Agency for Toxic Substances and Disease Registry 
Case Studies in Environmental Medicine (CSEM) 

Nitrate/Nitrite Toxicity
What Are the U.S. Standards for Nitrate/Nitrite Levels?

Learning Objectives

After completing this section, you will be able to

• describe EPA’s recommended limit for nitrates and nitrites in drinking water.

Introduction

EPA has set an enforceable standard called a maximum contaminant level (MCL) for nitrates at 10 ppm, and for nitrites at 1 ppm. EPA believes that exposure below this level is not expected to cause health problems. Given present technology and resources, this is also a level to which water systems can reasonably be required to remove this contaminant should it occur in drinking water. All public water supplies must abide by these regulations. Once a water source is contaminated, the costs of protecting consumers from nitrate exposure can be significant. Nitrate is not removed by conventional drinking water treatment processes; its removal requires additional, relatively expensive treatment units (30).

Intake Limits

The Joint Expert Committee on Food Additives (JECFA) of the Food and Agriculture Organization of the United Nations/World Health Organization and the European Commission's Scientific Committee on Food have set an acceptable daily intake (ADI) for nitrate of 0–3.7 mg nitrate ion/kg body weight. This intake appears to be safe for healthy neonates, children, and adults. The same is also true of the EPA reference dose (RfD) for nitrate of 1.6 mg nitrate nitrogen/kg body weight per day (equivalent to about 7.0 mg nitrate ion/kg body weight per day). JECFA has proposed an ADI for nitrite of 0–0.07 mg nitrite ion/kg body weight. EPA has set an RfD of 0.l mg nitrite nitrogen/kg body weight per day (equivalent to 0.33 mg nitrite ion/kg body weight per day) (31, 32).

Environmental Standards

The current water standard for nitrate is based on levels considered low enough to protect infants from methemoglobinemia. Some published results suggest an association between nitrate in drinking water and human malformations. However, a review of the toxicology in relation to possible adverse effects on reproduction and development offers no evidence for teratogenic effects attributable to nitrate or nitrite ingestion. The present maximum contaminant level appears to adequately protect even sensitive populations from nitrate-induced toxicity (33). Nitrate, however, has not undergone an evaluation of carcinogenic potential by EPA (34).

Key Points

• The current water standard for nitrate is based on protection of infants from methemoglobinemia.
• In vivo conversion of nitrates to nitrites significantly enhances nitrates’ toxic potency.

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