Toxicity Profiles

RAGs A Format for Nitrates - CAS Number 14797558

Nitrate (NO3-) is an inorganic anion resulting from the oxidation of elemental nitrogen. It is an essential nutrient for plant protein synthesis and plays a critical role in the nitrogen cycle of soil and water. Nitrates are produced by natural biological and physical oxidations and therefore are commonly found in the environment. Most nitrate compounds are strong oxidizing agents; some can react violently with oxidizable substances and may explode if exposed to heat or shock.. Organic molecules containing nitrate groups are manufactured primarily for explosives or for pharmacological effects. Most of the excess nitrates in the environment originate from inorganic chemicals manufactured for agriculture. Farmers often apply fertilizer in the form of ammonium or sodium nitrate in excess to their crops. When the concentration of nitrates in the soil is higher than the plants can use, the excess nitrates appear in the surface and ground waters and are often found in drinking water, especially in rural agricultural areas served by wells.

The primary toxic effect of inorganic nitrates is iron oxidation in hemoglobin of the blood, forming methemoglobin. Infants less than 6 months old comprise the most sensitive population. Epidemiological studies have shown that baby formula made with drinking water containing nitrate levels over 10 mg/L can result in methemoglobinemia, especially in infants less than 2 months of age. A secondary target for inorganic nitrate toxicity is the cardiovascular system. Nitrate intake can also result in a vasodilatory effect, which can complicate the anoxia resulting from methemoglobinemia. Organic nitrates can cause similar effects.

The possible carcinogenicity of nitrate depends on the conversion of nitrate to nitrite and the reaction of nitrite to form N-nitroso compounds that are carcinogenic. There is little human data, and the studies that have been reported are conflicting. Experiments with rats have shown that when given both nitrite and heptamethyleneimine in drinking water, an increase in the incidence of tumors occurs. Nitrate has not been classified as to its carcinogenicity by the EPA.

The following is a presentation of the toxicity information associated with Nitrates.

Noncarcinogenic Health Effects

• The Oral Chronic Reference Dose is 1.60E+00 (mg/kg-day).
• The Oral Chronic Reference Dose has a modifying factor of 1.
• The Oral Chronic Reference Dose has an uncertainty factor of 1.
• The Oral Chronic Reference Dose is based on the Walton study from 1951.
• The Oral Chronic Reference Dose study critical effect is early clinical signs of methemoglobinemia in excess of 10%.
• The overall confidence in the Oral Chronic Reference Dose is high.
• The Dermal Chronic Reference Dose is 8.00E-01 (mg/kg-day).
• The Dermal Chronic Reference Dose is based on a gastrointestinal absorption factor of 0.5000.