National Research Council to review the current basis of its MCLGs for nitrate and nitrite in drinking water and to determine whether they are protective of public health. The Research Council, through the Board on Environmental Studies and Toxicology in the Commission on Life Sciences, convened a subcommittee of the Committee on Toxicology and asked it to:

  • Review the current toxicologic and exposure data on nitrate and nitrite.

  • Characterize the risk associated with nitrate and nitrite exposure through drinking water.

  • Determine whether the current MCLGs for nitrate and nitrite are adequate to protect public health.

  • Identify data needs and make recommendations for future research.

Throughout this report, by the Subcommittee on Nitrate and Nitrite in Drinking Water, concentrations of nitrate and nitrite are expressed in terms of milligrams per liter (mg/L). Another common unit of measurement is milligrams of nitrate nitrogen or nitrite nitrogen per liter. The nitrogen oxides have multiple interconvertible forms, although the deleterious effects of concern arise through a common intermediate. Each of the precursors of that intermediate has a different molecular weight; using a weight measure, such as milligrams, to evaluate usefully the relative contribution of nitrite versus nitrate, for example, requires a conversion factor. The conversion factors are

1 mg of NO3- per liter = 0.226 mg of NO3- nitrogen per liter,

1 mg of NO3- nitrogen per liter = 4.429 mg of NO3-per liter,

1 mg of NO2- per liter = 0.304 mg of NO2- nitrogen per liter,


1 mg of NO2- nitrogen per liter = 3.290 mg of NO2- per liter.

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