Modeling global oceanic nitrogen deposition from food systems and its mitigation potential by reducing overuse of fertilizers.

Growing population and consumption pose unprecedented demands on food production. However, ammonia emissions mainly from food systems increase oceanic nitrogen deposition contributing to eutrophication. Here, we developed a long-term oceanic nitrogen deposition dataset (1970 to 2018) with updated ammonia emissions from food systems, evaluated the impact of ammonia emissions on oceanic nitrogen deposition patterns, and discussed the potential impact of nitrogen fertilizer overuse. Based on the chemical transport modeling approach, oceanic ammonia-related nitrogen deposition increased by 89% globally between 1970 and 2018, and now, it exceeds oxidized nitrogen deposition by over 20% in coastal regions including China Sea, India Coastal, and Northeastern Atlantic Shelves. Approximately 38% of agricultural nitrogen fertilizer was excessive, which corresponds to 15% of global oceanic ammonia-related nitrogen deposition. Policymakers and water quality managers need to pay increasingly more attention to ammonia associated with food production if the goal of reducing coastal nitrogen pollution is to be achieved for Sustainable Development Goals.

Stomatal responses of terrestrial plants to global change.

Quantifying the stomatal responses of plants to global change factors is crucial for modeling terrestrial carbon and water cycles. Here we synthesize worldwide experimental data to show that stomatal conductance (gs) decreases with elevated carbon dioxide (CO2), warming, decreased precipitation, and tropospheric ozone pollution, but increases with increased precipitation and nitrogen (N) deposition. These responses vary with treatment magnitude, plant attributes (ambient gs, vegetation biomes, and plant functional types), and climate. All two-factor combinations (except warming + N deposition) significantly reduce gs, and their individual effects are commonly additive but tend to be antagonistic as the effect sizes increased. We further show that rising CO2 and warming would dominate the future change of plant gs across biomes. The results of our meta-analysis provide a foundation for understanding and predicting plant gs across biomes and guiding manipulative experiment designs in a real world where global change factors do not occur in isolation.

Responses of soil greenhouse gas emissions to land use conversion and reversion-A global meta-analysis.

Exploring the responses of greenhouse gas (GHG) emissions to land use conversion or reversion is significant for taking effective land use measures to alleviate global warming. A global meta-analysis was conducted to analyze the responses of carbon dioxide (CO2 ), methane (CH4 ), and nitrous oxide (N2 O) emissions to land use conversion or reversion, and determine their temporal evolution, driving factors, and potential mechanisms. Our results showed that CH4 and N2 O responded positively to land use conversion while CO2 responded negatively to the changes from natural herb and secondary forest to plantation. By comparison, CH4 responded negatively to land use reversion and N2 O also showed negative response to the reversion from agricultural land to forest. The conversion of land use weakened the function of natural forest and grassland as CH4 sink and the artificial nitrogen (N) addition for plantation increased N source for N2 O release from soil, while the reversion of land use could alleviate them to some degree. Besides, soil carbon would impact CO2 emission for a long time after land use conversion, and secondary forest reached the CH4 uptake level similar to that of primary forest after over 40 years. N2 O responses had negative relationships with time interval under the conversions from forest to plantation, secondary forest, and pasture. In addition, meta-regression indicated that CH4 had correlations with several environmental variables, and carbon-nitrogen ratio had contrary relationships with N2 O emission responses to land use conversion and reversion. And the importance of driving factors displayed that CO2 , CH4 , and N2 O response to land use conversion and reversion was easily affected by NH4 + and soil moisture, mean annual temperature and NO3 - , total nitrogen and mean annual temperature, respectively. This study would provide enlightenments for scientific land management and reduction of GHG emissions.

Exploring global changes in agricultural ammonia emissions and their contribution to nitrogen deposition since 1980.

SignificanceAgricultural systems are already major forces of ammonia pollution and environmental degradation. How agricultural ammonia emissions affect the spatio-temporal patterns of nitrogen deposition and where to target future mitigation efforts, remains poorly understood. We develop a substantially complete and coherent agricultural ammonia emissions dataset in nearly recent four decades, and evaluate the relative role of reduced nitrogen in total nitrogen deposition in a spatially explicit way. Global reduced nitrogen deposition has grown rapidly, and will occupy a greater dominant position in total nitrogen deposition without future ammonia regulations. Recognition of agricultural ammonia emissions on nitrogen deposition is critical to formulate effective policies to address ammonia related environmental challenges and protect ecosystems from excessive nitrogen inputs.

Divergent responses of soil microbial functional groups to long-term high nitrogen presence in the tropical forests.

A massive rise in atmospheric nitrogen deposition (ND) has threatened ecosystem health through accelerating soil nitrogen (N) cycling rates. While soil microbes serve a crucial function in soil N transformation, it remains poorly understood on how excess ND affects microbial functional populations regulating soil N transformation in tropical forests. To address this gap, we conducted 13-year N (as NH4NO3) addition experiments in one N-rich tropical primary forest (PF) and two N-poor tropical reforested forests (rehabilitated and disturbed) in South China. Based on our data, 13-year N introduction markedly enhanced soil N2O generation in all forests, regardless of soil N status, but microbial functional groups showed divergent responses to excess N addition among the studied forests. In the PF, long-term N introduction markedly decreased presence of bacterial 16S rRNA gene, nitrifier (amoA) and denitrifier genes (nirK, nirS and nosZ) and bacteria/fungi ratio, which could be attributed to the decreases in soil pH, dissolved organic carbon to N ratio and understory plant richness. In the two reforested forests, however, long-term N introduction generally did neither alter soil properties nor the abundance of most microbial groups. We further found that the elevated N2O generation was related to the increased soil N availability and decreased nosZ abundance, and the PF has the highest N2O generation than the other two forests. Overall, our data indicates that the baseline soil N status may dominate response of microbial functional groups to ND in tropical forests, and N-rich forests are more responsive to excess N inputs, compared to those with low-N status. Forests with high soil N status can produce more N2O than those with low-N status. With the spread of elevated ND from temperate to tropical zones, tropical forests should merit more attention because ecosystem N saturation may be common and high N2O emission will occur.

A New Index Developed for Fast Diagnosis of Meteorological Roles in Ground-Level Ozone Variations.

China experienced worsening ground-level ozone (O3) pollution from 2013 to 2019. In this study, meteorological parameters, including surface temperature (T 2 ), solar radiation (SW), and wind speed (WS), were classified into two aspects, (1) Photochemical Reaction Condition (PRC = T 2 × SW) and (2) Physical Dispersion Capacity (PDC = WS). In this way, a Meteorology Synthetic Index (MSI = PRC/PDC) was developed for the quantification of meteorology-induced ground-level O3 pollution. The positive linear relationship between the 90th percentile of MDA8 (maximum daily 8-h average) O3 concentration and MSI determined that the contribution of meteorological changes to ground-level O-3 varied on a latitudinal gradient, decreasing from ∼40% in southern China to 10%-20% in northern China. Favorable photochemical reaction conditions were more important for ground-level O3 pollution. This study proposes a universally applicable index for fast diagnosis of meteorological roles in ground-level O3 variability, which enables the assessment of the observed effects of precursor emissions reductions that can be used for designing future control policies. ELECTRONIC SUPPLEMENTARY MATERIAL: Supplementary material is available in the online version of this article at 10.1007/s00376-021-1257-x.

Transmission of SARS-CoV-2 virus and ambient temperature: a critical review.

The coronavirus disease 2019 (COVID-19) pandemic has brought unprecedented public health, and social and economic challenges. It remains unclear whether seasonal changes in ambient temperature will alter spreading trajectory of the COVID-19 epidemic. The probable mechanism on this is still lacking. This review summarizes the most recent research data on the effect of ambient temperature on the COVID-19 epidemic characteristic. The available data suggest that (i) mesophilic traits of viruses are different due to their molecular composition; (ii) increasing ambient temperature decreases the persistence of some viruses in aquatic media; (iii) a 1°C increase in the average monthly minimum ambient temperatures (AMMAT) was related to a 0.72% fewer mammalian individuals that would be infected by coronavirus; (iv) proportion of zoonotic viruses of mammals including humans is probably related to their body temperature difference; (v) seasonal divergence between the northern and southern hemispheres may be a significant driver in determining a waved trajectory in the next 2 years. Further research is needed to understand its effects and mechanisms of global temperature change so that effective strategies can be adopted to curb its natural effects. This paper mainly explores possible scientific hypothesis and evidences that local communities and authorities should consider to find optimal solutions that can limit the transmission of SARS-CoV-2 virus.

Pollution evaluation and children's multimedia exposure of atmospheric arsenic deposition in the Pearl River Delta, China.

The populous Pearl River Delta (PRD) region in China suffers from serious air arsenic (As) pollution. The objective of this study was to explore the pollution situation of atmospheric arsenic deposition in the PRD region, and to evaluate the associated multimedia daily intake in children. The average deposition flux was 3921.7 µg/m2/year during the 2016-2017, and the pollution situation was even worse than that in 2015. A continuously increasing trend of arsenic atmospheric deposition was found. The bioaccessibility of As in the settled dust was determined as about 22% by a physiologically based extraction test (PBET). After corrected with the bioaccessibilities of As in the settled dust and food items, the geometry means (GM) value of daily uptake through multimedia ingestion of produce (dust and diet) originated from arsenic atmospheric deposition was 0.23 µg/kg/day for 1- to 6-year-old children. The contribution of the non-dietary oral exposure (settled dust) was negligible and just accounted for only 0.01% of the daily uptake. This estimated value was much lower than those in the literatures, in which the bioaccessibility of As was not taken into account, concluding that the role of the settled dust in the total daily intake may have been overestimated previously. Milk, eggs and freshwater fish were the dominant pathways for children to intake the products derived from atmospheric arsenic deposition. There still be a concern about the high non-carcinogenic and carcinogenic risk by long-term multimedia ingestion. Special care should be considered toward the emission sources of air arsenic, including the coal combustion from industries and construction dust, etc., to reduce the negative effect of air arsenic in children.

[Characteristics and Meteorological Factors of Complex Nonattainment Pollution of Atmospheric Photochemical Oxidant (Ox) and PM2.5 in the Pearl River Delta Region, China].

Based on the atmospheric pollutant data from twelve monitoring sites in the Guangdong-Hong Kong-Macao Pearl River Delta Regional Air Quality Monitoring Network, the mass concentration trends of atmospheric photochemical oxidants (Ox, NO2+O3) and PM2.5 during 2013-2017 were studied. The complex nonattainment pollution of Ox and PM2.5 is defined as the daily average mass concentration of NO2 and PM2.5 and daily maximum 8 h average (O3 MDA8) mass concentration of O3 simultaneously that exceeds the Chinese grade Ⅱ national air quality standard. The characteristics and meteorological factors that influence the complex nonattainment pollution of Ox and PM2.5 at different types of areas were analyzed. The results indicate that from 2013 to 2017, the annual average mass concentration of PM2.5 in the Pearl River Delta (PRD) region decreased from (44±7) µg·m-3 to (32±4) µg·m-3, which met the annual standard for three consecutive years. The annual average mass concentration of Ox decreased from (127±14) µg·m-3 in 2013 to (114±12) µg·m-3 in 2016 and then showed a general rebound trend to (129±13) µg·m-3 in 2017 when O3 concentrations increased significantly (10 µg·m-3). The proportion of pollution processes with O3 as the primary pollutant increased from 33% in 2013 to 78% in 2017, and the regional characteristics of simultaneous pollution in multiple cities have been highlighted. The complex nonattainment pollution of Ox and PM2.5 occurred 60 times during the study period, primarily in urban sites (78%) and suburban sites (22%). The largest number of days of complex nonattainment pollution occurred in autumn (52%) because of strong solar radiation that was conducive to ozone formation, and consequently, the high oxidization of the atmosphere promoted the secondary generation of PM2.5. The weather conditions that caused the complex nonattainment pollution in the PRD mainly include outflow-high-pressures (43%), subtropical-high-pressures(30%), and tropical-depressions (27%). In terms of specific meteorological conditions, when the temperature was in the range of 20-25℃ and relative humidity was in the range of 60%-75%, the proportion of complex nonattainment pollution was the highest (22%). When O3 pollution was substantial, the high relative humidity and low wind speed during the nighttime caused the concentration of NO2 and PM2.5 to rise significantly, and then the high temperatures during the day aggravated the complex nonattainment pollution.

Temporal and spatial patterns of nitrogen wet deposition in different weather types in the Pearl River Delta (PRD), China.

The temporal and spatial patterns of nitrogen wet deposition were investigated in the Pearl River Delta (PRD) under different weather types. The study was carried out in 27 monitoring sites with reliable meteorological data from 2010 to 2017. Large spatial variation data showed that both annual volume weighted mean (VWM) concentrations and fluxes were higher in the central PRD while lower in the outer area. The annual mean concentrations and fluxes were in the range of 0.8-1.3 mg N L-1 and 10.9-20.6 kg N ha-1 yr-1, respectively. The monthly mean concentrations and fluxes ranged from 0.1 to 0.2 mg N L-1 and 0.4 to 2.4 kg N ha-1, respectively. Further the study data revealed that the ratio of NH4+/NO3- was 1.1 which was much lower than the ratio reported in other regions like Northern China, Sichuan Basin, the US and Europe. The flux of NH4+ in urban sites was comparable to rural sites, implying that potential non-agricultural NH3 emissions were likely to be high in the PRD. The top three weather types were E, C and SE, with the total contribution of more than a half to the flux. Multiple linear regression was used to set up an equation to predict the variation of annual fluxes under the changes in weather conditions. The result hints that the variation on annual fluxes in the PRD tends to be stable in the next 30 years. Considering the increasing impact on the ecosystem, more effort should be exerted to reduce nitrogen wet deposition in the future.

Changes of nitrogen deposition in China from 1980 to 2018.

China has experienced a dramatic change in atmospheric reactive nitrogen (Nr) emissions over the past four decades. However, it remains unclear how nitrogen (N) deposition has responded to increases and/or decreases in Nr emissions. This study quantitatively assesses temporal and spatial variations in measurements of bulk and calculated dry N deposition in China from 1980 to 2018. A long-term database (1980-2018) shows that bulk N deposition peaked in around 2000, and had declined by 45% by 2016-2018. Recent bulk and dry N deposition (based on monitoring from 2011 to 2018) decreased from 2011 to 2018, with current average values of 19.4 ± 0.8 and 20.6 ± 0.4 kg N ha-1 yr-1, respectively. Oxidized N deposition, especially dry deposition, decreased after 2010 due to NOx emission controls. In contrast, reduced N deposition was approximately constant, with reductions in bulk NH4+-N deposition offset by a continuous increase in dry NH3 deposition. Elevated NH3 concentrations were found at nationwide monitoring sites even at urban sites, suggesting a strong influence of both agricultural and non-agricultural sources. Current emission controls are reducing Nr emissions and deposition but further mitigation measures are needed, especially of NH3, built on broader regional emission control strategies.

Meteorological variations impeded the benefits of recent NOx mitigation in reducing atmospheric nitrate deposition in the Pearl River Delta region, Southeast China.

The trends and variability of atmospheric nitrogen deposition in the Pearl River Delta (PRD) region for the period 2008-2017 were investigated by integrating ground- and satellite-based observations and a chemical transport model, in order to gauge the effects of emission reductions and meteorological variability. We show that dry deposition observation of oxidized nitrogen decreased at the rate of 2.4% yr-1 for a moderate reduction in NOx emissions by 27% in the past decade, while reduced nitrogen presented an increase at the rate of 2.3% yr-1 despite no regulated interventions for NH3 emissions, which is likely related to changes in atmospheric gas-particle partitioning of NH3 as reductions in SO2 and NOx emissions. These results coincide with the trends in ground-level concentrations of oxidized and reduced nitrogen compounds in the atmosphere during 2008-2017. The changes in annual deposition fluxes of total oxidized and reduced nitrogen are not statistically significant trends and largely related with the inter-annual variability in their corresponding wet depositions, which reflects combined effects of variability in precipitation amount, and changes in atmospheric nitrogen compounds which dominates wet deposition of the oxidized and reduced forms. The meteorological conditions can mask 34% and 25% decrease in total oxidized and reduced nitrogen deposition on the decadal timescale, respectively. We conclude that meteorology-driven variability probably have masked the full response of oxidized nitrogen deposition to NOx emissions reduction. Our results also imply that persistent and integrated emission control strategies on NOx and NH3 are needed to effectively reduce total nitrogen deposition fluxes towards the critical limit in the PRD region.

A quantitative analysis of the driving factors affecting seasonal variation of aerosol pH in Guangzhou, China.

Aerosol acidity is of great interest due to its effects on atmospheric chemical processes and impact on human health; however, the driving factors of aerosol acidity have only been scarcely investigated. This study characterized the aerosol acidity during the wet and dry seasons in Guangzhou, China, and systematically analyzed the seasonal variation and the corresponding driving factors of aerosol acidity followed by the discussion of their impact on gas-aerosol partitioning of NH3 and HNO3. It was demonstrated that the pH of PM2.5 was 0.08 unit lower (more acidic) during wet season than during the dry season and the aerosol acidity varied less in South China than that in North China. Additionally, our results showed that the meteorological parameters including temperature and relative humidity have larger effect on aerosol pH variation than chemical species. Particularly, the lower temperature during dry season had the positive influence (0.38 pH unit) on aerosol pH compared to the wet season; however, the negative effect due to relative humidity (RH) and chemical species resulted in a smaller seasonal variation of aerosol pH between these two seasons. The sensitivity analysis showed that the increase of temperature has negative impact (reducing pH) on aerosol pH with an almost linear relationship, while RH and chemical species represented a two-phase linear and nonlinear effect, respectively. Finally, the calculation of gas-aerosol partitioning indicated that the temperature had the largest influence on the seasonal variation of gas-aerosol partitioning for both HNO3 and NH3 followed by liquid water content and non-ideality, while aerosol acidity imposed the lowest impact, which suggests that all the parameters including meteorological and chemical species should be comprehensively evaluated to devise a PM2.5 control strategy.

Wet and dry deposition fluxes of heavy metals in Pearl River Delta Region (China): Characteristics, ecological risk assessment, and source apportionment.

The atmospheric deposition of heavy metals poses serious risks to the ecological system and human health. To advance our knowledge of atmospheric dry/wet heavy metal deposition in the PRD region, monthly fluxes were examined based on soluble/insoluble fractions of five heavy metal elements (Cu, Pb, Cd, Cr and Zn) in samples collected from January 2014 to December 2015 at Guangzhou (urban) and Dinghushan (suburban) sites. The ratios of wet/dry deposition fluxes indicated that heavy metal deposition was governed by wet deposition rather than dry deposition in the PRD region. Affected by the shifting of the Asian monsoon, wet deposition fluxes exhibited significant seasonal variation between summer monsoon seasons (April to September) and winter monsoon seasons (October to February) in this region. Cd was classified as an extremely strong potential ecological risk based on solubility and the Hakanson ecological risk index. Source contributions to wet deposition were calculated by PMF, suggesting that dust, biomass burning, industries, vehicles, long-range transport and marine aerosol sources in Guangzhou, and Zn fertilizers, marine aerosol sources, agriculture, incense burning, biomass burning, vehicles and the ceramics industry in Dinghushan, were the potential sources of heavy metals.

Model for Predicting Toxicities of Metals and Metalloids in Coastal Marine Environments Worldwide.

Metals can pose hazards to marine species and can adversely affect structures and functions of communities of marine species. However, little is known about how structural properties of metal atoms combined with current geographical and climatic conditions affect their toxic potencies. A mathematical model, based on quantitative structure-activity relationships and species sensitivity distributions (QSAR-SSD) was developed by use of acute toxicities of six metals (Cd, Cr, Cu, Hg, Ni, and Zn) to eight marine species and accessory environmental conditions. The model was then used to predict toxicities of 31 metals and metalloids and then to investigate relationships between acute water quality criteria (WQC) and environmental conditions in coastal marine environments. The model was also used to predict WQC in the coastal areas of different countries. Given global climate change, the QSAR-SSD model allows development of WQC for metals that will be protective of marine ecosystems under various conditions related to changes in global climate. This approach could be of enormous benefit in delivering an evidence-based approach to support regulatory decision making in management of metal and metalloids in marine waters.

Application of a self-organizing map and positive matrix factorization to investigate the spatial distributions and sources of polycyclic aromatic hydrocarbons in soils from Xiangfen County, northern China.

The concentrations of 16 priority polycyclic aromatic hydrocarbons (PAHs) were measured in 128 surface soil samples from Xiangfen County, northern China. The total mass concentration of these PAHs ranged from 52 to 10,524ng/g, with a mean of 723ng/g. Four-ring PAHs contributed almost 50% of the total PAH burden. A self-organizing map and positive matrix factorization were applied to investigate the spatial distribution and source apportionment of PAHs. Three emission sources of PAHs were identified, namely, coking ovens (21.9%), coal/biomass combustion (60.1%), and anthracene oil (18.0%). High concentrations of low-molecular-weight PAHs were particularly apparent in the coking plant zone in the region around Gucheng Town. High-molecular-weight PAHs mainly originated from coal/biomass combustion around Gucheng Town, Xincheng Town, and Taosi Town. PAHs in the soil of Xiangfen County are unlikely to pose a significant cancer risk for the population.

Probabilistic modeling of aggregate lead exposure in children of urban China using an adapted IEUBK model.

Lead, a ubiquitous pollutant throughout the environment, is confirmed to be neurotoxic for children by pulmonary and oral routes. As preschool children in China continue to be exposed to lead, we analyzed the available biomonitoring data for preschool children in urban China collected in the period 2004-2014 through a literature review. To identify apportionment of lead exposure sources for urban children in China, we modified the IEUBK model with a Monte Carlo module to assess the uncertainty and variability of the model output based on limited available exposure data and compared the simulated blood lead levels with the observed ones obtained through literature review. Although children's blood lead levels in urban China decreased statistically over time for the included studies, changes in blood lead levels in three economic zones and seven age groups except for two age-specific groups were no longer significant. The GM-predicted BLLs and the GM-observed BLLs agreed within 1µg/dL for all fourteen cities. The 95% CIs for the predicted GMs and the observed distribution (GM±GSD) overlapped substantially. These results demonstrated the plausibility of blood lead prediction provided by the adapted IEUBK model. Lead exposure estimates for diet, soil/dust, air, and drinking water were 12.01±6.27µg/day, 2.69±0.89µg/day, 0.20±0.15µg/day, and 0.029±0.012µg/day, respectively. These findings showed that the reduction of lead concentrations in grains and vegetables would be beneficial to limit the risk of dietary lead exposure for a large proportion of preschool children in urban China.

Air Quality Strategies on Public Health and Health Equity in Europe-A Systematic Review.

Air pollution is an important public health problem in Europe and there is evidence that it exacerbates health inequities. This calls for effective strategies and targeted interventions. In this study, we conducted a systematic review to evaluate the effectiveness of strategies relating to air pollution control on public health and health equity in Europe. Three databases, Web of Science, PubMed, and Trials Register of Promoting Health Interventions (TRoPHI), were searched for scientific publications investigating the effectiveness of strategies on outdoor air pollution control, public health and health equity in Europe from 1995 to 2015. A total of 15 scientific papers were included in the review after screening 1626 articles. Four groups of strategy types, namely, general regulations on air quality control, road traffic related emission control interventions, energy generation related emission control interventions and greenhouse gas emission control interventions for climate change mitigation were identified. All of the strategies reviewed reported some improvement in air quality and subsequently in public health. The reduction of the air pollutant concentrations and the reported subsequent health benefits were more significant within the geographic areas affected by traffic related interventions. Among the various traffic related interventions, low emission zones appeared to be more effective in reducing ambient nitrogen dioxide (NO2) and particulate matter levels. Only few studies considered implications for health equity, three out of 15, and no consistent results were found indicating that these strategies could reduce health inequity associated with air pollution. Particulate matter (particularly fine particulate matter) and NO2 were the dominant outdoor air pollutants examined in the studies in Europe in recent years. Health benefits were gained either as a direct, intended objective or as a co-benefit from all of the strategies examined, but no consistent impact on health equity from the strategies was found. The strategy types aiming to control air pollution in Europe and the health impact assessment methodology were also discussed in this review.

Atmospheric thorium pollution and inhalation exposure in the largest rare earth mining and smelting area in China.

Exposure to radionuclide thorium (Th) has generated widespread public concerns, mainly because of its radiological effects on human health. Activity levels of airborne 232Th in total suspended particulate (TSP) were measured in the vicinity of the largest rare earth mine in China in August 2012 and March 2013. The mean activity concentrations of 232Th in TSP ranged from 820µBqm-3 in a mining area in August 2012 to 39,720µBqm-3 in a smelting area in March 2013, much higher than the world reference of 0.5µBqm-3. Multistatistical analysis and Kohonen's self-organizing maps suggested that 232Th in TSP was mainly derived from rare earth mining and smelting practices. In addition, personal inhalation exposures to 232Th associated with respirable particulate (PM10) were also measured among local dwellers via personal monitoring. The mean dose values for different age groups in the smelting and mining areas ranged from 97.86 to 417µSvyear-1 and from 101.03 to 430.83µSvyear-1, respectively. These results indicate that people living in the study areas are exposed to high levels of widespread 232Th.

Applications of stochastic models and geostatistical analyses to study sources and spatial patterns of soil heavy metals in a metalliferous industrial district of China.

An extensive soil survey was conducted to study pollution sources and delineate contamination of heavy metals in one of the metalliferous industrial bases, in the karst areas of southwest China. A total of 597 topsoil samples were collected and the concentrations of five heavy metals, namely Cd, As (metalloid), Pb, Hg and Cr were analyzed. Stochastic models including a conditional inference tree (CIT) and a finite mixture distribution model (FMDM) were applied to identify the sources and partition the contribution from natural and anthropogenic sources for heavy metal in topsoils of the study area. Regression trees for Cd, As, Pb and Hg were proved to depend mostly on indicators of anthropogenic activities such as industrial type and distance from urban area, while the regression tree for Cr was found to be mainly influenced by the geogenic characteristics. The FMDM analysis showed that the geometric means of modeled background values for Cd, As, Pb, Hg and Cr were close to their background values previously reported in the study area, while the contamination of Cd and Hg were widespread in the study area, imposing potentially detrimental effects on organisms through the food chain. Finally, the probabilities of single and multiple heavy metals exceeding the threshold values derived from the FMDM were estimated using indicator kriging (IK) and multivariate indicator kriging (MVIK). The high probabilities exceeding the thresholds of heavy metals were associated with metalliferous production and atmospheric deposition of heavy metals transported from the urban and industrial areas. Geostatistics coupled with stochastic models provide an effective way to delineate multiple heavy metal pollution to facilitate improved environmental management.