Which unit is used to express soil clearance values?

Which unit is used to express soil clearance values?

• A. ug/ft2
• B. mg/L
• C. ppm
• D. ug/dL

Answer: (C)

Soil clearance values express how much lead remains in the soil as a concentration in a solid matrix. The natural unit for this is parts per million because it conveys lead per unit mass of soil (roughly 1 mg of lead per kg of soil equals 1 ppm). Other units fit other media: micrograms per square foot measures surface dust loading, milligrams per liter is used for liquids, and micrograms per deciliter is used for blood lead levels. So for soil, ppm is the appropriate unit.

Soil clearance values express how much lead remains in the soil as a concentration in a solid matrix. The natural unit for this is parts per million because it conveys lead per unit mass of soil (roughly 1 mg of lead per kg of soil equals 1 ppm). Other units fit other media: micrograms per square foot measures surface dust loading, milligrams per liter is used for liquids, and micrograms per deciliter is used for blood lead levels. So for soil, ppm is the appropriate unit.