Many of these organisms use oxygen in order to do decomposition. The dissolved oxygen levels drop, leaving no oxygen for the animals that live in the water. Nitrate levels testable with these test kits are of concern in natural bodies of water. In high concentrations, nitrate can affect human health, particularly that of unborn fetuses and young babies. Hemoglobin is an iron-containing compound in our blood that carries oxygen.
Fetal hemoglobin is replaced by the adult form as genes switch on and off after the baby is born.
Fetal hemoglobin combines irreversibly with nitrite, an ion that differs from nitrate by having one fewer oxygen atom, NO 2 . When nitrate is consumed in food or beverage, some of the nitrate is changed to nitrite in the stomach and absorbed into the blood. Chemically speaking, stomachs are reducing environments, low in oxygen. Ruminants such as sheep and cows are particularly low in oxygen and produce much higher levels of nitrite than humans with the same nitrate levels. No human deaths from nitrate pollution have occurred in the United States, but babies have died in Europe.