Human risk assessment of organic contaminants in reclaimed wastewater used for irrigation

Current water quality guidelines for reclaimed wastewater have predominantly addressed risks associated with the presence of microbial organisms. Comparatively, chemical parameters have been largely overlooked or inadequately considered. Acceptable levels of chemical parameters will be dependant on the proposed reuse applications for the water and, in many cases, site-specific factors such as the degree of dilution with water from other sources. However, some general principals for the determination of acceptable levels of chemical contaminants in reclaimed water may be applied universally. This study describes a general risk-assessment approach to the determination of acceptable contaminant concentrations. It provides some analysis of the principal functions of hazard identification, exposure assessment, dose-response relationship characterisation and risk characterisation as they relate to chemical contaminants in reclaimed water. Examples of some key modelling calculations for this process are provided for three selected contaminants (chloroform, 1,1,2-trichloroethane and pyrene) during hypothetical irrigation of agricultural areas. Predicted environmental concentrations were calculated and compared with predicted no effect concentrations. The results of the hypothetical modelling exercise indicate that the contaminants considered in this theoretical analysis pose an acceptable risk to human health via the single exposure path considered (uptake through food grown in the irrigated soil).