Soil lead distribution in Chicago, USA

Abstract

Identifying the distribution of soil lead (Pb) in urban areas can serve to quantify the location and magnitude of health risks, and thereby inform urban land use and Pb mitigation policies. We evaluated total soil Pb distribution across the third largest metropolitan region of the United States (U.S.), Chicago, a city with multiple historical sources of Pb deposition and previous reports of soil total Pb that exceed geogenic concentrations by orders of magnitude. Total Pb was quantified in Chicago soils obtained by grid sampling (n = 995) parkways and residential properties (n = 156). As anthropogenic modification of soils that entail Pb accumulation may also alter other properties, soil pH, clay content, and Olsen P were also measured. Median and mean total Pb was 220 and 282 mg kg−1 for parkway soils, and 146 and 352 mg kg−1 for residential soils. For parkway soils, 93% of the city area exceeded the conservative California EPA threshold of 80 mg kg−1 but 94% of the area was below the U.S. and Illinois EPA threshold of 400 mg kg−1. Hotspots of soil Pb exceeding the U.S. EPA inhalation risk threshold of 400 mg kg−1 occurred for an estimated area of ≈ 38 km2, representing ≈ 6% of the total area of 606 km2. Soil Pb distributions based on parkway sampling were higher by 100 mg kg−1 for ≈ 23% of the city compared to residential sampling. Soil properties of Olsen P, pH, clay, sand, and silt were unrelated to total Pb concentrations, though a significant negative linear relationship between Olsen P and soil pH was found for 13% of soil sampling locations. Across Chicago, the majority of soils in parkways and residential properties appear to be enriched in total Pb concentrations, indicating widespread but non-severe contamination.