Lead Stabilization and Arsenic Mobilization By Phosphate and Alternative Amendments: Implications on Urban Soil Remediation, Urban Agriculture and Public Health.

Phosphate amendment is being promoted as a cost effective means of reducing lead (Pb) hazards in soil via the formation of stable lead-phosphate minerals. However, the application of phosphate in soil can potentially mobilize arsenic (As), a known human carcinogen. This study uses a combination of lab and field experiments to examine the Pb binding and As mobilization potential for bone meal, triple super phosphate, and two types of composts, with or without iron and manganese amendments. Common produce was grown in test plots at a farm in New Jersey, where the soil mean concentration of As was 36 mg kg^-1 and Pb was 219 mg kg^-1. An in vitro method (modified from the RBA method: EPA 9200.2-86) is used to assess bioaccessibility of Pb and As for soils before and after treatments. In general, phosphate-bearing amendments didn’t have a significant effect on Pb bioaccessibility in soils but they increased As bioaccessibility. Overall, the effect of a plant type was more important than the effect of the various types of amendments on Pb and As vegetable concentration. In general, root crops had the highest concentrations of Pb and As, followed by leafy vegetables and then fruits. Evidence show that dust and dirt particles are the dominant contributors to plant tissue Pb or As concentrations. These findings support the idea to grow fruit crop in preference to leafy and root crops. Vegetable selection, best management practices (washing, peeling, etc.), dust control measures, and conservation practices should be applied to reduce exposure and to mitigate the health risk from soil contamination.