[Spatial Distribution of Soil Heavy Metals and Regional Control Strategies in China at Province Level].

It is important to understand the spatial distribution characteristics and health risks of soil heavy metals for the implementation of soil pollution control measures in different levels and regions. Based on the data of 706 core studies in the last 20 years, the spatial distribution characteristics, accumulation degree, and health risks of soil heavy metals in China were analyzed at the provincial level. The results showed that the soil heavy metals had obvious spatial differences on the provincial scale, with an overall trend of "high in the south and low in the north and high in the east and low in the west." The content of heavy metals in the soil of agricultural land and construction land was high, and the rate of exceeding the standard was higher than that of other land types. Soil heavy metal concentrations in most areas of China were higher than the regional background values and were highly cumulative. The accumulation indices were:Cd(1.80)>Pb(0.23)>Cu(0.17)>Zn(-0.05)>As(-0.56)>Cr(-0.69), with more than 85% of the provincial soils reaching moderate levels of Cd pollution. Non-ferrous metal resource-based provinces such as Yunnan, Guizhou, Guangxi, Hunan, and Jiangxi generally had higher soil heavy metal levels than those in other provinces, and local children faced higher cancer risks. Soil pollution in coastal areas such as Fujian, Zhejiang, Jiangsu, and Tianjin mainly originated from industrial production and urbanization construction. High intensity agricultural utilization was an important cause of soil heavy metal accumulation in Henan, Shandong, and Anhui.

Magnetic biochars have lower adsorption but higher separation effectiveness for Cd2+ from aqueous solution compared to nonmagnetic biochars.

Magnetic biochars were prepared by chemical co-precipitation of Fe3+/Fe2+ onto rice straw (M-RSB) and sewage sludge (M-SSB), followed by pyrolysis treatment, which was also used to prepare the corresponding nonmagnetic biochars (RSB and SSB). The comparison of adsorption characteristics between magnetic and nonmagnetic biochars was investigated as a function of pH, contact time, and initial Cd2+ concentration. The adsorption of nonmagnetic biochars was better described by pseudo-second-order kinetic model, and the adsorption of RSB and SSB was better described by Langmuir and Freundlich models, respectively. Magnetization of the biochars did not change the applicability of their respective adsorption models, but reduced their adsorption capabilities. The maximum capacities were 42.48 and 4.64 mg/g for M-RSB and M-SSB, respectively, underperforming their nonmagnetic counterparts of 58.65 and 7.22 mg/g for RSB and SSB. Such a reduction was fundamentally caused by the decreases in the importance of cation-exchange and Cπ-coordination after magnetization, but the Fe-oxides contributed to the precipitation-dependent adsorption capacity for Cd2+ on magnetic biochars. The qualitative and quantitative characterization of adsorption mechanisms were further analyzed, in which the contribution proportions of cation-exchange after magnetization were reduced by 31.9% and 12.1% for M-RSB and M-SSB, respectively, whereas that of Cπ-coordination were reduced by 3.4% and 31.1% for M-RSB and M-SSB, respectively. These reductions suggest that for adsorbing Cd2+ the choice of conventional biochar was more relevant than whether the biochar was magnetized. However, magnetic biochars are easily separated from treated solutions, depending largely on initial pH. Their easy of separation suggests that magnetic biochars hold promise as more sustainable alternatives for the remediation of moderately Cd-contaminated environments, such as surface water and agriculture soil, and that magnetic biochars should be studied further.

High-efficiency removal capacities and quantitative adsorption mechanisms of Cd2+ by thermally modified biochars derived from different feedstocks.

Adsorption characteristics of Cd2+ on the three biochars modified by pyrolysis and calcination were investigated that were derived from rice straw (TRSB), chicken manure (TCMB) and sewage sludge (TSSB). The pH effect, adsorption kinetics, isotherms and thermodynamics, and desorption were determined, and qualitative analysis of adsorption mechanisms was performed by SEM, XRD, FTIR and XPS. Maximum adsorption capacities reached 177.28, 96.03 and 74.04 mg/g for TCMB, TRSB and TSSB, respectively, which were higher than that of many previously reported biochars. Even after five adsorption-desorption cycles, TCMB showed the strongest reusability without losing significantly adsorption capacity. This suggested that thermally modified biochars, particularly TCMB, could be a preferred adsorbent for Cd2+. Relative distribution of adsorption mechanisms was examined by direct and indirect calculation, in which the precipitation and cation-exchange dominated the whole chemisorption process, jointly accounting for 84% (TRSB) to 95% (TCMB) of total adsorption. While the complexation was of minor importance in total adsorption accounting for 5%-16%. The relationship of each mechanism with the properties of biochar was also discussed. These provided new insights on the adsorption effectiveness and mechanisms for Cd2+ in the aqueous solution that was critical for evaluating the application of modified biochars.

[Improved Regression Kriging Prediction of the Spatial Distribution of the Soil Cadmium by Integrating Natural and Human Factors].

Mastering the spatial distribution of heavy metals in the soil plays an important supporting role in the scientific formulation of soil pollution risk management and control strategies. Few factors were considered and multiple collinearity between parallel variables existed,resulting in low prediction accuracy. OK (common Kriging method), NRK (regressive Kriging method based on natural factors only), and NARK (regressive Kriging based on natural-human factors)were used to simulate the spatial distribution of soil Cd by selecting 23 natural-artificial influencing factors. The prediction accuracy was evaluated based on an empirical study of the area around Shaoguan Qujiang smelter. The results showed that the above-standard rate of soil cadmium in this area reached 85.93%, and the effect on the spatial heterogeneity of soil cadmium was shown as air emissions from smelters > air emissions from steel plants > pH > organic matter > Euclidean distance to road > Euclidean distance to river. The root-mean-square error and average absolute error of NARK's prediction results for soil cadmium were 26.86% and 30.56% lower than that of the OK method, respectively. The model determination coefficient R2 increased from 0.78 to 0.88. Compared with that of NRK, it was reduced by 24.15% and 24.23% and R2 increased from 0.81 to 0.88. The NRK combining natural and human factors significantly improved the simulation accuracy of the spatial distribution of soil cadmium, and the addition of human factors as auxiliary variables, especially atmospheric point source pollution emissions, greatly contributed to the improvement of the model accuracy.

Qualitative and quantitative characterization of adsorption mechanisms for Cd2+ by silicon-rich biochar.

The adsorption characteristics of rice-husk biochar (RHB) rich in silicon (Si) for Cd2+ in solution and soil were investigated. Three biochars were produced at different pyrolytic temperatures of 300 °C(RHB300), 500 °C(RHB500) and 700 °C (RHB700). The pH effect, adsorption kinetics and isotherms were examined, and chemical analyses of Cd2+-loaded biochars were conducted by SEM-EDS, FTIR, XRD and Boehm titration. Biochars produced at higher temperature have much larger pH and surface area, resulting in greater adsorption capacities and faster adsorption kinetics. Maximum adsorption capacities calculated from Langmuir isotherm were 62.75, 77.37 and 93.50 mg/g for RHB300, RHB500 and RHB700, respectively. Cd2+ adsorption was primarily attributed to cation exchange and precipitation, which jointly contributed 59.55% (RHB300) to 76.05% (RHB700) of the total adsorption, but the mechanisms of complexation and coordination were of minor importance in total adsorption. The relationship of each mechanism with biochar's properties was further discussed. Si-containing minerals within biochar made a much larger contribution to precipitation than total adsorption, as the respective contribution proportion were 33.92% and 8.33% on average. When added to highly Cd-polluted soil, the biochars could effectively reduce the availability of Cd2+ after incubation for 35 days, and ameliorate soil acidification through the speediness of Si released into soil solutions. These demonstrate that rice husk-derived biochar, produced at high temperatures, can be suitable applied to mitigate Cd-contamination of soil and water, and the presented analyses shed light on the mechanisms underlying the adsorption by this Si-rich biochar.

Adsorption Behavior and Relative Distribution of Cd2+ Adsorption Mechanisms by the Magnetic and Nonmagnetic Biochars Derived from Chicken Manure.

The present study investigated the adsorption of Cd2+ by nonmagnetic and magnetic biochars (CMB and M-CMB) derived from chicken manure, respectively. The adsorption characteristics were investigated as a function of initial pH, contact time, initial Cd2+ concentration and magnetic separation. Adsorption process of both biochars were better described by Pseudo-second-order kinetic equation and Freundlich isotherm model, which were spontaneous and endothermic in nature. It was found that maximum capacities were 60.69 and 41.07 mg/g obtained at the initial Cd2+ concentration of 180 mg/L for CMB and M-CMB, and the turbidity of adsorption-treated solution was reduced from 244.3 to 11.3 NTU after magnetic separation of 0.5 min. These indicated that M-CMB had lower adsorption capacity of Cd2+ than CMB, though it was successfully separated from the treated solutions. Furthermore, both biochars before and after adsorption were analyzed by SEM-EDS, XRD and FTIR. Adsorption mechanisms mainly included precipitation, ion-exchange, complexation and Cπ-coordination, in which precipitation and ion-exchange dominated the adsorption process by CMB, while in M-CMB, precipitation was always predominant mechanism, followed by ion-exchange. The two other mechanisms of complexation and Cπ-coordination were trivial in both biochars, jointly contributing 7.21% for CMB and 5.05% for M-CMB to total adsorption. The findings deepen our understanding of the mechanisms governing the adsorption process, which are also important for future practical applications in the removal of heavy metals from wastewater by the biochars.

[Thoughts on and Construction of a Risk Management and Control System for Contaminated Sites in the Guangdong-Hong Kong-Macao Greater Bay Area].

Preventing the environmental risks linked to contaminated sites and guaranteeing the safety of human settlements are some of the challenges and tasks involved in the construction of world-class city clusters in the Guangdong-Hong Kong-Macao Greater Bay Area. Due to differences in the political systems and land property rights between Guangdong, Hong Kong, and Macao, as well as in the levels of urbanization, industrial structures, and environmental management capabilities of the nine cities in the Pearl River Delta, the risk management and control mode of contaminated sites varies considerably within the Greater Bay Area. In this context, an analysis of the features of risk management and control in the contaminated sites of typical cities can help strengthening technical communication and cooperation, optimizing risk management and control systems. This article briefly describes the risk management and control systems adopted for polluted sites in China; in particular it elaborates on the features of these systems in Guangzhou, Shenzhen, Dongguan, Hong Kong, and Macao, which have been subjected to monitoring, contamination assessments, and renovation procedures. During our study, the risk management and control systems adopted in different cities have been analyzed and compared; moreover, we elaborated thoughts and suggestions for land planning, policy feedback, information disclosure, and alliance mechanisms. We conclude that, overall, Hong Kong and several cities of the Pearl River Delta have established effective risk management and control systems for the polluted sites, which take into account certain local characteristics. However, with the further development and reuse of contaminated sites, the building of a world-class urban agglomeration in the Guangdong-Hong Kong-Macao Greater Bay Area will require safer, more refined, and more efficient risk management and control strategies. We highlight the need to exchange information among researchers in order to promote technical exchange and cooperation. This is particularly important for the risk management and control of polluted sites distributed within the two regions and nine cities of the Guangdong-Hong Kong-Macao Greater Bay Area, sine it would allow their safe reuse and efficient development.

[Pollution Characteristics and Migration of BTEX at a Chemical Contaminated Site in the Guangdong-Hong Kong-Macau Greater Bay Area].

In this study, we analyzed 247 soil and 20 groundwater samples from a typical chemical site in the Guangdong-Hong Kong-Macau Greater Bay Area and simulated the solute transport of pollutant benzene with the GMS software, in order to reconstruct the distribution and migration mechanism of benzene series (BTX) pollutants. The detected concentrations of benzene, ethylbenzene, m,p-xylene, and o-xylene exceeded the screening values in some soil and groundwater samples, indicating that the pollution of BTX in shallow groundwater was serious. Our simulation indicated an elliptical flow of benzene in groundwater (from northwest to southeast), mainly through convection, dispersion, and molecular diffusion. Along the vertical direction, the BTX was mainly distributed in the form of floating benzene, and some of the constituents were dissolved in the groundwater. Due to hydrodynamic mechanisms, the dissolved benzene tended to migrate faster and had hence a greater impact on the downstream groundwater. Through the model validation and analysis, we obtained a linear fitting correlation coefficient (R2) of 0.995 between the simulated and actual monitoring values, which indicates a good agreement between these two sets of data. The model had a high prediction accuracy, and could hence accurately determine the migration and distribution characteristics of benzene. Therefore, it provides a scientific basis for the accurate control and remediation of chemical contaminated sites in the Guangdong-Hong Kong-Macao Greater Bay Area.

[Spatial Distribution and Risk Assessment of Heavy Metals in Soils from a Typical Urbanized Area].

With the rapid urbanization in China, soil environments are facing high risks. Taking a typical urbanized area as a case study, a total of 106 surface soil samples (0-20 cm) and 96 subsurface soil samples (20-40 cm) were collected to determine the concentrations of heavy metals, and then, the Nemerow index and Hankson index methods were used to evaluate their degrees of ecological risk. The spatial distributions of ecological risks were also explored. Experimental results showed that the concentrations of Cr, Ni, Cu, Zn, As, Cd, Pb, and Hg in surface soil samples were 2.87-84.64, 1.40-56.00, 2.75-125.05, 15.05-201.39, 1.46-89.92, 0.001-0.92, 15.29-160.07, and 0.006-0.52 mg·kg-1, respectively, and those in subsurface soil samples were 3.56-75.14, 1.65-71.58, 3.28-290.04, 17.99-296.94, 3.07-65.67, 0.02-1.00, 11.10-97.59, and 0.01-0.41 mg·kg-1, respectively. According to the risk control standards for soil contamination of agricultural land, approximately 71.70%, 40.57%, 4.72%, 3.77%, and 0.94% of Cd, Cu, Pb, As, and Zn, respectively, in the surface soil samples exceeded the standards, while 72.92%, 39.58%, 6.25%, 3.13%, 3.13%, and 1.04% of Cd, Cu, As, Zn, Pb, and Ni, respectively, in the subsurface soil samples exceeded the standards. Obviously, the pollution by Cd and Cu was the most severe in the research area, and the main contaminated areas were distributed in the northern part of the land. The soil environmental quality pollution assessment illustrated that high risk areas were distributed in the northern part of the research area too. The risk assessment results indicated that the main pollution factor was Cd, which is accordance with the serious pollution findings for Cd. In response to these results, effective management and remediation methods should be taken to control the soil environment pollution in this typical urbanized area.

[Spatial Distribution and Potential Ecological Risk Assessment of Heavy Metals in Soils and Sediments in Shunde Waterway, Southern China].

Environmental quality of soils and sediments around water source area can influence the safety of potable water of rivers. In order to study the pollution characteristics, the sources and ecological risks of heavy metals Zn, Cr, Pb, Cu, Ni and Cd in water source area, surface soils around the waterway and sediments in the estuary of main tributaries were collected in Shunde, and ecological risks of heavy metals were assessed by two methods of potential ecological risk assessment. The mean contents of Zn, Cr, Pb, Cu, Ni and Cd in the surface soils were 186.80, 65.88, 54.56, 32.47, 22.65 and 0.86 mg · kg⁻¹ respectively, and they were higher than their soil background values except those of Cu and Ni. The mean concentrations of Zn, Cr, Pb, Cu, Ni and Cd in the sediments were 312.11, 111.41, 97.87, 92.32, 29.89 and 1.72 mg · kg⁻¹ respectively, and they were higher than their soil background values except that of Ni. The results of principal component analysis illustrated that the main source of Cr and Ni in soils was soil parent materials, and Zn, Pb, Cu and Cd in soils mainly came from wastewater discharge of local manufacturing industry. The six heavy metals in sediments mainly originated from industry emissions around the Shunde waterway. The results of potential ecological risk assessment integrating environmental bioavailability of heavy metals showed that Zn, Cu, Pb and Ni had a slight potential ecological risk. Cd had a slight potential ecological risk in surface soils, but a moderate potential ecological risk in surfaces sediments. Because the potential ecological risk assessment integrating environmental bioavailability of heavy metals took the soil properties and heavy metal forms into account, its results of risks were lower than those of Hakanson methods, and it could avoid overestimating the potential risks of heavy metals.

[Classification of Priority Area for Soil Environmental Protection Around Water Sources: Method Proposed and Case Demonstration].

Based on comprehensive consideration of soil environmental quality, pollution status of river, environmental vulnerability and the stress of pollution sources, a technical method was established for classification of priority area of soil environmental protection around the river-style water sources. Shunde channel as an important drinking water sources of Foshan City, Guangdong province, was studied as a case, of which the classification evaluation system was set up. In detail, several evaluation factors were selected according to the local conditions of nature, society and economy, including the pollution degree of heavy metals in soil and sediment, soil characteristics, groundwater sensitivity, vegetation coverage, the type and location of pollution sources. Data information was mainly obtained by means of field survey, sampling analysis, and remote sensing interpretation. Afterwards, Analytical Hierarchy Process (AHP) was adopted to decide the weight of each factor. The basic spatial data layers were set up respectively and overlaid based on the weighted summation assessment model in Geographical Information System (GIS), resulting in a classification map of soil environmental protection level in priority area of Shunde channel. Accordingly, the area was classified to three levels named as polluted zone, risky zone and safe zone, which respectively accounted for 6.37%, 60.90% and 32.73% of the whole study area. Polluted zone and risky zone were mainly distributed in Lecong, Longjiang and Leliu towns, with pollutants mainly resulted from the long-term development of aquaculture and the industries containing furniture, plastic constructional materials and textile and clothing. In accordance with the main pollution sources of soil, targeted and differentiated strategies were put forward. The newly established evaluation method could be referenced for the protection and sustainable utilization of soil environment around the water sources.

[Research progress and development trend of quantitative assessment techniques for urban thermal environment.] / åŸŽå¸‚çƒ­çŽ¯å¢ƒå®šé‡è¯„ä»·æŠ€æœ¯ç ”ç©¶è¿›å±•åŠå‘å±•è¶‹åŠ¿.

Quantitative assessment of urban thermal environment has become a focus for urban climate and environmental science since the concept of urban heat island has been proposed. With the continual development of space information and computer simulation technology, substantial progresses have been made on quantitative assessment techniques and methods of urban thermal environment. The quantitative assessment techniques have been developed to dynamics simulation and forecast of thermal environment at various scales based on statistical analysis of thermal environment on urban-scale using the historical data of weather stations. This study reviewed the development progress of ground meteorological observation, thermal infrared remote sensing and numerical simulation. Moreover, the potential advantages and disadvantages, applicability and the development trends of these techniques were also summarized, aiming to add fundamental knowledge of understanding the urban thermal environment assessment and optimization.

[Relationships between settlement morphology transition and residents commuting energy consumption].

Settlement morphology transition is triggered by rapid urbanization and urban expansion, but its relationships with residents commuting energy consumption remains ambiguous. It is of significance to understand the controlling mechanisms of sustainable public management policies on the energy consumption and greenhouse gases emission during the process of urban settlement morphology transition. Taking the Xiamen City of East China as a case, and by using the integrated land use and transportation modeling system TRANUS, a scenario analysis was made to study the effects of urban settlement morphology transition on the urban spatial distribution of population, jobs, and land use, and on the residents commuting energy consumption and greenhouse gasses emission under different scenarios. The results showed that under the Business As Usual (BAU) scenario, the energy consumption of the residents at the morning peak travel time was 54.35 tce, and the CO2 emission was 119.12 t. As compared with those under BAU scenario, both the energy consumption and the CO2 emission under the Transition of Settlement Morphology (TSM) scenario increased by 12%, and, with the implementation of the appropriate policies such as land use, transportation, and economy, the energy consumption and CO2 emission under the Transition of Settlement Morphology with Policies (TSMP) scenario reduced by 7%, indicating that urban public management policies could effectively control the growth of residents commuting energy consumption and greenhouse gases emission during the period of urban settlement morphology transition.

Spatial pattern of impervious surfaces and their impacts on land surface temperature in Beijing, China.

Land surface temperature (LST), which is heavily influenced by urban surface structures, is a significant parameter in urban environmental analysis. This study examined the effect impervious surfaces (IS) spatial patterns have on LST in Beijing, China. A classification and regression tree model (CART) was adopted to estimate IS as a continuous variable using Landsat images from two seasons combined with QuickBird. LST was retrieved from the Landsat Thematic Mapper (TM) image to examine the relationships between IS and LST. The results revealed that CART was capable of consistently predicting LST with acceptable accuracy (correlation coefficient of 0.94 and the average error of 8.59%). Spatial patterns of IS exhibited changing gradients across the various urban-rural transects, with LST values showing a concentric shape that increased as you moved from the outskirts towards the downtown areas. Transect analysis also indicated that the changes in both IS and LST patterns were similar at various resolution levels, which suggests a distinct linear relationship between them. Results of correlation analysis further showed that IS tended to be positively correlated with LST, and that the correlation coefficients increased from 0.807 to 0.925 with increases in IS pixel size. The findings identified in this study provide a theoretical basis for improving urban planning efforts to lessen urban temperatures and thus dampen urban heat island effects.