[Heavy Metal Contamination and Health Risk Assessment of Corn Grains from a Pb-Zn Mining Area].

A total of 92 corn grain samples, around the Pb-Zn mining area in Southwest China, were collected to evaluate the contamination and health risk of heavy metals. Heavy metals including Pb, Zn, Cd, Cr, and Ni in samples were analyzed. A single factor pollution index and comprehensive pollution index were calculated to assess the quality of corn grains. The potential health risks to adults and children due to the intake of these heavy metals through consumption of crops were evaluated using the health risk index. The results showed that the average contents of Pb, Zn, Cd, Cr, and Ni in corn grains were 0.30, 23.75, 0.21, 1.33, and 1.15 mg ·kg-1, respectively, Among the metals, the content of Zn, Pb, Cd, Cr, and Ni exceeded the national food hygiene standards. The Nemero index of Pb, Cd, Cr, and Ni ranged from 4.32 to 9.07, indicating an extremely high level, whereas the contamination of Zn reached an alarming level. The assessment results of the comprehensive health risk index for the corn grains indicated that the contamination of heavy metals poses health risks to adults and children by food ingestion; moreover, the children were more sensitive to various heavy metals than the adults. Principle component analysis revealed that the first main component dominated the sources of Pb, Cd, Cr, and Ni, while the second main component, Zn, might have originated from sources different from the other heavy metals. Positive correlations were not observed between the heavy metals in corns and soils.

[Principal Component Analysis and Ecological Risk Assessment of Heavy Metals in Farmland Soils around a Pb-Zn Mine in Southwestern China].

The farmland soil around a Pb-Zn mine in southwestern China was studied. One hundred forty-nine surface soil samples were taken from 0-20 cm depth, and the contents of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn were tested. The correlations among these heavy metals were studied with multivariate analysis, and the potential sources of the metals were identified. The environmental risk of the metals was evaluated with the Potential Ecological Risk Index method. The results showed that the amounts of Cd, Pb, and Zn were at relatively high level, with average concentrations of 15.56, 419.4, and 933.4mg·kg-1 respectively, indicating the soil was heavily polluted. The average concentrations of Hg and As were 0.13 and 37.3mg·kg-1, suggesting moderate soil pollution. The average concentrations of Cu, Ni, and Cr were lower than Yunnan soil background values. The multivariate analysis suggested that the sources of Cd, Pb, Zn, Hg, and As were similar and came mainly from smelting activities in the mining area. The sources of Cu, Ni, and Cr were similar and can be attributed to natural sources. The comprehensive potential ecological risk index was 2294.8, which suggested a high potential ecological risk. In general, the farmland soils in the research area were polluted seriously by the mining and industrial activities.

[Removal of volatile organic compounds in soils by soil vapor extraction (SVE)].

An experiment study has been carried out to investigate effects of the diameter of soil columns, the size of soil particulate and different contaminants on efficiency of simulated soil vapor extraction (SVE). Experiments with benzene, toluene, ethylbenzene and n-propylbenzene contaminated soils showed that larger bottom area/soil height (S/H) of the columns led to higher efficiency on removal of contaminants. Experiments with contaminated soils of different particulate size showed that the efficiency of SVE decreased with increases in soil particulate size, from 10 mesh to between 20 mesh and 40 mesh and removal of contaminants in soils became more difficult. Experiments with contaminated soils under different ventilation rates suggested that soil vapor extraction at a ventilation rate of 0.10 L x min(-1) can roughly remove most contaminants from the soils. Decreasing of contaminants in soils entered tailing stages after 12 h, 18 h and 48 h for benzene, toluene and ethylbenzene, respectively. Removal rate of TVOCs (Total VOCs) reached a level as high as 99.52%. The results of the experiment have indicated that molecule structure and properties of the VOCs are also important factors which have effects on removal rates of the contaminants. Increases in carbon number on the benzene ring, decreases in vapor pressure and volatile capability resulted in higher difficulties in soil decontamination. n-propylbenzene has a lower vapor pressure than toluene and ethylbenzene which led to a significant retard effect on desorption and volatilization of benzene and ethylbenzene.