High‐Iron Biosolids Compost–Induced Changes in Lead and Arsenic Speciation and Bioaccessibility in Co‐contaminated Soils

Urban Farm DB summary

Against a background in which the safety of urban farming has been questioned because of possible contamination in urban soils, this study tested whether high-iron biosolids-based composts could reduce the bioaccessibility of soil lead (Pb) and arsenic (As), using two laboratory incubations and a field trial. Pb and As bioaccessibility were assessed with an in vitro assay, and changes in Pb, As, and Fe speciation were analyzed on select samples using micro-X-ray fluorescence mapping and micro-XANES. A compost with iron added to wastewater-treatment residuals (Fe WTR compost), applied to soil at 100 g/kg, decreased Pb bioaccessibility in both laboratory incubations, though results for As were mixed. In contrast, the composts tested in the field trial (with iron added as Fe powder or FeCl) did not reduce bioaccessible Pb and showed only limited reductions in bioaccessible As; these same composts also had no effect on Pb bioaccessibility in the second laboratory incubation. The study concludes that high-iron biosolids compost is effective at reducing Pb accessibility only for certain types of iron-rich materials.