The primary goal of this study has been to carry out a rigorous, critical review and evaluation of all available documented epidemiological evidence with the aim of determining the significant, quantifiable, health effects on population groups directly or indirectly exposed to wastewater irrigation: through occupation; by residing in continguous communities or by consuming the sewage irrigated crops. Based on these findings, we have developed an epidemiological model predicting the degree of risk associated with various groups of pathogens.

Based on theoretical consideration of the model and confirmation by the empirical evidence collected and analyzed in this study, we have concluded that the risk of pathogen transmission by irrigation with raw wastewater for most developing countries is according to the following descending order: high - helminths (Ascaris, Trichuris, Ankalostoma and Taenia), lower - bacteria (Typhoid and Cholera); and lowest - viruses.

In general, it can be stated that based on both the theoretical and empirical findings of this study, there appears to be a basis for relaxing the conventional effluent quality standards for unrestricted crop irrigation. A guideline of no helmiths in 1 liter and a log mean of 1000 fecal coliforms/100 ml is proposed.

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