Nitrates

In inorganic chemistry, a nitrate is a salt of nitric acid with an ion composed of one nitrogen and three oxygen atoms (NO-3). In organic chemistry the esters of nitric acid and various alcohols are called nitrates.

Nitrate toxicosis in humans occurs through enterohepatic metabolism of nitrates to ammonia, with nitrite being an intermediate[3]. Nitrites oxidize the iron atoms in hemoglobin from ferrous iron (2+) to ferric iron (3+), rendering it unable to carry oxygen[4]. This process can lead to generalized lack of oxygen in organ tissue and a dangerous condition called methemoglobinemia. Methemoglobinemia can be treated with methylene blue, which reduces ferric iron (3+) in affected blood cells back to ferrous iron (2+).

Infants in particular are especially vulnerable to methemoglobinemia due to nitrate metabolizing triglycerides present at higher concentrations than at other stages of development. Methemoglobinemia in infants is colloquially know as "blue baby syndrome". Initial exposure is most often caused by high levels of nitrates in drinking water. However nitrate exposure may also occur if eating for instance vegetables containing high levels of nitrate. Lettuce may contain elevated nitrates under growth conditions such as reduced sunlight, undersupply of the essential micronutrients molybdenum (Mo) and iron (Fe), or high concentrations of nitrate due to reduced assimilation of nitrate in the plant. High levels of nitrate fertilization also contribute to elevated levels of nitrate in the harvested plant .

Activated carbon water filters cannot remove nitrates from tap water. A reverse osmosis system will remove 85-90% of arsenic to deliver safe drinking water.

* Some info courtesy of Wikipedia.

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