Using Aedes aegypti larvae to Assess Pesticide Contamination of Soil, Groundwater and Vegetables

In Benin, the use of synthetic pesticides in vegetable production poses a risk to the environment and human health. Vegetables, water and soil quality assessment is very important for monitoring and mitigation of these risks. The evaluation of pesticide contamination of vegetables and agricultural environment is often made using expensive methods. It is crucial for research in so-called developing countries to develop less expensive tools for pesticide risks assessment and monitoring. The aim of this study was to assess the potential of using Aedes aegypti larvae as a bio-indicator to measure the pesticide contamination of soil, groundwater and vegetables. Vegetables just before harvest, groundwater and soils samples from three production sites and vegetables samples from markets were collected from March to August 2011. Ethanol extracts of these samples were tested on first stage larvae of Aedes aegypti. The method made it possible to detect residues of chlorpyrifos-ethyl and deltamethrin in cabbage until 4 and 8 days respectively after treatment with the recommended doses for crop protection. It proved inappropriate to measure pesticides residues in market-gardening soils, since these soils contain some amounts of nitrite, nitrate and phosphate, coming from the decomposition of fertilizers which are poisonous for the first stage larvae of Aedes aegypti. Overall, the results revealed the presence of small amounts of pesticides residues in 12.5% of the vegetables collected from markets. Pesticides residues were also detected in 30.0% of vegetables collected just before harvest. Residues of pesticide were not detected in groundwater samples collected from vegetable growing areas. First stage larvae of Aedes aegypti could be used as a bio-indicator to characterize and monitor risk of pesticide contamination of vegetables in southern Benin. It could also be used for a monitoring program before running a more thorough chemical analysis to identify and quantify the pesticide molecules present in samples.