A simple kit to detect extractable lead concentrations in soil

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.