40 CFR § 116.2 - Abbreviations.

ppm = parts per million

mg = milligram(s)

kg = kilogram(s)

mg/l = milligrams(s) per liter= (approx.) ppm

mg/kg = milligram(s) per kilogram= (approx.) ppm

[43 FR 10474, Mar. 13, 1978]