Dynamic Behaviors of Newly Deposited Atmospheric Heavy Metals in the Soil-Pak Choi System

Dynamic behaviors of the newly deposited atmospheric heavy metals in the soil-pak choi (Brassica chinensis L.) system are investigated by a fully factorial atmospheric exposure experiment using soils exposed to 0.5-year and 1.5-year atmospheric depositions. The results showed approximately 17–87%, 19–64%, and 43–84% of the Cu, Cd, and Pb in pak choi edible parts were contributed from the new depositions, respectively. For the newly deposited metals, foliar uptake was the key pathway of shoot bioaccumulation rather than from root uptake of the deposited metals in soils, resulting in no significant soil contribution differences between pak chois growing in 0.5-year and 1.5-year exposed soils. Indeed, highly bioavailable metals in atmospheric deposition significantly increased the soil plant-bioavailable Cu, Cd, and Pb fractions; however, soil aging resulted in similar percentages of the plant-bioavailable fractions in 0.5-year and 1.5-year exposed soils, which indicated the bioavailability of metals deposited into soils rapidly decreased with aging. The soil aging process of the deposited metals was well fitted with the first-order exponential decay model, and soil organic matter and clay were the major driving factors. Our findings highlight high plant bioaccumulation rates and the rapid soil aging process of newly deposited metals during the plant growth period.