Chemical speciation of trace metals in atmospheric deposition and impacts on soil geochemistry and vegetable bioaccumulation near a large copper smelter in China

Abstract

Atmospheric deposition is an important source of trace metals to surface environments, but knowledge about plant bioavailability of recently deposited metals and their fate in the soil-plant system is limited. We performed a fully factorial soil and atmosphere exposure experiment with three vegetables (radish, lettuce, and soybean). Treatments included soil profiles collected from three sites located along a strong gradient of atmospheric deposition with each soil type deployed across the three sites for one year, which allowed to effectively distinguish impacts of recently deposited metals (<1 year) from longer-term trace metal exposures in soils. Results showed that recently deposited copper (Cu), cadmium (Cd), and lead (Pb) accounted for 0.5–15.2% of total soil Cu, Cd, and Pb pools at the site most heavily impacted by atmospheric deposition, while recent deposition contributed 15–76% of Cu, Cd, and Pb concentrations in edible parts of vegetables. In addition, soil geochemical extractions showed that bioavailable fractions of trace metals from recent deposition (52–73%) were higher compared to metals previously present in soils (7–42%). These findings highlight a preferential uptake and high rates of bioaccumulation of deposited metals in vegetables and suggest a high potential of environmental risks of food pollution under high atmospheric metal deposition.