Xuejun Wang

Peking University, Peping, Beijing, China

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Publications (46)128.41 Total impact

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    ABSTRACT: Soils contaminated by Polycyclic Aromatic Hydrocarbons (PAHs) are subject to significant non-point source (NPS) pollution during rainfall events. Recent studies revealed that the classic enrichment ratio (ER) approach may not be applicable to PAHs. This study developed a model to estimate the ER of PAHs which innovatively applies the fugacity concept. The ER model has been validated with experimental data, which suggested that the transport of PAHs not only depends on their physicochemical properties, but on the sediment composition and how the composition evolves during the event. The modeling uncertainty was systematically examined, and found to be highly compound-dependent. Based on the ER model, a strategy was proposed to practically evaluate the potential NPS loading of PAHs in watersheds with heterogeneous soils. The study results have important implications to modeling and managing the NPS pollution of PAHs (or other chemicals alike) at a watershed scale.
    Environmental Pollution. 01/2015; 196:1–11.
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    ABSTRACT: In recent years, an incentive for developing simple and cost-effective samplers that are capable of monitoring over an extended period and require nonattendance at remote locations was obvious. Compared to traditional active sampling approaches, passive samplers require no electric power and are more flexible in field deployment, thus they are more appropriate for screening applications and long-term sampling. However, the performance of passive samplers may be influenced by meteorological factors, therefore inducing bias for the result of passive sampling. In this study, the effects of temperature, relative humidity, and wind speed on the performance of a novel passive sampler for gaseous mercury were investigated. The meteorological factors were well controlled in an exposure chamber. The passive samplers were tested in different conditions: temperature ranging from −10 to 35 °C, relative humidity ranging from 25 to 90%, wind speed ranging from 0.5 to 5.0 m s−1. The results showed that temperature and relative humidity had no significant influence on the performance of the passive sampler. However, wind speed was found to have significant impact on the sampling rate of the passive sampler. Wind correction should be considered when making comparisons among samplings with different average wind speeds. In the field application in Beijing and Tibet site, the passively measured data were well correlated with the active measurements.
    Atmospheric Environment 11/2014; 97:310–315. · 3.11 Impact Factor
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    ABSTRACT: Considering the different ability of placental transfer, an assessment of the cord:maternal blood ratio for both methylmercury (MeHg) and inorganic mercury (IHg) is needed especially for interpreting the low-level prenatal exposure. In this study, we conducted a Monte Carlo-based meta-analysis to comprehensively estimate that ratio for MeHg (RMeHg) and IHg (RIHg). The obtained values followed log-normal distributions, with a mean (standard deviation) of 1.89 (0.98) and 1.01 (0.55) for RMeHg and RIHg, respectively. We also estimated the percentage of MeHg in the blood by means of THg in cord and maternal blood using the RMeHg and RIHg, and obtained a value very close to the measured one (relative deviation, -0.4%). In conclusion, the fetus is exposed to approximately twice as much MeHg and to the same level of IHg as in maternal blood; the introduced model provides a rough but reasonable estimate of the percentage of MeHg in the blood.
    Environmental Pollution 04/2014; 191C:25-30. · 3.73 Impact Factor
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    ABSTRACT: Urban stormwater runoff delivers a significant amount of polycyclic aromatic hydrocarbons (PAHs), mostly of atmospheric origin, to receiving water bodies. The PAH pollution of urban stormwater runoff poses serious risk to aquatic life and human health, but has been overlooked by environmental modeling and management. This study proposed a dynamic modeling approach for assessing the PAH pollution and its associated environmental risk. A variable time-step model was developed to simulate the continuous cycles of pollutant buildup and washoff. To reflect the complex interaction among different environmental media (i.e. atmosphere, dust and stormwater), the dependence of the pollution level on antecedent weather conditions was investigated and embodied in the model. Long-term simulations of the model can be efficiently performed, and probabilistic features of the pollution level and its risk can be easily determined. The applicability of this approach and its value to environmental management was demonstrated by a case study in Beijing, China. The results showed that Beijing's PAH pollution of road runoff is relatively severe, and its associated risk exhibits notable seasonal variation. The current sweeping practice is effective in mitigating the pollution, but the effectiveness is both weather-dependent and compound-dependent. The proposed modeling approach can help identify critical timing and major pollutants for monitoring, assessing and controlling efforts to be focused on. The approach is extendable to other urban areas, as well as to other contaminants with similar fate and transport as PAHs.
    Science of The Total Environment 03/2014; 481C:554-563. · 3.16 Impact Factor
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    ABSTRACT: Considering the different ability of placental transfer, an assessment of the cord:maternal blood ratio for both methylmercury (MeHg) and inorganic mercury (IHg) is needed especially for interpreting the low-level prenatal exposure. In this study, we conducted a Monte Carlo-based meta-analysis to comprehensively estimate that ratio for MeHg (RMeHg) and IHg (RIHg). The obtained values followed log-normal distributions, with a mean (standard deviation) of 1.89 (0.98) and 1.01 (0.55) for RMeHg and RIHg, respectively. We also estimated the percentage of MeHg in the blood by means of THg in cord and maternal blood using the RMeHg and RIHg, and obtained a value very close to the measured one (relative deviation, −0.4%). In conclusion, the fetus is exposed to approximately twice as much MeHg and to the same level of IHg as in maternal blood; the introduced model provides a rough but reasonable estimate of the percentage of MeHg in the blood.
    Environmental Pollution. 01/2014; 191:25–30.
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    ABSTRACT: Effort of reducing CO2 emissions in developing countries may require an increasing utilization of biomass fuels. Biomass pellets seem well-suited for residential biomass markets. However, there is limited quantitative information on pollutant emissions from biomass pellets burning, especially those measured in real applications. In this study, biomass pellets and raw biomass fuels were burned in a pellet burner and a conventional stove respectively, in rural households, and metal emissions were determined. Results showed that the emission factors (EFs) ranged 3.20-5.57 (Pb), 5.20-7.58 (Cu), 0.11-0.23 (Cd), 12.67-39.00 (As), 0.59-1.31 mg/kg (Ni) for pellets, and 0.73-1.34 (Pb), 0.92-4.48 (Cu), 0.08-0.14 (Cd), 7.29-13.22 (As), 0.28-0.62 (Ni) mg/kg for raw biomass. For unit energy delivered to cooking vessels, the EFs ranged 0.42-0.77 (Pb), 0.79-1.16 (Cu), 0.01-0.03 (Cd), 1.93-5.09 (As), 0.08-0.19 mg/MJ (Ni) for pellets, and 0.30-0.56 (Pb), 0.41-1.86 (Cu), 0.04-0.06 (Cd), 3.25-5.49 (As), 0.12-0.26 (Ni) mg/MJ for raw biomass. This study found that moisture, volatile matter and modified combustion efficiency were the important factors affecting metal emissions. Comparisons of the mass-based and task-based EFs found that biomass pellets produced higher metal emissions than the same amount of raw biomass. However, metal emissions from pellets were not higher in terms of unit energy delivered.
    Scientific reports. 01/2014; 4:5611.
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    ABSTRACT: In this study, we examined the heterogeneous reduction of Hg(II) on the coal fly ash samples and synthetic aerosols under different light conditions in a controlled laboratory reactor. Three types of coal fly ashes were studied: a high carbon fly ash from a stoker boiler, a low carbon/low sulfate fly ash from a pulverized coal combustor burning low sulfur coal, and a high sulfate fly ash from a pulverized coal combustor burning high sulfur coal. The rate of Hg(II) reduction on the three diverse fly ash samples was found to be relatively fast with an average half-life of 1.6 h under clear sky atmospheric conditions (under the irradiance of 1000 W/m2). The reduction rate in the low sulfate/low carbon fly ash was approximately 1.5 times faster than with the other coal fly ash samples. Synthetic aerosols made of carbon black and levoglucosan produced Hg(II) reduction rates similar to coal fly ashes. However, aerosols composed of adipic acid resulted in reduction rates that were 3–5 times faster. The sensitivity of adipic acid reduction to light source wavelength was found to be greater than for the coal fly ash and other synthetic aerosols. Aerosols made from the water extracts of coal fly ash samples produced reduction rates equal to or slightly higher than with the native fly ash suggesting that the soluble components of fly ash play a significant role in the reduction mechanism. The measured reduction rates are likely important in the chemical processing of mercury in power plant plumes and potentially in the atmosphere and should be considered for incorporation in atmospheric transport models that are used to understand the fate of atmospheric mercury.
    Atmospheric Research 01/2014; 138:324–329. · 2.20 Impact Factor
  • Wei Zhang, Yan Zhu, Xuejun Wang
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    ABSTRACT: Design of treatment strategy considering the behavior of pollutant with respect to runoff hydrograph is important for effective management of storm runoff. In this study, a mathematical model for storm runoff management was developed. The model determines the storm runoff management strategy and the associated probability under the constraint of regulatory discharge limit, and can quantify the volume or fraction of a storm runoff that should be treated. The model application was demonstrated for total suspended solids (TSS) and benzo(a)pyrene (BaP) in urban storm runoff. The samples were collected from 15 storm runoff events in six impervious sites in Beijing urban area, and. For TSS, the probability that the whole runoff can be discharged without treatment was 46 %, and the whole runoff should be intercepted for treatment was 31 %. While under the constraint of the discharge limit for BaP, the dominant strategy was that the whole runoff should be intercepted for treatment, with a probability of 88 %. Compared with the treatment strategies, it was noted that the need for runoff treatment was more for BaP than TSS. This was because the pollution level of TSS was lower than BaP from the aspect of compliance with discharge limit. Because the most seriously contaminated and toxic pollutant should be taken as the primary indicator for runoff treatment, the treatment option for the study area should follow the strategies for BaP. This methodology may be applied for other pollutants in different watersheds.
    Water Resources Management 01/2014; · 2.46 Impact Factor
  • Wei Zhang, Wen Wei, Dan Hu, Yan Zhu, Xuejun Wang
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    ABSTRACT: Among various sources, mercury emissions from biomass fuel combustion have received growing attention. Mercury emission from biomass fuels can be estimated on the basis of the combustion amount and the emission factors (EFs). Although mercury emissions from biomass fuel combustion occur mostly in developing countries, most EFs have been measured in developed countries, leading to bias in mercury emission inventories. In this study, mercury EFs for 25 species of fuelwood, eight species of crop residues, and two types of biomass pellets were determined according to the real-life practice of residential burning. Results showed that the EFs ranges were 0.65–28.44 ng g–1 for fuelwood, 3.02–12.05 ng g–1 for crop residues, and 5.22–8.10 ng g–1 for biomass pellets. Hg0 is the dominant form of mercury emitted from biomass fuel combustion. The proportion of Hg0, Hg2+, and Hgp was 76 ± 17, 6 ± 5, and 18 ± 14% for fuelwood; 73 ± 11, 4 ± 5, and 23 ± 13% for crop residues; and 97 ± 1, 1 ± 0.2, and 2 ± 0.7% for biomass pellets, respectively. Biomass pellets can reduce mercury emissions compared with the uncompressed raw materials. On the basis of the measured EFs, inventories of mercury emission from biomass fuel combustion in rural China from 2000–2007 were estimated. The annual mercury emission ranged from 1.94 to 5.07 Mg, of which crop residues and fuelwood accounted for 62 and 38%, respectively.
    Energy & Fuels 10/2013; 27(11):6792–6800. · 2.85 Impact Factor
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    ABSTRACT: The fate and transfer of mercury in urban river is an important environmental concern. In this study, QWASI (Quantitative Water-Air-Sediment Interaction) model was selected to estimate the levels of total mercury and three mercury species in water and sediment, and was used to quantify the fluxes of mercury at water/air and sediment/water interfaces of an urban river. The predicted mercury levels in water and sediments were closed to the measured values. Water inflow, re-suspension of sediment and diffusion from sediment to water are major input sources of mercury in water. The net mercury transfer flux from water to air was 0.16 ng/(m(2) h). At the sediment/water interface, a net total mercury transfer of 1.32 ng/(m(2) h) from water to sediment was seen. In addition to the existing dynamic flux chambers measurement, this model method could provide a new perspective to identify the distribution and transfer of mercury in the urban river.
    Environmental Pollution 09/2013; 184C:54-61. · 3.73 Impact Factor
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    ABSTRACT: A laboratory reactor system was developed to examine the role of light and aerosol composition in the reduction of oxidized mercury (Hg(ii)) in laboratory-generated aerosols. Aerosolized sodium chloride, doped with mercury chloride, was exposed to light in a fixed-bed flow-through reactor. Three spectral ranges (UV, visible and a simulated solar spectrum) were examined, along with dark experiments, to investigate the role of light conditions in mercury reduction. In addition, the role of iron in the aerosol matrix was examined. The effluent from the reactor was analyzed for Hg(0) as evidence of reduction of Hg(ii) in the reactor. Significant reduction of Hg(ii) (1.5-9.9%) was observed for all three light sources and the rate of mercury reduction was proportional to the light irradiance. The presence of iron in the aerosol matrix inhibited the reduction rate and the degree of inhibition was dependent on the chemical form of the iron in the aerosol. The observed reduction reactions may be important chemical processes in the atmosphere and could be incorporated in atmospheric transport models that are used to understand the fate of atmospheric mercury.
    Environmental science. Processes & impacts. 08/2013;
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    ABSTRACT: Polycyclic Aromatic Hydrocarbons (PAHs) transported from contaminated soils by surface runoff pose significant risk for aquatic ecosystems. Based on a rainfall-runoff simulation experiment, this study investigated the impact of carbonaceous materials (CMs) in soil, identified by organic petrology analysis, on the transport of soil-bound PAHs under rainfall conditions. The hypothesis that composition of soil organic matter significantly impacts the enrichment and transport of PAHs was proved. CMs in soil, varying significantly in content, mobility and adsorption capacity, act differently on the transport of PAHs. Anthropogenic CMs like black carbon (BC) largely control the transport, as PAHs may be preferentially attached to them. Eventually, this study led to a rethink of the traditional enrichment theory. An important implication is that CMs in soil have to be explicitly considered to appropriately model the nonpoint source pollution of PAHs (possibly other hydrophobic chemicals as well) and assess its environmental risk.
    Environmental Pollution 08/2013; 182C:233-241. · 3.73 Impact Factor
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    ABSTRACT: Biomass burning is an important contributor of atmospheric mercury emissions. An inventory of mercury emissions from biomass burning with a high resolution and long time span is necessary for mercury transport modeling and emission reduction. In this study, an inventory of mercury emissions from biomass burning in China, with high spatial resolution and decade period (2000–2010), is presented, and the emission in 2020 is projected. Results showed that during 2000–2010, the annual average mercury emission from crop residues burning as fuel in household, crop residues burning as waste in fields, fuelwood burning in households, fuelwood burning for production, forest fires, and grassland fires was 2.30, 0.97, 1.66, 0.49, 0.78, and 0.01 Mg, respectively. The total emission was 6.20 Mg yr−1, lower than the results of previous studies. The majority of mercury species is in the form of Hg0, accounting for 78.9%, followed by Hgp (15.5%) and Hg2+ (5.6%). During 2000–2010, mercury emission from biomass burning decreased from 6.08 Mg in 2000 to 5.12 Mg in 2010. For spatial distribution, the mercury emissions were high in the eastern and central regions of China. Results from scenario analysis showed that mercury emission in 2020 is projected to be 6.18 Mg under the growth condition following the trend in 2005–2010 and 3.00 Mg under the condition of the anticipated new development mode. The results of this inventory study could provide useful information for further assessment of global mercury source attribution and mercury transport modeling.
    Journal of Geophysical Research: Atmospheres. 01/2013; 118(21).
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    ABSTRACT: An inventory of mercury emissions originating from waste incineration in China, including municipal solid waste, rural household waste and agricultural waste, was calculated for the period of 2004–2010. During this period, mercury emissions from waste incineration increased at an average annual rate of 3.9%, and reached 16.6 t y−1 by the end of 2010. From 2004 to 2010, the mercury emissions from rural household waste incineration accounted for 46.6% of the total waste emissions, followed by agricultural waste (30.7%) and municipal solid waste (22.7%). However, the growth rate of mercury emissions was largest for municipal solid waste incineration, with an annual rate of 37.3%, while the emissions from rural household waste showed a negative growth rate (−5.8%). The mercury emissions from waste combustion is projected to be 18.6 t y−1 by 2015, with the contribution of municipal solid waste, rural household waste and agricultural waste being 46.4%, 27.1% and 26.5%, respectively.
    Atmospheric Environment 12/2012; 62:359–366. · 3.11 Impact Factor
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    ABSTRACT: The aggregation kinetics of single-walled (SWNTs) and multi-walled (MWNTs) carbon nanotubes dispersed using sodium dodecylbenzene sulfonate (SDBS) were investigated using time-resolved dynamic light scattering (DLS), in the presence of several electrolytes, and humic acid (HA). The effects of changes in the concentration of monovalent (NaCl, 5–200 mmol/L) and divalent (CaCl2, 0.2–5 mmol/L) electrolytes and the solution pH (3–10) on the aggregation behavior were evaluated. The results showed that the carbon nanotubes (CNTs) could be effectively suspended in aqueous solution using the surfactant (SDBS), and that increased electrolyte concentrations induced aggregation. At a solution pH of 6.3 ± 0.2 (without HA), the critical coagulation concentration (CCC) values of NaCl were calculated as 90 and 120 mmol/L for SWNTs and MWNTs, respectively; the values for CaCl2 were calculated as 0.82 and 2.6 mmol/L, respectively. Increases in the solution pH from 3 to 10 led to a significant decrease in CNT aggregation, indicating the presence of functional groups on the CNTs’ surface. However, the impact of HA on the aggregation of CNTs in suspension depended on the type of the electrolyte that it was exposed to. In a NaCl solution, the stability of the CNTs was increased. For HA concentrations of 1, 5, and 20 mg/L, the CCC values of NaCl for the MWNTs increased to 130, 160, and 240 mmol/L, respectively. The effect was attributed to the steric repulsion induced by the adsorbed HA molecules. However, this effect was negligible in CaCl2 solutions. The results of this study elucidated the effects of surfactants, solution chemistry, and HA on the aggregation kinetics of CNTs, all of which may have significant influences on the behavior of CNTs in the environment.
    Colloids and Surfaces A Physicochemical and Engineering Aspects 09/2012; 409:159–166. · 2.11 Impact Factor
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    ABSTRACT: Carbon dioxide (CO2) and carbon monoxide (CO) impact climate change and human health. The uncertainties in emissions inventories of CO2 and CO are primarily due to the large variation in measured emissions factors (EFs), especially to the lack of EFs from developing countries. China's goals of reducing CO2 emissions require a maximum utilization of biomass fuels. Pelletized biomass fuels are well suited for the residential biomass market, providing possibilities of more automated and optimized systems with higher modified combustion efficiency (MCE) and less products from incomplete combustion. However, EFs of CO2 and CO from pellet biomass fuels are seldom reported, and a comparison to conventional uncompressed biomass fuels has never been conducted. Therefore, the objectives of this study were to experimentally determine the CO2 and CO EFs from uncompressed biomass (i.e., firewood and crop residues) and biomass pellets (i.e., pine wood pellet and corn straw pellet) under real residential applications and to compare the influences of fuel properties and combustion conditions on CO2 and CO emissions from the two types of biomass fuels. For the uncompressed biomass examples, the CO2 and CO EFs were 1649.4 ± 35.2 g kg−1 and 47.8 ± 8.9 g kg−1, respectively, for firewood and 1503.2 ± 148.5 g kg−1 and 52.0 ± 14.2 g kg−1, respectively, for crop residues. For the pellet biomass fuel examples, the CO2 and CO EFs were 1708.0 ± 3.8 g kg−1 and 4.4 ± 2.4 g kg−1, respectively, for pellet pine and 1552.1 ± 16.3 g kg−1 and 17.9 ± 10.2 g kg−1, respectively, for pellet corn. In rural China areas during 2007, firewood and crop residue burning produced 721.7 and 23.4 million tons of CO2 and CO, respectively.
    Atmospheric Environment 09/2012; 56:136–142. · 3.11 Impact Factor
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    ABSTRACT: Polycyclic Aromatic Hydrocarbons (PAHs) transported by surface runoff result in nonpoint source pollution and jeopardize aquatic ecosystems. The transport mechanism of PAHs during rainfall-runoff events has been rarely studied regarding pervious areas. An experimental system was setup to simulate the runoff pollution process on PAHs-contaminated soil. The enrichment behavior of soil-bound PAHs was investigated. The results show that soil organic matters (SOM), rather than clay particles, seem to be the main carrier of PAHs. The enrichment is highly conditioned on runoff and erosion processes, and its magnitude varies among PAH compounds. It is not feasible to build a simple and universal relationship between enrichment ratio and sediment discharge following the traditional enrichment theory. To estimate the flux of PAHs from pervious areas, soil erosion process has to be clearly understood, and both organic carbon content and composition of SOM should be factored into the calculation.
    Environmental Pollution 08/2012; 171:85-92. · 3.73 Impact Factor
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    ABSTRACT: Biomass pellets are emerging as a cleaner alternative to traditional biomass fuels. The potential benefits of using biomass pellets include improving energy utilization efficiency and reducing emissions of air pollutants. To assess the environmental, climate, and health significance of replacing traditional fuels with biomass pellets, it is critical to measure the emission factors (EFs) of various pollutants from pellet burning. However, only a few field measurements have been conducted on the emissions of carbon monoxide (CO), particulate matter (PM), and polycyclic aromatic hydrocarbons (PAHs) from the combustion of pellets. In this study, pine wood and corn straw pellets were burned in a pellet burner (2.6 kW), and the EFs of CO, organic carbon, elemental carbon, PM, and PAHs (EF(CO), EF(OC), EF(EC), EF(PM), and EF(PAH)) were determined. The average EF(CO), EF(OC), EF(EC), and EF(PM) were 1520 ± 1170, 8.68 ± 11.4, 11.2 ± 8.7, and 188 ± 87 mg/MJ for corn straw pellets and 266 ± 137, 5.74 ± 7.17, 2.02 ± 1.57, and 71.0 ± 54.0 mg/MJ for pine wood pellets, respectively. Total carbonaceous carbon constituted 8 to 14% of the PM mass emitted. The measured values of EF(PAH) for the two pellets were 1.02 ± 0.64 and 0.506 ± 0.360 mg/MJ, respectively. The secondary side air supply in the pellet burner did not change the EFs of most pollutants significantly (p > 0.05). The only exceptions were EF(OC) and EF(PM) for pine wood pellets because of reduced combustion temperatures with the increased air supply. In comparison with EFs for the raw pine wood and corn straw, EF(CO), EF(OC), EF(EC), and EF(PM) for pellets were significantly lower than those for raw fuels (p < 0.05). However, the differences in EF(PAH) were not significant (p > 0.05). Based on the measured EFs and thermal efficiencies, it was estimated that 95, 98, 98, 88, and 71% reductions in the total emissions of CO, OC, EC, PM, and PAHs could be achieved by replacing the raw biomass fuels combusted in traditional cooking stoves with pellets burned in modern pellet burners.
    Environmental Science & Technology 05/2012; 46(11):6409-16. · 5.48 Impact Factor
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    ABSTRACT: A marine food web in Bohai Bay, China, was selected to study methylmercury (MeHg) bioaccumulation, and an aquivalence-based mass balance model was established to explore the possibility of predicting the MeHg concentrations and quantifying MeHg bioaccumulation in the food web. Results showed that both total mercury (THg) and MeHg were biomagnified in the food web. The calculated MeHg concentrations in the selected species agreed well with the measured values, which shows the model could be a useful tool in MeHg concentration prediction in food web. Model outputs also showed that metabolism and growth dilution could be the dominant mechanisms for the reduction of MeHg levels in aquatic organisms. With the increase of trophic level, the contribution of food as a MeHg source for organism is increasing, and MeHg from prey was the dominant source.
    Environmental Pollution 04/2012; 166:89-97. · 3.73 Impact Factor
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    ABSTRACT: Due to the high costs and deployment difficulties associated with automated sampling technologies, few investigations have been published on atmospheric mercury in typical urban and rural areas in developing countries. In this study, a novel passive sampler for gaseous elemental mercury was developed and applied to characterize trends in atmospheric mercury levels across an urban–rural transect. The sampling transect originated in the city of Beijing and extended ∼150 km southward into a rural region. Field deployment was conducted during September–October (autumn) and November–December (winter) in 2010. The mercury concentrations in air obtained using the passive sampler were consistent with synchronous automated measurements performed during the field deployment. The results demonstrated that atmospheric mercury concentrations increased along the urban–rural gradient in the following order in both of the two periods: urban > suburban > rural (populated) > rural (farmland).
    Atmospheric Environment 02/2012; 47:26–32. · 3.11 Impact Factor