Health-Risk Assessment of Nitrite and Nitrate in the Drinking Water in Mashhad, Iran

Nitrate and nitrite contamination is a major concern in most water supplies in Iran, as well as other countries. The present study aimed to determine the concentrations of nitrate and nitrite in the drinking water of Mashhad distribution network and examine the possible health risks.  In this study, 72 water samples were collected from five regions in Mashhad city in spring and summer during March-September 2017.Chemical analysis and in-situ measurement were conducted to determine the nitrate and nitrite concentrations using a standard, validated methodology.  Mean concentrations of nitrate and nitrite were 16.63±10.88 and 0.02±0.01 mg/l, respectively. The average daily dose (ADD) of nitrate through the ingestion pathway was within the range of 2.87-0.32 mg/kg/day in children, while it varied within the range of 1.423-0.16 mg/kg/day in adults. The ADD of nitrite changed from 0.0022 mg/kg/day to 0.0005 mg/kg/day in children and from 0.0011 mg/kg/day to 0.0003 mg/kg/day in adults. However, the hazard quotient (HQ) values for nitrate and nitrite in drinking water through ingestion exposure did not exceed the threshold of the HQ for adult, while this value was higher than one in children in some of the studied regions, including stations 11, 13, 14, 21, 28, and 33.  According to the results, the health risks associated with nitrate and nitrite contamination were higher than the threshold of the HQ for children in some areas of the water distribution network in Mashhad city. Therefore, it is critical to adopt specific strategies to reduce the nitrate concentration in the water distribution network in Mashhad.