM) and Bioneem(TM)) on all species tested. The toxic and molt inhibitory activity of the insecticides were species, dose and time dependent. Among the test animals, water fleas was the most sensitive to Neemix(TM), Bioneem(TM)) and pure AZA with LC50 of 0.071, 0.034, and 0.382 mug AZA/mL, respectively. Next to water fleas, mosquito, oyster and blue crab were found to be very sensitive to Neemix(TM) and Bioneem(TM)) with low LC50 values. Crayfish and freshwater snails showed the least sensitivity to Neemix(TM) Bioneem(TM) and pure AZA. The LC50 values of (Neemix(TM) were 4.705 mug AZA/mL for crayfish and 4.257 mug AZA/mL for snails. (Neemix(TM) and Bioneem(TM)) were found to be toxic to both hybridoma and oyster cells at concentration 1 mug AZA/mL and higher. The toxicity of both insecticides decreased with higher temperature, light, and time, but Bioneem(TM)) remained more toxic at 37°C than Neemix(TM) and appears to be less sensitive to environmental factors. Nonvolatile fractions exhibited significantly lower LC50 values (1.023 muL fraction/mL) than the full formulations of both insecticides. The volatile fraction of Bioneem(TM) showed lower toxicity than that of corresponding nonvolatile fractions. Whereas, the volatile fraction from Neemix(TM) was not toxic to water fleas. These results suggest that increased use of neem-based insecticides, resulting in increased agricultural run-off, may have direct adverse effects on aquatic organisms, contrary to the common belief that plant-derived insecticides (e.g. Neemix(TM) and Bioneem(TM)) pose no risk to the ecosystem.

ISBN

9780599636132

Pages

146

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