Hoda M Nasr and Mohamed EI Badawy
Earthworms play key roles in soils and sub lethal effects of environmental toxicants on these organisms should be taken seriously, since they might have detrimental effects on higher ecological levels. In laboratory experiments, we have assessed to investigate the toxicity of two insect growth regulators (IGRs) flufenoxuron and pyriproxyfen at different application rates and exposure times against mature stage earthworms Aporrectodea caliginosa. The effects of these pesticides on the growth rate in relation to the activities of acetylcholinesterase (AChE), polyphenol oxidase (PPO) and glutathione S-transferase (GST) as biomarker indicators were evaluated to elucidate the mechanisms of action. Toxicity studies indicated that pyriproxyfen was more harmful to mature earthworms than flufenoxuron with LC50=42.63 and 60.66 mg/kg after four weeks, respectively. The reduction in growth rate of all pesticide-treated worms was dosedependent over the 28-day exposure period which was accompanied by a decrease in AChE, PPO and GST activities. Relationships between growth rate and enzyme activities provided strong evidence for the involvement of pesticidal contamination in the biochemical changes of earthworms, which can be used as a bioindicator of soil contamination by pesticides.
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