Investigating the association between Nitrate in drinking water and the incidence of respiratory diseases in California, USA

This research, titled as “Investigating the association between Nitrate in drinking water and the incidence of respiratory diseases in California, USA” is conducted by Hamed Gharibi under the supervision of Prof. Ricardo Cisneros in the University of California Merced in the year 2022. This is the first study on the effect of Nitrate on the health of people with focusing on respiratory diseases. California, the leading US state in agricultural activity, produces nearly 400 commodities (more than 30% of the country’s vegetables and 60% of the country’s fruits and nuts); the abundance of agricultural activity in this state has resulted in the increased application of Nitrogen fertilizers. The application of such fertilizers over decades resulted in leaching of nitrate to the water resources in California. Previous studies reported that California has the highest mean concentration of Nitrate over the maximum contaminant level (MCL) in drinking water, compared to all other states in the US. In addition, it is found that the greatest average annual number of people served by systems in violation of nitrate standard level is in California. The MCL for nitrate in the public drinking water is 45 mg/l-NO3 or 10 mg/l-N; however, this MCL is aimed to protect infants from methemoglobinemia and it is not for protecting people from other possible diseases in relation with long-term exposure to nitrate. According to the statistics released by State Water Resources Control Board, the highest number of violations happened in San Bernardino (1021 times), Los Angeles (945 times), Fresno (729 times), San Diego (173 times), Kern (147 times), Stanislaus (123 times), Riverside (115 times), Santa Clara (86 times) and Ventura (80 times). Based on the total population served in each county, Los Angeles (population served: 6,972,171), San Diego (1,727,098), San Bernardino (1,477,920) and Fresno (731,215) has the greatest average number of people served by systems in violation. Most of the violations occurred after year 2000; in other words, 46.41%, 33.00% and 14.79% of the violations in the California, USA occurred between 2010 to 2015, 2005 to 2009 and 2000 to 2004, respectively. There have been a few numbers of animal studies on the effect of nitrate on the lungs. In these studies, a correlation was found between nitrate in drinking water and the high methemoglobin levels, and pathologic changes in bronchi and lung parenchyma; namely, frequent dilation of bronchi with lymphocytic infiltration; atrophy of mucosa and muscles; frequent purulent bronchial exudates and interstitial round cell infiltration; and fibrosis at certain areas. The health effects of Nitrate is related to its concentration in the drinking water and also the formation of reactive free radicals of nitric oxide (NO·) and oxygen (O·). There are few studies focusing on the association between Nitrate in drinking water and the incidence of respiratory diseases around the world. In this study, it is aimed to apply different methods, namely, generalized linear model (GLM) of Poisson family (a population-based study), and Decision Trees (DT) to evaluate the association between Nitrate in drinking water and the incidence of respiratory diseases in California from 2005 to 2015