Mohammadreza Vesali Naseh

Understanding nitrate–nitrite (NO􀀁3 􀀁 NO􀀁2 ) levels in drinking water and the associated non-carcinogenic and carcinogenic health risks are essential to protect public health. The non-carcinogenic risk assessment of NO􀀁3 –NO􀀁2 in drinking water has been well documented, however, there remains a knowledge gap in under-standing and quantification of the carcinogenic risk of NO􀀁3 –NO􀀁2 . This study develops a non-threshold–based model for estimation of carcinogenic risk of NO􀀁3 –NO􀀁2 ingested through drinking water for a densely populated urban area with a case study of Tehran’s potable water (TPW). In this regard, 200 tap water samples from different parts of the city were taken in wet (May 2018) and dry (October 2018) periods to determine NO􀀁3 –NO􀀁2 concentration in the TPW and the associated health risks across different groups of end-users. Sampling results reveal higher concentrations of NO􀀁3 –NO􀀁2 during the dry period, which can be associated to the significant contribution of nitrogen–rich groundwater in supplying the city’s water demands during the dry period. Findings suggest concerns associated with the non-carcinogenic risk of NO􀀁3 –NO􀀁2 in the TPW, especially for children. More than 55% of the samples taken during the dry period show a positive carcinogenic risk for all groups of end- users (68% for men, 72% for women, and 56% for children) whilst just 8% of the samples are deemed unsafe with regards to the permissible NO􀀁3 level in drinking water, i.e. 50 mg/L. Approximately, 45% of the samples taken during the wet period show a positive carcinogenic risk for adults whilst the maximum concentration of NO􀀁3 was about 23 mg/L, i.e. two times less than the permissible level in drinking water. The findings emphasize on the necessity of reducing the permissible level of NO􀀁3 in drinking water, set out by the existing water quality standards, to safeguard public health against the carcinogenic risks. The model developed within this study recommen