Yuangen Yang

Natural and anthropogenic lead in soils and vegetables around Guiyang city, southwest China: A Pb isotopic approach

Soils, vegetables and rainwaters from three vegetable production bases in the Guiyang area, southwest China, were analyzed for Pb concentrations and isotope compositions to trace its sources in the vegetables and soils. Lead isotopic compositions were not distinguishable between yellow soils and calcareous soils, but distinguishable among sampling sites. The highest (207)Pb/(206)Pb and (208)Pb/(206)Pb ratios were found for rainwaters (0.8547-0.8593 and 2.098-2.109, respectively), and the lowest for soils (0.7173-0.8246 and 1.766-2.048, respectively). The (207)Pb/(206)Pb and (208)Pb/(206)Pb ratios increased in vegetables in the order of roots<stems<leaves<fruits. Plots of the (207)Pb/(206)Pb ratios versus the (208)Pb/(206)Pb ratios from all samples formed a straight line and supported a binary end-member mixing model for Pb in vegetables. Using deep soils and rainwaters as geogenic and anthropogenic end members in the mixing model, it was estimated that atmospheric Pb contributed 30-77% to total Pb for vegetable roots, 43-71% for stems, 72-85% for leaves, and 90% for capsicum fruits, whereas 10-70% of Pb in all vegetable parts was derived from soils. This research supports that heavy metal contamination in vegetables can result mainly from atmospheric deposition, and Pb isotope technique is useful for tracing the sources of Pb contamination in vegetables.

Atmospheric Deposition-Carried Pb, Zn, and Cd from a Zinc Smelter and Their Effect on Soil Microorganisms

Abstract Dust emissions from smelters, as a major contributor to heavy metal contamination in soils, could severely influence soil quality. Downwind surface soils within 1.5 km of a zinc smelter, which was active for 10 years but ceased in 2000, in Magu Town, Guizhou Province, China were selected to examine Pb, Zn, and Cd concentrations and their fractionation along a distance gradient from a zinc smelter, and to study the possible effects of Pb, Zn, and Cd accumulation on soil microorganisms by comparing with a reference soil located at a downwind distance of 10 km from the zinc smelter. Soils within 1.5 km of the zinc smelter accumulated high levels of heavy metals Zn (508 mg kg −1 ), Pb (95.6 mg kg −1 ), and Cd (5.98 mg kg −1 ) with low ratios of Zn/Cd (59.1–115) and Pb/Cd (12.4–23.4). Composite pollution indices (CPIs) of surface soils (2.52–15.2) were 3 to 13 times higher than the reference soils. In metal accumulated soils, exchangeable plus carbonate-bound fractions accounted for more than 10% of the total Zn, Pb, and Cd. The saturation degree of metals (SDM) in soils within 1.5 km of the smelter (averaging 1.25) was six times higher than that of the reference soils (0.209). A smaller soil microbial biomass was found more frequently in metal accumulated soils (85.1–438 μg C g −1 )thanin reference soils (497 μg C g −1 ), and a negative correlation ( P 0.01) of soil microbial biomass carbon to organic carbon ratio (C mic /C org ) with SDM was observed. Microbial consumption of carbon sources was more rapid in contaminated soils than in reference soils, and a shift in the substrate utilization pattern was apparent and was negatively correlated with SDM ( R = −0.773, P 0.01). Consequently, dust deposited Pb, Zn, and Cd in soils from zinc smelting were readily mobilized, and were detrimental to soil quality mainly in respect of microbial biomass.

Total concentrations and bioavailability of rare-earth elements in latesol in Hainan Province, China

Total and bioavailable concentrations of rare earth elements (REEs) in the latesol of Hainan Province, China, were measured by ICP-MS, and the distribution characteristics of REEs were discussed in various latesol profiles. The results show that the total concentrations of REEs were higher than the average statistical data of the whole China. The correlation coefficients between the total and bioavailable concentrations of REEs were from 0.66 to 0.95 (P<0,001, n=63). This suggests that it is necessary to study the bioavailable and total heavy metal concentrations in soils in order to assess the ecological and environmental effects, and to provide scientific information on REEs application as micro-elemental fertilizers, and consequently their potential health risks. The percentage of the bioavailable concentrations in the latesol derived from some kinds of parent materials was up to 50%, indicating that it was unnecessary to apply REE micro-elemental fertilizers in the soils. The application of REE micro-elemental fertilizers should be based on specific kinds of soils in order to maintain the agro-ecosystem and protect soil resources.

Rare Earth Element (REE) Geochemistry During Red Soil Formation in Southern China

The distribution of rare earth elements (REEs) in red soil profiles in southern China was studied in detail. Much higher total REE contents were observed in red soils than in the bedrocks. The highest total REE contents were found in gneiss-, limestone- and granite- derived red soils and the lowest in quartzitic sediments. There were no significant differences in total REE contents between the red soil horizons although soluble REEs accumulated in the lower horizons of the profiles. Amounts varied greatly with parent materials. There was a significant exponential relationship between the total REEs and soluble REEs in red soils. Soluble REEs were also positively correlated to a chemical index of alteration (CIA) values and clay contents, but were negatively correlated with organic matter, pH values and Al2O3/Fe2O3 mole ratios. These results imply that soluble REE contents could be a useful indicator of red soil development. Total REE contents were negatively correlated with SiO2/Al2O3, Al2O3/Fe2O3 mole ratios, but were positively correlated with the R2O3/SiO2 mole ratio, reflecting the fact that REEs are mainly inherited from parent rocks. It was concluded that soluble REEs tended to be leached out from the red soils at an early stage of soil development and that residual forms became enriched at a later stage. The main form of REEs in red soils is as a residual phase associated with primary minerals inherited from the parent rocks, while the non-residual forms are closely related to the laterization process.

Research on natural plants in the lead/zinc mine in northwestern Guizhou Province

area increased from 153 ha to 431 ha and the mine dump area increased from 67 ha to 413 ha. It is also found that mining in 1990-1995 was very violent, which caused the areas for mining and mine dump to increase greatly. Thereafter, since mining went to deeper areas, the area for mining did not change obviously, but that for mine dump still increased stably. From this, it can be seen that the impact of mining on ecological environment is very great. It can also be seen that remote sensing is a very efficient way to monitor the ecological change of mining areas.