Editing Nitrogen cycle (section)

=== Impacts on human health: nitrate accumulation in drinking water ===
Leakage of [[Reactive nitrogen|Nr (reactive nitrogen)]] from human activities can cause nitrate accumulation in the natural water environment, which can create harmful impacts on human health. Excessive use of N-fertilizer in agriculture has been a significant source of nitrate pollution in groundwater and surface water.<ref name="Power 1989" /><ref name="Strebel 1989" /> Due to its high solubility and low retention by soil, nitrate can easily escape from the subsoil layer to the groundwater, causing nitrate pollution.  Some other [[Nonpoint source pollution|non-point sources]] for nitrate pollution in groundwater originate from livestock feeding, animal and human contamination, and municipal and industrial waste. Since groundwater often serves as the primary domestic water supply, nitrate pollution can be extended from groundwater to surface and drinking water during [[Drinking water|potable water]] production, especially for small community water supplies, where poorly regulated and unsanitary waters are used.<ref name="Fewtrell 2004" />

The [[World Health Organization|WHO]] standard for [[drinking water]] is 50&nbsp;mg {{chem2|NO3-}} L<sup>−1</sup> for short-term exposure, and for 3&nbsp;mg {{chem2|NO3-}} L<sup>−1</sup> chronic effects.<ref name="c3aLP" /> Once it enters the human body, nitrate can react with organic compounds through [[nitrosation]] reactions in the [[stomach]] to form [[nitrosamine]]s and [[N-Nitrosamides|nitrosamides]], which are involved in some types of cancers (e.g., [[oral cancer]] and [[gastric cancer]]).<ref name="Canter 2019" />