CFR /  Title 40  /  Part 116  /  Sec. 116.2 Abbreviations.ppm=parts per millionmg=milligram(s)kg=kilogram(s)mg/l=milligrams(s) per liter= (approx.) ppmmg/kg=milligram(s) per kilogram= (approx.) ppm [43 FR 10474, Mar. 13, 1978]