Soil as an archive of coal-fired power plant mercury deposition

Bibliometric analysis on mercury emissions from coal-fired power plants: a systematic review and future prospect

Coal-fired power plants (CFPPs) are one of the most significant sources of mercury (Hg) emissions certified by the Minamata Convention, which has attracted much attention in recent years. In this study, we used the Web of Science and CiteSpace to analyze the knowledge structure of this field from 2000 to 2022 and then reviewed it systematically. The field of Hg emissions from coal-fired power plants has developed steadily. The research hotspots can be divided into three categories: (1) emission characterization research focused on speciation changes and emission calculations; (2) emission control research focused on control technologies; (3) environmental impact research focused on environmental pollution and health risk. In conclusion, using an oxygen-rich atmosphere for combustion and installing high-efficiency air pollution control devices (APCDs) helped to reduce the formation of Hg0. The average Hg removal rates of APCDs and modified adsorbents after ultra-low emission retrofit were distributed in the range of 82-93% and 41-100%, respectively. The risk level of Hg in combustion by-products was highest in desulfurization sludge (RAC > 10%) followed by fly ash (10% < RAC < 30%) and desulfurization gypsum (1% < RAC < 10%). Additionally, we found that the implementation of pollution and carbon reduction policies in China had reduced Hg emissions from CFPPs by 45% from 2007 to 2015, increased the efficiency of Hg removal from APCDs to a maximum of 96%, and reduced global transport and health risk of atmospheric Hg. The results conjunctively achieved by CiteSpace, and the literature review will enhance understanding of CFPP Hg emission research and provide new perspectives for future research.

Centennial-scale source shift in potentially toxic metal(loid)s in Yangtze River

Estuarine sedimentation is an important historical record of potentially toxic metal (PTM) emissions from human activities that can be used to improve environmental management. However, the contribution of different human activities to PTM deposition has not been accurately estimated, and their coupled relationship with riverine organic matter is typically not considered. In this study, we reconstruct the century-scale PTM depositional history of sediment cores from the Yangtze Grand Delta. Eight potential metal sources (PMSs) were identified using positive matrix factorization, and the results of lagged correlation determined the PMSs associated with the riverine discharge of the Yangtze River. Riverine PTMs were predominantly composed of Cr (79.0%), Ni (77.3%), and Pb (64.1%) but were deprived in Cu (34.9%). Glomalin-related soil protein (GRSP), which is a typical terrestrial refractory carbon, has a strong affinity for Cu, and contributed to 2.82-22.6% Cu deposition. The change in the PMS is mainly related to power generation, whereas the GRSP-bound PTM is mainly related to road construction and transportation. We advocate for responsible management of human activities in river catchments, particularly on coal-based power generation and road transportation, to maintain ecological security and promote the overall achievement of the Sustainable Development Goals.

A remote sensing-based strategy for mapping potentially toxic elements of soils: Temporal-spatial-spectral covariates combined with random forest

The selection of predictor variables is a crucial issue in building a digital mapping model of potentially toxic elements (PTEs) in soil. Traditionally, the predictor variables for mapping models of soil PTEs have been chosen from sets of spatial parameters or spectral parameters derived from geographical environmental data. However, the enrichment of soil PTEs exhibits significant variations in both spatial and temporal dimensions, with the temporal dimension often being overlooked in the selection of predictor variables for digital mapping models. This limitation hampers the robustness and generalizability of the models. Therefore, multi-source geographical data were used in this study to determine three temporal indices for characterizing the enrichment process of soil PTEs in temporal dimensions, and additionally to construct the temporal-spatial-spectral (TSS) covariate combinations. The random forest (RF) algorithm was used to map soil PTEs at a regional scale. Results showed that: (1) When using spatial parameters or spectral parameters as predictor variables and measured Pb content as the dependent variable, the values of the model performance indicator RPIQ (ratio of performance to inter-quartile range) were 2.66 and 2.27, respectively. After incorporating the temporal parameters into the model input, values of RPIQ for the RF model reached 3.55 (using spatial-temporal covariates) and 3.21 (using spectral-temporal covariates), representing performance improvements of 33.46% and 41.41%, respectively. (2) The RF model constructed with the temporal-spatial-spectral covariates achieved satisfactory mapping accuracy (R2 = 0.85; RMSE = 0.80 mg kg-1; RPIQ = 4.09). (3) The soil Pb content in the western and northeastern regions was relatively high, while the remaining areas exhibited lower Pb levels, mainly due to industrial activities. (4) The mapping results of Pb obtained in this study were superior to other mapping methods, such as ordinary kriging, artificial neural networks, and multivariate linear regression methods. The soil PTE mapping technique employed in this study that combined TSS covariates with the RF provided an effective methodological approach for preventing soil pollution, controlling environmental risk, and improving soil management.

A State-of-the-Science Review on Metal Biomarkers

PURPOSE OF REVIEW

Biomarkers are commonly used in epidemiological studies to assess metals and metalloid exposure and estimate internal dose, as they integrate multiple sources and routes of exposure. Researchers are increasingly using multi-metal panels and innovative statistical methods to understand how exposure to real-world metal mixtures affects human health. Metals have both common and unique sources and routes of exposure, as well as biotransformation and elimination pathways. The development of multi-element analytical technology allows researchers to examine a broad spectrum of metals in their studies; however, their interpretation is complex as they can reflect different windows of exposure and several biomarkers have critical limitations. This review elaborates on more than 500 scientific publications to discuss major sources of exposure, biotransformation and elimination, and biomarkers of exposure and internal dose for 12 metals/metalloids, including 8 non-essential elements (arsenic, barium, cadmium, lead, mercury, nickel, tin, uranium) and 4 essential elements (manganese, molybdenum, selenium, and zinc) commonly used in multi-element analyses.

RECENT FINDINGS

We conclude that not all metal biomarkers are adequate measures of exposure and that understanding the metabolic biotransformation and elimination of metals is key to metal biomarker interpretation. For example, whole blood is a good biomarker of exposure to arsenic, cadmium, lead, mercury, and tin, but it is not a good indicator for barium, nickel, and uranium. For some essential metals, the interpretation of whole blood biomarkers is unclear. Urine is the most commonly used biomarker of exposure across metals but it should not be used to assess lead exposure. Essential metals such as zinc and manganese are tightly regulated by homeostatic processes; thus, elevated levels in urine may reflect body loss and metabolic processes rather than excess exposure. Total urinary arsenic may reflect exposure to both organic and inorganic arsenic, thus, arsenic speciation and adjustment for arsebonetaine are needed in populations with dietary seafood consumption. Hair and nails primarily reflect exposure to organic mercury, except in populations exposed to high levels of inorganic mercury such as in occupational and environmental settings. When selecting biomarkers, it is also critical to consider the exposure window of interest. Most populations are chronically exposed to metals in the low-to-moderate range, yet many biomarkers reflect recent exposures. Toenails are emerging biomarkers in this regard. They are reliable biomarkers of long-term exposure for arsenic, mercury, manganese, and selenium. However, more research is needed to understand the role of nails as a biomarker of exposure to other metals. Similarly, teeth are increasingly used to assess lifelong exposures to several essential and non-essential metals such as lead, including during the prenatal window. As metals epidemiology moves towards embracing a multi-metal/mixtures approach and expanding metal panels to include less commonly studied metals, it is important for researchers to have a strong knowledge base about the metal biomarkers included in their research. This review aims to aid metals researchers in their analysis planning, facilitate sound analytical decision-making, as well as appropriate understanding and interpretation of results.

Fate of selenium in a Se-enriched region of North China: Translocation, bioaccumulation, source, and health benefits

There are limited studies on the translocation and bioaccumulation of selenium (Se) in weak alkaline cultivated Se-enriched soil, and the sources and speciation of Se in wheat grains remain unclear. In this study, we measured the Se levels in soils, roots, stems, and wheat grains from Se-enriched cultivated land in Ci County, China, which has a high incidence of esophageal cancer. The Se levels in the roots were higher than those in the soils, indicating that wheat plants bioaccumulated high concentrations of Se from the soil (enrichment coefficient [EC] range from the soil to the root: 0.94-3.29). Redundancy analysis indicated that the bioaccumulated factor, translocation coefficient, and EC were mainly controlled by phosphorus, pH, and Fe₂O₃ (contribution rates: 37.5%, 19.5%, and 15.9%, respectively). Linear regression analysis revealed that the sources of Se in grains were mainly from the water-soluble fraction (R² = 0.55, at p < 0.05), the weakly acidic fraction (R² = 0.84, at p < 0.05), the reducible fraction (R² = 0.84, at p < 0.05), and the oxidizable fraction (R² = 0.70, at p < 0.05), as well as from atmospheric deposition (R² = 0.37, at p < 0.01). There is a significant correlation between the Se from atmospheric deposition and the oxidizable fraction (R² = 0.62, at p < 0.01) and the residual fraction (R² = 0.33, at p < 0.01). The contribution of Se input flux from atmospheric deposition was 5.50 g/hm² for one year. Furthermore, the average content of organic Se in wheat grains was 58.93%. The Se concentrations found in wheat grains were considered beneficial for human health based on a comparison with the Chinese Society of Nutrition standard and worldwide levels. The results of this study will increase the overall knowledge on the theme, which could help prevent and control the harmful effects of undesirable concentrations of Se on human health.

Differentiated emission control strategy based on comprehensive evaluation of multi-media pollution: Case of mercury emission control

In order to comprehensively evaluate the environmental impact of multi-media mercury pollution under differentiated emission control strategies in China, a literature review and case studies were carried out. Increased human exposure to methylmercury was assessed through the dietary intake of residents in areas surrounding a typical coal-fired power plant and a zinc (Zn) smelter, located either on acid soil with paddy growth in southern China, or on alkaline soil with wheat growth in northern China. Combined with knowledge on speciated mercury in flue gas and the fate of mercury in the wastewater or solid waste of the typical emitters applying different air pollution control devices, a simplified model was developed by estimating the incremental daily intake of methylmercury from both local and global pollution. Results indicated that air pollution control for coal-fired power plants and Zn smelters can greatly reduce health risks from mercury pollution, mainly through a reduction in global methylmercury exposure, but could unfortunately induce local methylmercury exposure by transferring more mercury from flue gas to wastewater or solid waste, then contaminating surrounding soil, and thus increasing dietary intake via crops. Therefore, tightening air emission control is conducive to reducing the comprehensive health risk, while the environmental equity between local and global pollution control should be fully considered. Rice in the south tends to have higher bioconcentration factors than wheat in the north, implying the great importance of strengthening local pollution control in the south, especially for Zn smelters with higher contribution to local pollution.

Shale weathering profiles show Hg sequestration along a New York-Tennessee transect

Shale-derived soils have higher clay, organic matter, and secondary Fe oxide content than other bedrock types, all of which can sequester Hg. However, shales also can be Hg-rich due to their marine formation. The objectives of this study were to determine the concentration and phase partitioning of Hg in seven upland weathering profiles from New York to Tennessee USA and use geochemical normalization techniques to estimate the extent of Hg inheritance from weathering of shale bedrock or sequestration of atmospheric Hg. Total Hg concentrations in unweathered shale ranged from 3 to 94 ng/g. Total Hg concentrations decreased with depth in the Ultisols and Alfisols, with total Hg concentrations ranging from 18 to 265 ng/g. Across all shale soils and rocks, the oxidizable fraction of Hg (15% H₂O₂ extraction) comprised a large portion of the total Hg at 68% ± 8%. This fraction was dominated by organic matter as confirmed with positive correlations between Hg and %LOI, but could also be impacted by Hg sulfides. Across all sites, the reducible fraction of Hg (citrate-bicarbonate-dithionite extraction) was only 10% ± 4% of the total Hg on average. Thus, secondary Fe oxides did not contain a significant portion of Hg, as commonly observed in tropical soils. Although colder sites had a higher organic matter and sequestered more Hg, τ values for Hg indexed to Ti suggest that atmospheric deposition, such as pollution sources in Ohio River Valley, drove the highest enrichment of Hg along the transect. These results demonstrate that shale-derived soils have a net accumulation and retention of atmospheric Hg, primarily through stabilization by organic matter.

Reconstructing atmospheric Hg levels near the oldest chemical factory in central Europe using a tree ring archive

The Chemical Factory in Marktredwitz (CFM) is known as the oldest chemical factory in Germany (1778-1985), and from the beginning of the 20^th century focused primarily on the production of mercury (Hg) compounds. Due to extensive pollution, together with employee health issues, the CFM was shut in 1985 by a government order and remediation works proceeded from 1986 to 1993. In this study, tree ring archives of European Larch (Larix decidua Mill.) were used to reconstruct changes of air Hg levels near the CFM. Mercury concentrations in larch boles decreased from 80.6 μg kg^-1 at a distance of 0.34 km-3.4 μg kg^-1 at a distance of 16 km. The temporal trend of atmospheric Hg emissions from the CFM reconstructed from the tree ring archives showed two main peaks. The first was in the 1920s, with a maximum tree ring Hg concentration 249.1 ± 43.9 μg kg^-1 coinciding with when the factory had a worldwide monopoly on the production of Hg-based seed dressing fungicide. The second peak in the 1970s, with a maximum tree ring Hg concentration of 116.4 ± 6.3 μg kg^-1, was associated with a peak in the general usage and production of Hg chemicals and goods. We used the tree ring record to reconstruct past atmospheric Hg levels using a simple model of Hg distribution between the larch tree rings and atmosphere. The precision of the tree ring model was checked against the results of air Hg measurements during the CFM remediation 30 years ago. According to the tree ring archives, the highest air Hg concentrations in the 1920s in Marktredwitz were over 70 ng m^-3. Current air Hg levels of 1.18 ng m^-3, assessed in the city of Marktredwitz, indicate the lowest air Hg in the past 150 years, underscoring the effective remediation of the CFM premises 30 years ago.

Relating mercury occurrence in soil gases at establishments hosting children to historical mercury-using activities in Paris, France

Volatile pollutants from former industrial sites can degrade the buildings' indoor air quality that were built after the industrial activities. Since 2010, environmental assessments have been conducted in French establishments hosting sensitive populations identified as being on or near potentially contaminated former industrial sites. These projects are based on historical studies traditionally carried out as part of managing contaminated sites, to determine which substances should be analyzed. They pinpoint former activities likely to have stored or used pollutants. We show that the historical information collected is not effective in targeting sites with increased probability of mercury being present in soil gases. Environmental history has demonstrated the existence of large-scale artisanal contamination, both prior to and concomitant with the industrial era. Classic historical studies would not take into account artisanal activities, which are less documented than industrial activities. We carried out additional research for three schools located in three different Parisian districts. Although information on activities which could have emitted mercury was relatively imprecise (in terms of location, type and duration of activities) and uncertainties exist about the completeness of the archival documents available, our investigations identified several mercury-using activities that had not been identified during the classic historical study. However, we have shown that the number of activities identified does not provide information on how mercury has affected soil gas. Consequently, although a more extensive historical research improves knowledge about the presence of potential mercury-using activities, our study shows that a systematic analysis of mercury as part of the assessment of establishments hosting sensitive populations remains relevant. This approach should be applied to other cities around the world.

Assessing Vegetation Decline Due to Pollution from Solid Waste Management by a Multitemporal Remote Sensing Approach

Nowadays, the huge production of Municipal Solid Waste (MSW) is one of the most strongly felt environmental issues. Consequently, the European Union (EU) delivers laws and regulations for better waste management, identifying the essential requirements for waste disposal operations and the characteristics that make waste hazardous to human health and the environment. In Italy, environmental regulations define, among other things, the characteristics of sites to be classified as “potentially contaminated”. From this perspective, the Basilicata region is currently one of the Italian regions with the highest number of potentially polluted sites in proportion to the number of inhabitants. This research aimed to identify the possible effects of potentially toxic element (PTE) pollution due to waste disposal activities in three “potentially contaminated” sites in southern Italy. The area was affected by a release of inorganic pollutants with values over the thresholds ruled by national/European legislation. Potential physiological efficiency variations of vegetation were analyzed through the multitemporal processing of satellite images. Landsat 5 Thematic Mapper (TM) and Landsat 8 Operational Land Imager (OLI) images were used to calculate the trend in the Normalized Difference Vegetation Index (NDVI) over the years. The multitemporal trends were analyzed using the median of the non-parametric Theil–Sen estimator. Finally, the Mann–Kendall test was applied to evaluate trend significance featuring areas according to the contamination effects on investigated vegetation. The applied procedure led to the exclusion of significant effects on vegetation due to PTEs. Thus, waste disposal activities during previous years do not seem to have significantly affected vegetation around targeted sites.

Bayesian G-Computation for Estimating Impacts of Interventions on Exposure Mixtures: Demonstration With Metals From Coal-Fired Power Plants and Birth Weight

The importance of studying the health impacts of exposure mixtures is increasingly being recognized, but such research presents many methodological and interpretation difficulties. We used Bayesian g-computation to estimate effects of a simulated public health action on exposure mixtures and birth weights in Milwaukee, Wisconsin, in 2011-2013. We linked data from birth records with census-tract-level air toxics data from the Environmental Protection Agency's National Air Toxics Assessment model. We estimated the difference between observed and expected birth weights that theoretically would have followed a hypothetical intervention to reduce exposure to 6 airborne metals by decommissioning 3 coal-fired power plants in Milwaukee County prior to 2010. Using Bayesian g-computation, we estimated a 68-g (95% credible interval: 25, 135) increase in birth weight following this hypothetical intervention. This example demonstrates the utility of our approach for using observational data to evaluate and contrast possible public health actions. Additionally, Bayesian g-computation offers a flexible strategy for estimating the effects of highly correlated exposures, addressing statistical issues such as variance inflation, and addressing conceptual issues such as the lack of interpretability of independent effects.

Recycling of mullite from high-alumina coal fly ash by a mechanochemical activation method: Effect of particle size and mechanism research

High-alumina coal fly ash (HAFA) is a special solid waste since its alumina content can reach 40-50 wt%, which is seen as a potential resource for mullite material production. However, obtaining an ideal mullite material from HAFA is difficult because of its low Al₂O₃/SiO₂ mass ratio. In this work, the microstructure characteristics of HAFA were systematically analyzed by combining multiple characterization techniques. It was found that HAFA had a core-shell structure with a mullite/corundum crystal core and a silica-rich amorphous phase shell. The novel mechanochemical activation-desilication process was used to remove amorphous phase from HAFA and elevate the Al₂O₃/SiO₂ mass ratio. In particular, the effect of particle size after mechanical treatment and mechanism of the desilication process were extensively investigated. On decreasing the particle size, a high leaching rate of alumina was achieved during mechanochemical activation, thus generating a hydroxysodalite coating layer as desilication was suppressed, and the amorphous phase was effectively removed. The mineralogical phase of the desilicated HAFA is mainly mullite and corundum, and the Al₂O₃/SiO₂ mass ratio was elevated from 1.29 to 3.02. Mullite refractory obtained from the desilicated HAFA exhibited excellent physical properties. This study provides insights into further high-valued utilization of HAFA.

Trends in soil mercury stock associated with pollution sources on a Mediterranean island (Majorca, Spain)

Hg is a global concern given its adverse effects on human health, food security and the environment, and it requiring actions to identify major local Hg sources and to evaluate pollution. Our study provides the first assessment of Hg stock trends on the entire Majorca surface, identifying major Hg sources by studying the spatiotemporal soil Hg variation at two successive times (2006 and 2016-17). The Hg soil concentration ranged from 14 to 258 μg kg^-1 (mean 52 μg kg^-1). Higher concentrations (over 100 μg kg^-1) were found in two areas: (i) close to the Alcudia coal-fired power plant; (ii) in the city of La Palma. During the 11-year, the total Hg stock in Majorcan soil increased from 432.96 tons to 493.18 tones (14% increase). Based on a block kriging analysis, soil Hg enrichment due to power plant emissions was clearly detectable on a local scale (i.e. a shorter distance than 18 km from the power plant). Nonetheless, a significant island-wide Hg increase due to diffuse pollution was reported. This result could be extrapolated to other popular tourist destinations in the Mediterranean islands where tourism has increased in recent decades In short, more than 60 tons of Hg have accumulated on Majorca island in 11 years.

Evaluation and Integration of Geochemical Indicators for Detecting Trace Levels of Coal Fly Ash in Soils

Coal combustion residuals (CCRs), in particular, coal fly ash, are one of the major industrial solid wastes in the U.S., and due to their high concentrations of toxic elements, they could pose environmental and human health risks. Yet detecting coal fly ash in the environment is challenging given its small particle size. Here, we explore the utility and sensitivity of using geochemical indicators (trace elements, Ra nuclides, and Pb stable isotopes), combined with physical observation by optical point counting, for detecting the presence of trace levels of coal fly ash particles in surface soils near two coal-fired power plants in North Carolina and Tennessee. Through experimental work, mixing models, and field data, we show that trace elements can serve as a first-order detection tool for fly ash presence in surface soils; however, the accuracy and sensitivity of detection is limited for cases with low fly ash proportion (i.e., <10%) in the soil, which requires the integration of more robust Ra and Pb isotopic tracers. This study revealed the presence of fly ash particles in surface soils from both the recreational and residential areas, which suggests the fugitive emission of fly ash from the nearby coal-fired power plants.

Spatial distribution, risk assessment, and source identification of the potentially toxic elements in the water-level fluctuation zone of the Dahuofang Reservoir, Northeast China

Potentially toxic elements (PTEs), including cadmium (Cd), copper (Cu), lead (Pb), zinc (Zn), mercury (Hg), and chromium (Cr), in the water-level fluctuation zone (WLFZ) of the Dahuofang Reservoir were surveyed in regard to their concentrations, spatial distributions, risks, and possible sources. Sediment samples were collected at 12 typical sites located in the WLFZ of the Dahuofang Reservoir. The median values of Cd, Cu, Pb, Zn, and Cr all exceeded the soil background values in Liaoning Province. Based on the spatial distributions of these PTEs, the highest enrichment occurred at the R12 site. Cadmium, Cu, and Pb attained the highest contents at R12. The mean geoaccumulation index (I_geo) value of Cd indicated heavy contamination, and that of Pb indicated moderate to heavy contamination, while those of Cu and Zn indicated none to moderate contamination. The negative I_geo values of Cr and Hg indicated the uncontaminated level. According to the potential ecological risk index (RI), Pb posed a moderate risk, while Cd posed a high risk, Zn, Cr, Hg, and Cu posed a low risk. The R12 site exhibited the highest ecological risk. By applying multivariate statistical analysis, two principal components were extracted representing 62.992% of the total variance, and the results showed that the accumulation of Cr, Pb, and Hg might be ascribed to a nearby coal-fired electric power plant. Cadmium, Cu, and Zn were enriched owing to mineral sources, agricultural contamination, and coal combustion.

Spatial methods to analyze the relationship between Spanish soil properties and cadmium content

In this study, concentrations of cadmium using 3778 samples encompassing the total size of Spain (about 505 km²) were investgated. Two novel spatial methods namely Moran eigenvector spatially varying coefficient (MESVC) and spatially filtered unconditional quantile regression (SF-UQR) were employed with the aim of avoiding the problem of local collinearity which is prevalent in regression models. Additionally, the spatially varying coefficients methods were applied to assess the influence of soil properties together with soil texture on the spatial variations of cadmium. It was indicated that the overall level of cadmium is low compared to the concentrations found around the world. In particular, the values of Cd varied between 0.01 and 2.00 mgkg^-1, with the median of 0.23 mgkg^-1. The residual standard error and adjusted R² produced by MESVC were 0.16 and 0.69, respectively which are better than 0.21 and 0.39 yielded by the SF-UQR model. Both of these models outperformed compared to the geographically weighted regression (GWR) and the performance of MESVC was also better than the traditional method of kriging. For instance, in terms of willmott index (d) and root mean squared relative error (RMSRE), the MESVC had superior performance with values equal to 0.612 and 0.275 compared to 0.399 and 0.379 obtained for the ordinary kriging. The MESVC and GWR demonstrated that CaCO₃, sand, silt and clay had a negligible influence on spatial variations of cadmium whereas, EC had the largest contribution followed by SOM and pH.

Source apportionment and spatial distribution of potentially toxic elements in soils: A new exploration on receptor and geostatistical models

Potentially toxic element (PTE) pollution is considered as the main soil environmental problem in the world. Source apportionment and spatial pattern of soil PTEs are essential for soil management. US-EPA positive matrix factorization (EPAPMF) and sequential Gaussian simulation (SGS) are general modeling tools for source apportionment and spatial distribution, respectively. Factor analysis with nonnegative constraints (FA-NNC) and stochastic partial derivative equations (SPDE) provided potential tools for this issue. We compared the performance of FA-NNC with PMF and the performance of SPDE with SGS, based on a dataset containing 9 PTEs in 285 topsoil samples. Three factors were determined by the two receptor models, and the source contributions were similar, suggesting that FA-NNC can validly identify quantitative sources of soil PTEs. The average source contributions were calculated based on the PMF and FA-NNC. Natural sources dominated the contents of As, Co, Cr, Cu, Ni, and Zn and affected 56.0%, 38.7%, and 84.8% of the Cd, Hg, and Pb concentrations, respectively. A total of 59.8% of Hg and 12.0% of Pb were associated with atmospheric deposition from coal combustion, industrial and traffic emissions, respectively. Agricultural and industrial activities contributed 37.2% of Cd concentration. SPDE proved to be an effective geostatistical technique to simulate the spatial patterns of soil PTEs with higher prediction accuracy than SGS. Co, Cr, Cu, and Ni had similar spatial patterns with hotspots randomly distributed across the study area. The common hotspots of As, Cd, Hg, Pb, and Zn in central parts inherited their high geochemical background in mudstone, while intensive human inputs in these areas also contributed to the accumulation of Cd, Hg, and Pb.

Soil and ambient air mercury as an indicator of coal-fired power plant emissions: a case study in North China

Coal-fired power plants (CFPPs) are an important anthropogenic mercury (Hg) source in China, and it is crucial to understand the environmental impacts of this detrimental element emitted from this source. In the present study, field experiments were conducted for measuring Hg in ambient atmosphere and upland agricultural soils within a radius of 10 km surrounding a large scale coal-fired power plant (1550 MW) in Tangshan, Hebei province. Short-term (20 min) average of gaseous elemental mercury (GEM or Hg0) in ambient air varying from 1.5 to 9.0 ng/m3 and total Hg (THg) in surface agricultural soil (0-20 cm) varying from 9.2 to 43.5 μg/kg at different sites were observed. THg in two soil cores decreased with depth, with concentrations being 2-2.5 times higher in the surface layer than that in the deep layer (50-60 cm), indicating the possibility of the atmospheric input of Hg. Based on the information of the total atmospheric Hg emission since this CFPP's operation in 1970s and the increased THg in nearby soils, it was estimated that about 3.9% discharged Hg has accumulated in the nearby agricultural soils. The low retention rate of the total emitted Hg by soils is a result of high proportion of Hg0 (79.5%) in stack gas emission and potential loss of Hg from soil surface reemission. The positive shifting (~ 0.5‰) of Hg isotopic signature (δ202Hg) from deep soil to surface soil reflected Hg deposition from nearby CFPP emissions that are featured with much heavier Hg isotopic signatures inherited from feed coal (δ202Hg: -0.50‰) and different combustion products (δ202Hg: -0.95 to 3.71‰) compared with that in deep soil layer (δ202Hg: ca -1.50‰). Overall, this study demonstrated that this CFPP has a slight but distinguishable effect on the elevation of ambient GEM and agricultural soil THg in the local environment.

Spatial assessment models to evaluate human health risk associated to soil potentially toxic elements

Quantifying source apportionment of potentially toxic elements (PTEs) in soils and associated human health risk (HHR) is essential for soil environment regulation and pollution risk mitigation. For this purpose, an integrated method was proposed, and applied to a dataset consisting of As, Cd, Cr, Cu, Hg, Ni, Pb, Se, and Zn in 273 soil surface samples. Positive matrix factorization (PMF) was used to quantitatively examine sources contributions of PTEs in soils; and the HHR arising from the identified source was determined by combining source profiles and health risk assessment; at last, sequential Gaussian simulation (SGS) was used to identify the areas with high HHR. Four sources were identified by PMF. Natural and agricultural sources affected all 9 PTEs contents with contributions ranging from 19.2% to 62.9%. 41.9% of Cd, 40.8% of Pb, 58.6% of Se, and 29.8% of Zn were controlled by industrial and traffic emissions. Metals smelting and mining explained 35.5%, 30.5%, and 24.9% of Cr, Cu, and Ni variations, respectively. Hg was dominated by atmospheric deposition from coal combustion and coking (58.7%). The mean values of the total non-carcinogenic risks of PTEs were 1.55 × 10^-1 and 9.40 × 10^-1 for adults and children, and the total carcinogenic risk of PTEs had an average value of 8.86 × 10^-5. Based on source-oriented HHR calculation, natural and agricultural sources were the most important factor influencing HHR, explaining 51.0% and 49.1% of non-carcinogenic risks for children and adults, and 44.2% of carcinogenic risk. SGS indicated that 1.1% of the total area was identified as hazardous areas with non-carcinogens risk for children.

Health risk assessment of trace elements exposure through the soil-plant (maize)-human contamination pathway near a petrochemical industry complex, Northeast China

The trace elements contamination of agricultural soils near petrochemical industry complexes is a concern due to the risk of accumulating in food systems and subsequently affecting human health. We measured representative trace elements (Cu, Ni, Cr, Pb, Zn, Pb, Hg and As) through the soil-plant (maize)-human contamination pathway near a petrochemical industry complexes in an agricultural region from September 20 to 28, 2016. We found that the soil was mildly to moderately polluted by multiple trace elements, which was also confirmed by the contamination factor and enrichment factor values. Cd (enrichment factor = 2.28), Cu (2.75), Zn (1.85) and Pb (1.70) should be given more attention and prioritized over the other trace elements due to their higher potential risks. Furthermore, the trace elements contamination in maize grains was lower than the corresponding limits. The sequence of the transfer coefficient values was Zn > Cd > Cu > Hg > Ni > As > Cr > Pb. Maize grain safety was threatened mainly by Zn, Cd and Cu. There was no risk to humans through soil ingestion, while a potential health risk from maize grain consumption existed. Children were more sensitive than adults to the non-carcinogenic risks of maize grain consumption. Trace element As was found to be the priority metal for risk control. For carcinogenic risk, adults were more sensitive than children; As, Cr and Cd were the priority metals for risk control, with CR_maize values exceeding the risk threshold (1 × 10^-4). Overall, strict, intensive monitoring, especially of Cr and Cd, and soil protection measures are needed to prevent any furthertrace elements contamination and to ensure food safety. This study also provides a reference for similar studies worldwide.

Effect of soil mercury pollution on ginger (Zingiber officinale Roscoe): Growth, product quality, health risks and silicon mitigation

The mercury residue in soil not only poisons plants, but also bioaccumulates and biomagnifies through the food chain, causing a significant risk to human health. As an essential condiment on the table, the food safety of ginger should be focused on. Using soil culture experiments, this study aimed to identify the response of ginger growth to mercury pollution, assess the transmission and residue of mercury in different product organs and explore the mitigation mechanism of silicon on mercury toxicity. Effects of soil mercury pollution on ginger growth showed hormesis and time effect. Long-term mercury pollution led to growth inhibition and quality degradation of ginger, eventually reducing its yield by 25.96% (mercury = 9 mg kg-1). Contents of mercury and silicon in different organs both were the highest in root, followed by rhizome, less in stem and leaf, especially the mercury residue in rhizome manifested as Mother-ginger > Son-ginger > Grandson-ginger. At 6 mg kg-1 soil mercury level, the mercury residue of Mother-ginger exceeds the edible pollutant limit standard (China) by 10.7 times, which makes no obvious risk after being consumed by adults, but poses a potential health threat to children. Notably, it is safer to consume the newly sprouted and inflated tender ginger. Application of silicon fertilizer could alleviate mercury toxicity, mainly by promoting ginger root growth and leaf pigment synthesis, stimulating water-gas exchange system, fluorescence system and antioxidant system to make an anti-stress response. 2 mg kg-1 silicon fertilizer had the most significant mitigation effect on mercury stress, which increased the yield of ginger by 24.85% and reduced the mercury residue of ginger block by 44.44%-60.17%.

Detrimental effects of SO2 on gaseous mercury(II) adsorption and retention by CaO-based sorbent traps: Competition and heterogeneous reduction

Reliable gaseous Hg(II) measurement is crucial to mercury emissions control from coal-fired flue gas, but Hg(II) sampling under SO₂ condition could probably increase the uncertainty of sorbent traps. CaO-AcS synthesized from calcium acetate and porous support were previously demonstrated to be effective for Hg(II) trapping under SO₂-free condition. This work further evaluated SO₂ influence on its Hg(II) retention ability via integrating experimental and DFT computational studies. Increased breakthrough rate of HgCl₂ was found in a two-section CaO-AcS trap under SO₂ conditions. Significant basicity and porosity loss of CaO-AcS were attributed to the formation of agglomerate CaSO₃. Hg⁰ release from CaO-AcS samples suggested potential reactions between Hg(II) and SO₂. The detected HgO and Hg₂SO₄ species by Hg-TPD in CaO-AcS further confirmed this speculation. Moreover, both competition and reduction effects of SO₂ on surface-bound Hg(II) species were substantiated by DFT calculations. SO₂ showed a stronger interaction with CaO than HgCl₂ because SO₂ has a lower LUMO level and can accept electrons easier. Reaction pathways indicated Hg(II) was partially reduced to Hg₂SO₄ under SO₂-deficient condition, or directly reduced to Hg⁰ under SO₂-rich condition. This work fully proposed the SO₂ influence mechanisms and improvement countermeasures for practical gaseous Hg(II) sampling.

Mercury accumulation in soil from atmospheric deposition in temperate steppe of Inner Mongolia, China

Mercury (Hg) is a toxic and persistent pollutant and has long-term impacts on ecological systems and human health. Coal-fired power plants (CFPPs) are the main source of anthropogenic Hg emission, and the emitted atmospheric Hg is deposited to the surrounding environments which causes soil pollution. To assess the effects of atmospheric Hg from CFPPs in China on the temperate steppe, Hg contents in the topsoil and subsoil were analyzed for samples collected from 80 sites in central Inner Mongolia during 2012-2015. The average content of Hg in topsoil and subsoil were 14.9 ± 10.4 μg kg^-1 and 8.9 ± 5.8 μg kg^-1, respectively. The principal components analysis (PCA) indicated that the soil organic matter content and atmospheric deposition were the main factors determining soil Hg content in Inner Mongolia. We used the power plant impact factor (PPIF) to evaluate the impacts of the surrounding CFPPs. The PPIF results showed the most positive correlation with Hg content in topsoil at more than 400 km distances, indicating that the contribution of the long-range transport of Hg emitted from CFPPs is regional in scale. Considering the potential of Hg accumulation in soil, long-term and regional measurements of soil Hg and stricter emission-limit standards for power plants should be implemented to control soil Hg pollution in China.

Mercury and selenium concentrations in fishes of the Upper Colorado River Basin, southwestern United States: A retrospective assessment

Mercury (Hg) and selenium (Se) are contaminants of concern for fish in the Upper Colorado River Basin (UCRB). We explored Hg and Se in fish tissues (2,324 individuals) collected over 50 years (1962-2011) from the UCRB. Samples include native and non-native fish collected from lotic waterbodies spanning 7 major tributaries to the Colorado River. There was little variation of total mercury (THg) in fish assemblages basin-wide and only 13% (272/1959) of individual fish samples exceeded the fish health benchmark (0.27 μg THg/g ww). Most THg exceedances were observed in the White-Yampa tributary whereas the San Juan had the lowest mean THg concentration. Risks associated with THg are species specific with exceedances dominated by Colorado Pikeminnow (mean = 0.38 and standard error ± 0.08 μg THg/g ww) and Roundtail Chub (0.24 ± 0.06 μg THg/g ww). For Se, 48% (827/1720) of all individuals exceeded the fish health benchmark (5.1 μg Se/g dw). The Gunnison river had the most individual exceedances of the Se benchmark (74%) whereas the Dirty Devil had the fewest. We identified that species of management concern accumulate THg and Se to levels above risk thresholds and that fishes of the White-Yampa (THg) and Gunnison (Se) rivers are at the greatest risk in the UCRB.

Mercury and methylmercury levels in soils associated with coal-fired power plants in central-northern Chile

Mercury pollution is a worldwide problem, and is associated with a number of natural and anthropogenic processes. The present work, conducted in Chile, a country that has traditionally depended heavily on fossil fuels for power generation, examines total mercury (THg) and monomethylmercury (MMHg) concentrations in soils across different sites exposed to coal fired power plant emissions. Samples from four selected (Renca, Laguna Verde, Las Ventanas, Huasco) and 1 control (Quintay) sites were analyzed using cold vapour and fluorescence spectroscopy (CV-AFS) for THg determination and chromatographic separation with atomic fluorescence detection (DI-GC-AFS) was followed for speciation analysis. From the sites analyzed, Renca and Las Ventanas showed high concentrations of total mercury, exhibiting ranges between 135 - 568 and 94-464 ng g^-1 respectively, while Laguna Verde and Huasco exhibited lower values ranged 5-27 and 9-44 ng g^-1 respectively. Conversely, analysis of MMHg concentrations showed that only Renca site possessed high values, ranging between 0.1 and 3.0 ng g^-1, resulting in this site being considered contaminated. Conversely, other sites showed minimal values comparable to the control site (0.024 ± 0.003 ng g^-1) in terms of MMHg concentrations. An analysis of the differences between MMHg and THg concentrations in contaminated sites, suggests an overall absence of methylation in soils of Las Ventanas, probably related to the very high levels of soil heavy metals, especially copper. Moreover, the influence of the composition and physicochemical properties of the different soils on the mobility of the species was assessed. Results obtained (as Log Kd) were 3.5 and 4.1 for Renca and Las Ventanas respectively, suggesting low mobility of mercury species in the environment for both sites. Finally, the data obtained allowed us to establish a first approximation of the differences in concentration and mobility of total and MMHg associated with coal fired power plants emission in central-northern Chile, an area previously understudied in a country heavily dependent on fossil-fuels.

Evidence of mercury sequestration by carbon nanotubes and nanominerals present in agricultural soils from a coal fired power plant exhaust

Mercury (Hg) in agricultural soils could have negative effects on the environment and the human health. The exposure to high level of Hg through different absorption pathways, such as ingestion and diet through soil-plant system could permanently damage developing foetus of animals and humans. With the aim to assess the potential environmental and health risk and to study the behaviour and fate of Hg from agricultural soils to the environment, 47 soil samples were collected around a thermoelectric power plant in the Santa Catarina (Brazil). The Hg concentration measured by inductively coupled plasma mass spectrometry (ICP-MS) ranged from 0.16 to 0.56 mg kg^-1. The distribution obtained by kriging interpolation allowed the identification of the main pollution sources. To see the morphology and composition of soil samples, field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM) were used combined with energy dispersive X-ray spectroscopy (EDS), showing that the carbon nanotubes and magnetite as nanomineral contributed to Hg retention. The mentioned molecular characterization, and the low Contamination Factors (CF) values obtained, suggested that there is low risk to the food security of the agro-ecosystems area near to the CFPP in the terms of Hg inputs and contamination.

Sources, toxicity, and remediation of mercury: an essence review

Mercury (Hg) is a pollutant that poses a global threat, and it was listed as one of the ten leading 'chemicals of concern' by the World Health Organization in 2017. The review aims to summarize the sources of Hg, its combined effects on the ecosystem, and its remediation in the environment. The flow of Hg from coal to fly ash (FA), soil, and plants has become a serious concern. Hg chemically binds to sulphur-containing components in coal during coal formation. Coal combustion in thermal power plants is the major anthropogenic source of Hg in the environment. Hg is taken up by plant roots from contaminated soil and transferred to the stem and aerial parts. Through bioaccumulation in the plant system, Hg moves into the food chain, resulting in potential health and ecological risks. The world average Hg concentrations reported in coal and FA are 0.01-1 and 0.62 mg/kg, respectively. The mass of Hg accumulated globally in the soil is estimated to be 250-1000 Gg. Several techniques have been applied to remove or minimize elevated levels of Hg from FA, soil, and water (soil washing, selective catalytic reduction, wet flue gas desulphurization, stabilization, adsorption, thermal treatment, electro-remediation, and phytoremediation). Adsorbents such as activated carbon and carbon nanotubes have been used for Hg removal. The application of phytoremediation techniques has been proven as a promising approach in the removal of Hg from contaminated soil. Plant species such as Brassica juncea are potential candidates for Hg removal from soil.

Evaluation of Mercury Transformation and Benthic Organisms Uptake in a Creek Sediment of Pearl River Estuary, China

A large fraction of mercury contaminant in the environment is from industrial production, and it potentially impairs human health once entering the food chain. Millions of people reside in the Pearl River Delta region, and water quality in the estuary directly affects their drinking water safety. Considering the highly intense anthropogenic activities and industrial productions, we attempted to measure the sediment mercury concentration in the Pearl River estuary. In this work, samples of a creek sediment within this region were collected and mercury concentrations were quantified. Total mercury, simultaneously extracted mercury, methylmercury, and bio-accumulated mercury were individually assayed. Results indicated that total mercury concentrations of investigated sites ranged from 1.073 to 4.450 µg/g dry sediment. The mercury in the sediment also transformed into more toxic methylmercury, which then adversely affected benthos biodiversity. Correlation analysis revealed that, mercury was accumulated into benthic microorganisms, mainly through the uptake of methylmercury. High concentrations of acid-volatile sulfide in the sediment indicated the presence of active sulfate-reducing bacteria, which could also catalytically transform inorganic mercury into methylmercury. Correlation analysis further showed that sulfate-reducing bacteria activity accounted for methylmercury formation.

Feasibility study on the use of thiosulfate to remediate mercury-contaminated soil

The feasibility of using sodium thiosulfate to remediate the mercury-contaminated soil around a local chemical plant in northeastern China has been investigated. Effects of solid-to-reagent ratio and temperature on mercury extraction from soil samples with thiosulfate solutions were examined. BCR (European Community Bureau of Reference) analysis indicated that more than 90% of weak acid soluble and reducible mercury in the soil sample could be extracted by thiosulfate solution. Mercury extraction kinetics can be described by the two-step first-order reaction model in which the readily extractable fraction and the less extractable fraction of mercury were associated with their own rate constants. Mercury extraction with thiosulfate solutions could be slightly promoted when the contaminated soil was pre-oxidized with hydrogen peroxide. The results suggest that thiosulfate is a potentially effective complexing lixiviant in mercury-contaminated soil remediation.

Multivariate receptor models and robust geostatistics to estimate source apportionment of heavy metals in soils

Absolute principal component score/multiple linear regression (APCS/MLR) and positive matrix factorization (PMF) were applied to a dataset consisting of 10 heavy metals in 300 surface soils samples. Robust geostatistics were used to delineate and compare the factors derived from these two receptor models. Both APCS/MLR and PMF afforded three similar source factors with comparable contributions, but APCS/MLR had some negative and unidentified contributions; thus, PMF, with its optimal non-negativity results, was adopted for source apportionment. Experimental variograms for each factor from two receptor models were built using classical Matheron's and three robust estimators. The best association of experimental variograms fitted to theoretical models differed between the corresponding APCS and PMF-factors. However, kriged interpolation indicated that the corresponding APCS and PMF-factor showed similar spatial variability. Based on PMF and robust geostatistics, three sources of 10 heavy metals in Guangrao were determined. As, Co, Cr, Cu, Mn, Ni, Zn, and partially Hg, Pb, Cd originated from natural source. The factor grouping these heavy metals showed consistent distribution with parent material map. 43.1% of Hg and 13.2% of Pb were related to atmosphere deposition of human inputs, with high values of their association patterns being located around urban areas. 29.6% concentration of Cd was associated with agricultural practice, and the hotspot coincided with the spatial distribution of vegetable-producing soils. Overall, natural source, atmosphere deposition of human emissions, and agricultural practices, explained 81.1%, 7.3%, and 11.6% of the total of 10 heavy metals concentrations, respectively. Receptor models coupled with robust geostatistics could successfully estimate the source apportionment of heavy metals in soils.

An integrated approach to identify quantitative sources and hazardous areas of heavy metals in soils

Identifying quantitative sources and hazardous areas of heavy metals is a crucial issue for soil management. For this purpose, an integrated approach composed of finite mixture distribution modeling (FMDM), positive matrix factorization (PMF) and sequential Gaussian co-simulation (SGCS) was proposed. FMDM was used to establish background standards and pollution thresholds. PMF supported by FMDM background standards was applied to estimate the source apportionment. Hazardous areas of single metals were delineated using SGCS with FMDM pollution thresholds and uncertainty analysis, and overall hazardous areas were defined by the presence of multiple metals. This integrated approach was applied to a dataset of seven metals as a case study. FMDM indicated that the distributions of Cr, Cu, Ni, and Zn were fitted to two-dimensional mixture distributions, representing a background distribution and a moderately polluted distribution. The distributions of Cd, Hg, and Pb were composed of a three-component lognormal mixture distribution, corresponding to the background, moderate, and high pollution distributions. Three sources were apportioned. Cr, Cu, Ni, and Zn were dominated by parent materials. Parent materials contributed 52.6%, 45.8%, and 81.9% of Cd, Hg, and Pb concentrations, respectively. Human emissions from coal combustion, industrial work and traffic had significant influences on Hg, Cd, and Pb, with contributions of 49.8%, 26.9%, and 15.6%, respectively. Agricultural practices were exclusively associated with 20.5% of Cd. Overall, hazardous areas exceeding moderate pollution thresholds covered 17.4% of the total area, corresponding to urban areas and industrial sites, whereas overall hazardous areas above high pollution thresholds were limited to 0.01% of the total area.

Multi-scale analysis of heavy metals sources in soils of Jiangsu Coast, Eastern China

Since the development of Jiangsu Coast was proposed as a national strategy by the Chinese Government in 2009, Jiangsu Coast has been experiencing rapid and intensive development in industry and tidal flat reclamation, which has inevitably led to the accumulation of heavy metals in its soils. A total of 239 samples (0-20 cm) were collected from topsoils of Jiangsu Coast, and their concentrations of Cd, Cr, Cu, Hg, Ni, Pb, and Zn were determined. Factorial kriging was applied to examine the scale-dependent correlations between heavy metals and to generate the spatial components at multiple scales, and multivariate stepwise regression was used to explore the relationships between the spatial multi-scale components of heavy metals and environmental factors. Linear model of co-regionalization (LMC) fitting indicated that the multi-scale variation comprised a nugget effect, an exponential structure with a range of 15 km (local scale), and a spherical structure with a range of 135 km (regional scale). The spatial correlations of seven heavy metals depended on their spatial scales, and their correlations increased with the increasing scales. Spatial variations in Cr and Ni were associated with natural geochemical sources on both local and regional scales. Parent material influenced the basic spatial variations in Cd, Cu, Pb and Zn on both local and regional scales, but human activity also contributed to the spatial variations in these four metals. The human inputs of Cd, Cu, Pb, and Zn differed on these two scales. Hg was dominated by industrial emissions and agricultural practices on both scales.

Wood and bark of Pinus halepensis as archives of heavy metal pollution in the Mediterranean Region

Natural levels of heavy metals (HM) have increased during the industrial era to the point of posing a serious threat to the environment. The use of tree species to record contamination is a well-known practice. The objective of the study was to compare HM levels under different pollution conditions: a) soil pollution due to mining waste; b) atmospheric pollution due to coal-fired power plant emissions. We report significant HM enrichment in Pinus halepensis tissues. Near a burning power plant, Pb content in a tree wood was 2.5-fold higher that in natural areas (no pollution; NP). In mining areas, Cd content was 25-fold higher than NP. The hypothesis that HM contents in tree rings should register pollution is debatable. HM uptake by pines from soil, detoxification mechanisms and resuspended local soil dust is involved in HM contents in wood and bark.

Source identification and spatial distribution of metals in soils in a typical area of the lower Yellow River, eastern China

In this study, 234 soil samples were recently collected from Gaoqing County (a typical area of the lower Yellow River) to determine the contents of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn. Multivariate statistical analyses such as correlation analysis, principal components analysis, and one-way ANOVA were applied to identify the source of metals in the soil. Geostatistical methods were used to analyze the spatial structure and distribution of the metals. The results indicated that the mean contents of all metals exceeded the background value of the lower Yellow River, especially for As, Cu, and Hg (1.23, 1.20, and 1.29 times that of the BV, respectively), indicating that these metals were enriched in the study area to different degrees. The results derived from multivariate analysis suggested that As, Cd, Cr, Cu, Ni, Pb, and Zn were mainly controlled by the combination of human activities and soil parent material, and the human activities included industrial emissions, traffic emissions, and agricultural practices. In addition, Hg mainly originated from anthropogenic inputs, such as textile printing, plastics processing, and petrochemical engineering. The contents of metals in different types of land use and parent materials are clearly different. The mean content for eight elements in urban construction land was significantly higher than that of the other land use types; in addition to Hg, the mean content of the other elements was the highest in the lacustrine deposit. The elements of As, Cd, Cr, Cu, Ni, Pb, and Zn had similar hotspots in the urban area, indicating the significant human influence. In addition, these seven metals showed high values in the southeast lacustrine deposit area. The high-value areas of Hg were concentrated in the southwest and northeast study area, which were consistent with the spatial pattern of the industrial sites.

Atmospheric deposition of mercury and cadmium impacts on topsoil in a typical coal mine city, Lianyuan, China

Mercury (Hg) and cadmium (Cd) in the atmosphere from coal combustion emissions play an important role in soil pollution. Therefore, the purposes of this study were to quantitatively evaluate the atmospheric Hg and Cd deposition and to determine the influence of atmospheric deposition on Hg and Cd contents in surface soil in a typical coal mine city. Atmospheric deposition samples were collected from May 2015 to May 2016 at 17 sites located in industrial, agricultural and forest areas in the Lianyuan city. Atmospheric Hg and Cd deposition fluxes in the different land use types showed high variability. Curvilinear regression analysis suggested that the atmospheric Hg deposition fluxes were positively related with Hg contents in soils (R² = 0.86359, P < 0.001). In addition, atmospheric Cd deposition fluxes were also positively correlated with Cd contents in soils when the site LY02, LY04 and LY05 (all belong to agricultural land) were not included in the fitting (R² = 0.82458, P < 0.001). When they were included, there was no significant relationship between them (R² = 0.2039, P = 0.05). The accumulation of Hg and Cd concentration in topsoil due to the influence of atmospheric deposition will increase rapidly in the next 30 years, and the mean value of the increment will reach 2.6007 and 33.344 mg kg^-1. After 30 years, the Hg and Cd concentration will increase slowly. The present study advocates that much attention should be paid to the potential ecological hazards in soil resulting from the atmospheric Hg and Cd deposition.

Concentrations of polycyclic aromatic hydrocarbons and trace elements in Arctic soils: A case-study in Svalbard

A combined assessment on the levels and distribution profiles of polycyclic aromatic hydrocarbons (PAHs) and trace elements in soils from Pyramiden (Central Spitsbergen, Svalbard Archipelago) is here reported. As previously stated, long-range atmospheric transport, coal deposits and previous mining extractions, as well as the stack emissions of two operative power plants at this settlement are considered as potential sources of pollution. Eight top-layer soil samples were collected and analysed for the 16 US EPA priority PAHs and for 15 trace elements (As, Be, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sn, Tl, V and Zn) during late summer of 2014. The highest levels of PAHs and trace elements were found in sampling sites located near two power plants, and at downwind from these sites. The current PAH concentrations were even higher than typical threshold values. The determination of the pyrogenic molecular diagnostic ratios (MDRs) in most samples revealed that fossil fuel burning might be heavily contributing to the PAHs levels. Two different indices, the Pollution Load Index (PLI) and the Geoaccumulation Index (Igeo), were determined for assessing soil samples with respect to trace elements pollution. Samples collected close to the power plants were found to be slightly and moderately polluted with zinc (Zn) and mercury (Hg), respectively. The Spearman correlation showed significant correlations between the concentrations of 16 PAHs and some trace elements (Pb, V, Hg, Cu, Zn, Sn, Be) with the organic matter content, indicating that soil properties play a key role for pollutant retention in the Arctic soils. Furthermore, the correlations between ∑16 PAHs and some trace elements (e.g., Hg, Pb, Zn and Cu) suggest that the main source of contamination is probably pyrogenic, although the biogenic and petrogenic origin of PAHs should not be disregarded according to the local geology.

Persistent Mercury Contamination in Shooting Range Soils: The Legacy from Former Primers

Mercury (Hg) compounds were used in the past in primers for rifle and handgun ammunition. Despite its toxicity, little is known about the contamination of shooting-range soils with this metal. We present new data about the Hg contamination of surface soils from numerous shooting ranges of Switzerland. Our study demonstrates that Hg is measurable at high levels in surface soils from the shooting ranges. In three of the investigated ranges, concentrations above the maximum Swiss guidance value of Hg in soil of 500 µg kg^-1 were measured. Since the use of mercury-containing ammunition was stopped in the 1960s, our results demonstrate the high persistence of Hg in soils and their slow recovery by natural mechanisms.

Entomopathogenic nematode food webs in an ancient, mining pollution gradient in Spain

Mining activities pollute the environment with by-products that cause unpredictable impacts in surrounding areas. Cartagena-La Unión mine (Southeastern-Spain) was active for >2500years. Despite its closure in 1991, high concentrations of metals and waste residues remain in this area. A previous study using nematodes suggested that high lead content diminished soil biodiversity. However, the effects of mine pollution on specific ecosystem services remain unknown. Entomopathogenic nematodes (EPN) play a major role in the biocontrol of insect pests. Because EPNs are widespread throughout the world, we speculated that EPNs would be present in the mined areas, but at increased incidence with distance from the pollution focus. We predicted that the natural enemies of nematodes would follow a similar spatial pattern. We used qPCR techniques to measure abundance of five EPN species, five nematophagous fungi species, two bacterial ectoparasites of EPNs and one group of free-living nematodes that compete for the insect-cadaver. The study comprised 193 soil samples taken from mining sites, natural areas and agricultural fields. The highest concentrations of iron and zinc were detected in the mined area as was previously described for lead, cadmium and nickel. Molecular tools detected very low numbers of EPNs in samples found to be negative by insect-baiting, demonstrating the importance of the approach. EPNs were detected at low numbers in 13% of the localities, without relationship to heavy-metal concentrations. Only Acrobeloides-group nematodes were inversely related to the pollution gradient. Factors associated with agricultural areas explained 98.35% of the biotic variability, including EPN association with agricultural areas. Our study suggests that EPNs have adapted to polluted habitats that might support arthropod hosts. By contrast, the relationship between abundance of Acrobeloides-group and heavy-metal levels, revealed these taxa as especially well suited bio-indicators of soil mining pollution.

Historical anthropogenic contributions to mercury accumulation recorded by a peat core from Dajiuhu montane mire, central China

Mercury (Hg) accumulation records spanning the last 16,000 years before present (yr BP, relative to AD 1950) were derived from a peat core collected from Dajiuhu mire, central China. The natural Hg concentration and accumulation rate (free from anthropogenic influence) were 135.5 ± 53.9 ng g(-1) and 6.5 ± 4.5 μg m(-2) yr(-1), respectively. The increase in Hg flux that started from a core depth of 96.5 cm (3358 cal yr BP) is independent of soil erosion and organic matter content. We attribute this to an increase in atmospheric Hg deposition derived from regional anthropogenic activities. Anthropogenic Hg accumulation rates (Hg-ARA) in the pre-industrial period peaked during the Ming and the early Qing dynasties (582-100 cal yr BP), with Hg-ARA of 9.9-24.6 and 10.7-24.4 μg m(-2) yr(-1), respectively. In the industrial interval (post∼1850 AD), Hg-ARA increased progressively and reached 32.7 μg m(-2) yr(-1) at the top of the core. Our results indicate the existence of regional atmospheric Hg pollution spanning the past ∼3400 years, and place recent Hg enrichment in central China in a broader historical context.