Heavy metal soil contamination is associated with potential toxicity to humans or ecotoxicity. Scholars have increasingly used a combination of geographical information science (GIS) with ...geostatistical and multivariate statistical analysis techniques to examine the spatial distribution of heavy metals in soils at a regional scale. A review of such studies showed that most soil sampling programs were based on grid patterns and composite sampling methodologies. Many programs intended to characterize various soil types and land use types. The most often used sampling depth intervals were 0–0.10 m, or 0–0.20 m, below surface; and the sampling densities used ranged from 0.0004 to 6.1 samples per km2, with a median of 0.4 samples per km2. The most widely used spatial interpolators were inverse distance weighted interpolation and ordinary kriging; and the most often used multivariate statistical analysis techniques were principal component analysis and cluster analysis. The review also identified several determining and correlating factors in heavy metal distribution in soils, including soil type, soil pH, soil organic matter, land use type, Fe, Al, and heavy metal concentrations. The major natural and anthropogenic sources of heavy metals were found to derive from lithogenic origin, roadway and transportation, atmospheric deposition, wastewater and runoff from industrial and mining facilities, fertilizer application, livestock manure, and sewage sludge. This review argues that the full potential of integrated GIS and multivariate statistical analysis for assessing heavy metal distribution in soils on a regional scale has not yet been fully realized. It is proposed that future research be conducted to map multivariate results in GIS to pinpoint specific anthropogenic sources, to analyze temporal trends in addition to spatial patterns, to optimize modeling parameters, and to expand the use of different multivariate analysis tools beyond principal component analysis (PCA) and cluster analysis (CA).
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•Critically reviewed field studies of regional distribution of heavy metal in soil.•Reviewed studies combined GIS with multivariate statistical analysis.•Summarized the most common sampling strategies, GIS method, and multivariate technique.•Identified determining and correlating factors for soil heavy metals.•Discussed major natural and anthropogenic sources of soil heavy metals.
The integration of GIS and multivariate statistical analysis is a valuable tool in studying the regional distribution of heavy metals in soil.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Microplastics (MPs) are an emerging concern and potential risk to marine and terrestrial environments. Surface soils are reported to act as a sink. However, MP vertical mobility in the subsurface ...remains uncertain due to a lack of scientific data. This study focused on MP penetration in sand soil column experiments. Here we report the mobility of five different MPs, which consisted of polyethylene (PE) and polypropylene (PP) particles of various sizes and densities. We observed that the smallest sized PE MPs (21 μm) had the greatest movement potential. Moreover, it was found that when these MPs were subjected to greater numbers of wet-dry cycles, the penetration depth significantly increased, with an apparent linear relationship between depth and wet-dry cycle number (r2 = 0.817). In comparison, increasing the volume of infiltration liquid or the surface MP concentration had only negligible or weak effects on migration depth (r2 = 0.169 and 0.312, respectively). Based on the observed wet-dry cycle trend, we forecast 100-year penetration depths using weather data for 347 cities across China. The average penetration depth was calculated as 5.24 m (95% CI = 2.78–7.70 m), with Beijing Municipality and Hebei, Henan and Hubei provinces being the most vulnerable to MP vertical dispersion. Our results suggest that soils may not only represent a sink for MPs, but also a feasible entryway to subsurface receptors, such as subterranean fauna or aquifers. Finally, research gaps are identified and suggested research directions are put forward to garner a better understanding MP vertical migration in soil.
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•MP size, plastic type, and wet-dry cycles were related to sand penetration depth.•Infiltration volume and concentration had negligible or weak effects on MP migration.•The average forecasted 100-year penetration depth for 347 cities in China was 5.24 m.•Beijing Municipality and Hebei, Henan and Hubei Provinces were the most vulnerable.•Soils may not only represent a sink, but also a feasible entryway to the subsurface.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Widespread soil contamination threatens living standards and weakens global efforts towards the Sustainable Development Goals (SDGs). Detailed soil mapping is needed to guide effective ...countermeasures and sustainable remediation operations. Here, we review visible and infrared reflectance spectroscopy (VIRS) based detection methods in combination with machine learning. To date, proximal, airborne and spaceborne carrier devices have been employed for soil contamination detection, allowing large areas to be covered at low cost and with minimal secondary environmental impact. In this way, soil contaminants can be monitored remotely, either directly or through correlation with soil components (e.g. Fe-oxides, soil organic matter, clay minerals). Observed vegetation reflectance spectra has also been proven an effective indicator for mapping soil pollution. Calibration models based on machine learning are used to interpret spectral data and predict soil contamination levels. The algorithms used for this include partial least squares regression, neural networks, and random forest. The processes underlying each of these approaches are outlined in this review. Finally, current challenges and future research directions are explored and discussed.
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•VIRS based detection serves as a sustainable way in mapping soil pollution.•The combination of machine learning enables VIRS to provide an accurate result.•Heavy metals and organic pollutants in soil can be monitored this way.•Fe-oxide, clay minerals and soil organic matters are influential factors.•Field-based study is requisite to improve this method.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The modern society is increasingly demanding sustainable practices in engineering fields. In the specific case of engineering practices for restoring contaminated land, there is an ongoing ...sustainable remediation movement which has rapidly drawn attention from both the industry and governments. It is well recognized that decision making in contaminated land remediation depends on the interaction of a variety of stakeholders. However, there is still no consensus as for how various stakeholders perceive sustainable practices in remediation, and how stakeholders interact in decision making that may lead to sustainable practices. The present study proposes a hypothetical model depicting the mediating effect of stakeholder perception in decision making. Using empirical experiences, questionnaire survey, and qualitative interview results, the present study found that there is divergent perception by various stakeholders regarding how sustainable behavior is adopted and how it is affected by stakeholder influence. The divergent view was attributed to varying organizational objectives, information access, and self-perception. Moreover, it found that incorporating sustainability into real engineering practice is transdisciplinary and requires transdisciplinary processes that can help various stakeholders to reach consensus.
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CEKLJ, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The stability of mercury (Hg) contamination in soil environments can change over time. This has implications for agricultural sites under long-term management after in situ treatment involving soil ...amendments. In this study, rice husk biochar (RHB) and sulfur modified rice husk biochar (SRHB) were synthesized and applied (dosage = 5% dry wt.) to a Hg polluted agricultural soil collected from Guizhou province, Southern China (soil total Hg content = 28.3 mg/kg; C = 2%; and, S = 0.1%). The long-term stabilization effectiveness of the soil treatments was evaluated by a combined approach involving: (i) accelerated aging for 104 simulated years; (ii) soil extraction as a proxy for plant uptake; and, (iii) sequential extraction to identify Hg fractions. The SRHB amendment raised the soil’s total S content by approximately an order of magnitude (to 0.9%), which remained at a generally constant level throughout the simulation. The initial pH levels for the untreated and treated soils were alkaline and remained between 7.0 and 7.5 for the first 50 years of simulated aging, before decreasing as the simulation time increased further. The pH of the SRHB treated soils did not drop below that of untreated soils during the simulation. Soil extraction tests with 0.1 M HCl solution indicated that RHB and SRHB treatments could effectively immobilize the Hg in soil for at least 50 and 75 simulated years, respectively. At simulated year 50, the amount of Hg extracted from RHB and SRHB treated soils was <200 ng/L and <100 ng/L, respectively. Thus, showing SRHB to be a particularly promising remedial option. The soil Hg was mostly associated with the stable sequential extraction fractions (F3-5). By the end of the simulation, the F5 fraction for SRHB and RHB treated soils reduced by 44.6%, and 42.0%, respectively, whereas the F4 fraction increased by >400% in both cases. In summary, SRHB may provide long-lasting Hg stabilization at contaminated sites. Therefore, further research toward the development of this stabilization technology is warranted.
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•Rice husk biochar (RHB) and sulfur-modified RHB (SRHB) stabilized Hg contaminated soil.•RHB and SRHB were effective for >50 and > 75 simulated years, respectively.•SRHB raised the soil’s total S content by a factor of ∼10.•The pH of the SRHB treated soil did not drop below that of the untreated soil.•The soil Hg content was mostly associated with stable fractions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Potentially toxic elements such as heavy metals are ubiquitous in the environment. Risk-based environmental management relies upon identifying pollution sources, pathways, and the exposed population. ...In a Chinese urban setting, many residents live in high-rise buildings without private gardens. Therefore, the main residential risk of exposure to contaminated soils and dusts may be associated with public open spaces. As children are the most vulnerable receptor, playgrounds represent an important yet often overlooked exposure point. The present study assessed plausible sources of heavy metals at children's playgrounds in a representative metropolitan environment. Soil and equipment dust samples were collected from 71 playgrounds across Beijing, which were analyzed for 11 different heavy metals. Principal component analysis (PCA) was used to identify the latent constructs which control heavy metal variability and reflect potential sources. Cluster analysis (CA) was conducted to group sampled locations, which provided further insights on plausible sources. The main factors extracted from the PCA were then subject to geostatistical analysis. The systematic combination of GIS with multivariate statistical analysis proved valuable for elucidating anthropogenic and natural sources. Elevated Be, V, Cr, Mn, Co, Ni, As in playground soils were found to derive mainly from the natural background (spatial autocorrelation = 2 km), while elevated Cu and Pb was attributed to traffic activities (spatial autocorrelation = 17 km), especially along the routes of Beijing's inner ring-roads, the major roads toward the northwest and northeast, and the international airport. These results suggest that heavy metals in playground equipment dust may derive mainly from atmospheric deposition of air pollution of both natural and anthropogenic origin (spatial autocorrelation = 11–13 km). Among them, Be, V, Mn, Co, Cu, As, Pb were attributed to atmospheric pollution deriving from the north of Beijing, brought by the prevailing northern wind in the winter season; whereas, Cr and Ni may possibly be brought from the southeast by the summer season winds. Knowledge of anthropogenic vs. natural origins of heavy metals in playgrounds is critical in assessing health impact and designing policy instruments for metropolitan areas.
•Knowledge of anthropogenic vs. natural origins of heavy metals is critical.•Systematic combination of GIS with multivariate statistical analysis proved valuable.•Playgrounds represent an important yet often overlooked exposure point.•Cu and Pb in playground soils were attributed to traffic activities.•Most heavy metals in playground dusts may naturally derive from the north of Beijing.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Soil contamination by potentially toxic elements (PTEs) has led to adverse environmental impacts. In this review, we discussed remediation of PTEs contaminated soils through immobilization techniques ...using different soil amendments with respect to type of element, soil, and amendment, immobilization efficiency, underlying mechanisms, and field applicability. Soil amendments such as manure, compost, biochar, clay minerals, phosphate compounds, coal fly ash, and liming materials are widely used as immobilizing agents for PTEs. Among these soil amendments, biochar has attracted increased interest over the past few years because of its promising surface properties. Integrated application of appropriate amendments is also recommended to maximize their use efficiency. These amendments can reduce PTE bioavailability in soils through diverse mechanisms such as precipitation, complexation, redox reactions, ion exchange, and electrostatic interaction. However, soil properties such as soil pH, and clay, sesquioxides and organic matter content, and processes, such as sorption/desorption and redox processes, are the key factors governing the amendments' efficacy for PTEs immobilization in soils. Selecting proper immobilizing agents can yield cost-effective remediation techniques and fulfill green and sustainable remediation principles. Furthermore, long-term stability of immobilized PTE compounds and the environmental impacts and cost effectiveness of the amendments should be considered before application.
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•Comprehensive review on immobilization of potentially toxic elements by soil amendments•Immobilization efficiency with respect to type of soil and amendment is reviewed.•Combined application of appropriate amendments maximizes their use efficiency.•Immobilization mechanisms, field applicability, and future research are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Groundwater related research papers from 1978 to 2017 were collected.•The number of published studies increased by >10% per year on average.•Institutions based in developed countries ...have led groundwater research output.•China and India have experienced strong growth in output in recent years.•Depletion and sustainability have increased as a percentage of groundwater studies.
Long-term over-exploitation and unsustainable practices have caused severe groundwater depletion and deterioration across many regions throughout the world. This has triggered a series of negative impacts on human populations and the natural environment. To understand groundwater-related processes and explore ways to mitigate pertaining issues, large numbers of groundwater-related studies have been performed by the research community. In this study, all research papers published between 1978 and 2017 incorporating “groundwater” in the title, keywords, or abstract, were retrieved from the Web of Science Core Collection (WSCC). Of these, a total of 80,763 papers were identified as being groundwater-related publications. Our analysis revealed that groundwater research output increased significantly during this period, at average annual rate of 10.1%, exceeding the general trend for the WSCC (3.4%). Institutions based in developed countries have held predominance in publishing groundwater research, however, research output from developing countries, such as China and India, experienced much growth in recent years. Development trends were assessed among the research topics of groundwater depletion, contamination, remediation technology, and sustainable management, all of which experienced increased research output. Among sub-topics, groundwater depletion and sustainable management research have increased as a percentage of total groundwater studies, while studies of arsenic, chlorinated solvents, BTEX, bioremediation, and natural attenuation have dropped off in recent years. Additionally, as groundwater-related research output has increased rapidly, robust secondary analyses and meta-analyses are called for in order to make sense of the rapidly expanding body of groundwater research literature. Moreover, owing to the many complexities surround groundwater issues, greater interdisciplinary collaboration is also called for.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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