DEVELOPING AND DEPLOYING A FIELD TEST KIT FOR BIOACCESSIBLE LEAD IN SOILS

Lead (Pb) presents a significant health hazard for millions of children around the world, yet many developing countries do not have the resources to test for lead in soil, let alone lead in blood. The goal of this project is to reduce child exposure to Pb with the deployment of a simple colorimetric kit to determine the level of bioaccessible Pb in soils. The kit method is a modification of the widely used glycine and hydrochloric acid extraction of Drexler and Brattin (2007), which was calibrated by feeding various contaminated soils to swine and measuring the Pb content of their blood. The kit method was first applied to samples from India, Indonesia, Peru, the Philippines, and Uruguay, representing a variety of soil and contamination types. Total concentrations of Pb were measured in the soil by X-ray fluorescence (XRF). Concentrations of Pb in the extract were also measured by XRF, with confirmation of a subset by inductively coupled plasma mass spectrometry, as well as visually as low, medium, or high after adding sodium rhodizonate. The kit was also deployed by a dozen mothers in four small towns in the Peruvian Andes impacted by mine tailings after a gridded XRF survey of the area.

The first batch of 63 soil samples analyzed by the field test kit ranged from 40 to 50,000 mg/kg total Pb and 10 to 7400 mg/kg leachable Pb. All 25 samples with the color ranking “low” had leachate levels below the EPA standard of 400 mg/kg Pb for safe soil, and 15 of all 18 samples with the color ranking “high” had Pb levels over the EPA standard of 1,200 mg/kg for contaminated soil, though all were above 750 mg/kg. Soil samples measured by XRF in the four Peruvian communities ranged from 20 to 10,000 mg/kg, and identified two hot spots of contamination above 1,200 mg/kg; two towns had no hot spot. Mean soil Pb concentrations ranged from 400-700 mg/kg. Local parents used the field kit to collect approximately 90 samples. Local sampling identified an area of high contamination that was missed by the gridded XRF survey. The test kit results from the field were consistent with those from the laboratory. With further improvements and simplification, we hope the kit can be deployed by individual households on a much larger scale in areas where children are likely to be exposed to Pb through contaminated soil.