Methodological challenges and uncertainties in human health risk assessment of nitrate exposure.

Safe and clean water is a fundamental requirement for human health and well-being. Both the quantity and quality of drinking water directly affect population health, which makes the investigation of contaminants and their associated health risks a matter of growing scientific and public concern. Among the many waterborne contaminants, nitrate is of particular importance. It is a recalcitrant compound found in most water bodies, originating from both natural sources and anthropogenic activities such as agriculture and wastewater discharge. Numerous studies have attempted to evaluate the health risks of nitrate exposure across different age groups, including infants, children, and adults. However, in reviewing the literature, we have identified recurring methodological inconsistencies that may compromise the reliability of risk estimates. In this discussion paper, we examine key methodological issues in nitrate-related human health risk assessment, including the misapplication of nitrate reference dose (RfD) values across different population groups, inconsistencies in chemical units and nomenclature, and uncertainties arising from the conversion of nitrate to nitrite during exposure and risk assessment. Examples from published research will be used to illustrate and critically analyse these common methodological pitfalls.