Soil Screening by High School Students to Map Lead Contamination From Mining in Peru

Soil contamination with toxicants such as lead (Pb) is notoriously patchy and requires considerable effort to map. In the present study of three mining-impacted Peruvian towns, nearly 2,000 students collected and tested 1,500 soil samples using a field kit that combines simulated gastric extraction with visual detection of a purple Pb rhodizonate precipitate. An additional 2,000 soil samples were tested by our team's field staff. The combined results were mapped and compared with total soil Pb concentrations measured by X-ray fluorescence (XRF). The degree of soil contamination varied across sites and within each site. Quality control was provided by reanalyzing a subset of 120 soil samples from the three sites in the laboratory. Overall, total Pb concentrations were highest in Cerro de Pasco with 64% and 30% of samples in the 201-2,000 and 2,001-20,000 mg/kg range, respectively. Total Pb concentrations were somewhat lower in La Oroya with 88% of samples in the 201-2,000 mg/kg range and even lower in Callao with 79% below 200 mg/kg. However, extractable Pb proportions followed an inverse pattern, with the sum of the proportions of medium and high visual readings increasing from 46% to 57% and 69% in Cerro de Pasco, La Oroya, and Callao, respectively. This trend relates more closely to blood-Pb concentrations in children measured at the three sites 2 decades ago than total Pb concentrations. The study demonstrates that student-conducted soil screening can effectively identify Pb contamination patterns while providing valuable science education.