[Pollution Source Apportionment of Heavy Metals in Cultivated Soil Around a Red Mud Yard Based on APCS-MLR and PMF Models].

In order to explore the characteristics and sources of heavy metal pollution in cultivated soil around a red mud yard in Chongqing， the content and spatial distribution characteristics of eight heavy metal elements （Cd， Cr， Hg， Ni， Pb， As， Cu， and Zn） in the soil were analyzed， and the single factor pollution index method and Nemerow comprehensive pollution index method were used to evaluate the characteristics of heavy metal pollution in soil. On the basis of correlation analysis， the APCS-MLR and PMF models were used to quantitatively analyze the sources of heavy metals. The results showed that the average contents of the other seven heavy metal elements were higher than the background values of Chongqing soil， except for that of Cr. The heavy metals Cd， Hg， and As were moderately polluted， and Pb， Cu， Ni， and Zn were mildly polluted. The spatial distribution pattern of Cr， Ni， Pb， Cu， and Zn in the soil was similar， and there was a very significant positive correlation between them （P < 0.01）. The spatial distribution characteristics of Cd， Hg， and As were significantly different， and there was no significant correlation between them （P > 0.05）. The source apportionment showed that the sources of heavy metals in the soil in the study area were relatively complex， and the APCS-MLR and PMF models could identify the same four pollution sources， namely red mud yard percolation emission and natural sources， thermal power generation emission sources， agricultural activities and natural sources， and non-ferrous metal smelting emission sources. There was little difference in the results of source apportionment between the two models. The contribution rates of the four pollution sources in the APCS-MLR model were 51.8%， 18.0%， 15.9%， and 14.3%， respectively， whereas those in the PMF model were 45.9%， 12.8%， 21.5%， and 19.8%， respectively.

[Characteristics and Risk Evaluation of Heavy Metal Contamination in Paddy Soils in the Three Gorges Reservoir Area].

Soil Cd, Hg, Pb, As, Cr, Cu, Zn, and Ni of 12 districts in the Three Gorges Reservoir area (Chongqing section) were analyzed, and different evaluation methods were used to assess the degree of contamination, potential ecological risk, and human health risk of soil heavy metals in paddy soils. The results showed that the average values of all heavy metals except Cr in paddy soils in the Three Gorges Reservoir area exceeded the background values of soils in the Three Gorges Reservoir area, and the contents of Cd, Cu, and Ni in 12.32%, 4.35%, and 2.54% of the soil samples exceeded the screening values, respectively. The variation coefficients of the eight heavy metals were 29.08%-56.43%, which belonged to the medium and above-intensity variation levels and were influenced by anthropogenic activities. The eight heavy metals were contaminated in the soil, and 16.30%, 6.52%, and 2.90% of the soil Cd, Hg, and Pb were heavily contaminated. At the same time, the potential ecological risk of soil Hg and Cd were in the medium risk level on the whole. Wuxi County and Wushan County had relatively high pollution levels among the 12 districts, the Nemerow pollution index showed a moderate pollution level, and the comprehensive potential ecological risks were also at a moderate ecological hazard level. The results of the health risk evaluation showed that hand-mouth intake was the main exposure path of non-carcinogenic risk and carcinogenic risk. Soil heavy metals presented no non-carcinogenic risk for adults (HI<1), but 12.68% of the sites had non-carcinogenic risk for children (HI>1). As and Cr were the main influencing factors for non-carcinogenic and carcinogenic risks in the study area, and their total contributions to non-carcinogenic and carcinogenic risks were more than 75% and 95%, respectively, which was cause for concern.

[Mercury Speciation, Distribution, and Potential Sources in Surface Waters of the Yangtze and Yellow River Source Basins of Tibetan Plateau During Wet Season].

To understand the mercury (Hg) biogeochemical cycle in alpine regions under global warming, it is critical to identify the distribution and sources of Hg in aquatic ecosystems of the Tibet Plateau. The spatial distribution pattern and potential sources of Hg species including total mercury (THg), particulate mercury (PHg), and dissolved mercury (DHg) were investigated in surface waters of the Yangtze and Yellow River source basins during the wet season. The results showed that average ρ(DHg) in surface water of the Yangtze and Yellow River source basins were comparable[(2.96±1.26) ng·L-1 and (2.47±0.83) ng·L-1, respectively], whereas the average ρ(THg)[(10.69±11.14) ng·L-1] and ρ(PHg)[(8.46±11.41) ng·L-1] in the source basin of the Yangtze River were significantly higher than that in surface water of the Yellow River source basin[(3.37±2.03) ng·L-1 and (1.13±1.02) ng·L-1, respectively]. It is worth noting that the ecological risk of Hg in the study area was limited because of low Hg concentration and methylation level. In addition, the correlation analysis illustrated that the THg was mainly concentrated by PHg in the source basin of the Yangtze River. Specifically, the concentration variations in Hg were mainly affected by the input of glacier meltwater, soil erosion, and precipitation. By contrast, the main species of Hg in the source basin of the Yellow River was DHg, the distribution pattern of which was mainly controlled by DOC. Spatially, a significant negative correlation was found between ρ(PHg) and longitude in the source basin of the Yangtze River (R2=0.46, P<0.01). The spatial distribution differences of river slope and soil erosion intensity were identified as the key factors leading to the decreasing trend of ρ(PHg) and ρ(THg) along the river flow in the source basin of the Yangtze River. The results of the PMF model further demonstrated that in the surface waters of the source regions of the Yangtze and Yellow Rivers, 51.4% of Hg derived from long-distance atmospheric deposition, 38.8% from erosion of soil rock or sediment via stream flow, and 9.7% from soil runoff or seepage input.

[Spatial Distribution Trends and Influencing Factors of Typical Heavy Metals in Subtropical Alpine Forest Soils: A Case Study from Ailao Mountain in Yunnan Province].

In this study, we hypothesized that the distribution patterns of trace metal elements in montane regions would be controlled by the local climate, human activities, vegetation distribution and soil development. Hence, we selected nine forest sites among the elevation of 850 m to 2650 m on the windward (western slope) and leeward (eastern slope) slopes of Ailao Mountain in Yunnan Province of China to determine the typical heavy metal concentrations in forest surface soils, and their differences for distribution trends along with the increasing elevations, and the corresponding environmental factors. The results showed that surface soil Cd, Sb, As, Cr, and Pb had relatively higher concentrations and distinct enrichment factors both on eastern and western slopes. Specifically, the concentrations of Cd and Sb in surface soils of the eastern and western slopes and Pb on the western slope all had obvious altitude distribution trends, which showed their concentrations increased with the increasing elevation. In addition, we found the concentrations of Cd, Sb, As, and Cr in surface soils of the western slope were significantly higher than those of the eastern slope at the same altitude. The correlation analysis and principal component analysis further depicted that the elevation trends of Cd and Sb were mainly controlled by the strong combining effects from long-range atmospheric input and soil organic matter strong absorption, and there was an obvious "cold trapping" effect in high altitude areas. The distribution variations of As and Cr were mainly derived from the weathering difference of soil parent material, while the variations for Pb were controlled by the weathering of bedrock minerals. This study highlights the important role of combining effects from long-range atmospheric input, and from precipitation and vegetation (such as "cold trapping" effect, promoting canopy filtration, litterfall deposition and bedrock weathering) on the distribution trends of trace metals in remote alpine soils.

[Structural Characteristics of Zooplankton and Phytoplankton Communities and Its Relationship with Environmental Factors in a Typical Tributary Reservoir in the Three Gorges Reservoir Region].

Based on the data of zooplankton, phytoplankton, and water environmental factors in different seasons in a typical tributary reservoir in the Three Gorges Reservoir Region (Changshou Lake), this study explored the relationships between the structures of the zooplankton and phytoplankton communities and environmental factors using Pearson correlation analysis. The results showed that there were a total of 107 species of 8 phyla of phytoplankton, and cyanobacteria was the most critical constituent with a relative abundance of 61%. The dominant populations included Phormidium tenue, Merismopedia punctata, and Anabaena oscillarioides. A total of 82 species of 4 phyla of zooplankton were identified, and rotifers was the most abundant with a relative abundance of 88%. The dominant populations included six species, such as Keratella cochlearis, Asplanchna priodonta, and Asplanchna girodi. The spatial differences in the abundances, biomass, and biodiversity indexes of zooplankton and phytoplankton were not significant, whereas the seasonal differences in all the other indexes were significant, except for the zooplankton biodiversity indexes. The abundance of phytoplankton was the highest in summer, followed by spring, and it was the lowest in winter. The maximum abundance of zooplankton occurred in spring, and the biomass of zooplankton and phytoplankton in spring was significantly higher than that in winter. The number of phytoplankton species and the Shannon-Wiener index, Pielou's uniformity index, and Margalef richness index in summer were significantly lower than those in winter and spring. The water quality evaluation showed that Changshou Lake was in a clean to oligo-pollution state in winter and spring and a moderate-pollution state in summer, thereby suggesting that Changshou Lake was in an overall eutrophic state. The environmental factors, including Chla, DOC, nutrients (TP, NO2--N, NO3--N, and NH4+-N), DO, Eh, and T, influenced the structures of the zooplankton and phytoplankton communities in Changshou Lake, and there were seasonal differences in the environmental factors.

[Effects of Chitosan-modified Biochar on Formation of Methylmercury in Paddy Soils and Its Accumulation in Rice].

Rice is well known to accumulate methylmercury (MeHg) and the consumption of rice in mercury (Hg) polluted areas has been confirmed to be a primary source of MeHg exposure. Therefore, how to inhibit the formation and accumulation of MeHg in the paddy field system needs to be solved urgently. Chitosan modified biochar, a potential inhibitor, was selected in this study to explore its effect on MeHg production and accumulation in the paddy field system by analyzing the mercury content of interstitial water, soil, and rice plant tissues. The results showed that the addition of chitosan modified biochar could significantly reduce MeHg concentration in the soil with the decreased methylation rate of 51.1%-79.1%, and could also decrease the total mercury (THg) and MeHg content of interstitial water. At the maturation stage of rice, the MeHg content of rice roots treated with chitosan modified biochar (CMBC) was 73.1% lower than without biochar (CK1) and 62.0% lower than with unmodified biochar (CK2), and the rice MeHg was 75.8% lower than that of CK1 and 72.9% lower than that of CK2. In addition, the application of biochar could promote the growth of rice with the plant biomass of CMBC and CK2 of 1.6 and 1.7 times higher than that of CK1. Generally, the application of chitosan modified biochar into paddy soil could not only promote the growth of rice, but also inhibit the accumulation of MeHg in rice, suggesting that the chitosan modified biochar has a certain application value in the inhibition of the MeHg formation and accumulation in paddy field system.

[Spatial Distribution and Risk Assessment of Heavy Metals in Sediments of the Ruxi Tributary of the Three Gorges Reservoir].

Sediment column and soil samples collected from 12 sampling sites in four regions of the Ruxi River, a typical tributary of the Three Gorges Reservoir, were analyzed for eight selected heavy metals including Cr, Ni, Cu, Mn, Zn, Cd, Pb, and Hg to evaluate their spatial and vertical distribution, source, and biological toxic effects. The results showed that the average concentrations of heavy metals were (79.60±11.87), (41.340±4.999), (32.69±8.70), (823.34±125.76), (122.11±22.82), (0.393±0.140), and (29.122±6.811) mg·kg-1 for Cr, Ni, Cu, Mn, Zn, Cd, and Pb, respectively, and (74.84±39.50) µg·kg-1 for Hg, all of which exceeded the sediment background values of the Yangtze River. A spatial trend of decreasing metal concentrations was observed from the reach influenced by the human activities of Ruxi town to the backwater zone and then to the natural river reach. Moreover, in the backwater zone, the heavy metals in sediments and soil along the river were significantly lower than those in sediments, indicating that the sediments and soil were not one primary source for these metals in backwater zone sediment. From the vertical distribution of sediment, in addition to Pb, the highest level of metals was observed at 8 cm in the reach influenced by human activities, and their concentrations decreased with sediment depth in the backwater zone and natural river beach. Significant correlation was found between all the heavy metals (P<0.01, except Ni), indicating a potential homology of these metals in the Ruxi River. Evaluation results of the geoaccumulation index reveal that there exists light to partial moderate Cd and Zn pollution in the Ruxi River. The evaluation of biotoxicity effects showed that Ni was likely to have toxic effects on organisms with a probability of 10% to 75%, and Cd, Zn, Hg, Cu, Pb, and Cr are likely to have biotoxic effects at<10% probability. The combined effect values of multiple metals indicated that the risk of adverse effects was between low and lower medium in the sediments of the Ruxi River.

[Use of the Nitrogen/Carbon Ratio (N/C) and Two End-Member Sources Mixing Model to Identify the Origins of Dissolved Organic Matter from Soils in the Water-Level Fluctuation Zones of the Three Gorges Reservoir].

Soil dissolved organic matter (soil DOM) plays a crucial role in the environmental fate of pollutants because of its exceptional biogeochemical reactivity. Therefore, tracing the sources and understanding the properties of DOM through chemical characterization is important for clarifying the "structure-reactivity" of DOM in the environment. In this study, traditional elementary analysis methods including nitrogen/carbon ratio (N/C) determinations and derived two end-member source-loads mixing models were applied to soil DOM extracted from the water-level fluctuation zones of the Three Gorges Reservoir (TGR) area. The results were further compared to other characterization techniques that operate on the molecular scale (e. g., FTIR and analytical pyrolysis techniques). The ultimate objective was to assess the performance of N/C ratio and two end-member modeling for identifying the DOM sources. Additionally, a photo-bleaching kinetic experiment was conducted to test the correlation between DOM reactivity and its source-loadings. Results showed, based on the N/C ratio and mixing modeling, all soil DOM samples in the TGR area share "dual-source" characteristics, namely, allochthonousness (e. g., terrestrial) and autochthonousness (e. g., internal) attributes, which is in agreement with other advanced characterization tools. The traditional method results were comprehensible in light of the data from molecular techniques, but the information revealed only reflects certain aspects of DOM compositional characteristics. It can be concluded that the N/C ratio and mixing modeling can validate general sources of soil DOM, but not information about specific components. Meanwhile, the significant correlation between the photo-bleaching kinetic constant and N/C and source-loadings indicated that these two parameters can be used as rapid indicators to estimate soil DOM reactivity in photochemical processes. However, it should be emphasized that it remains essential to employ multiple characterization methods to investigate the biogeochemistry of soil DOM, so as to increase the characterization resolution with regard to the heterogeneity of DOM.

[Temporal and Spatial Variation of Mercury in the Water of the Ruxi River Estuary, a Typical Tributary of the Three Gorges Reservoir Area].

Four typical estuaries located in the Ruxi River, a tributary of the Yangtze River, were selected to investigate the possibility of mercury pollution in tributary estuaries from the Three Gorges reservoir water storage. Water samples were collected during the water storage period (September to October), the flooding period (November to December), the water withdrawal period (February to March), and the drying period (May to June) to determine the levels of mercury species including total mercury (THg), particulate mercury (PHg), dissolved mercury (DHg), reactive mercury (RHg), total methylmercury (TMeHg) and dissolved methylmercury (DMeHg). The results showed that the concentration of THg and TMeHg in the estuary of the Ruxi River was comparable with that of other reservoirs or natural waters in China. There was a significant difference in the concentration of DHg and TMeHg in the water at different depths, because DHg and TMeHg might be derived from the release of sediment to the overlying water. Comparing the concentrations of different mercury species in the four estuaries during the same period, it was found that the difference of water flow direction during the water storage period could lead to an uneven concentration distribution of THg and PHg in the estuary areas. During the water withdrawal period, the particles in the estuary water could adsorb and carry a large amount of PHg, resulting in higher THg concentration in the water in comparison with other periods. The concentration of TMeHg in the flooding and the drying periods was higher than in the other two periods, indicating that the stable water level might be conducive to the accumulation of methylmercury in the water, and the severe disturbance of the water level could significantly reduce the concentration of TMeHg in the water.

[Mercury Distribution Characteristics and Its Mass Balance in a Multifunctional Urban Wetland].

The distribution characteristics and the source-sink relationship of total mercury (THg) and methyl mercury (MeHg) were studied in a wastewater treatment area and in a lake deep purification area of a multifunctional urban wetland that integrates domestic sewage treatment plant effluent, water purification, and leisure entertainment in Chongqing. The results showed that the THg concentration ranged from 1.98 ng·L-1 to 38.03 ng·L-1[average concentration was (9.10±5.84) ng·L-1] and MeHg concentration ranged from 0.09 ng·L-1 to 0.84 ng·L-1[average concentration was (0.34±0.08) ng·L-1] in an outlet of wastewater treatment area. In the deep purification zone, the THg concentration ranged from 0.37 ng·L-1 to 85.69 ng·L-1[average concentration of (6.76±2.29) ng·L-1] and the MeHg concentration ranged from 0.04 ng·L-1 to 1.47 ng·L-1[average concentration of (0.35±0.17) ng·L-1]. The interference of human activities on mercury concentration is prominent. The vertical distribution of THg in the water is consistent with that of MeHg, the surface layer has lower values than the deep layer. Material balance suggested that THg in the wetland system decreases by 155.50 g per year, and MeHg decreases by 1.65 g per year, which has a protective effect on the downstream water.

[Distribution Characteristics of Mercury in Different Urban Constructed Wetlands].

To explore the spatial and temporal distribution and the methylation characteristics of mercury in different constructed wetlands in cities, and to understand the potential ecological exposure of mercury in urban wetlands, four artificial wetlands in Chongqing were studied from March 2017 to March 2018. The water samples were collected separately in four quarters, and the mass concentration of total mercury (THg) and methyl mercury (MeHg) was researched for one year. The results showed that the THg concentration in the four wetland waters is higher than the background value of the world's lakes and reservoirs for dam construction, but it is far lower than the waters with pollution history. The THg mass concentration of the water inside the wetlands is slightly higher than in the inlet and outlet. In addition, the THg mass concentration in the aquatic plant growing area, the construction area, the cruise ship parking area, and the frequent play area has an increasing trend, indicating that urban wetlands have a trapping and converging effect of the water's THg, so human activities influence total mercury a lot. The mass concentration of MeHg in the four wetland waters was slightly higher than that in other water bodies. With the exception of the Caiyun Lake, where the mass concentration of MeHg at the outlet was higher than that of the water inlet, the other three wetlands showed lower MeHg mass concentration in the outlet than the inlet. The mass concentration of MeHg in the wetland water increased with increasing water depth. The ratio of MeHg concentration to THg mass concentration (MeHg/THg) was higher than in other waters, indicating that urban wetlands have effect on net mercury methylation from waters. The photoreduction of mercury and its absorption by aquatic plants can reduce the mercury load from urban wetlands to downstream watersheds. The THg mass concentration of the four urban wetland water bodies was high in the spring and autumn, with a slight decrease in the summer, and lowest in the winter. The mass concentration of MeHg was the lowest in winter, and in the other three seasons it was basically flat, about three times higher than in winter. This study clarifies the temporal and spatial distribution and methylation of mercury in urban wetlands. It explores the degree of disturbance of human activities on wetlands and the response characteristics, as well as the impact of wetland mercury on downstream watersheds. To avoid potential mercury exposure, measures need to be established for the construction of artificial wetlands.

[Hair Mercury Concentrations in Residents of Fuling and Zhongxian in the Three Gorges Reservoir Region and Their Influence Factors].

To evaluate the mercury (Hg) exposure risk for residents of the Three Gorges Reservoir Region (TGRR), hair samples were collected from 238 local residents within the central regions of the TGRR (Fuling District and Zhongxian County) in this study. Subsequently, total mercury (THg) and methylmercury (MeHg) concentrations were determined. The results obtained showed that the average THg and MeHg concentrations in hair samples of the residents within these two areas were (0.50±0.54) µg·g-1 and(0.35±0.25) µg·g-1, respectively. Specifically, the average THg and MeHg concentrations in hair samples of Fuling residents were(0.71±0.87) µg·g-1 and(0.53±0.46) µg·g-1, respectively. Both these values were higher than those in hair samples of Zhongxian County residents [THg(0.41±0.36) µg·g-1 and MeHg (0.28±0.26) µg·g-1]. It is noteworthy that the hair Hg levels in residents of these two areas are both well below the U.S. Environmental Protection Agency's reference dose (1 µg·g-1). Hair Hg levels varied slightly among different age groups; higher Hg levels were detected in residents in the age group of 40-50 years(P<0.05). However, there was no significant difference between the hair Hg levels among genders(P>0.05). Hair Hg levels in females were slightly above those in males. Hair Hg levels were significantly correlated with the frequency of fish consumption. Furthermore, hair Hg levels in non-fishermen were significantly lower than those in fishermen. An elevated mean value of (1.44±0.79) µg·g-1(P<0.01), which exceeds the RfD of 1 µg·g-1, was detected in fishermen. Moreover, hair Hg levels in smokers of Fuling and Zhongxian County[(0.55±0.24) µg·g-1 and (0.58±0.54) µg·g-1, respectively] were both markedly higher than those in non-smokers[(0.51±0.30) µg·g-1 and (0.36±0.26) µg·g-1respectively]. In conclusion, the risk of Hg exposure to residents of the TGRR was lower. However, in this study, it was determined that fishermen are at significant risk of Hg exposure.

[Migration and Transformation of Mercury in Unsubmerged Soil and Sediment at One Typical Forest Reservoir in Southwest China].

Mercury (Hg) has been regarded as a global pollutant due to its volatility and toxicity. The sediment in the reservoirs or lakes is an important compartment for Hg methylation and it has also been considered as a sensitive area of Hg. In this study, a typical forest reservoir surrounding by evergreen broad-leaved forest in Chongqing of southwest China was selected to investigate the migration and transformation of Hg in unsubmerged soil and sediment. The unsubmerged soil and sediment were also replaced to each other to observe the dynamics of THg and TMeHg concentrations in equilibrium processes. The results were as follows:① The THg and TMeHg mean concentrations in Dahonghai reservoir water were (1.89±0.72) ng·L-1 and (0.13±0.04) ng·L-1, respectively, which were lower than the first class water quality standards in environmental quality standard of China and other reservoirs or lakes, implying that this study area did not affect by Hg pollution. Meanwhile, the THg and TMeHg mean concentrations in unsubmerged soil and sediment were also lower than those in other reservoirs or lakes. ② Seasonal variations of THg and TMeHg concentrations in reservoir water and soil were both observed higher in warm seasons, and more obvious variations occurred for TMeHg which probably influenced by meteorological parameters, such as, temperature and rainfall. ③Compared with unsubmerged soil, the THg and TMeHg mean concentrations in sediment were both elevated, suggesting the sediment was an important sink of Hg. While, the sediment would be a source of Hg (especially TMeHg) with a high THg and TMeHg level. ④ The THg and TMeHg mean concentrations in unsubmerged soil and sediment after situ replacement were equilibrated with ambient soil in a short time (one or two months), implying the hydro-fluctuation belt of reservoir promoting the geochemical cycle of Hg.

[Diversity of the Microbial Community in Rice Paddy Soil with Biogas Slurry Irrigation Analyzed by Illumina Sequencing Technology].

In order to explore the variation in soil microbial community diversity in paddy fields with different irrigation periods, we collected in situ rice field soils during different biogas irrigation periods and analyzed the microbial community structures of these soils by high-throughput sequencing. The results showed that as the biogas irrigation period increased, the soil pH decreased gradually, while organic matter, nitrate nitrogen, phosphate, and other nutrients were accumulated. Years of continued biogas irrigation was not conducive to improving rice yields. The results showed that as the biogas irrigation period increased, the richness in microbial species in paddy soils decreased gradually, and the diversity in the microbial communities was also reduced. Proteobacteria accounts for the largest proportion in rice paddy soil with biogas slurry irrigation. With the increase of biogas irrigation years, the proportion of ß-Proteobacteria, Bacteroidia, Bacteroidales, Burkholderiales, Bacteroides, and Thiobacillus increased, while the proportion of Gemmatimonadetes and α-Proteobacteria decreased gradually. Dissolved organic carbon (F=2.67, P=0.09) had the greatest effect on microbial community structures in the studied paddy soils.

[Effects of Agricultural Activities on Soil Mercury Changes in the Water-Level-Fluctuating Zone of the Three Gorges Reservoir].

Farming in the water-level-fluctuating zone (WLFZ) of the Three Gorges reservoir, China, may result in a wide range of environment problems when the sediment is exposed to air. In this study, Qukou, Chongqing, was selected as the research site due to its large WLFZ area and significant agricultural activities. Four kinds of land use types, including rice, maize, vegetables, and grassland, were selected to investigate the distribution of mercury (Hg) in the surface soil. The results showed that the mean concentrations of soil total Hg (THg), bioavailable Hg (Hg-wh), and methylmercury (MeHg) in the surface soil were 25.80-68.74 ng ·g-1, 0.44-0.88 ng ·g-1, and 0.08-0.85 ng ·g-1, respectively. The concentrations of THg, Hg-wh, and MeHg in non-cultivated soil were higher than those in cultivated soil, indicating that farming disturbances could accelerate soil Hg loss. The MeHg concentrations in both non-cultivated and cultivated soil increased up to the maximum value 1-2 months after drying, and then gradually decreased to a relatively stable level. The peak value was approximately four times higher than that at the end of flooding. The percentage of MeHg to THg (% MeHg) was similar to the distribution of soil MeHg, and the peak value occurred at 1 month after drying. However, when% MeHg decreased to the stable level, no significant difference was found compared to the value at the end of flooding (P>0.05). Furthermore, the soil% MeHg had a significantly positive correlation with Hg-wh (r=0.642, P<0.01), while there was no significant correlation with THg (P>0.05), suggesting that Hg methylation was mainly affected by the bioavailability of Hg in the seasonally inundated soil of the WLFZ.

[Characteristics of Mercury Transformation in Soil and Accumulation in Rice Plants in an Acidic Purple Paddy Soil Area].

A pot experiment was conducted to analyze the characteristics of mercury (Hg) accumulation during the rice growth period in acidic purple paddy soil. Results showed that the soil total Hg concentration was stable with time during the rice growth period, while methylmercury (MeHg) increased greatly. Therefore, the ratio of MeHg/THg was mainly affected by MeHg concentration. THg concentration in rice plant parts followed the trend:root > grain > stalk > leaf > husk at the mature grain stage, while MeHg concentration followed grain > root > stalk > leaf > husk. The average of MeHg/THg in rice (24.03%) far exceeded that in soil (3.05%), suggesting that rice plants have a strong affinity for MeHg accumulation. This conclusion was supported also by the great difference in average of bio-concentration factors between MeHg (8.16) and THg (2.31) or the transfer factor in the grain, which was more than 1. Moreover, the bio-concentration factor for grain was higher than that for roots, stalks, and leaves, suggesting MeHg was prone to accumulation in grain compared with other part of rice plants.

[Distribution Characteristics and Risk Assessment of Heavy Metals in the Sediments of the Estuary of the Tributaries in the Three Gorges Reservoir, SW China].

To investigate the pollution status of sediments at the junction of the Three Gorges Reservoir area, sediment samples were collected over four seasons from the junction of the estuary located at a tributary of the Ruxi River and the Yangtze River. The content of eight heavy metals (HMs), including Cr, Zn, Mn, Ni, Cu, As, Cd, and Pb, in sediments was determined by ICP-MS. The results showed the average levels of investigated HMs (in mg·kg-1) were Cr (45.24), Zn (46.46), Mn (406.14), Ni (20.885), Cu (12.49), As (7.02), Cd (0.253), and Pb (11.042). The distribution analysis indicated that the levels of HMs at the river mouth were higher than that of the tributaries of the middle reaches and the two sections nearby. The seasonal distribution shows that the heavy metal content in the spring sediment is higher than in summer, autumn and winter. In addition, the correlation analysis indicated that the eight HMs possessed similar homologous characteristics and had common exogenous inputs. The assessment of the Geo Accumulation Index showed slight Cd pollution in the estuary of Ruxi River, and the Potential Ecological Risk index showed that Cd presented moderate ecological risks. The toxic effect of benthonic organisms was possibly correlated to Ni contamination at the intersection of the tributary and main stream, which was supported by the evidence from the sediment quality criteria. In conclusion, the rating of ecological risk at the mouth of the Ruxi River tributary is slight.

Tracing aquatic bioavailable Hg in three different regions of China using fish Hg isotopes.

To trace the most concerned bioavailable mercury (Hg) in aquatic environment, fish samples were collected from three typical regions in China, including 3 rivers and 1 lake in the Tibetan Plateau (TP, a high altitude background region with strong solar radiation), the Three Gorges Reservoir (TGR, the largest artificial freshwater reservoir in China), and the Chinese Bohai Sea (CBS, a heavily human-impacted semi-enclosed sea). The Hg isotopic compositions in fish muscles were analyzed. The results showed that anthropogenic emissions were the main sources of Hg in fish from TGR and CBS because of the observed negative δ202Hg and positive Δ199Hg in these two regions (TGR, δ202Hg: - 0.72 to - 0.29‰, Δ199Hg: 0.15 - 0.52‰; CBS, δ202Hg: - 2.09 to - 0.86‰, Δ199Hg: 0.07 - 0.52‰). The relatively higher δ202Hg and Δ199Hg (δ202Hg: - 0.37 - 0.08‰, Δ199Hg: 0.50 - 1.89‰) in fish from TP suggested the insignificant disturbance from local anthropogenic activities. The larger slopes of Δ199Hg/Δ201Hg in fish from TGR (1.29 ± 0.14, 1SD) and TP (1.25 ± 0.06, 1SD) indicated methylmercury (MeHg) was produced and photo-reduced in the water column before incorporation into the fish. In contrast, the photoreduction of Hg2+ was the main process in CBS (slope of Δ199Hg/Δ201Hg: 1.06 ± 0.06, 1SD). According to the fingerprint data of Hg isotopes, the most important source for aquatic bioavailable Hg in TP should be the long-range transported Hg, contrasting to the anthropogenic originated MeHg from surface sediments and runoffs in TGR and inorganic Hg from continental inputs in CBS. Therefore, the isotopic signatures of Hg in fish can provide novel clues in tracing sources and behaviors of bioavailable Hg in aquatic systems, which are critical for further understanding the biogeochemical cycling of Hg.

[Characteristics of Mercury Emissions from Coal-fired Power Plants in Chongqing].

Four typical coal-fired power plants in Chongqing, representing two different boiler types (circulating fluidized bed boiler and pulverized coal boiler), were chosen to investigate mercury emission characteristics through a mercury mass balance method by analyzing mercury contents in all input and output raw materials in order to accurately estimate mercury emissions. The results showed coal with mercury concentrations ranging (80.77±6.39)-(266.83±4.71) µg·kg-1 could be a significant contributor of input mercury in these four studied power plants. Most mercury output from these power plants entered into solid waste with high proportion of mercury entering the fly ash in CFB plants and entering the fly ash and desulfurization gypsum in PC plants. Mercury removal efficiencies of studied plants were in the range of 72.89%-96.05%, and these efficiencies in CFB plants were higher than those in PC plants. The mercury emission factors for EFelectricity and EFcoal of these four plants were 4.66-29.47 µg·(kW·h)-1 and 8.55-71.77 mg·t-1, respectively. The mercury emission was also calculated to be 6.13-429.17 g·d-1. Mercury emissions from coal-fired power plants were associated with the content of mercury in coal, boiler type, generation load, pollution control equipment, and so on. To control the mercury emissions, more attention should be paid to improving the generation load, increasing the mercury removal efficiency of flue gas cleaning equipment, and strengthening the supervision of solid waste re-utilization.

[Experimental Research of Hg2+Removal by TiO2/Bentonite Composite].

The TiO2/bentonite composite was synthesized by modifying calcium-based bentonite with Nano-TiO2. The products before and after modification were characterized via the approach of X-ray power diffraction(XRD) and scanning electron microscope(SEM).The effect of TiO2/bentonite composite on mercury removal from aqueous solutions of HgCl2was studied at different dosage, pH, adsorption time and the initial concentration of Hg2+ was investigated and compared with the bentonite by indoor simulation experiment, as well as the orthogonal experiments to determine the optimal condition of Hg2+ adsorption. The experimental results showed:after modified by TiO2, TiO2/bentonite composite particles were apparently smaller, the basal spacing was increased and with a loose and porous structure. The adsorption rates of TiO2/bentonite composite on Hg2+ were increased compared with bentonite. The Hg2+ adsorption rates were increased with the increasing dosages, pH and adsorption time. The adsorption rates were higher than 98.0% when the dosage was 1.5 g·L-1, pH 7.0, and the adsorption time was 120 min. The adsorption rates became smaller with increasing initial concentration of Hg2+. False secondary dynamic equation could describe the adsorption of TiO2/bentonite composite on Hg2+, and the chemical adsorption was dominant. The adsorption isotherm of Hg2+ conformed to Langmuir equation, indicating that the adsorption of Hg2+ was typical monolayer adsorption. The optimal experimental condition was:dosage of 2.0 g·L-1, pH 8.0, adsorption time of 16 h and the initial Hg2+concentration of 45 mg·L-1. Under this condition, the adsorption rate was 99.9%, and the equilibrium concentration of Hg2+ was 0.034 mg·L-1.