Potential bioavailability of lead, arsenic, and polycyclic aromatic hydrocarbons in compost-amended urban soils

Urban soils may contain harmful concentrations of contaminants, such as lead (Pb), arsenic (As), and polycyclic aromatic hydrocarbons (PAHs), that can transfer from soil to humans via soil ingestion and consumption of food crops grown in such soils. The objective of this research was to assess the effectiveness of adding different compost types to reduce both direct (soil-human) and indirect (soil-plant-human) exposure of Pb, As, and PAHs to humans. A field experiment was conducted in 2011 and 2012 at an urban garden site with elevated concentrations of Pb (475 mg kg), As (95 mg kg), and PAHs (23-50 mg kg). Soil amendments were composted biosolids, noncomposted biosolids, mushroom compost, leaf compost, and a nonamended control. Collard greens, tomatoes, and carrots were then grown in the amended and nonamended soils and nonamended soils that received urea in 2011. At the beginning of the second season, N-P-K fertilizer was added to all plots. The potential for direct and indirect exposure was evaluated. Soil Pb bioaccessibility was 1 to 4.3%, and As bioaccessibility was 7.3 to 12.3%. Composted biosolids reduced the bioaccessibility of soil Pb by ∼17% compared with the control but temporarily increased the bioaccessibility of As by ∼ 69% compared with the control when soluble inorganic P concentration in soil was elevated by P fertilizer application in 2012. The bioaccessibility of soil Pb decreased by ∼38% in all treatments when soluble inorganic P concentration in soil was elevated by P fertilizer. Compost amendments reduced the concentrations of low molecular weight PAHs in soil. Regardless of the treatments, the concentrations of Pb, As, and PAHs measured in the vegetables were low or nondetectable, except for Pb in carrots. Consumption of vegetables grown at this site will cause insignificant transfer of Pb, As, and PAHs to humans.