Metal concentrations and bioaccessibility in urban community gardens with implications for human exposure

Urban agriculture is growing in popularity, but toxic metals and metalloids in garden soil raise concerns about human health risks associated with gardening. Gardeners might be exposed to toxic elements because they directly handle the garden soil and grow edible produce in it. This study examined community gardens in the City of St. Louis, Missouri, US and surrounding municipalities, areas with a history of soil contamination by metals, particularly Pb. To improve the current understanding of soil contamination patterns in garden soil and implications for exposure to metals/metalloids, the study (1) measured total metal/metalloid concentrations (Pb, As, Cd, Cu, Co, Ni, Mo, Ca, Mg, Fe, and Zn) in soil from twenty gardens, (2) tested in-vitro Pb bioaccessibility in soil samples, and (3) administered surveys to gardeners. Overall, our measurements suggest that Pb is a metal of concern in St. Louis community gardens. While soil in 21% of sampled plots contained Pb concentrations above recommended thresholds for gardens, Pb bioaccessibility was low (< 5.4% of the total soil concentration), suggesting that the Pb bioavailability in the case of accidental ingestion of soil particles was limited. Total metal/metalloid concentrations in soil varied spatially across plots within gardens, highlighting the importance of sampling multiple plots. Pb and As concentrations were positively correlated with garden age. Survey results revealed the common gardening habits, the type of produce grown in urban gardens, and exposure parameters. These findings contribute to improving the design of soil sampling, providing insights for exposure assessment, and informing contamination mitigation measures.