Which unit is used to report thresholds for soil lead in play areas?

Which unit is used to report thresholds for soil lead in play areas?

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

Answer: (A)

Concentrations of lead in soil are reported by weight, using units that express how much lead is present per amount of soil. Parts per million (ppm) is the standard way this is communicated for soil thresholds, because it directly describes milligrams of lead per kilogram of soil. For example, a threshold of 400 mg/kg is the same as 400 ppm. The other units shown are oriented toward liquids (µg/mL) or water measurements (ng/L), not soil. Although mg/kg technically conveys the same concentration as ppm, ppm is the conventional reporting unit for soil lead thresholds in play areas, which is why it’s the best choice here.

Concentrations of lead in soil are reported by weight, using units that express how much lead is present per amount of soil. Parts per million (ppm) is the standard way this is communicated for soil thresholds, because it directly describes milligrams of lead per kilogram of soil. For example, a threshold of 400 mg/kg is the same as 400 ppm. The other units shown are oriented toward liquids (µg/mL) or water measurements (ng/L), not soil. Although mg/kg technically conveys the same concentration as ppm, ppm is the conventional reporting unit for soil lead thresholds in play areas, which is why it’s the best choice here.