Urban legacies and soil management affect the concentration and speciation of trace metals in Los Angeles community garden soils

Heavy metals in urban soils can compromise human health, especially in urban gardens, where gardeners may ingest contaminated dust or crops. To identify patterns of urban garden metal contamination, we measured concentrations and bioavailability of Pb, As, and Cd in soils associated with twelve community gardens in Los Angeles County, CA. This included sequential extractions to partition metals among exchangeable, reducible, organic, or residual fractions. Proximity to road increased all metal concentrations, suggesting vehicle emissions sources. Reducible Pb increased with neighborhood age, suggesting leaded paint as a likely pollutant source. Exchangeable Cd and As both increased with road proximity. Only cultivated soils showed an increase in exchangeable As with road proximity, potentially due to reducing humic acid interactions while Cd bioavailability was mitigated by organic matter. Understanding the geochemical phases and metal bioavailability allows incorporation of contamination patterns into urban planning. - Highlights: • Road proximity, legacies, and management affect garden soil metal concentrations. • Soil near old houses had high reducible Pb, likely due to lead paint. • Pb, As, and Cd all increased with proximity to road. • As and Cd reacted with organic matter to become more or less bioavailable to crops. - Road proximity, legacies, and management affect garden soil metal concentrations. Soil near old houses had high reducible Pb due to lead paint, while all metals increased near the road