Introduction

EPA has set an enforceable standard called a maximum contaminant level (MCL) in water for nitrates at 10 parts per million (ppm) (10 mg/L) and for nitrites at 1 ppm (1 mg/L) [EPA 2002; EPA 2012].

• EPA believes that exposure below this level is not expected to cause significant health problems.
• All public water supplies must abide by these regulations.
• Given present technology and resources, this MCL is also a level to which water systems can reasonably be required to remove this contaminant should it occur in drinking water.

Once a water source is contaminated, the costs of protecting consumers from nitrate exposure can be significant. This is because:

• Nitrate is not removed by conventional drinking water treatment processes, and
• Its removal requires additional, relatively expensive treatment units [EPA 2004].

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 milligrams (mg) nitrate ion/kilogram (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) [EPA 2002; EPA 2012].

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) [Mensinga et al. 2003; Abadin et al. 1998; EPA 2002; EPA 2012].

Bottled Water and Food Additives Limits

The FDA regulates allowable levels of inorganic nitrate and nitrite in bottled water [FDA 2005] as well as levels allowable in foodstuffs [FDA 2003].

The FDA's bottled water standard is based on the EPA standards for tap water. The bottled water industry must also follow FDA's Current Good Manufacturing Practices (CGMPs) for processing and bottling drinking water. If these standards are met, water is considered safe for most healthy individuals. However, although not often reported, bottled water outbreaks do occur. More information on bottled water can be found at http://www.cdc.gov/healthywater/drinking/bottled/index.html

Bottled water

Allowable levels in bottled water:

• Nitrate 10 mg/L (as nitrogen)
• Nitrite 1 mg/L (as nitrogen)
• Total nitrates, nitrites 10 mg/L (as nitrogen)

Allowable levels as an additive to foods:

• As a preservative and color fixative, with or without sodium nitrite, in
  • Smoked, cured sablefish
  • Smoked, cured salmon
  • Smoked, cured shad
  so that the level of sodium nitrate does not exceed 500 parts per million (ppm) and the level of sodium nitrite does not exceed 200 ppm in the finished product.
• As a preservative and color fixative, with or without sodium nitrite, in meat-curing preparations for the home curing of meat and meat products (including poultry and wild game), with directions for use which limit the amount of sodium nitrate to not more than 500 ppm in the finished meat product and the amount of sodium nitrite to not more than 200 ppm in the finished meat product.
• The food additive potassium nitrate may be safely used as a curing agent in the processing of cod roe, in an amount not to exceed 200 ppm of the finished roe.

The U.S. Department of Agriculture's (USDA's) Food Safety and Inspection Service (FSIS) regulates food ingredients approved for use in the production of meat and poultry products. This includes inspection for required labeling of meat products when substances such as sodium nitrate are used in meat packaging [USDA 2012].

Environmental Standards

The current water standard for nitrate is based on levels considered low enough to protect infants from methemoglobinemia.

• Some published results suggest a possible association between nitrate exposure during pregnancy and human malformations [Croen et al 2001; Brender et al 2004; Brender et al 2011].
• 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 [Manassaram et al 2006; Huber et al 2013].
• The present maximum contaminant level appears to adequately protect even sensitive populations from nitrate-induced toxicity [Fan and Steinberg 1996; EPA 2006].
• EPA concludes that the evidence in the literature showing an association between exposures to nitrate or nitrites and cancer in adults and children is conflicting [EPA 1991, 2002, 2006].

Progress Check