A simple kit to detect extractable lead concentrations in soil

• Simplified soil Pb test kit uses purple-turning cotton swab and costs <$1. • Tested on 201 samples from US/Peru, eliminates filtration step of original. • Kit shows 85 % sensitivity/specificity for detecting ∼200 mg/kg extractable Pb. • Kit enables community/household lead testing without complex lab procedures. Lead (Pb) contamination of soil is often spatially very heterogeneous and therefore difficult to map and remediate. To address the issue, we simplified a previously developed screening method that relies on an acidic glycine solution to extract Pb from soil using a 10:1 solution to soil ratio and the precipitation of purple Pb rhodizonate as a visual indicator to avoid filtration of the extract. The simplified kit consists of a plastic test tube, a soluble gel capsule of glycine hydrochloride crystals, a strip of pH paper, and a commercially available cotton swab impregnated with sodium rhodizonate designed for testing Pb-based paint. The swab turns purple at a concentration in the extract equivalent to a concentration of ∼200 mg/kg Pb in soil. The swab method was evaluated using 201 dried and sieved soil samples from the US and Peru spanning the 100–10,000 mg/kg range in total Pb concentrations. Excluding 14 samples from Peru with an extract pH > 3, the results show a sensitivity and selectivity of 85 % relative to an extractable Pb concentration of 200 mg/kg in the kit extract measured by X-ray fluorescence. The kit extracts about a third of the Pb released from soil using US EPA Method 1340. Depending on the proportion of extractable Pb in a specific soil sample, the kit could therefore help households and communities detect soil contamination from mining, smelting, battery recycling, or flaking paint down to 3 times the recently lowered US EPA screening level of 200 mg/kg for total Pb in soil.