A Comparison of Screening Tests for Soil Pb

Soil has been identified as a significant source of lead (Pb) exposure for both children and adults. Therefore, identifying possibly contaminated soils by soil testing is important to protect public health. Soil Pb test results are usually reported as total Pb (mg kg(-1)), carried out using a concentrated nitric acid digestion procedure by hot plate (EPA method 3050) or microwave (EPA method 3051) followed by inductively coupled plasma atomic emission spectrometry to determine total Pb in the digest. However, this procedure is both time-consuming and expensive, sometimes costing homeowners and gardeners over $50 per sample. To make soil Pb testing more economically accessible to homeowners and gardeners, several university soil-testing laboratories offer less expensive screening tests designed to estimate total soil Pb. The first objective of this study was to compare three commonly used screening tests, modified Morgan (MM), Mehlich 3 (M3), and 1 M nitric acid (HNO(3)), to the standard total Pb testing method (EPA method 3051) to find which extractant is the most reliable predictor of total Pb. The second objective was to investigate the effect that different degrees of soil grinding have on the total Pb test and the extracted Pb concentration measured from the 1 M HNO(3) test. Results indicate that the strongest predictor of total Pb is 1 M HNO(3), followed by M3, and MM, and that thorough grinding is necessary if using less than five grams of soil in a Pb test, in order to adequately homogenize Pb-contaminated samples and achieve acceptable testing reproducibility.