Heavy metals accumulation and risk assessment in a soil-maize (Zea mays L.) system around a zinc-smelting area in southwest China

Distribution of trace metals in a soil-tea leaves-tea infusion system: characteristics, translocation and health risk assessment

The effects of metal pollution on tea are of great concern to consumers. We apply Geographic information systems technology to study the distribution of heavy metal elements in tea plantation ecosystems in Jiangsu Province, explore the relationships among metals in the soil, tea leaves and tea infusions, and assess the human safety risks of metals. The concentrations of nine metals in a soil-tea leaves-tea infusion system were studied at 100 randomly selected tea plantations in Jiangsu Province, China. Concentrations of selected metals, zinc (Zn), nickel (Ni), manganese (Mn), chromium (Cr) and copper (Cu), were quantified using an inductively coupled plasma-optical emission spectrometer (ICP-OES), and cadmium (Cd), arsenic (As), plumbum (Pb) and mercury (Hg) were quantified using inductively coupled plasma-mass spectrometry (ICP-MS). Arc-Map 10.3 was used for the spatial analysis of metals in soil, tea leaves and tea infusions. We found that the contents of Mn, Ni and Zn are high level in soil, tea leaves and tea infusions. The Mn level showed a spatial distribution pattern with greater concentrations at the junction of Nanjing and Yangzhou, southwest of Changzhou and west of Suzhou. The hazard index (HI) values in north-central Nanjing, southern Suzhou, southwestern Changzhou and northern Lianyungang were relatively greater. The Zn, Ni, Mn, Cr and Cu levels in the soil-tea infusion system were 17.3, 45.5, 54.5, 1.5 and 14.3%, respectively. The order of the leaching rates of the elements was Ni > Cr > Zn > Mn > Cu. The relative contribution ratios of HI were in the order of Mn > Ni > Cu > Zn > Cr > Pb > Cd > As > Hg. In tea infusions, the Mn level has the greatest potential health risks to consumers. Moreover, using C_soil it was inferred that the safety thresholds of Zn, Ni, Mn, Cr and Cu in soil were 27,700, 50, 1230, 493,000 and 16,800 mg L^-1, respectively. The content of heavy metals in soil and tea varies greatly in different regions of Jiangsu Province, 92% of the soil has heavy metal content that meets the requirements of pollution-free tea gardens, 91% of tea samples met the requirements of green food tea. The thresholds for Ni (50 mg L^-1) and Mn (1230 mg L^-1) can be used as maximum limits in tea plantation soils. The consumption of tea infusions did not pose metal-related risks to human health.

Distribution and Interactive Effects of Heavy Metals in Soil-Maize (Zea Mays L.) System in the Mercury Mining Area, Southwestern China

The concentrations and interactive effects of beneficial elements (i.e., Se, Mo, and Zn) and heavy metals (As, Cd, Hg, and Pb) of maize (Zea mays L.) grown on lime soil and/or soil with mercury tailing were investigated in this study. The results show that the concentrations of heavy metals (i.e., As, Hg, and Pb) in soil with tailing were higher than those in lime soil. The concentrations of beneficial elements (i.e., Mo and Zn) in maize grown on soil with tailing were higher than those of maize grown on lime soil. The mean concentrations of Se, Mo, and Zn in maize grown on soil with tailing were 3.67 mg/kg, 0.530 mg/kg, and 27.4 mg/kg. The pH and an antagonistic effect played an important role in the concentrations of Mo and Zn in maize. The Se concentration in maize was controlled by the planting media.

Source Identification and Superposition Effect of Heavy Metals (HMs) in Agricultural Soils at a High Geological Background Area of Karst: A Case Study in a Typical Watershed

Exogenous sources and the superposition effect of HMs in agricultural soils made the idenfication of sources complicated in a karst area. Here, a typical watershed, a research unit of the karst area, was chosen as the study area. The smaller-scale study of watersheds allowed us to obtain more precise results and to guide local pollution control. In this study, sources of HMs in agricultural soil were traced by a CMB model. Superposition effects were studied by spatial analysis of HMs and enrichment factor (EF) and chemical fraction analysis. The average concentrations of Cd, Pb, Cr, Cu, Ni and Zn in surface soils were 8.71, 333, 154, 51.7, 61.5 and 676 mg∙kg^-1, respectively, which exceeded their corresponding background values. The main sources of Cd, Pb and Zn in agricultural soil were rock weathering, atmospheric deposition and livestock manure, and their contributions were 47.7%, 31.0% and 21.2% for Cd; 7.63%, 78.7% and 13.4% for Pb; and 17.0%, 52.3% and 28.1% for Zn. Cr mainly derived from atmospheric deposition (73.8%) and rock weathering (20.0%). Cu and Ni mainly came from livestock manure (81.3%) and weathering (87.5%), respectively, whereas contributions of pesticides and fertilizers were relatively limited (no more than 1.04%). Cd, Pb, Zn and Cu were easily enriched in surface soils near the surrounding pollution sources, whereas Cr and Ni were easily enriched in the high-terrain area, where there was less of an impact of anthropogenic activities. The superposition of exogenous sources caused accumulation of Cd, Pb and Zn in topsoil, contaminated the subsoil through leaching and improved bioavailability of Cd and Pb, causing high ecological risk for agricultural production. Therefore, Cd and Pb should be paid more attention in future pollution control.

Pretreatment of straw using filamentous fungi improves the remediation effect of straw biochar on bivalent cadmium contaminated soil

Carbonized products of waste agricultural straws used for soil remediation can reduce impact of heavy metals on soil ecology and crop growth. Here, we demonstrated straw fermentation residues to be suitable for preparation of soil remediation agents by pyrolysis. Lignocellulose degradability of filamentous fungi during fermentation was found to significantly enhance properties of biochar for cadmium (Cd (II))-contaminated paddy soil remediation. Obtained biochars were indicated to have rich oxygen-containing groups, thus showing enhanced removal ability of Cd (II). Adsorption capacity of biochar (BaWS) prepared from wheat straw, which has been fermented by Trichoderma asperellum T-1, reached 105.9 mg g^-1, 372.8% higher than that from natural wheat straw (BWS). Fermentation of straws by Trichoderma reesei QM6a can also improve the adsorption performance of biochar, but the effect is much weaker. The content of bioavailable Cd (II) in paddy soil reduced 83.7% within 15 days after addition of 1% BaWS. Significantly, adding 1% BaWS had better effect on increasing soil pH and removing available Cd (II) , than adding 3% BWS. These results suggest that the used dosage of microbial pretreated straw biochar for the remediation of Cd (II)-contaminated paddy soil was only 1/3 of that of conventional biochar. The enhanced property of biochar was attributed to deconstruction of straws by filamentous fungi before being pyrolyzed. Thus, fermented straws were indicated more suitable for the preparation of biochar used as effective soil remediation agents.

Metal(loid)s Spatial Distribution, Accumulation, and Potential Health Risk Assessment in Soil-Wheat Systems near a Pb/Zn Smelter in Henan Province, Central China

To understand the influence of Pb/Zn smelter on surrounding environment, 110 soil and 62 wheat grain samples (62 paired samples) were collected nearby a Pb/Zn smelter in Jiaozuo City, Henan Province, China. The content and spatial distribution of metal(loid)s in the soil-wheat system, and the potential health risk via consumption of wheat grains were determined. Results showed that the average content of Pb, Cd, As, Cu, Zn, and Ni in soil were 129.16, 4.28, 17.95, 20.43, 79.36, and 9.42 mg/kg, respectively. The content of Cd in almost all soil samples (99.1%) exceeded the national limitation of China (0.6 mg/kg). Spatial distribution analysis indicated that atmospheric deposition might be the main pollution source of Pb, Cd, As, and Zn in soil. In addition, the average content of Pb, Cd, As, Cu, Zn, and Ni in wheat grain were 0.62, 0.35, 0.10, 3.7, 35.77, and 0.15 mg/kg, respectively, with the average Pb and Cd content exceeding the national limitation of China. The average bioaccumulation factor of these metal(loid)s followed the following order: Zn (0.507) > Cu (0.239) > Cd (0.134) > Ni (0.024) > Pb (0.007) > As (0.006). Health risk assessment indicated that the average noncarcinogenic risk of children (6.78) was much higher than that of adults (2.83), and the carcinogenic risk of almost all wheat grain is higher than the acceptable range, with an average value of 2.43 × 10−2. These results indicated that humans who regularly consume these wheat grains might have a serious risk of noncarcinogenic and carcinogenic diseases.