A Comparison of Screening Tests for Soil Pb

Abstract

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 (HNO3), 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 HNO3 test. Results indicate that the strongest predictor of total Pb is 1 M HNO3, 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.

Concentrations of lead, cadmium and barium in urban garden-grown vegetables: The impact of soil variables

“…Most critically, much of the vegetable content of Pb appears to be due to physical contamination by soil particles or aerosols, a process that is highly random by nature. Finally, our studies have shown that metals such as Pb and Ba are not distributed homogeneously in these urban soils, but are concentrated in “nuggets” (Wharton et al, 2012), a characteristic that complicates the assessment of metal bioavailability and its relationship to metal concentration in soils. The particularly high Pb concentrations in some garden beds present a risk, but also a need and opportunity for intervention and management to reduce exposure.…”

“…Highly variable spatial distribution of Pb in soils of urban environments, from the scale of several hundred meters (Säumel et al, 2012; Shinn et al, 2000) to the minute scale of the root zone, soil aggregates and microscopic particles (Tai et al, 2013; Wharton et al, 2012). …”

Agreement ℜ of Four Analytical Methods Applied to Pb in Soils from the Small City of St. John’s, Newfoundland, Canada

“…There are many Pb assessment methods used in the USA and throughout the world [ 21 ]. Advanced studies such as a Pb isotope measurements study in London determined the links between current atmospheric Pb and leaded petrol used during the 20th century [ 22 ].…”

Potentially Harmful Elements in Urban Soils

“…Additionally, several studies have tested simpler extraction procedures to be used as predictors of the total PHE content in soil. Wharton et al (2012), for example, compared three commonly used screening tests, i.e. the modified Morgan, Mechlich 3 1-M HNO 3 extraction with the standard total Pb testing method (US EPA 2007).…”