Mercury (Hg) is ubiquitary, naturally enriched in volcanic regions, and has wide applications in science, industry, and agriculture. Recently, the increasing awareness of Hg toxicity has led to the ...replacement of Hg in many areas; however, anthropogenic activities such as coal burning and smelting of metal ores continue to release large amounts of Hg into the environment. In particular, the atmospheric distribution of the highly volatile Hg around the globe can result in the pollution of pristine regions without local emission sources. The chemical speciation of Hg determines its mobility and toxicity; in flooded soils and sediments, microbial methylation can occur. Bioaccumulative (mono)methylmercury (MeHg; CH
3
Hg
+
) can affect human health particularly via the consumption of contaminated fish and rice since methylmercury is a potent neurotoxin. Also, elemental Hg vapor is harmful for the central nervous system, while inorganic Hg compounds primarily affect the kidney. This review summarizes recent knowledge on the behavior of Hg in soils and sediments as well as in other environmental elements including implications on human health and discusses future research needs.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
Discarded plastics and microplastics (MPs) in the environment are considered emerging contaminants and indicators of the Anthropocene epoch. This study reports the discovery of a new type of plastic ...material in the environmentplastic–rock complexesformed when plastic debris irreversibly sorbs onto the parent rock after historical flooding events. These complexes consist of low-density polyethylene (LDPE) or polypropylene (PP) films stuck onto quartz-dominated mineral matrices. These plastic–rock complexes serve as hotspots for MP generation, as evidenced by laboratory wet–dry cycling tests. Over 1.03 × 108 and 1.28 × 108 items·m–2 MPs were generated in a zero-order mode from the LDPE– and PP–rock complexes, respectively, following 10 wet–dry cycles. The speed of MP generation was 4–5 orders of magnitude higher than that in landfills, 2–3 orders of magnitude higher than that in seawater, and >1 order of magnitude higher than that in marine sediment as compared with previously reported data. Results from this investigation provide strong direct evidence of anthropogenic waste entering geological cycles and inducing potential ecological risks that may be exacerbated by climate change conditions such as flooding events. Future research should evaluate this phenomenon regarding ecosystem fluxes, fate, and transport and impacts of plastic pollution.
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IJS, KILJ, NUK, PNG, UL, UM
Vanadium(V) is a highly toxic multivalent, redox-sensitive element. It is widely distributed in the environment and employed in various industrial applications. Interactions between V and ...(micro)organisms have recently garnered considerable attention. This Review discusses the biogeochemical cycling of V and its corresponding bioremediation strategies. Anthropogenic activities have resulted in elevated environmental V concentrations compared to natural emissions. The global distributions of V in the atmosphere, soils, water bodies, and sediments are outlined here, with notable prevalence in Europe. Soluble V(V) predominantly exists in the environment and exhibits high mobility and chemical reactivity. The transport of V within environmental media and across food chains is also discussed. Microbially mediated V transformation is evaluated to shed light on the primary mechanisms underlying microbial V(V) reduction, namely electron transfer and enzymatic catalysis. Additionally, this Review highlights bioremediation strategies by exploring their geochemical influences and technical implementation methods. The identified knowledge gaps include the particulate speciation of V and its associated environmental behaviors as well as the biogeochemical processes of V in marine environments. Finally, challenges for future research are reported, including the screening of V hyperaccumulators and V(V)-reducing microbes and field tests for bioremediation approaches.
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Floodplain soils across Central Elbe River (CER), Germany, vary considerably in potentially toxic element (PTE) content. However, there has never been a comprehensive study that links PTE levels with ...human health risk for children and adults. Our objective was to determine the contamination of 13 PTEs in 94 soil profiles along CER and assess the associated health risk via diverse indices for adults and children. Of 94 soil profiles, we measured soil properties and total content of arsenic, barium, chromium, copper, nickel, lead, rubidium, tin, strontium, vanadium, zinc, and zirconium using x-ray fluorescence spectrometer (XRF). We calculated the Contamination Factor and the Pollution Load Index (PLI), and assessed the health risk for male and female adults as well as for children. Topsoil median contents of Cr (84 mg kg−1), Cu (42), Ni (33), and Zn (195) exceeded the Precautionary Values for sandy soils according to the German Federal Soil Protection and Contaminated Sites Ordinance, while As, Pb, and V were 32, 73, and 77 mg kg−1, respectively. Median topsoil PLI was 1.73, indicating elevated multi-element contamination, with 90th percentile and maximum values being 3.20 and 4.31, respectively. All PTE concentrations were higher in top- compared to subsoils. Also at the 50th percentile the most enriched elements were Sn and As, followed by Zr and Rb, while in the 90th percentile Sn and As were followed by Zn, Pb and Cu. Median children's hazard index (HI) was higher than unity (HI = 2.27) and the 90th percentile was 5.53, indicating elevated health risk. Adult median HIs were 0.18 for male and 0.21 for female persons. Arsenic was found to be the primary contributor to total risk, accounting of 57.4% of HI in all three-person groupings, with Cr (17.3%) being the second, and V (10.2%) the third. Children's health is at dramatically higher risk than that of adults; also As, Cr, Pb, and V have a predominant role in contamination-related health risks. The presence of V, a less-expected element, among those of major risk contribution, reveals the necessity of monitoring areas at large scale. Our results demonstrate that our study may serve as a model for similar works studying multi-element-contaminated areas in future.
•Tin had the highest enrichment in soil based on all studied contamination indices.•Tin was followed by As, Zn, Pb and Cu at 90th percentile.•Zirconium and Rb seem to originate from non-anthropogenic inputs.•Hazard Index for children was higher than unity, showing significant health risks.•Risk assessment indicated As as the predominant risk factor, followed by Cr, V, Pb.•The study is a model for works addressing contamination risks in extended areas.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The release dynamics of dissolved arsenic (As), barium (Ba), cadmium (Cd), copper (Cu), lead (Pb), and strontium (Sr) was determined in seven different paddy soils under controlled-redox conditions ...by using an automated biogeochemical microcosm apparatus. Seven surface soils were collected from five major rice-cultivating states in the United States (Arkansas, California, Louisiana, Mississippi, and Texas), and from two Asian regions: Hangzhou (China) and Java (Indonesia). The impact of redox potential (EH), pH, dissolved organic carbon (DOC), iron (Fe), manganese (Mn), and sulfur (S) on the release dynamics of the elements was quantified. The experiment was conducted stepwise from reducing (−270mV) to oxidizing (+676mV) soil conditions. Soil pH increased with decreasing soil EH. Concentrations of DOC and dissolved As, Fe, Mn were increased under reducing conditions as compared to oxidizing conditions. In opposite — the release of Ba, Cd, Cu, and Sr to soil solution increased under oxidizing conditions as compared to reducing conditions. The decrease of Ba, Cd, Cu, and Sr concentrations under reducing conditions could be caused by the relatively high pH and/or metal-sulfide precipitation. Lead showed an inconsistent trend with EH in the studied soils (All Soils). Factor analysis demonstrates that As, Fe, Mn, and DOC were associated in one group, while Ba, Sr, Cd, Cu, and EH were banded together in one cluster. These results indicate that the chemistry of DOC, Fe, and Mn might be stronger linked to the dynamics of As than to the dynamics of Ba, Cd, Cu, Pb, and Sr in these soils.
The canonical discrimination analysis explained 85% of the variability of the geochemical behavior of the different soils and showed that the individual soils can clearly differentiate from each other. However, the Arkansas and Louisiana soils were relatively similar in their geochemical behavior, and the Indonesian and Texas soils were close, while and the California soil showed a different geochemical behavior. The behavior of Sr, Ba, S, DOC, and EH, respectively, was mainly responsible for the discrimination of the soils. In particular, our findings suggest that aerobic conditions can lead to a release of Ba, Cd, Cu, Pb, and Sr while a release of As under anaerobic conditions was observed. These results provide critical information on the potential risk of toxic elements for the sustainable management of paddy rice soils.
•Seven paddy soils from five states in the U.S.A. and from China and Indonesia were studied.•Flooding was simulated using an automated biogeochemical microcosm apparatus.•Concentrations of As, Fe, Mn, DOC were high under anoxic conditions.•Release of Ba, Cd, Cu, and Sr was high under oxic conditions.•Individual soils can be discriminated based on their geochemical behavior.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Biochar has triggered a black gold rush in environmental studies as a carbon-rich material with well-developed porous structure and tunable functionality. While much attention has been placed on its ...apparent ability to store carbon in the ground, immobilize soil pollutants, and improve soil fertility, its temporally evolving in situ performance in these roles must not be overlooked. After field application, various environmental factors, such as temperature variations, precipitation events and microbial activities, can lead to its fragmentation, dissolution, and oxidation, thus causing drastic changes to the physicochemical properties. Direct monitoring of biochar-amended soils can provide good evidence of its temporal evolution, but this requires long-term field trials. Various artificial aging methods, such as chemical oxidation, wet–dry cycling and mineral modification, have therefore been designed to mimic natural aging mechanisms. Here we evaluate the science of biochar aging, critically summarize aging-induced changes to biochar properties, and offer a state-of-the-art for artificial aging simulation approaches. In addition, the implications of biochar aging are also considered regarding its potential development and deployment as a soil amendment. We suggest that for improved simulation and prediction, artificial aging methods must shift from qualitative to quantitative approaches. Furthermore, artificial preaging may serve to synthesize engineered biochars for green and sustainable environmental applications.
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Knowledge about the behavior and reactions of separate soil components with trace elements (TEs) and their distribution coefficients (Kds) in soils is a key issue in assessing the mobility and ...retention of TEs. Thus, the fate of TEs and the toxic risk they pose depend crucially on their Kd in soil. This article reviews the Kd of TEs in soils as affected by the sorption system, element characteristics, and soil colloidal properties. The sorption mechanism, determining factors, favorable conditions, and competitive ions on the sorption and Kd of TEs are also discussed here. This review demonstrates that the Kd value of TEs does not only depend on inorganic and organic soil constituents, but also on the nature and characteristics of the elements involved as well as on their competition for sorption sites. The Kd value of TEs is mainly affected by individual or competitive sorption systems. Generally, the sorption in competitive systems is lower than in mono-metal sorption systems. More strongly sorbed elements, such as Pb and Cu, are less affected by competition than mobile elements, such as Cd, Ni, and Zn. The sorption preference exhibited by soils for elements over others may be due to: (i) the hydrolysis constant, (ii) the atomic weight, (iii) the ionic radius, and subsequently the hydrated radius, and (iv) its Misono softness value. Moreover, element concentrations in the test solution mainly affect the Kd values. Mostly, values of Kd decrease as the concentration of the included cation increases in the test solution. Additionally, the Kd of TEs is controlled by the sorption characteristics of soils, such as pH, clay minerals, soil organic matter, Fe and Mn oxides, and calcium carbonate. However, more research is required to verify the practical utilization of studying Kd of TEs in soils as a reliable indicator for assessing the remediation process of toxic metals in soils and waters.
MS: Mono-sorption system; CS: competitive sorption system; Fluvial: fluvial soil (Entisols); Lacus: Lacustrine soil (Entisols); Marine: sandy soil (Entisols); Aridis: Aridisols; Entis: Entisols; Vertis: Vertisols; Mollis: Mollisols; Histos: Histosols; Alfis: Alfisols.
Effect of soil types on Cd and Zn distribution coefficient, Kd medium (Lkg−1) under mono-metal and competitive sorption system. Display omitted
•Distribution coefficient (Kd) of trace elements (TEs) in soils has been reviewed.•Proves the link between Kd and sorption system, element types, and soil properties•The element Kd in competitive sorption is lower than in mono-metal system.•Strongly sorbed TEs (Pb, Cu) are less affected by competition than mobile elements (Cd, Ni, Zn).•Values of Kd decreased with an increase of the added concentration in the test solution.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Knowledge on the redox geochemistry of Ni is behind in comparison to other heavy metals. Hence, this article reviews the direct and indirect impact of redox potential (EH) on mobilization and release ...dynamics of Ni in soils and sediments across the world. Nickel can show a different behavior in response to EH. Mobilization of Ni increased at low EH in various soils; however, oxic conditions can lead to an increased mobilization of Ni in other soils. Those differences occur because the mobilization of Ni is often indirectly affected by EH, e.g. through EH-dependent pH changes, co-precipitation with iron (Fe) and manganese (Mn) (hydr)oxides, complexation with soil organic carbon, similar position of Ni and magnesium (Mg) in the soil solid phase, and/or precipitation as sulphides. Dissolved concentrations of Ni showed a similar pattern like Fe and increased at low EH in many soils, which might be explained by the reductive dissolution of Fe (hydr)oxides and the release of the co-precipitated/sorbed Ni. Few other studies indicated that Ni might be associated with Mn oxides rather than with Fe oxides. Additionally, the formation of soluble complexes with dissolved organic carbon may contribute to a mobilization of Ni at low EH. Nickel and Mg are similarly affected by redox changes especially in serpentine soils. This review summarizes the recent knowledge about the redox chemistry of Ni and contributes thus to a better understanding of the potential mobilization, hazard, and eco-toxicity of Ni in frequently flooded soils and sediments as agricultural ecosystems.
•The impact of redox potential (EH) on mobilization of Ni in soils was reviewed.•Mobilization of Ni increased under reducing conditions in various soils.•Oxic conditions can lead to an increase mobilization of Ni in other soils.•Mobilization of Ni in soils is indirectly affected by EH-dependent pH changes.•Dynamics of Ni were controlled mainly by the chemistry of Fe, Mn, Mg, and DOC.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Discharge of wastewater is the most important entry route of NPs in the environment.•NPs are derived away from their pristine state through various dynamic transformations.•Biological, physical and ...chemical transformations are interconnected.•Transformation is regulated by NPs characteristics and environmental conditions.•In the natural environment, NPs undergoes multiple transformations simultaneously.
The ever increasing production and use of nano-enabled commercial products release the massive amount of engineered nanoparticles (ENPs) in the environment. An increasing number of recent studies have shown the toxic effects of ENPs on different organisms, raising concerns over the nano-pollutants behavior and fate in the various environmental compartments. After the release of ENPs in the environment, ENPs interact with various components of the environment and undergoes dynamic transformation processes. This review focus on ENPs transformations in the various environmental compartments. The transformation processes of ENPs are interrelated to multiple environmental aspects. Physical, chemical and biological processes such as the homo- or hetero-agglomeration, dissolution/sedimentation, adsorption, oxidation, reduction, sulfidation, photochemically and biologically mediated reactions mainly occur in the environment consequently changes the mobility and bioavailability of ENPs. Physico-chemical characteristics of ENPs (particle size, surface area, zeta potential/surface charge, colloidal stability, and core-shell composition) and environmental conditions (pH, ionic strength, organic and inorganic colloids, temperature, etc.) are the most important parameters which regulated the ENPs environmental transformations. Meanwhile, in the environment, organisms encountered multiple transformed ENPs rather than the pristine nanomaterials due to their interactions with various environmental materials and other pollutants. Thus it is the utmost importance to study the behavior of transformed ENPs to understand their environmental fate, bioavailability, and mode of toxicity.
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•Biochar-DOM may pose positive and negative effects on the soil environment.•DOM can affect (in)mobilization of coexisting contaminants and soil eco-functions.•DOM nature, target ...pollutants, and environmental conditions are the determining factors.•Customizing and assessing the multiple roles of biochar is essential for effective soil amendment.
Biochar is an emerging, cost-effective, and renewable carbonaceous material with abundant functional groups and tuneable mesoporous structure, showing a promising performance in fertility improvement, nutrient retention, microbial activity enhancement, and contaminant immobilization, etc. Dissolved organic matter (DOM) from biochar, which can be readily mobilized during soil application, is a key component for the soil matrix, microbial community, and the fate of contaminants. Comprehensive assessments of both positive and negative effects of biochar-derived DOM present critical environmental implications. This paper is the first of its kind to critically review the compositions and structures of biochar-derived DOM as well as its multiple roles in soil application. The effects of biochar-derived DOM on stabilization or migration/mobilization of contaminants/nutrients, as well as stimulation or inhibition of microbial activity and plant growth, depend on the nature of biochar-derived DOM, pollutant properties, soil characteristics, and environmental conditions including weather and hydrological conditions. The long-term stability of biochar-derived DOM is vital during soil application and involves various interactions such as physical disintegration, infiltration, sorption, and biotic/abiotic oxidation. Further studies of biochar-derived DOM are necessary for us to understand the fate of DOM and minimize the ecological and environmental risks (e.g., toxicity, competitive sorption, blockage effect, and solubilization) of biochar application.
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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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