Fruit lead concentrations of tomato (Solanum lycopersicum L.) grown in lead-contaminated soils are unaffected by phosphate amendments and can vary by season, but are below risk thresholds

Abstract

Urban agriculture in post-industrial cities faces concerns on human health risks posed by elevated lead (Pb) concentrations of edible plant tissues grown in Pb-enriched soils. A recommended mitigation strategy to decrease soil Pb bioavailability to humans is the addition of soluble phosphate (PO43−-P), but it is unclear if this strategy can also reduce crop Pb uptake and accumulation in edible tissues. Across urban agriculture sites in Chicago, Illinois (6 site-years) with elevated total soil Pb, we tested the hypothesized decrease in tomato fruit Pb following soil-based application of three phosphate-based mitigation amendments: triple superphosphate, composted biosolids, and air dried biosolids. Fruit Pb concentrations (mg Pb kg−1 dry mass) and loads (mg Pb m−2) were unaffected by mitigation amendments. However, fruit Pb concentrations were higher by an order of magnitude in 2020 (≥0.13 mg kg−1) compared to 2019 (0.01 mg kg−1) for two of the three sites. Though highly variable across site-years, the bioconcentration factor (BCF) of Pb from soil to fruit varied was unaffected by mitigation amendments. Relatively low BCF values were consistent with fruit Pb concentrations being below FAO/WHO risk limits. Collectively, our findings support previous propositions that fruits of plants grown in soils with elevated Pb generally pose lower risk to consumers. To mitigate health risks of consuming tomatoes grown in soils with Pb contamination, the seasonality of Pb uptake should be investigated, and greater focus should be placed on where tomatoes are grown rather than phosphate-based immobilization strategies originally designed to mitigate human bioavailability.