The EPA recommends a concentration of no more than 10 mg of nitrogen from nitrate, NO3-–N, per L of water. This is equivalent to 10 parts per million (ppm).
Nitrate pollution can be expressed as either NO3- or NO3--N, but these two terms are not interchangeable or represented by the same value.
Converting the weight of nitrate nitrogen to the molecular weight of nitrate is simple. Let's start by building the nitrate molecule.