Carnivorous Insects as Bioindicators of Environmental Contamination: Rganochlorine Insecticide Residues Related to Insect Distribution in Terrestrial Ecosystems

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Abstract
The impact of organochlorinated insecticides on the relative contamination of ants and sapro-necrophagous and carnivorous beetles has been evaluated in various agricultural and forested areas in Belgium. A novel micromethod of organochlorinated insecticide extraction and clean-up at trace levels is described. This analytical procedure involves sample clean-up on Sep-Pak Florisil microcartridges and high resolution gas chromatography analysis with an automatic solid sampler. The efficiency of extraction, clean-up and gas chromatography analysis is discussed. In spite of the legal interdiction of most organochlorine insecticides in this country (with the exception of lindane), residues of DDT and dieldrin were still detected in beetles and in ants. The contamination of insects was generally low (mean values ranged from 3 to 70 ppb according to the nature of insecticide) although a few samples contained high concentrations of prohibited insecticides (up to 274 ppb of dieldrin and 419 ppb of DDT metabolites). The authors suggest that insect contamination by organochlorine insecticide residues in forested areas would not result from a direct intoxication due to utilization of these xenobiotics on the sampling sites. Indeed, codistillation phenomenon conjugated with atmospheric transport of contaminated particles could induce environment contamination far away from the sites of insecticide applications in the direction of the West dominant winds in Belgium. The consequences of such a contamination of insects by organochlorine insecticide residues are discussed.

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