Influence of environmental changes on the biogeochemistry of arsenic in a soil polluted by the destruction of chemical weapons: A mesocosm study

Arsenic species in soil profiles from chemical weapons (CWs) burial sites of China: Contamination characteristics, degradation process and migration mechanism

In this study, soil profiles and pore water from Japanese abandoned arsenic-containing chemical weapons (CWs) burial sites in Dunhua, China were analyzed to understand the distribution of arsenic (As) contamination, degradation, and migration processes. Results of As species analysis showed that the As-containing agents underwent degradation with an average rate of 87.55 ± 0.13%, producing inorganic pentavalent arsenic (As5+) and organic arsenic such as 2-chlorovinylarsonic acid (CVAOA), triphenylarsenic (TPA), and phenylarsine oxide (PAO). Organic arsenic pollutants accounted for 1.27-18.20% of soil As. In the vertical profiles, total As concentrations peaked at about 40-60 cm burial depth, and the surface agricultural soil exhibited moderate to heavy contamination level, whereas the contamination level was insignificant below 1 m, reflecting As migration was relatively limited throughout the soil profile. Sequential extraction showed Fe/Al-bound As was the predominant fraction, and poorly-crystalline Fe minerals adsorbed 33.23-73.13% of soil As. Oxygen-susceptible surface soil formed poorly-crystalline Fe3+ minerals, greatly reducing downward migration of arsenic. However, the reduction of oxidizing conditions below 2 m soil depth may promote As activity and require attention.

Biogeochemical behaviour of geogenic As in a confined aquifer of the Sologne region, France

Arsenic (As) is one of the main toxic elements of geogenic origin that impact groundwater quality and human health worldwide. In some groundwater wells of the Sologne region (Val de Loire, France), drilled in a confined aquifer, As concentrations exceed the European drinking water standard (10 μg L^-1). The monitoring of one of these drinking water wells showed As concentrations in the range 20-25 μg L^-1. The presence of dissolved iron (Fe), low oxygen concentration and traces of ammonium indicated reducing conditions. The δ³⁴S_SO4 was anticorrelated with sulphate concentration. Drilling allowed to collect detrital material corresponding to a Miocene floodplain and crevasse splay with preserved plant debris. The level that contained the highest total As concentration was a silty-sandy clay containing 26.9 mg kg^-1 As. The influence of alternating redox conditions on the behaviour of As was studied by incubating this material with site groundwater, in biotic or inhibited bacterial activities conditions, without synthetic organic nutrient supply, in presence of H₂ during the reducing periods. The development of both AsV-reducing and AsIII-oxidising microorganisms in biotic conditions was evidenced. At the end of the reducing periods, total As concentration strongly increased in biotic conditions. The microflora influenced As speciation, released Fe and consumed nitrate and sulphate in the water phase. Microbial communities observed in groundwater samples strongly differed from those obtained at the end of the incubation experiment, this result being potentially related to influence of the sediment compartment and to different physico-chemical conditions. However, both included major Operating Taxonomic Units (OTU) potentially involved in Fe and S biogeocycles. Methanogens emerged in the incubated sediment presenting the highest solubilised As and Fe. Results support the hypothesis of in-situ As mobilisation and speciation mediated by active biogeochemical processes.

Risk management for arsenic in agricultural soil-water systems: lessons learned from case studies in Europe

Chronic exposure to arsenic may be detrimental to health. We investigated the behaviour, remediation and risk management of arsenic in Freiberg, Germany, characterized by past mining activities, and near Verdun in France, where World War I ammunition was destroyed. The main results included: (1) pot experiments using a biologically synthesized adsorbent (sorpP) with spring barley reduced the mobility of arsenic, (2) the Omega-3 Index ecotoxicological tests verified that sorpP reduced the uptake and toxicity of arsenic in plants, (3) reverse osmosis membrane systems provided 99.5% removal efficiency of arsenic from surface water, (4) the sustainability assessment revealed that adsorption and coagulation-filtration processes were the most feasible options for the treatment of surface waters with significant arsenic concentrations, and (5) a model was developed for assessing health risk due to arsenic exposure. Risk management is the main option for extensive areas, while remediation options that directly treat the soil can only be considered in small areas subject to sensitive use. We recommend the risk management procedure developed in Germany for other parts of the world where both geogenic and anthropogenic arsenic is present in agricultural soil and water. Risk management measures have been successful both in Freiberg and in Verdun.

Influence of agricultural amendments on arsenic biogeochemistry and phytotoxicity in a soil polluted by the destruction of arsenic-containing shells

Agricultural soils can contain high arsenic (As) concentrations due to specific geological contexts or pollution. Fertilizer amendments could influence As speciation and mobility thus increasing its transfer to crops and its toxicity. In the present study, field-relevant amounts of fertilizers were applied to soils from a cultivated field that was a former ammunition-burning site. Potassium phosphate (KP), ammonium sulfate and organic matter (OM) were applied to these soils in laboratory experiments to assess their impact on As leaching, bioavailability to Lactuca sativa and microbial parameters. None of the fertilizers markedly influenced As speciation and mobility, although trends showed an increase of mobility with KP and a decrease of mobility with ammonium sulfate. Moreover, KP induced a small increase of As in Lactuca sativa, and the polluted soil amended with ammonium sulfate was significantly less phytotoxic than the un-amended soil. Most probable numbers of AsIII-oxidizing microbes and AsIII-oxidizing activity were strongly linked to As levels in water and soils. Ammonium sulfate negatively affected AsIII-oxidizing activity in the un-polluted soil. Whereas no significant effect on As speciation in water could be detected, amendments may have an impact in the long term.

Environmental and human health risks of arsenic in gold mining areas in the eastern Amazon

Knowledge of arsenic (As) levels in gold (Au) mining areas in the Amazon is critical for determining environmental risks and the health of the local population, mainly because this region has the largest mineral potential in Brazil and one of the largest in the world. The objective of this study was to assess the environmental and human health risks of As in tailings from Au exploration in the eastern Amazon. Samples were collected from soils and tailings from different exploration forms from 25 points, and the total concentration, pollution indexes and human health risk were determined. Concentrations of As were very high in all exploration areas, especially in tailings, whose maximum value reached 10,000 mg kg^-1, far above the investigation value established by the Brazilian National Council of the Environment, characterizing a polluted area with high environmental risk. Exposure based on the daily intake of As demonstrated a high health risk for children and adults, whose non-carcinogenic risk indexes of 17.8, extremely above the acceptable limit (1.0) established by the United States Environmental Protection Agency. High levels of As in reactive fractions in underground, cyanidation, and colluvium mining areas, as well as extremely high gastric and intestinal bioaccessibility were found, suggesting that high levels may be absorbed by the local population. The results show that the study area is highly polluted through Au mining activities, putting the environment and population health at risk, and that there is an urgent need for intervention by the environmental control agencies for remediation.

Synthesis of nitrogen-doped porous hollow carbon nanospheres with a high nitrogen content: A sustainable synthetic strategy using energetic precursors

Improving the recovery and utilization efficiency of obsolete energetic materials (EMs) is essential for addressing environmental pollution. In this sense, a sustainable one-step high-temperature carbonization strategy using 2,2',4,4',6,6'-hexanitrostilbene-based (HNS-based) energetic hollow nanospheres as energetic precursors was used to fabricate nitrogen-doped (N-doped) porous hollow carbon nanospheres with a high N content. The experimental results suggested carbon-based materials with a hollow spherical framework nanostructure can be obtained by the high-temperature carbonization of energetic precursors. The obtained samples possessed N-doped contents of 19.54 wt% at the carbonization temperature of 600 °C and even 6.10 wt% at 900 °C. In addition, hollow carbon nanospheres with a large number of hierarchical pores and a high surface area (503.5 m²/g) were produced at 900 °C. This strategy prevented unnecessary safety risks and improved recovery and utilization efficiency in a more sustainable and economic manner than conventional disposal methods of EMs. Therefore, this work provides a proof-of-principle concept for the fabrication of carbon-based fundamental functional materials from obsolete EMs.

Microbial community response to environmental changes in a technosol historically contaminated by the burning of chemical ammunitions

The burning of chemical weapons in the 1926-1928 period produced polluted technosols with elevated levels of arsenic, zinc, lead and copper. During an eight-month mesocosm experiment, these soils were submitted to two controlled environmental changes, namely the alternation of dry and water-saturated conditions and the addition of fragmented organic forest litter to the surface soil. We investigated, by sequencing the gene coding 16S rRNA and 18S rRNA, (1) the structure of the prokaryotic and eukaryotic community in this polluted technosol and (2) their response to the simulated environmental changes, in the four distinct layers of the mesocosm. In spite of the high concentrations of toxic elements, microbial diversity was found to be similar to that of non-polluted soils. The bacterial community was dominated by Proteobacteria, Acidobacteria and Bacteroidetes, while the fungal community was dominated by Ascomicota. Amongst the most abundant bacterial Operational Taxonomic Units (OTUs), including Sphingomonas as a major genus, some were common to soil environments in general whereas a few, such as organisms related to Leptospirillum and Acidiferrobacter, seemed to be more specific to the geochemical context. Evolution of the microbial abundance and community structures shed light on modifications induced by water saturation and the addition of forest litter to the soil surface. Co-inertia analysis suggests a relationship between the physico-chemical parameters total organic carbon, Zn, NH₄⁺ and As(III) concentrations and the bacterial community structure. Both these results imply that microbial community dynamics linked to environmental changes should be considered as factors influencing the behavior of toxic elements on former ammunition burning sites.

Determining landscape-level drivers of variability for over fifty soil chemical elements

Syntheses of large datasets have allowed increased clarity of distribution patterns and variation in soil major and trace elements. However, the drivers of variation in topsoil elements across biogeographical scales are not well understood. Our aim was to (1) identify how landscape-scale climate, geographical features, and edaphic factors influence soil elements, and (2) determine key environmental thresholds for shifts in soil element concentration. We analyzed patterns of variation in topsoil elements using 9830 samples collected across 39,000km² in subtropical land in southeast China. Canonical correlations and multiple linear regressions were used to model variations of each element across mean annual temperature (MAT), mean annual precipitation (MAP), land use, spatial topography, and soil pH. Element concentrations show significant latitudinal and longitudinal trends, and are significantly influenced by climate, land use, spatial topography, and soil pH. Longitude, pH, MAT, and MAP were the environmental factors most tightly correlated with element concentrations. Climate and soil pH drove positive or negative alterations in soil elements, with threshold indicators of MAP=1000mm/1500mm, MAT=17.8°C/18.0°C, and pH=5.8/5.0, respectively. Our results indicate topsoil elements have structural and functional thresholds of climate and soil pH in relatively wet and acidic environments. Our findings can facilitate holistic soil element concentration predictions and help elucidate the specific influences of climate and soil pH, enabling development of more complete biogeochemical models.