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Geochemical background and baseline values are important parameters for understanding the geochemical characteristics of soil elements, but the research degree of these two parameters is lacking in Hebei Province. Therefore, data from the multi-purpose regional geochemical survey and land quality geochemical assessment in Hebei Province from 2004 to 2018 were collected, covering approximately 71% of the land area of the whole province. Based on the data of surface soil and deep soil, scientific and robust methods including median value and median absolute deviation were used to calculate the geochemical background values, geochemical baseline values, as well as variation ranges of 54 indexes (Ag, Al 2 O 3 , As, Au, B, Ba, Be, Bi, Br, CaO, Cd, Ce, Cl, Co, Cr, Cu, F, Fe 2 O 3 , Ga, Ge, Hg, I, K 2 O, La, Li, MgO, Mn, Mo, N, Na 2 O, Nb, Ni, P, Pb, pH, Rb, S, Sb, Sc, Se, SiO 2 , Sn, Sr, Th, Ti, Tl, U, V, W, Y, Zn, Zr, total carbon (TC), and organic carbon (C org )) in Hebei Province and 11 prefecture-level cities. The change rate in geochemical background for each index was also calculated. The results showed that the geochemical background and baseline values of most soil chemical elements in Hebei Province were lower than those nationwide, but the values of Ba, Br, Cl, MgO, Na 2 O, P, pH, S, Sr, and TC were higher, with CaO being the highest. Compared with those in north China, there was no significant difference in the geochemical background and baseline values for the 54 indexes, with the ratios of 0.83-1.17 and 0.79-1.19, respectively. Significant changes in the geochemical background for C org , Hg, N, P, S, and Se were observed in Hebei Province, indicating that these indexes were greatly influenced by human factors. Preliminary analysis suggests that coal burning emissions and agricultural chemical use were two very important inducing factors.

Investigating the pollution conditions of trace elements in the Poyang Lake basin, identifying the pollution sources, evaluating the ecological risks play an important part in formulating the effective strategies for protecting the basin ecosystem. To understand the concentration characteristics, pollution levels, and ecological risks of twelve trace elements (Cd, Hg, Pb, As, Cu, Zn, Cr, Ni, Mn, Sb, W, and Sn) in the floodplain sediments of the five main tributaries in Poyang Lake basin in the past twenty years, we used the enrichment factor (EF) and modified pollution index (MPI) to quantify the pollution levels of the trace elements, and analyzed and discussed the pollution sources in the areas with significant pollution level changes. The results indicated that the concentrations of cadmium, zinc, manganese, tungsten and lead in the floodplain sediments of the Poyang Lake basin during the past twenty years have increased by 134%, 26%, 41%, 25%, and 8%, respectively, and mercury, arsenic, chromium, nickel, antimony, and tin have decreased by 35%, 15%, 22%, 10%, 14%, and 13%, respectively, while copper has not changed significantly. The concentrations of cadmium in the Raohe River, Ganjiang River, and Xinjiang River basins have increased by 331%, 151%, and 107%, while mercury decreased in the Fuhe River, Ganjiang River, and Xiushui River basins by 87%, 41%, and 40%, respectively. The classification results based on the EF indicated that the changes in the pollution levels of trace elements in the Poyang Lake basin were characterized by the aggravation of cadmium pollution and the degradation of mercury pollution, the pollution level of cadmium in the Ganjiang River basin was upgraded to moderate and significant, the pollution level of cadmium in the Le'an River was upgraded to very high, and the pollution level of mercury in the Fuhe River basin was reduced to unpolluted or minimal. The MPI classification results established that the increase in the cadmium pollution had intensified the comprehensive pollution in the Poyang Lake basin, causing the proportion of severely and heavily polluted sites to be raised from 17% to 33%. The MRI classification results also demonstrated that the proportion of very high ecological risk sites have increased from 11% to 22%. The element with the highest MRI contribution rate changed from mercury to cadmium, which was caused by the reduction of the ecological risk level from very high to moderate. The results demonstrated that the significant pollution changes in the trace elements in the floodplain sediments of the Poyang Lake basin were primarily caused by human activities, such as mineral exploitation, smelting, and industrial and agricultural production. Our findings can provide scientific evidence for the prevention and control of river pollution and the optimal management of a watershed ecosystem.

Heavy metals (HMs) are naturally occurring elements that have high natural background levels in the environment. Therefore, it is important to conduct ecological risk assessment and identify potential sources of HMs. In the past, studies were conducted at the regional scale. The accuracy of those studies could not meet the needs of spatial planning and natural resource management. Therefore, it is necessary to conduct ecological risk assessment at the township scale. In this study, 1092 soil samples (from 0-20 cm depth) were collected in the town of Reshui, an area with high background levels of soil HMs with the parent material of carbonatite, which is commonly found in Southwest China. The town of Reshui is a multi-ecological risk superimposed area where the ecological risk is high. In this study, concentrations of HMs (Cd, Cr, As, Hg, Pb, Cu, Zn, and Ni) in the topsoil were analyzed, and statistical analysis (SA), geographic information system (GIS) modeling, and positive matrix factorization (PMF) analysis were performed. The geoaccumulation index ( I geo ) and potential ecological risk index (PERI) were applied for the ecological risk assessment and quantification of the sources of the soil HMs. The mean values of HM concentrations in the topsoil were 18.1, 1.18, 174.1, 202.2, 0.09, 71.1, 34.9, and 167.2 mg ·kg -1 for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, respectively, which were considerably higher than the average background value (ABV) in soils in Yunnan Province except for As and Pb. The average concentrations of Cd, Cr, Cu, and Ni exceeded the screening values specified in the soil contamination risk in agricultural land (GB 15618-2018) by 5.82, 1.16, 4.04, and 1.02 times, respectively. The I geo value shows that the major pollutant is Cu in the surface soil of the study area, followed by Cr, and Cd. Speciation analysis of HMs indicates that HMs (Cr, As, Pb, Cu, Zn, and Ni) mainly exist in the residual form, mostly from the geological background with low bioavailability. The potential effective components of Hg have higher levels, but the total amount of Hg and its pollution risk are lower. Cd has a high bioavailability ratio, is easy to enter the soil solution and be absorbed by crops, and is the HM with the highest pollution risk in the study area. The PERI shows that the proportions of low ecological risk, moderate risk, and high risk soil samples are 44.23%, 54.40%, and 1.37% of the total number of samples, respectively. Hg and Cd were the major sources of risk because of their high toxicity coefficient. The PMF analysis indicates that there are four major sources of HMs in the study area: human activity, natural sources, coal mining and traffic emissions, and agricultural sources with the risk contribution ratios of 9.29%, 53.67%, 11.23%, and 25.81%, respectively. The PMF analysis effectively quantified the ecological risk from these sources, providing a reference for further pollution control and prevention measures.

To build a soil environmental quality monitoring network and collect the systematic soil geochemical data of heavy metals before and after the construction of Xiong'an New District(XND), long-term variations in soil heavy metal levels during the XND construction were monitored based on the land quality geochemical survey monitoring data and the geochemical distribution of heavy metals. Parameters such as sampling density, sampling quantity, and sampling period were estimated to construct the geochemical monitoring network, which provides a reference for the future long-term monitoring of soil heavy metal geochemistry in XND. The results indicate that variations in the amount of heavy metals As, Cd, Cu, Hg, and Pb are greater than 36%, while the nugget coefficients of Cd, Cu, and Pb are greater than 75% because of the superposition of manmade sources on the high natural background levels. At the 95% and 90% confidence levels, while the allowable error Δ of the sample mean value is 5%, 10%, and 15% and heavy metals as As, Cd, Cu, Hg,Ni, Pb and Zn is monitored in soil environmental quality monitoring network, the proper numbers in the study area are 1077, 270, 120 and 767, 192, 86, respectively. The minimum detectable change(MDC)of each heavy metal species is between 0.0025 and 2.54 mg ·kg -1 . Soil heavy metal monitoring requires different revisit intervals under different annual change rates, but in the study area, revisit intervals of soil monitoring are approximately two years under the current conditions of constant annual change rates.

Urban soils are more easily subjected to modification, especially by contamination because of various human activities, and the environmental problems caused by urban soil pollution have become more prominent. To systematically investigate concentration characteristics, pollution levels, and exposure risks of 13 trace metals in urban soils of planning areas for 193 cities above the prefectural level, located in 31 provinces (autonomous regions and municipalities) of China, levels of pollution in urban soil were evaluated using the geoaccumulation index and integrated pollution index of trace metals, and health risks of residents exposed to urban soils were quantified using the health risk assessment method recommended by the US Environmental Protection Agency (USEPA). The results show that the median concentrations of As, Be, Cd, Co, Cr, Cu, Hg, Ni, Pb, Se, Tl, V, and Zn in topsoils of urban planning areas were 9.25, 2.14, 0.174, 12.4, 68.4, 28.2, 0.095, 27.7, 31.1, 0.29, 0.61, 82.7, and 82.2 mg·kg -1 , respectively. Compared with the corresponding urban soil background values, the concentrations of Cd, Hg, and Se changed significantly. The geoaccumulation index ( I geo ) values showed that Hg in urban soils of the planning area was the most severe pollutant, followed by Se and Cd, which caused pollution levels of uncontaminated to moderately contaminated levels, while other trace metals were uncontaminated. The Nemerow IPI (IPI N ) revealed that the soils in 22 urban planning areas were heavily polluted and 16 urban planning areas were moderately polluted; in addition, the most polluted city in China was Zhuzhou in the Hunan province. The results of health risk assessment indicate that the soils in the five urban planning areas-Chenzhou City, Huangshi City, Zhuzhou City, Xiangtan City, and Longyan City-posed potential non-carcinogenic risks to children, and the major factor triggering risks was ingestion of Pb. To understand the soil pollution status and distribution of contaminated land parcel, it is suggested to carry out detailed investigation in cities with integrated moderate to heavy pollution to establish the list of contaminated land parcel and implement pollution control and restoration.

This study uses 68 sets of paddy soil and rice grain samples collected from an area of carbonate rocks in Guangxi Province, China, to explore the ecological risks of heavy metals (As, Cd, Cr, Cu, Hg, Pb, Ni, and Zn) in soils from a high background area. We analyzed the concentrations of these heavy metals in soil and grain samples, and their chemical speciation in soil, and use these data to assess the associated ecological risks by means of statistics, a geo-accumulation index, bioconcentration factors (BCF), and correlation analysis. The arithmetic mean values of heavy metals concentrations in soil samples from the study area were (75.8±50.1), (1.91±1.02), (467.0±253.1), (48.5±9.8), (0.21±0.08), (76.2±28.1), (84.2±25.0), and (258.0±122.6) mg·kg -1 for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, respectively, which were remarkably higher than of those from other regions within Guangxi Province and China. In comparison to China's soil environmental quality standard risk screening values (GB 15618-2018), the over-standard rates of Cd, As, and Cr were 95.6%, 86.8%, and 69.1%, respectively. In comparison to risk intervention values, the over-standard rates of Cd, As, and Cr were 27.9%, 17.6%, and 5.9%, respectively. Speciation analysis on heavy metals indicated that As, Cr, Cu, Ni, Pb, and Zn were mainly found in a residual form, and accounted for>80% of the total concentrations, and had a low bioavailability. The bioactive components (F 1 +F 2 +F 3 ) of Cd accounted for 21%, and the bioactivity of Cd was higher than other elements. The potential bioavailable components (F 4 +F 5 +F 6 ) of Hg accounted for 44%, with low total concentrations, which are understood to have little potential ecological harm for crops. However, the over-standard rates of Pb, Cd, and Cr in rice grains were only 23.5%, 8.8%, and 2.9%, respectively. Correlation analysis showed that there was no significant correlation between the concentrations of heavy metals in soils and the corresponding rice grains. The mean BCFs of each heavy metal were <0.1, and the BCFs of Hg, Pb, As, Cr, and Ni were <0.05. Overall, we found relatively high concentrations, low activity, and low ecological risks for heavy metals in the study area. For high geological background materials such as carbonate rocks, factors such as metal speciation, biological activity, and crop over-standard rates should be taken into account along with the traditional use of the total amount of heavy metals in a soil as the evaluation standard when formulating pollution control policies.