The accumulation and health risk of heavy metals in vegetables around a zinc smelter in northeastern China.

Mining and smelting activities engender soil contamination by metals severely. A field survey was conducted to investigate the present situation and health risk of heavy metals (Cd, Pb, Zn, Cu, Cr, As, and Hg) in soils and vegetables in the surrounding area of an 80-year-old zinc smelter in northeastern China. Soil pH, organic matter (SOM), and cation exchange capacity (CEC) were determined, and their relations with heavy metal contents in edible parts of vegetables were analyzed. Results showed that the smelting had led to the significant contamination of the local soils by Cd and Zn, with average concentrations of 3.88 and 403.89 mg kg-1, respectively. Concentrations of Cd and Zn in greenhouse soils were much lower than those in open farmland soils. Cd concentrations in vegetable edible parts exceeded the permissible limits severely, while other metal concentrations were much lower than the corresponding standards. Leaf and root vegetables had higher concentrations and bioaccumulation factors (BCFs) of Cd than fruit vegetables. Hazard quotient and hazard index showed that cadmium is imposing a health risk to local residents via vegetable consumption. Cd uptake of some vegetables can be predicted by empirical models with the following parameters: soil pH, SOM, CEC, Zn concentrations, and Cd concentrations. Vegetables such as cabbage, Chinese cabbage, tomato, cucumber, and green bean were screened out as being suitable to grow in the studied area.

Multi-Seasonal Nitrogen Recoveries from Crop Residue in Soil and Crop in a Temperate Agro-Ecosystem.

In conservation tillage systems, at least 30% of the soil surface was covered by crop residues which generally contain significant amounts of nitrogen (N). However, little is known about the multi-seasonal recoveries of the N derived from these crop residues in soil-crop systems, notably in northeastern China. In a temperate agro-ecosystem, 15N-labeled maize residue was applied to field surfaces in the 1st year (2009). From the 2nd to 4th year (2010-2012), one treatment halted the application of maize residue, whereas the soil in the second treatment was re-applied with unlabeled maize residue. Crop and soil samples were collected after each harvest, and their 15N enrichments were determined on an isotope ratio mass spectrometer to trace the allocation of N derived from the initially applied maize residue in the soil-crop systems. On average, 8.4% of the maize residue N was recovered in the soil-crop in the 1st year, and the vast majority (61.9%-91.9%) was recovered during subsequent years. Throughout the experiment, the cumulative recovery of the residue N in the crop increased gradually (18.2%-20.9%), but most of the residue N was retained in the soil, notably in the 0-10 cm soil layer. Compared to the single application, the sequential residue application significantly increased the recovery of the residue N in the soil profile (73.8% vs. 40.9%) and remarkably decreased the total and the initially applied residue derived mineral N along the soil profile. Our results suggested that the residue N was actively involved in N cycling, and its release and recovery in crop and soil profile were controlled by the decomposition process. Sequential residue application significantly enhanced the retention and stabilization of the initially applied residue N in the soil and retarded its translocation along the soil profile.

[Effects of soil type and crop genotype on cadmium accumulation in peanut (Arachis hypogaea) kernels].

Taking burozem and fluvo-aquic soil in the main peanut (Arachis hypogaea) production areas of China as test soil types and selecting three widely cultivated peanut genotypes Baisha 1016, Huayu 22, and Zhanyou 27 as test crops, a pot experiment with no Cd addition (control) and added with 1.5 mg x kg(-1) of Cd was conducted to elucidate the effects of soil type and crop genotype on the cadmimum (Cd) accumulation in peanut kernels. In the control, the Cd concentrations in the kernels of the three peanut genotypes growing on the two soil types were lower than the national food safety standard. In treatment Cd addition, the opposite was observed. For the same soil types, the Cd concentrations in the kernels of the three peanut genotypes were significantly higher in treatment Cd addition than in the control. The Cd accumulation in the kernels of the three peanut genotypes was in the order of Zhanyou 27 > Baisha 1016 > Huayu 22, and the Cd concentrations in the kernels of the peanut genotypes growing on the two soil types were higher on burozem than on fluvo-aquic soil. The values of the Cd bioaccumulation factor for the kernels of the three peanut genotypes were all higher than 1.0 in the control but lower than 1.0 in treatment Cd addition, suggesting that the peanut kernels had a stronger ability in accumulating the Cd from soil, and, when the soil Cd concentration increased, this ability decreased.