Lixia Wang

Regional assessment of cadmium pollution in agricultural lands and the potential health risk related to intensive mining activities: A case study in Chenzhou City, China

The purpose of this study was to assess the extent of cadmium (Cd) contamination in agricultural soil and its potential risk for people. Soils, rice, and vegetables from Chenzhou City, Southern China were sampled and analyzed. In the surface soils, the 95% confidence interval for the mean concentration of Cd varied between 2.72 and 4.83 mg/kg (P < 0.05) in the survey, with a geometric mean concentration of 1.45 mg/kg. Based on the GIS map, two hot spot areas of Cd in agricultural soils with high Cd concentrations were identified to be located around the Shizhuyuan, Jinshiling, and Yaogangxian mines, and the Baoshan and Huangshaping mines, in the center of the city. About 60% of the total investigated area, where the agricultural soil Cd concentration is above 1 mg/kg, is distributed in a central belt across the region. The critical distances, at which the soil Cd concentration were increased by the mining activities, from the mines of the soils were 23 km for the Baoshan mine, 46 km for the Huangshaping mine, and 63 km for the Shizhuyuan mine, respectively. These are distances calculated from models. The Cd concentrations in rice samples ranged from 0.01 to 4.43 mg/kg and the mean dietary Cd intake from rice for an adult was 191 microg/d. Results of risk indexes showed that soil Cd concentrations possessed risks to local residents whose intake of Cd from rice and vegetables grown in soils in the vicinity of the mine was 596 microg/d.

Speciation of Cu and Zn during composting of pig manure amended with rock phosphate

Pig manure usually contains a large amount of metals, especially Cu and Zn, which may limit its land application. Rock phosphate has been shown to be effective for immobilizing toxic metals in toxic metals contaminated soils. The aim of this study work was to investigate the effect of rock phosphate on the speciation of Cu and Zn during co-composting of pig manure with rice straw. The results showed that composting process and rock phosphate addition significantly affected the changes of metal species. During co-composting, the exchangeable and reducible fractions of Cu were transformed to organic and residue fractions, thus the bioavailable Cu fractions were decreased. The rock phosphate addition enhanced the metal transformation depending on the level of rock phosphate amendment. Zinc was found in the exchangeable and reducible fractions in the compost. The bioavailable Zn fraction changed a little during the composting process. The composting process converted the exchangeable Zn fraction into reducible fraction. Addition of an appropriate amount (5.0%) of rock phosphate could advance the conversion. Rock phosphate could reduce metal availability through adsorption and complexation of the metal ions on inorganic components. The increase in pH and organic matter degradation could be responsible for the reduction in exchangeable and bioavailable Cu fractions and exchangeable Zn fraction in rock phosphate amended compost.

Changes in Phosphorus Fractions and Nitrogen Forms During Composting of Pig Manure with Rice Straw

Abstract The study was conducted to reveal P fractions and N forms changing characters during composting of pig manure with rice straw. During composting, the NH 4 + -N concentration decreased and reached at a relatively low value ( −1 ) in the final compost, while the NO 3 − -N concentration increased. Total N losses mainly occurred during thermophilic phase due to the high temperature, the high NH 4 + -N concentration and the increase of pH value. Labile inorganic P was dominated in the pig manure and initial compost mixture. During composting, the proportion of labile inorganic P of total extracted P decreased, while the proportion of Fe+Al-bound P, Ca+Mg-bound P and residual P increased. The evolutions of the proportion of labile inorganic P, Fe+Al-bound P and Ca+Mg-bound P were well correlated with the changes of pH value, organic matter and C/N ratio. Therefore, composting could increase the concentration of N and P and decrease the presence of NH 4 + -N and labile P fractions which might cause environmental issues following land application.

Temporal variability of iron concentrations and fractions in wetland waters in Sanjiang Plain, Northeast China.

Chemical forms, reactivities and transformation of iron fractions in marshy waters were investigated with cross-flow filtration technique to study the iron environmental behavior. Iron fractions were divided into four parts: acid-labile iron (pre-acidification of unfiltered marshy water samples, > 0.7 microm), high-molecular-weight iron (0.7-0.05 microm), medium-molecular-weight iron (0.05-0.01 microm), and low-molecular-weight iron (< 0.01 microm). The cross-flow filtration suggested that iron primarily exist in both the > 0.7 microm and < 0.01 microm size fractions in marshy waters. Rainfall is the key for rain-fed wetland to determine fate of iron by changing the aquatic biochemical conditions. By monitoring the variation of iron concentrations and fractions over three years, it was found that dissolved iron and acid-labile iron concentrations exhibit a large variation extent under different annual rainfalls from 2006 to 2008. The seasonal variation for iron species proved that the surface temperature could control some conversion reactions of iron in marshy waters. Low-molecular-weight iron would convert to acid-labile iron gradually with temperature decreasing. The photochemical reactions of iron fractions, especially low-molecular-weight iron had occurred under solar irradiation. The relative proportion of low-molecular-weight in total dissolved iron ranging from 28.3% to 43.2% were found during the day time, which proved that the observed decreasing concentration of acid lability iron was caused by its degradation to low molecular weight iron.

Flux characteristics of total dissolved iron and its species during extreme rainfall event in the midstream of the Heilongjiang River

The occurrence of extreme rainfall events and associated flooding has been enhanced due to climate changes, and is thought to influence the flux of total dissolved iron (TDI) in rivers considerably. Since TDI is a controlling factor in primary productivity in marine ecosystems, alteration of riverine TDI input to the ocean may lead to climate change via its effect on biological productivity. During an extreme rainfall event that arose in northeastern China in 2013, water samples were collected in the midstream of the Heilongjiang River to analyze the concentration and species of TDI as well as other basic parameters. The speciation of TDI was surveyed by filtration and ultrafiltration methods. Compared with data monitored from 2007 to 2012, the concentration of TDI increased significantly during this event, with an average concentration of 1.11 mg/L, and the estimated TDI flux reached 1.2×10(5) tons, equaling the average annual TDI flux level. Species analysis revealed that low-molecular-weight complexed iron was the dominant species, and the impulse of TDI flux could probably be attributed to the hydrological connection to riparian wetlands and iron-rich terrestrial runoff. Moreover, dissolved organic matter played a key role in the flux, species and bioavailability of TDI. In addition, there is a possibility that the rising TDI flux could further influence the transport and cycling of nutrients and related ecological processes in the river, estuary coupled with the coastal ecosystems, which merits closer attention in the future.

The effect of reclamation on the distribution of heavy metals in saline–sodic soil of Songnen Plain, China

The spatial distribution of total concentrations and the chemical speciation of heavy metals (Cu, Zn, Pb and Hg) in saline–sodic soil at different periods of time since reclamation (rain-fed arable land converted into paddy field) were investigated. The fluxes of different input sources of heavy metals were also analyzed. The results showed that long-term reclamation caused a decrease in soil pH and significant Hg accumulation in saline–sodic surface soil. Increasing Hg concentrations were identified at sites that had been reclaimed for longer periods, especially because the Songhua River was polluted by Hg between the 1960s and 1982; therefore, irrigation was assumed to be the predominant contributor of Hg accumulation in soil. Sequential leaching experiment revealed that a greater proportion of Hg occurred in the residual fraction, while the Cu, Zn and Pb were easily bound to oxidizable fraction in saline–sodic soil. Assessed by the spatial distribution of heavy metal concentrations in reclaimed soil, reclamation of saline–sodic soil in the Songnen Plain appeared to decrease the mobility of heavy metals, and did not pose the risk of accumulation in soil.

Application of stable isotope tracing technologies in identification of transformation among waters in Sanjiang Plain, Northeast China

In order to investigate the transformation among the precipitation, groundwater, and surface water in the Sanjiang Plain, Northeast China, precipitation and groundwater samples which were collected at the meteorological station of the Sanjiang Mire Wetland Experimental Station, Chinese Academy of Sciences and the surface water which collected from the Wolulan River were used to identify the transformation of three types of water. The isotope composition of different kinds of water sources were analyzed via stable isotope (deuterium and oxygen-18) investigation of natural water. The results show a clear seasonal difference in the stable isotopes in precipitation. During the cold half-year, the mean stable isotope in precipitation in the Sanjiang Plain reaches its minimum with the minimum temperature. The δ18O and δD values are high in the rainy season. In the Wolulan River, the evaporation is the highest in August and September. The volume of evaporation and the replenishment to the river is mostly same. The groundwater is recharged more by the direct infiltration of precipitation than by the river flow. The results of this study indicate that the water bodies in the Sanjiang Plain have close hydrologic relationships, and that the transformation among each water system frequently occurs.

Fluorescence characteristics of dissolved organic matter during composting at low carbon/nitrogen ratios

We investigated the composting of swine manure at low carbon/nitrogen (C/N) ratios (about 13). The purpose was to elucidate organic matter transformation during composting by means of chemical and spectral methods. Swine manure was composted with two bulking agents (rice straw and leaves) at a ratio of 2:1 (manure:bulking agent; v:v) respectively. Low initial C/N ratios (about 13) did not prevent the swine manure from composting, which would greatly decrease the usage of bulking agent. A high organic matter mineralization rate was observed in the co-composting of straw and manure paired with a high maximum temperature and long thermophilic phase. Fluorescence excitation-emission matrix spectra were also used to monitor the component changes in the dissolved organic matter. Fluorescence parameters, including peak location, peak intensity, the ratio of peak intensity and fluorescence regional integration, were displayed and discussed as the maturity index. The fluorescence regional integration, showing higher correlation coefficient than the fluorescence intensity peaks, could be used as a valuable tool for assessing compost maturity.