Variability of bioaccessible lead in urban garden soils

The aim of this research was to evaluate the variability of Pb bioaccessibility in urban garden soils and how it is affected by phosphate, organic content, soil pH and soil mineral species. The bioaccessibility of Pb in 49 soil samples was assessed using the U.S. EPA method 1340 (extraction with a simulated gastric acid at pH 1.5) and a modified protocol (same solution at pH at 2.5). Overall, bioaccessibility values were highly variable (14%–86% at pH 1.5 and 14%–73% at pH 2.5), reflecting the heterogeneous nature of urban soils and the influence of soil mineralogy and other factors on the stability and leachability of Pb. There was a negative relationship between phosphate and Pb bioaccessibility, but this was only observed when the modified protocol was used. Organic content also had a negative relationship with Pb bioaccessibility. Principal component analysis based on leaching solution chemistry (proxy to mineral speciation) suggested that carbonate and Fe/Mn hydroxide effects on Pb bioaccessibility are not as significant as phosphate and organic matter. These findings not only confirm the value of applying phosphorus and organic amendments to reduce Pb bioaccessibility in urban garden soils, but also highlight the complexity of the factors controlling health risks to gardeners. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.