Lead concentration thresholds in soil are typically reported in which unit?

Lead concentration thresholds in soil are typically reported in which unit?

• A. ppm
• B. mg/kg
• C. mg/L
• D. µg/m3

Answer: (A)

Lead concentrations in soil are expressed on a mass-per-mass basis, meaning how many milligrams of lead are present per kilogram of soil. This is written as mg/kg, and it’s the standard way to report soil contamination because it directly relates the contaminant to the amount of soil. In practice, ppm (parts per million) is just another way to express the same ratio, because 1 mg of lead per 1 kg of soil equals 1 ppm by weight. That’s why thresholds for soil are commonly stated as ppm—the unit is familiar and directly comparable to mg/kg values. The other units don’t fit soil measurements: mg/L measures concentration in liquids, and µg/m3 measures concentration in air. So they aren’t appropriate for reporting soil lead thresholds.

Lead concentrations in soil are expressed on a mass-per-mass basis, meaning how many milligrams of lead are present per kilogram of soil. This is written as mg/kg, and it’s the standard way to report soil contamination because it directly relates the contaminant to the amount of soil. In practice, ppm (parts per million) is just another way to express the same ratio, because 1 mg of lead per 1 kg of soil equals 1 ppm by weight. That’s why thresholds for soil are commonly stated as ppm—the unit is familiar and directly comparable to mg/kg values.

The other units don’t fit soil measurements: mg/L measures concentration in liquids, and µg/m3 measures concentration in air. So they aren’t appropriate for reporting soil lead thresholds.