No abstract

Due to rapid urbanization, urban lands have been expanded into existing agricultural areas. With such spatial changes, agricultural lands in the expanding cities or peri-urban areas are easily exposed to contaminants generated by anthropogenic activities such as traffic. Therefore, this study aimed to investigate heavy metal concentrations in major roadside agricultural soils by distance in medium-sized cities, Jinju and Changwon, and to identify the influence of roadside dust on metal contamination. The roadside arable soils of paddy and upland, roadside tree soil, and roadside dust were sampled. In paddy, the heavy metal concentration changes by the distance from the road were not observed because of soil puddling and waterlogging. However, in upland, Cu and Zn concentrations gradually decreased with the increased distance from the road. In roadside dust, Cu and Zn concentrations were very high, exceeding Korean guidelines, which indicates roadside dust could be a primary source of Cu and Zn contamination in agricultural soils. Moreover, the roadside tree soil, which is not disturbed by agricultural activities, showed higher heavy metal concentrations in topsoil rather than subsoil, even though the soil was newly introduced for tree planting. This implies that road dust containing the metal contaminants may accumulate in the nearby soils. Many scientists have thought that eco-friendly compost is the main reason for increasing Cu and Zn in urban agricultural soils. However, roadside dust needs to be more focused on as a principal source of contamination.

In Korea, 90% of the population lives in urban areas, so urban agriculture is commonly carried out. However, research on the safety of urban soils for growing food still needs to be done. Thus, this study was conducted to evaluate the suitability of urban soil for crop cultivation by investigating the heavy metal concentration of soil and plant from urban gardens in Jinju. Soils and crop leaves were collected from 23 urban gardens, and the concentrations of As, Cd, Cr, Cu, Ni, Pb, and Zn were analyzed. The average concentrations of garden soils in Jinju were As 5.31, Cd 0.59, Cr 30.09, Cu 33.05, Ni 21.14, Pb 23.28, and Zn 121.68 mg kg -1 , which did not exceed the Korean guidelines except for Zn in one study site. Geoaccumulation Index, calculated using the background values of heavy metals in Korean soil, showed that contamination of Cd, Cu, Pb, and Zn was in progress. The inflow of Cu and Zn into the garden soils would be from the atmosphere and direct entry into the soil by adding livestock manure. Differently, the other elements were more predominantly introduced from the atmosphere. Particularly, a significant amount of Pb was introduced into the soils from the atmosphere in a couple of gardens. Overall, the results from this study indicated that continuous monitoring for heavy metals in urban garden soils is required for food safety.

Heavy metals exist in soils in various chemical forms including free metal ions and organo-metal complexes. The ratio of free metal ions has been known to be highly associated with the plant absorption of heavy metals. This study aims to understand the effect of free ions and organo-metal complexes on the absorption of lead (Pb) and cadmium (Cd) by plants. For this, lettuce grown in a hydroponic system for 28 days was consequently grown another 48 hours using Pb and Cd solutions. The ratios of free ion to organo-metal complexes in the solutions were adjusted at 100:0, 90:10, 70:30, 60:40 by four different organic acids (citric, oxalic, acetic, and humic acid). After that, the concentration of Pb and Cd in lettuce were analyzed. The Pb and Cd absorption by lettuce was more relied on the types of organic acids treated and the type of metals rather than the ratio of free metal ions. For example, citric acid increased the Pb absorption while it decreased the Cd absorption by lettuce. There was no significant relationship between free metal ion ratios and both Pb and Cd uptake by lettuce. It could be explained that citric acid, a relatively higher molecular weight organic acid, has higher ion binding capacity, so it forms organo-Pb complex easily due to the higher affinity of Pb on the binding site in comparison with Cd. Consequently, this complexation would assist Pb uptake by lettuce.