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From 2004 to 2018, c. 73% of the land area in Hebei Province was surveyed by a 1:250 000 land quality geochemical survey of the National Geochemistry Survey of Land Quality. Based on the topsoil (0–20 cm) datasets (50 724 analysis samples) and attribute analysis of the key area with a semivariance function model, geographic detector model and random forest model, the content and spatial distribution of soil selenium (Se) in Hebei Province and the influencing factors of the distribution of Se in the Shijiazhuang–Xingtai–Handan area were obtained. The soil Se content in Hebei Province is low, ranging from 0.02 to 3.23 mg kg –1 , with an average of 0.20 mg kg –1 . The spatial distribution of soil Se was heterogeneous, and the marginal Se (0.125–0.175 mg kg –1 ) area and the sufficient Se (0.175–0.40 mg kg –1 ) area were widely distributed, but the acreage of the Se-rich (0.40–3.0 mg kg –1 ) area was very limited, accounting for only 2.43% of the total survey area. However, the Shijiazhuang–Xingtai–Handan area was a significant Se enrichment area. The spatial distribution of Se in this area was restricted by natural and socioeconomic factors. Soil organic matter was the most influential factor and showed good coordination with Se. Coal burning superimposed on natural factors promotes the spatial differentiation of soil Se to a certain extent.

Changsha-Zhuzhou-Xiangtan is a heavy industry area in China. Many studies just focused on the basic contamination statues of heavy metals there; however, few of them had a deep study on chemical species in micro aggregate or samples with different particle sizes. This study focused on a comprehensive research of Pb in typical arable soil collected from Zhuzhou. Soil properties, particle size distributions, and Pb chemical species in different soil particles were investigated. Species of Pb were characterized by sequential extraction and X-ray absorption fine structure (XAFS) spectra. Little variance was shown on basic properties between different soil fractions, expect for mass distribution and Pb concentration. Sequential extraction results suggested that Pb species were similar in different soil fractions and about 90% of Pb species were consisted of carbonate binding, Fe/Mn oxide binding, and organic binding fraction. The percentage of water-soluble and exchangeable fraction Pb was less than 1%. XAFS was further applied to confirm the Pb chemical species. Results showed that the chemical species of Pb in soil were mainly consisted of PbSO4, Pb(OH)2, and PbO. However, 8.2% of Pb3O4 was presented in 250–53 μm fraction, which was different from other particle size fractions. The XAFS analysis suggested that the dominant chemical species was PbSO4 which was corresponding to the species of Fe/Mn oxide binding fraction in sequential extraction method. Pb(OH)2 was the secondary species that can be explained as carbonate and organic binding fraction. These combined results indicated that Pb in the studied soil was in a uniform, stable, and less bioavailability state within all particle sizes.

Carbon and nitrogen are the essential elements constituting living organisms and are closely coupled during biogeochemical cycles. Due to the atmospheric nitrogen deposition and increased agricultural nitrogen fertilizer input, the effect of nitrogen on the sequestration of soil organic carbon (SOC) is controversial. To facilitate a comprehensive understanding of this issue, the progress of recent studies on the different SOC stabilization mechanisms is reviewed. Based on the differences in the stability and fate mechanisms of particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), nitrogen input can increase POC input and inhibit microbial decomposition of POC by increasing terrestrial biomass, changing the quality of litter and promoting the formation of aggregates. N input reduces the chemical stability of MAOC by altering the chemical bonding of mineral–organic complexes. This study has promising implications for understanding the effect of N on SOC transformation by different stabilization mechanisms to promote soil carbon sequestration.

More nuclear power plants continue to be built in China. Due to its long half-life, radiotoxicity and potential application as an environmental tracer, 236U is one of the most important artificial radionuclides deserving more study since activity data are important for risk assessment. However, the ultra-trace activity of 236U and its dilution by natural uranium isotopes make it difficult to distinguish its sources and there are only limited global fallout 236U data for present in Chinese environmental samples. In order to understand the background levels for uranium isotopes, especially 236U, and clarify their sources, inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) was applied to analyze uranium isotopes in 48 soil samples from Hunan Province, China. The 234U, 235U, 238U and 236U concentrations were measured as 9.91–33.7, 0.312–1.43, 6.63–28.7 Bq kg−1 and (1.61–21.3) × 107 atoms g−1, while, the 236U/238U, 234U/238U and 235U/238U atom ratios were (0.470–4.91) × 10−8, (5.10–9.31) × 10−5, and (7.11–7.82) × 10−3, respectively. The uranium isotopic fractionation may be due to irrigation of the agricultural lands where the samples were collected. Considering the facts that neither previous nuclear tests nor nuclear accidents had occurred in Hunan Province and the present 236U/238U atom ratios were included in the range of global fallout values in other areas, it may be concluded that 236U in soils from Hunan Province is mainly from global fallout. To the best of the authors’ knowledge, the presence of global fallout 236U in soil samples from China has been confirmed for the first time, and these values may be useful as background data for risk assessment in the future.

Forest ecosystems have been confirmed to be a sink of the global mercury (Hg) in the biogeochemical cycle. However, few studies have investigated the distribution of Hg in forest ecosystems on a regional scale in China. This work aimed to investigate the concentrations, distribution and influential factors of Hg in the Qinling Mountains forests in central China. Foliage, litter and soil profile samples were collected at 24 sampling sites across the Qinling Mountains forests. The results of the present study showed that the concentrations of Hg in foliage, litter, organic soils and mineral soils were maintained at relatively low levels compared with those in subtropical forests of Southwest China. The average Hg concentrations followed the order litter (74 ± 34 ng g

The geochemistry of rare earth elements (REEs) was studied in rock samples from host formations, ore samples from two mineral deposits (the Hetaoping Cu-Pb-Zn mine: HTP and the Heiyanao Fe-Cu-Pb-Zn mine: HYA) and the overlying or nearby soils to better understand REE concentrations, distributions and behaviour during weathering from different parent materials at the regional scale, Baoshan area, Yunnan Province, SW China. The mudstone and sandstone formations have the highest total REE (ΣREE) contents. Chondrite-normalized diagrams for rocks and ores show significant light REEs (LREEs) enrichments and Eu depletion (except for ores in HYA). Cerium displays an obvious negative anomaly in carbonate rocks (Є-3-R, C-R, D-R, T-1-R and T-2-R). Soils overlying carbonate rock formations (T-1-S, C-S and Є-3-S) have the highest ΣREE contents, while soils overlying basalts have the lowest ΣREE contents. Soils show enrichments in LREEs with negative Eu anomalies and slight Ce anomalies in the studied soils. Soils with high ∑LREE/∑heavy REE (HREE) values may result from the preferential absorption of LREEs by organic matter. Negative Eu anomalies in soils occur for parent materials in the study area lacking feldspar, especially soils developed from carbonates. Compared to the parent materials, most soils show REE enrichment because alkali metals are removed and REEs are concentrated by low mobility in surficial processes and positive Ce anomalies because of weathering dissolution of other trivalent REEs with ionic radii similar to that of Ca2+. Supplementary material: Additional data (Tables S1 and S2) and sample locations (Fig. S1) are available at https://doi.org/10.6084/m9.figshare.c.5303140

Figure S1 and Tables S1 and S2

A better knowledge on soil development under different land use/cover is critical for restoring eco-environmental integrity in degraded mining areas. This study aims at evaluating the impacts of different reclaimed land uses on topsoil properties over time in an opencast coalmine located at Pingshuo, Shanxi province, China. Over two hundred soil samples at the depth of 0–30 cm were collected and analyzed by using descriptive statistic, spatial statistic, and geostatistical method. The results showed that significant differences existed in soil particle distribution, organic carbon (OC), total nitrogen (N), available potassium (AK), and cation exchangeable capacity (CEC) between reclaimed and unmined lands. However, pH, N, total phosphorus (P), available phosphorus (AP) and AK significantly differentiated from each other under different reclaimed land uses, while OC and N were the highest in cultivated soil, followed by forest, grass and barren soils. In addition, the results showed a strong global autocorrelation for pH, OC, N, P, AP and AK. Moreover, the changes of OC and N exhibited U-shape trajectory under forest and grass land, indicating that approximate 20 years were required for reclaimed forest and grass land to restore OC and N comparable to unmined land.

This study aims to better understand, at a regional scale, the concentration and distribution of selected chemical elements in surface environments and the influence of natural factors (geological background, geomorphology) and anthropogenic factors (mining activities, land-use, agricultural fertilization) on their distribution in the Baoshan area, Yunnan province, southwest China. Mineral resources (such as copper, lead, zinc, mercury, gold, silver) and carbonate and basalt parent materials in this area often lead to elevated potentially toxic metals (PTMs), which are widely distributed where mining activities have rapidly developed since last 20–30 years. This study makes use of 1574 surface soil data and 425 deep soil data from the National Geochemistry Survey of Land Quality project (NGSLQ), and 1585 archived river sediment data which were collected and analyzed for the Regional Geochemistry-National Reconnaissance program (RGNR). These data, once log-ratio (clr) transformed have been studied by compositional data analysis (CoDA), principle components analysis (PCA) and spatial analysis. In the Baoshan area, the concentration of elements As, B, (Br), Co, Cr, Cu, Hg, (I), Mn, (N), Ni, Sb, (Sc), (Se), V, Fe2O3Total and (COrgonic) are enriched compared to the China Soil Geochemical Baselines program (CGB) and RGNR data sets; while elements Sr and Na2O are depleted compared to CGB and RGNR data sets. Influencing factors on surface soil, deep soil and river sediment composition of the study area are revealed. The distribution of most elements in surface soil, deep soil and river sediment are influenced by natural factors such that: Co, Cr, Cu, Ni, Sc, Ti, V, Fe2O3Total and MgO are controlled by the distribution of basic igneous rocks; Ca, Mg, Sr and pH are controlled by the distribution of carbonate rocks and basic igneous rocks; As, Hg, Sb, (Ag), Cd, Pb and Zn are controlled by mineralization; and other elements normally controlled by the distribution of clastic rocks and acid-intermediate rocks; while the organic matter such as Br, N, (P), S, COrgonic and CTotal in soil data set are controlled by geomorphic (altitude and temperature). Anthropogenic factors are also recognized in the soil data set. For example: high pH values in paddy land and grassland, and low pH values in forested land, garden plot and dry cultivated land; in agricultural area fertilization has caused enrichment of the nutrient elements (COrgonic, CTotal, N, P, etc.,) in surface soil; while in areas of mining, surface soils are contaminated by PTMs (incl. Hg, As, Sb, Cu, Pb, Zn and Cd).

Geochemical fluxes in rock-soil systems are important tools in the evaluation of soil environmental risk, especially where the geological background (parent materials) are enriched in potential toxic elements (PTE). In the Baoshan area, the presence of mineral resources along with carbonate and basalt parent materials often leads to PTE being elevated in soils. In this study, we compared rock and soil geochemical compositions by collecting rock samples from the host formations and ore samples from two mineral deposits (Cu–Pb–Zn and Fe–Cu–Pb–Zn) and their overlying soils. This research demonstrates enrichment of PTE (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) in soils relative to their parent materials. The enrichment in soils may be due to the removal of mobile elements (e.g., Ca, Na, Mg, and Sr), and coprecipitation (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) and/or adsorption by Fe-oxy-hydroxides (Cr and Ni) under the influence of high pH values during soil formation. The results point to a parent lithological origin and natural enrichment of PTE in Baoshan soils. However, anthropogenic contamination of soils near mining areas is also possible. Soils forming from carbonate rocks, basalts, and especially from mineralized formations have higher PTE concentrations, and in places, levels can exceed the risk screening values for soil contamination of agricultural land of China. Where the latter is the case, it is suggested that ecological monitoring be implemented in the study area. The conventional use of the geo-accumulation index (Igeo) and enrichment factor (EF) methods is challenged in this research and found to underestimate the PTE contamination. A compositional data analysis approach (using clr biplots) is presented which shows that comparison with regional-scale background datasets is essential to provide a more informative approach to evaluate the risk of soil contamination, especially in regions with elevated levels of PTE in parent materials.

Environmental contamination by heavy metals is a public health concern. However, understandings of sources and pathways of heavy metal accumulation in crops, especially in major agricultural areas, is insufficient. In this study, atmospheric dust, coal, vehicle exhaust particles, maize and corresponding soils were collected from a major agricultural area in Northeast China and analyzed for heavy metal (Cd, Hg, Pb, As, Cu, Zn, Ni, Cr) contents and Pb isotopic compositions. Compared to the risk screening values for soil contamination of agricultural land in China, the soils in the study area have relatively low heavy metal concentrations. However, the contamination factor (CF), pollution load index (PLI) and geo-accumulation index (Igeo) indicated a slight degree of heavy metal (particularly Cd) accumulation during the past few decades. The concentrations of Cd, Cu, Hg and Pb decreased from leaves, roots, stalks to grains, whereas it decreased from roots, grains, leaves to stalks for Zn and from roots, leaves, stalks to grains for As, Cr and Ni. The calculated bioconcentration factor (BCF) values indicated that Cd had a high possibility of entering maize roots from soil, while it was relatively difficult for Cr and Pb to accumulate in maize roots. The order of the mean translocation factor (TF) values was Zn (1.41) > Cu (0.31) > Hg (0.27) > Cd (0.15) > Pb (0.11) > Cr (0.11) > As (0.11) > Ni (0.08), suggesting that Zn had the highest mobility from root to grain, while >90% of absorbed Ni was sequestered in roots. Based on a simple binary model, the approximate contributions of Pb in vehicle emissions and coal to atmospheric dust were 78.1% and 21.9%, respectively, suggesting that Pb in atmospheric dust was mainly from vehicle emissions. For maize organs, airborne Pb was the dominant source contributor to maize stalks and grains, with approximate contributions of 78.3% and 15.1% to leaves and roots, respectively. Our study suggested that Pb accumulation in maize plants might be mainly derived from atmospheric deposition related to vehicle emissions. Hence, more efficient managerial strategies should be adopted to protect food safety and human health.

More nuclear power plants continue to be built in China. Due to its long half-life, radiotoxicity and potential application as an environmental tracer

A systematic geochemical lake sediment survey has been carried out in major freshwater lakes in China. Surface lake sediment (0–20 cm) at a density of 1 sample/4 km 2 and deep lake sediment (150–180 cm) at a density of 1 sample/16 km 2 were collected and analyzed with standard procedures. This overview provides a current ecological risk assessment for toxic metal contamination (As, Cd, Cr, Cu. Hg, Ni, Pb, and Zn) in the surface sediments of major freshwater lakes in China. Lake sediment in China poses a moderate ecological risk on a nationwide basis using a potential ecological risk index (PERI). Mercury ranked as presenting the greatest ecological risk, followed by Cd, As, Pb, Cu, Ni, Cr, and Zn. Liangzi Lake was classified as having high ecological risk; Dalonghu Lake, Dianchi Lake, Dongting Lake, Fuxian Lake, and Qilu Lake as having moderate ecological risk; while the other surveyed lakes were classified as having low ecological risk. Uncertainties of risk assessment are also discussed by considering geochemical background, the eco-toxicity of metals and the sensitivities of local benthic communities. These comprehensive findings have provided valuable information for improvement of lake management and pollution prevention and control in China.

For a safety of public health, it is crucial to understand the soil quality in suburban metropolis with rapid urbanization. The levels and compositional patterns of 13 phthalate esters (PAEs) in both surface and deep soil were analyzed in suburban Beijing for the first time. The geochemical distribution was mapped to identify several "hot spots" in the southern and southeastern areas, which could direct the future management and remediation. PAEs were ubiquitous contaminants and di(2-ethylhexyl) phthalate (DEHP), di-isobutyl phthalate (DiBP) together with di-n-butyl phthalate (DBP) were three dominant species in both layers. The total concentrations in the surface and deep soils were 0.02-2.90 mg kg(-1) (median: 0.38 mg kg(-1)) and 0-1.51 mg kg(-1) (lower median: 0.12 mg kg(-1)), respectively. The assessment of eco-toxicological effect of the abundant PAEs suggests that no environmental risk would occur at the present level in suburban Beijing. The modeling volatilization flux of six EPA-PAEs was from 5.07 x 10(-3) ng h(-1) for dimethyl phthalate (DMP) to 1.88 x 10(-6) ng h(-1) for di-n-octyl phthalate (DOP). A relationship between volatilization flux (F-v) and octanol-water partition coefficient (K-ow) was employed to predict the fluxes of other PAEs from soil to atmosphere. The surface soil could continue to be the source of atmospheric contamination of PAEs in a long term, which deserves further attentions. (C) 2015 Elsevier B.V. All rights reserved.

A large Pt–Pd geochemical province within the Emeishan basalt province has been identified previously and was considered as an exploration target for platinum-group element (PGE) mineralization. To evaluate thoroughly the prospect of economic Pt–Pd mineralization in this region, a series of geochemical surveys was conducted in a selected area, with an exploration strategy involving the progressive reduction of the target area and stepwise increase in the sampling density. A regional Pt and Pd geochemical anomaly was delineated by a stream sediment survey at a sampling density of 1 sample km −2 over an area of mafic intrusive bodies and basalts in Miyi County, Sichuan Province. In a follow-up phase, three local Pt and Pd geochemical anomalies were defined by data from a stream sediment survey with a density of 4 samples km −2 . Finally, PGE mineralization within a gabbroic rock was discovered in the geochemical anomalies delineated by the following more detailed survey, namely a soil survey with a 100 m × 20 m sampling grid. The level of Pt+Pd mineralization was 0.33 μg g −1 . A new concealed mafic–ultramafic intrusive body containing PGE mineralization was predicted.The success of this case has provided an excellent example of how to identify possible PGE target areas in the basalt environment using geochemical surveys at various scales.

This overview provides an up-to-date assessment of the trace metal contamination (As, Cd, Cr, Cu. Hg, Ni, Pb, Sb, Se, and Zn) in urban soils of 31 metropolises in China. This systematic soil geochemical survey summarizes the characteristics of trace metals in Chinese urban soils, including concentration, accumulation, spatial distribution, and major sources. Mercury was ranked first followed by Cd and Se in geo-accumulation among all of the contaminant metals in urban soils in China; this finding is likely due to the Hg and Se emissions from fossil fuels. However, the lack of studies on Se contamination in urban soils, not only in China but also in the rest of the world, implies that Se contamination may have been unobserved for a long time. Shanghai, Kunming, Shenyang, and Changsha may be some of the most heavily contaminated Chinese cities based on the concentrations, spatial dimensions, and associations among the contaminant metals. Numerous hotspots with high concentrations of metals were found in Changsha, Shanghai, and Shenyang, clearly indicating a significant contribution from both the metallurgical industry and smelt mining to the contamination of urban soils. Conversely, the levels of Sb, Cu, and Cd in Kunming originated from their naturally high geochemical background in soils. Heavy Se contamination was found in Guiyang and Taiyuan. The natural source of Se may be important in defining the pattern of pollution in Guiyang, whereas anthropogenic sources are likely more accurate than is the natural background in Taiyuan city. We review the existing limits and types of pollutants in the current soil guidelines and find that an international agreement on the range of the limits and the types of pollutants contained in the soil guidelines is urgently needed.

Tropical arable soils were sampled from Hainan Island. The particle size fractions associated Cr, As, Cd and Pb were characterized and their leachability was analyzed as well. The pollution of heavy metals in the arable soils was not severe except Cr (204 mg kg− 1) in Haikou. The distribution of heavy metals increased with decrease of particle size. Although the smallest fractions (

article i nfo Since 1999, a new geochemical mapping project, the National Multi-Purpose Regional Geochemical Survey (NMPRGS), has been carried out in the agriculturally and industrially developed regions of China, covering mainly the plains of the eastern and central parts of the country. The primary purpose of this project is to generate systematic multi-medium geochemical data that can be used by subject-matter experts to support the development of policies for protecting the surface environment, improving the efficiency of agriculture and supporting land use planning. Surface (0-20 cm) soils were collected at a density of 1 sample/km 2 and deep soils (150-180 cm) were taken at a density of 1 sample/4 km 2 . Samples from 4 km 2 for surface soils, 16 km 2 for deep soils, were composited for chemical analysis. Additionally, lake sediments and near-shore sediments were collected at a lower density. Each sample was analyzed for total content of 52 components (Ag, As, Au, B, Ba, Be, Bi, Br, Cd, Ce, Cl, Co, Cr, Cu, F, Ga, Ge, Hg, I, La, Li, Mn, Mo, N, Nb, Ni, P, Pb, Rb, S, Sb, Sc, Se, Sn, Sr, Th, Ti, Tl, U, V, W, Y, Zn, Zr, SiO2 ,A l2O3, TFe2O3, MgO, CaO, Na2O, K2O and total carbon), organic carbon and pH. As of the end of 2012, sampling of 1.7 million km 2 has been completed and samples from 1.5 million km 2 have been analyzed. Preliminary achievements have been made in the studies of geochemical variations, the establishment of the natural background and eco-geochemical assessment. An encouraging progress has been made in the application of geochemical knowledge to protecting the surface environment, improving the efficiency of agriculture and promoting sustainable land use.

This paper provides a history of the development of exploration geochemistry in China. Over the past 60 years, geochemists in China have made great efforts to develop geochemical exploration methods to cover large areas and even all of China or the whole world, as well as to more elements with emphasis on high sensitivity and accuracy. The new innovative exploration concept and strategies established by the Chinese geochemists have greatly contributed to discoveries of the mineral deposits and to the environmental regulations.

This study aimed to characterize atmospheric mercury (Hg) as well as the Hg exchange flux between soil and air surfaces in the urban area of Guangzhou. Total gaseous Hg (TGM) concentration and Hg exchange flux were measured in situ using a dynamic flux chamber coupled with a Mercury Vapor Analyzer. The TGM averaged 6.3 ± 2.2 ng·m− 3 at five sites, and average Hg exchange flux was 7.8 ± 7.1 ng·m− 2·h− 1. Both Hg content and soil pH were significantly correlated with Hg fluxes, suggesting that soil properties affected Hg exchanges. The Hg exchange fluxes showed significantly positive correlations with solar radiation and soil temperature. Comparisons demonstrated that vegetation significantly interfered with the Hg emission flux. The annual Hg emission from soil in Guangzhou urban area was 51.46 g·km− 2·yr− 1 or 25.73 kg·yr− 1.

Mercury (Hg) concentration and its change trend in soils was investigated at different periods in Beijing. An Hg-enriched area with 1000 ng·g − 1 Hg concentration was delineated within the Third Ring Road of the city, where the capital of the Ming Dynasty was situated approximately 500 years ago. The Hg concentration was attributed to the historical use of Hg and coal burning. The geometric mean of Hg concentration in Beijing was 714 ng·g − 1 in 1987, 375 ng·g − 1 in 2000, 294 ng·g − 1 in 2005, and 251 ng·g − 1 in 2009, indicating a drop in Hg concentration in the soil since 1987. The results show that the environmental quality of the soil Hg in Beijing had been significantly improving since 1987. The average topsoil Hg density (0 cm to 20 cm) decreased from 411 mg·m − 2 in 1987 to 178.0 mg·m − 2 in 2005, with an annual decrease of 4661 kg and an annual average drop rate of 3.15%. The sharp decrease in soil Hg content is attributed to tight emission controls implemented by the Beijing Government since 2000 and Hg emission from topsoil. However, the amount of Hg emission from urban soils is comparable with the value of Hg emission from fuel coal, oil, and natural gas in Beijing, implying that natural Hg emissions from the soil are another important atmospheric Hg source expected for emissions from fuel combustion.

The direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol is one attractive way for the reduction of greenhouse gas emission and the utilization of carbon resources. Recent progress in the direct synthesis of DMC from CO2 and methanol is reviewed with the focus on the catalyst systems, including organic metal compounds catalyst, base catalyst, acetate catalyst, metal oxide and supported metal oxide catalysts, heteropolyacid catalyst and photocatalyst. Moreover, the application of supercritical system, ionic liquid system, electrochemical system, membrane reactor and nitriles hydration in the direct synthesis of DMC are also introduced. Finally, future research direction in this area is proposed.

Soil organic carbon changes monitoring is of importance to identify sources or sinks of atmospheric CO 2 . Multi-period soil organic carbon (SOC) data in Da'an region, Jilin Province in Northeast China, were obtained by National Soil Survey, the National Multi-Purpose Regional Geochemical Survey (NMPRGS) project. Loss or gain of SOC was estimated during 1984–2004. Results show the clear trend of carbon loss from soil to the atmosphere in the period, with a smaller SOC decrease rate in 2004–2008 than the rate in 1984–2004. The NMPRGS project has been carried out since 1999 by collecting topsoil samples (0–20 cm) with an average density of one sample per 1 km 2 and one composite sample per 4 km 2 for analyses. An area of 1,650,000 km 2 has been covered by the survey up to 2010 in China. Based on the large amount of SOC data, a new project has been launched to study the loss and gain of soil organic carbon across China, which will provide the basic information to improve the land use management and agricultural operations in the country.

For the valid use of urban land and the safety of public health, an extensive contamination survey of organochlorine pesticides from five soil cores was conducted in the highly urbanized areas of Beijing in China. For topsoils in five soil cores, level of ∑HCHs and ∑DDTs varied from 0.174 to 4,783 ng g(-1) and 0.62 to 57,849 ng g(-1), respectively. The profile in topsoil of cores displayed that levels of pollutants in four soil cores from the urban areas with dense population are higher than that from outskirts. The depth characteristics of pollutants indicated that the level of ∑HCHs and ∑DDTs in BY and WU was close to/below the background value of soil in China (50 ng g(-1)), but those in some soil samples from A, B and ZX core, especially A and B, was above the threshold value for the soil safety (1,000 ng g(-1)). In views of the usage history of the land and profiles of contaminants, the source in A and B probably came from the dumped waste chemical materials in the old chemical factories. The study of soil cores sampled revealed the existence of chemical "time bomb" in urban regions of Beijing. Also, the finding indicated the absolute necessity of assessing the soil quality with the unprecedented land use changes in the big city community.

Mercury contamination is a serious problem in Chinese cities. In the present study, mercury contamination was evaluated in topsoil and subsoil samples collected in an urban area of Beijing. The level of total mercury in topsoil ranged from 12.1 to 8,487 ng g(-1), and a significant correlation (R = 0.58145, p < 0.0001) with polycyclic aromatic hydrocarbons was observed. Higher levels were generally observed in the suburbs and urban centers, with the highest levels being observed in the urban centers. The fraction of water soluble, ion exchangeable, Fe-Mn in the oxide-bound and organic phase was 0.78%, 0.18%, 0.25% and 3.42%, respectively. For subsoils, the level of total mercury ranged from 7.0 to 924.6 ng g(-1), and the higher levels were primarily located in the suburbs. This study showed that mercury has possibly affected the environmental quality of soil and groundwater in urban areas of Beijing.

To assess the contamination trends and potential bio-availability of sediment-bound heavy metals, concentrations of heavy metals in acid-leaching fraction and in bulk sediments from the two typical bays (the Meiliang Bay and Xuhu Bay) of the Taihu Lake, East China, were studied. Pb and Zn showed elevated concentrations in the sediments from both areas, although sedimentation history and degree of pollution are different between the two bays. In the Meiliang Bay, both Pb and Zn pollutions started in the late 1970’s, the same time as the beginning of eutrophication of the lake, while the in the Xuhu Bay the metal contamination started since recent 10 years. The concentrations of acid-leachable Pb in the sediments from the Meiliang Bay are correlated with the historical eutrophication process. Before the eutrophication and heavy metal pollution, the chemical properties of the lake sediments were the same as the source compositions of the Xiashu loess. Both Pb and Zn in the sediments mainly occur in leachable forms by nitric or hydrochloric acid, whilst most of Cu is in residual fraction. The results indicate that both Pb and Zn may have higher mobility and bioavailability in water and biology than Cu.

Regional-, national- and global-scale geochemical mapping projects have been carried out in China since the late 1970s. These geochemical mapping projects have provided high-quality data for both mineral resource investigations and environmental assessments. Four national-scale geochemical mapping projects in China are described here. (1) The Regional Geochemistry–National Reconnaissance (RGNR) project is China9s largest national-scale geochemical mapping project and has covered more than 6 million km 2 of the country9s hilly and mountainous regions since 1978. Generally, stream-sediment samples were collected at a density of 1 sample per km 2 and four samples were composited into one analytical sample for analysis of 39 elements. (2) The Deep-penetrating Geochemical Mapping (DEEPMAP) project has been conducted in covered terrains, including basins, at a density of 1 sample per 100 km 2 with analysis of 30–70 elements since 1994. In the past ten years, an area of approximately 800 000 km 2 has been covered. (3) The 76 Geochemical Element Mapping (76 GEM) project has been carried out since 1999. Approximately 1 million km 2 has been completed at present. (4) Multi-purpose eco-geochemical mapping projects have been conducted in the Quaternary plains of eastern China to provide data for environmental regulation and for improvement of agricultural practices since 1999. The data generated continue to play an important role in finding mineralization targets and ore deposits. China is also playing a leadership role in international geochemical mapping projects by transferring its expertise in sampling, chemical analysis and map generation to the developing countries through bilateral and multilateral collaboration. China is a leader in two large projects on a global scale: (1) the Environmental Geochemical Monitoring Network (EGMON) Project aims not only to have a quick overview of the geochemistry in China, but also to provide a pilot study for choosing the optimum sampling medium for geochemical mapping projects at a global scale; (2) the Geochemical Mapping Project uses delta and floodplain sediments of large rivers at a global scale.

Since the projects of “International Geochemical Mapping (IGCP259)” and “Global Geochemical Baseline (IGCP360)” were met with approval by UNESCO in 1988, decisive contributions of working out the methodological guidance and the technical standard of global geochemical mapping have been made by China and Europe. Though demonstrations have been made by China and Europe through carrying out the projects of “Environmental Geochemical Monitoring Network and Dynamic Geochemical Mapping (EGMON)” and “FOREG geochemical baseline mapping”, respectively, the expectation of acquiring a general picture of global geochemistry in 10 years has not yet been realized. Geochemists from China and Norway are now deliberating, through International Association of Hydrological Sciences/International Commission on Continental Erosion (IAHS/ICCE), about a major international cooperative project on “Global Geochemical Mapping and Sediment-Bound Flux of Major World Rivers”, on carrying out a new round global geochemical mapping, and planning to start working first on the Arctic region under the project of the Year of Polar (IPY317). The practical plan for the global geochemical mapping is based on the “Draft of Sampling Plan of Floodplain Sediments” for the global geochemical mapping suggested by China and the “Draft of Sampling Plan of Overbank Sediments in Deltas” suggested by Norway, thereby further strengthening the advantages of Chinese methodology in geochemical mapping. After analyzing the opportunities and challenges to China, this article suggests that the competent authorities of science and technology should take the initiative of supporting the new round global geochemical mapping.

Forty-five pooled subsoil samples, collected from the outskirts of Beijing at the depths of 1.5-1.8 m, were analyzed for 17 polycyclic aromatic hydrocarbons (PAHs) using gas chromatography and mass spectrometry (GC-MS) to determine their total contents and distribution patterns. The sum of 17 PAHs concentrations varied from not detected to 0.982 mu g g(-1) in subsoil. The higher total contents of PAHs were observed in the southeast areas where there are some industries. PAHs in most of the subsoil were lower than those in the topsoil (0.016-3.884 mu g g(-1)). PAHs concentrations displayed no relationship with the organic materials. In subsoil, the dominated PAHs were perylene > benzo(a)pyrene > benzo(g,h,i)perylene > indeno(1,2,3-cd)pyrene. It was notable that the content of 8 carcinogenic PAHs represented 47% of the total priority PAHs and the concentration of benzo(a)pyrene in the subsoil was comparable to that in the topsoil, which was much higher. The distribution of target compounds especially perylene and the fluoranthene/pyrene ratio shows that the sources in the subsoil are characterized by combustion such as traffic and incorporation of the diagenetic PAHs. (c) 2005 Published by Elsevier B.V.

Research undertaken by IGCP 259 (International Geochemical Mapping) indicates that wide-spaced sampling is a fundamental concept of international geochemical mapping as it appears to provide the only practical way to obtain a relative rapid (10–20 years) overview of global geochemistry. The main aim of this study is to test the suitability of floodplain sediment as a global sampling medium. Thirteen floodplain sediment samples and 13 stream sediment samples were taken at the exit of 13 super large drainage basins (SCB). The areal extents of these basins are in the order of 1000–10,000 km 2 . Within each SCB, 3–11 stream sediment samples each representing a component catchment basin (CCB) of 100–1000 km 2 were also taken. Fourty nine elements were analyzed. The results were compared with the average values derived from calculating thousands of stream sediment data available from China's National Geochemical Mapping (RGNG) program. Strong similiarities were demonstrated in distribution and trends among the three levels of data. The set of floodplain sediment data shows great coincidence with RGNR stream sediment data.

During the period 1985 to 1991, a systematic study was done on the geochemical characteristics of the Karatungk nickelcopper deposit in the Xinjiang-Uygur Autonomous Region in northwestern China. Surface rock and drill core sampling and CHIM surveying were carried out. Geochemically anomalous distribution patterns of Cu, Ni, Co, Cr, Ag, Mo, Ba, B, and As were outlined. A preliminary study showed that Cu, Ni and Co are diagnostic indicators for outcropping Ni-Cu-bearing intrusives, but are much less useful for concealed Ni-Cu-bearing bodies. Distinct anomalous associations of Ba, As, Mo, B, Ag, and Cr have been found over concealed intrusive bodies containing Cu-Ni deposits. Geochemical criteria for evaluating the nickel potential in basic-ultrabasic intrusive bodies in the Ertix ore belt were identified and a series of new anomalies discovered. Since completion of the study, two nickeliferous basic intrusives have been intersected by drilling.

The concentrations, spatial distribution and compositional patterns of extensively used hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) in urban dustfall in a metropolis-Beijing are presented in this paper. The potential sources are discussed and soil burdens are predicted based on the fluxes. The hotspots in commercial areas are identified by spatial distribution maps and the fractional value isomers indicates that dustfall in urban Beijing are affected by both current and historical usage of DDTs. It is worth noticing that there is possible application "dicofol-type of DDTs" in Beijing. The measured atmospheric deposition flux is 1.14×10(5) ng h(-1) m(-2) for HCHs and 1.47×10(5) ng h(-1) m(-2) for DDTs, respectively. However, when compared with atmospheric deposition flux, the volatilization flux estimated from concentrations in soils by fugacity model is significantly lower for HCHs (2.41 ng h(-1) m(-2)) and DDTs (0.07 ng h(-1) m(-2)). The net atmospheric flux to the soil suggests that the levels of HCHs and DDTs in soil are dominated by atmospheric deposition and the urban soil in Beijing would be a sink for HCHs and DDTs in the long term.

A total of 10 surface soil samples representing the entire area of Linfen City were collected and analyzed for the presence of 16 polycyclic aromatic hydrocarbons. The total polycyclic aromatic hydrocarbon concentration ranged from 1.1 to 63.7 microg g(-1). Analysis of the sources of contamination revealed that polycyclic aromatic hydrocarbons in the soil were derived from combustion sources. Specifically, the primary source of polycyclic aromatic hydrocarbons was coal combustion, but the samples were also effected to varying degrees by traffic emissions. Furthermore, increased levels of contamination were observed in northeast Linfen due to the distribution of industrial plants.

Sixteen priority polycyclic aromatic (PAHs) in PM(2.5) and PM(2.5-10) samples collected from 20 sites in Beijing, China in December 2005 and January 2006 were analyzed to determine the composition, spatial distribution and sources. Total PAHs of PM(2.5) and PM(2.5-10) ranged from 5.2 to 1062.2 ng m(-3) and 7.6 to 759.7 ng m(-3), respectively, categorized as heavier pollution. Among five kind of functional zones involved, industrial center, commercial area and village were heavily polluted. The mean concentration of PAHs in PM(2.5) of 407 ng m(-3) was 1.67-fold of that in PM(2.5-10), which was relatively high compared to the previous studies (winter in 2001 and 2002). The most evident change was the increase of Flu, BbkF and InP, which are believed to be less harmful and related to the increasing use of clean energy. However, pollution distribution was spatially heterogeneous inside the city. The most polluted sites located in the southeast of the city. Unlike previous studies, fluoranthene was the most abundant component quantified, which could be associated with increasing use of natural gas as clean energy. Compositional analysis and principal component analysis (PCA) suggested that different kinds of combustion were the main source of the PAHs in PM, though contribution of coal was still evident.

Eighteen organochlorine pesticides (OCPs) in air particulate matter (PM) samples collected from 20 sites in Beijing, China in 2005 and 2006 were analyzed to determine the composition, spatial distribution and sources. Total OCPs of PM2.5 and PM10 ranged from 32.59 pg m(-3) to 9232.31 pg m(-3) and 80.96 pg m(-3) to 9434.97 pg m(-3), respectively, categorized as heavier pollution compared to other cities of China. Among six kinds of functional zones involved, commercial areas and industrial centers were heavily polluted. Distinct concentrations variations were detected in PM with different particle diameters. Pollution distribution was spatially heterogeneous inside the city. The most heavily polluted sites located in the southeast part of the city, where laid many chemical factories. Compositional analysis and principal component analysis (PCA) suggested that past usage of OCPs was the main source, though there were new inputs in some sites.

Concentrations of HCH isomers, DDT, and its metabolites have been measured in 63 soil samples collected in the urban area and outskirts of Beijing City. HCHs and DDTs were observed in all samples and their geometric mean levels were 5.78 and 38.21 ng g(-1), respectively. The spatial distribution of OCPs in Beijing was clearly showed by the contour map, suggesting the sites with the higher level of OCPs are located in the west and the south region and urban areas within the study regions." Furthermore, a t-test showed a significant difference of the level of some compounds between urban and outskirts areas. The temporal distribution of HCHs and DDTs suggested that the historical application of OCPs has a great effect on the residual level. The ratios of (alpha-/gamma -HCH (p,p'-DDE+p,p'-DDD)/p,p'-DDT, and o,p'-DDT/p,p'-DDT indicated the present of lindane and impure dicofol besides technical HCHs and technical DDTs in Beijing. The potential risk of HCHs and DDTs was assessed on the basis of some current guideline values for soil. The level of OCPs in our study area was compared with other studies.

Surface soils from the outskirts of Beijing were analyzed for 16 priority polycyclic aromatic hydrocarbons (PAHs) using gas chromatography and mass spectrometry (GC-MS). The distribution map of total PAHs content was obtained as a contour plot. The concentration range of 16 PAHs varied by over two orders of magnitude from 0.016 mu g g(-1) in rural to 3.884 mu g g(-1) in suburban soils with the relatively standard deviation of 70.5%, showing large differences in the extent of PAHs pollution at the various sampling sites. It was notable that the concentration of BaP was 0.005-0.270 mu g g(-1) with a mean of 0.055 mu g g(-1). In general, the distribution of PAHs centered on the high molecular weight PAHs known to be carcinogenic. The 4-6 ring PAHs represented about 66% in rural samples and 70% in suburban soils of the total PAHs found. There was relatively good relationship among most of the individual PAHs and the compounds of Pyr, BaA, Flu, BbF, BaP, Chr and Ph gave strong correlation (r > 0.8) with the sum of PAHs. The selected marked compounds, a principal component analysis (PCA) and special PAHs compound ratios (Ph/An vs Flu/Pyr; Sigma COMB/Sigma EPA - PAHs) suggest the pyrogenic origins, especially traffic exhausts, are the dominant sources of PAHs in Beijing outskirts soils. (c) 2004 Elsevier Ltd. All rights reserved.