Determination of the Parasitic Contamination of Irrigated Vegetables

Abstract

In countries with limited water resources, the agricultural use of treated wastewater represents an interesting alternative. The recent World Health Organisation guidelines (1989) for the microbiological quality of treated wastewaters used for crop irrigation require an arithmetic mean of ≤ 1 intestinal nematode egg per litre. In this study diverse methods have been tried for recovering parasitic nematode eggs from vegetables artificially contaminated by Ascaris eggs. The vegetables examined were lettuce and tomatoes. Vegetables were seeded with Ascaris eggs at different levels from 3 to 900 eggs. Eggs elution was realized with chemical solution (distilled water, aceto-acetic buffer pH 4.5, formalin 20%, anionic detergent DDN50®, cationic detergent hyamine®) and/or mechanical treatment (brush - scrub or brush - scrub coupled with glass powder treatment). Concentration was performed by flotation technique with a 55% zinc sulphate solution (d=1.3). Recovery was low for all samples after chemical elution. When we tested the association of chemical and mechanical treatments the percent recovery were ranging from 72 to 100% for vegetables contaminated with 10 to 400 eggs. The method proposed includes an elution with a glass powder suspension in a cationic detergent (50/50), a concentration with ZnSO4 55% solution (d=1.3) and a quantification with a counting cell. The sensitivity threshold of the proposed method lies at about 10 eggs per samples.