What is a typical EPA MCL for nitrate as nitrogen?

• A. 45 mg/L.
• B. 10 mg/L.
• C. 1 mg/L.
• D. 0 mg/L.

Answer: (B)

The key idea is that the drinking water limit for nitrate is set for health protection, especially to prevent methemoglobinemia in infants. The EPA’s primary standard is 10 mg per liter of nitrate expressed as nitrogen (mg/L as N). This means the nitrate concentration is limited to 10 mg/L when the measurement is reported as nitrogen content. In practice, that same level corresponds to about 45 mg/L when expressed as nitrate (NO3−) because nitrate weighing is higher than nitrogen by roughly a factor of 4.4. So the correct choice reflects the “as nitrogen” measurement, not nitrate with its full molecular weight. The other numbers don’t match the standard wording: 1 mg/L as N would be the nitrite-n limit, and 0 mg/L isn’t the regulatory value, while 45 mg/L as N would be just a different expression of the same contaminant but not the “as nitrogen” form.