Antimony (Sb) is an emerging contaminant and until recently it was assumed to behave in a similar way to arsenic (As). Arsenic and Sb often co-occur in contaminated sites, yet most investigations consider their toxicity to plants singly. More research is needed to understand the interactions between As and Sb in soils and plants. This study investigated the interactive effect of As and Sb in terms of soil bioavailability, plant toxicity and bioaccumulation on the commercially important agricultural plant, water spinach (Ipomoea aquatica) using a pot experiment. Plants were exposed to As and Sb individually (As ₍ᵢₙdᵢᵥᵢdᵤₐₗ₎, Sb ₍ᵢₙdᵢᵥᵢdᵤₐₗ₎) and as a mixture (As + Sb ₍cₒₘbᵢₙₑd₎) at different concentrations. Plant growth was measured using shoot and root dry mass, length and chlorophyll a content of leaves. At the end of the bioassay, bioavailable metalloids were extracted from the soil as per a sequential extraction procedure (SEP) and plant tissue was analysed for metalloid content. For As, there were no differences observed between the bioavailability of As in the As + Sb ₍cₒₘbᵢₙₑd₎ and As ₍ᵢₙdᵢᵥᵢdᵤₐₗ₎ treatments. For Sb, no increase in bioavailability was observed with co-contamination compared to single-Sb exposures for most concentrations except at 1250 mg/kg. Single-Sb was not toxic to I. aquatica shoot dry mass and length, but there was greater shoot Sb accumulation in the As + Sb ₍cₒₘbᵢₙₑd₎ than the Sb ₍ᵢₙdᵢᵥᵢdᵤₐₗ₎ treatment. In contrast, single-As was toxic to I. aquatica growth. When As and Sb were present together in the soil, there was a synergistic toxicity to shoot dry mass (EC₅₀ Toxic Unit (TU) was less than 1) and additive toxicity (EC₅₀ equal to 1 TU) to shoot length. This work shows that the co-occurrence of As and Sb in soil increases Sb bioavailability and can cause synergistic toxicity to an important agricultural crop.

This work aims to study the pseudo-total content, geochemical fractions, and species of arsenic (As) in the bulk soil and in the coarse and fine particles of top soil and soil profiles collected from active and abandoned gold mine spoils in Ghana. The human health risk for adults (male and female) and children has been assessed. To achieve our aims, we collected 51 samples, characterized them, determined the total As content, and sequentially extracted the geochemical fractions of As including water-soluble and un-specifically bound As (FI); specific-sorbed/exchangeable As (FII); poorly (FIII)- and well-crystalline (IV) Fe oxide; and residual/sulphide fraction (FV). In selected samples, As species were determined using synchrotron-based X-ray absorption near edge structure (XANES). Pseudo-total As contents varied from 1807 to 8400 mg kg⁻¹, with the extremes occurring at the abandoned mine spoil. Arsenic was almost 10-fold higher in the fine particles (<0.63 μm) than in the coarse particles. Arsenic was mainly associated with FIII and FV, indicating that the distribution of As in these spoils is governed by their contents of amorphous Fe oxides, sulphides and As bearing minerals. The XANES results indicated that scorodite (FeAsSO₄ = 65–76%) and arsenopyrite (FeAsS = 24–35%) are the two major As-containing minerals in the spoils. The potential mobility (PMF = ∑FI-FIV) of As in the fine particles of the top soil was higher (48–61%) than in the coarse particles (25–44%). The mobile fraction (MF) (FI+FII) and PMF of As in the coarse particles of the profiles increased with depth while it decreased in the fine particles. The median hazard index values indicated an elevated human health risk, especially for children. The high contamination degree and potential mobility of As at the studied mine spoils indicate high potential risk for human and environmental health.

This study presents the distribution characteristics and possible sources of fine particulate matter (PM₂.₅) and its components, as well as policy-related pollution reduction in the Chinese cities of Jinan, Shijiazhuang (SJZ), Chengdu, Wuxi, Wuhan, and Harbin (HRB). PM₂.₅ samples were collected using mid-volume samplers during the autumn of 2017 in all six cities. The samples were analyzed to determine the ambient PM₂.₅ compositions, including the concentrations of water-soluble inorganic ions (WSIIs), carbonaceous aerosols, and elements concentrations. The chemical ratios of organic carbon to elemental carbon and nitrate to sulfate as well as the enrichment factors of elements were calculated to establish the possible sources of PM₂.₅ in all six cities. The highest PM₂.₅ concentration was 152 μg/m³ in SJZ, while the lowest concentration was 47 μg/m³ in HRB. During the sampling period in these six cities, the PM₂.₅ concentrations exceeded the World Health Organization recommended daily average air quality guidelines by 2.4–6.1 times, and WSIIs, carbonaceous aerosols, and elements accounted for 31.8%–61.6%, 9.8%–35.1%, and 0.9%–2.5% of the PM₂.₅, respectively. In 2013, the Chinese government formulated the Air Pollution Prevention and Control Action Plan (APPCAP) for controlling air pollution, and effective measures have been implemented since then. Compared with previous studies conducted during 2009–2013 before the implementation of the APPCAP, the concentrations of PM₂.₅ and most of its components decreased to varying degrees, and large changes in the chemical ratios of PM₂.₅ components were observed. These results indicate that PM₂.₅ sources vary among these six cities and that China has improved the ambient air quality in these cities through the implementation of air pollution control policies. The APPCAP have achieved considerable results in continuously reducing pollution concentrations, although the air pollution concentrations observed in this study remain high compared with those of other countries.

Nitrate is one of the most common pollution sources in groundwater, particularly in highly vulnerable karst aquifers. The potential for nitrification and denitrification within karst aquifers varies in different settings depending on the extent of anthropogenic inputs, so that accurate identification of nitrate sources can be difficult. Geochemical data and dual nitrate isotopes were measured in this study, incorporating a Bayesian isotopic mixing model, and used to identify nitrate sources, nitrification and denitrification, and quantitatively determine nitrate sources under different extents of anthropogenic inputs in three karst catchments within Chongqing Municipality, SW China: Laolongdong (an urbanized area), Qingmuguan (a suburban village), and Shuifang Spring (a protected natural area). At the Laolongdong catchment, the groundwater was in a reducing condition and enriched in δ¹⁵NNO₃ (averaging 18.9 ± 6.9‰) and δ¹⁸ONO₃ (averaging 8.5 ± 4.6‰). Manure and sewage waste were the main contributing nitrate sources. A slope of 1.8: 1 of the dual isotopes suggested a denitrification process occurring in anaerobic conduit flow. Within the Qingmuguan catchment, groundwater had average δ¹⁵NNO₃ and δ¹⁸ONO₃ values of 9.7 ± 3.5‰, and 1.9 ± 3.4‰, respectively. The data showed evidence for nitrification, and the contribution of soil organic nitrogen was 52.1%, followed by a contribution of 44.8% from manure and wastewater. At the Shuifang Spring catchment, the mean δ¹⁵NNO₃ and δ¹⁸ONO₃ values in groundwater were 8.8 ± 2.9‰, 2.3 ± 4.6‰, respectively. Nitrification was the dominant process and most of the nitrate was derived from soil organic nitrogen. This study suggests that karst underground rivers overlain by urban land use undergo denitrification, while the suburban and relatively pristine karst aquifers are dominated by nitrification, allowing development of a conceptual model for nitrate sources and transformations in karst aquifers from the categories of land use (i.e., urban, suburban, and pristine areas).Anthropogenic activities can change biogeochemical nitrogen dynamics of vulnerable karst aquifers, such that the groundwater overlain by an urban settlement has undergone denitrification, while suburban and pristine areas have been dominated by nitrification.

Recently, numerous studies concerning dye-labeled microplastic beads have reported on the end-of-life, environmental effects of microplastics because of their ubiquitous commercial usage. Less is understood about the toxicity and bioaccumulation of plastics other than microplastic beads, which can also harm the environment (e.g., fragments, fibers, foams, and films). Expanded polystyrene (EPS) is widespread in the environment owing to its many uses, however, limited research has been conducted on EPS foams. This study focuses on developing an efficient method for the preparation of micro-sized EPS foams for research purposes and compares it with previous microplastics preparation methods reported in 68 previous studies. It was demonstrated that the iced EPS block method (iced EPS block + water) generated larger quantities of smaller-sized EPS foams (20–200 and 200–500 μm) compared to the EPS + ice + water and EPS + water methods. The optimal protocol includes 1) iced EPS block preparation, 2) grinding and sieving, and 3) collecting. Additionally, it was confirmed that the iced EPS block method requires less money, labor, and time compared to previously reported methods in the literature. The method proposed in this research can assist future investigations into the environmental effects of EPS foams.

Household air pollution is the dominant contributor to population air pollutant exposure, but it is often of less concern compared with ambient air pollution. One of the major knowledge gaps in this field are detailed quantitative source contributions of indoor pollutants, especially for gaseous compounds. In this study, temporally, spatially, and vertically resolved monitoring for typical indoor gases including CO₂, CO, formaldehyde, methane, and the total volatile organic compounds (VOCs) was conducted to address pollution dynamics and major sources in an urban apartment. The indoor concentrations were significantly higher than the simultaneously measured outdoor concentrations. A new statistic approach was proposed to quantitatively estimate contributions of different sources. It was estimated that outdoor CO₂ contributed largely to the indoor CO₂, while main indoor sources were human metabolism and cooking. Outdoor infiltration and cooking contributed almost equally to the indoor CO. The contribution of outdoor infiltration to methane was much higher than that to formaldehyde. Cooking contributed to 24%, 19%, and 25% of indoor formaldehyde, methane, and VOCs, whereas the other unresolved indoor sources contributed 61%, 19%, and 35% of these pollutants, respectively. Vertical measurements showed that the uplifting of hot air masses led to relatively high concentrations of the pollutants in the upper layer of the kitchen and in the other rooms to a lesser extent.

An upsurge in global population due to speedy urbanization and industrialization is facing significant challenges such as rising energy-demand, enormous waste-generation and environmental deterioration. The waste-to-energy nexus based on the 5R principle (Reduce, Reuse, Recycle, Recovery, and Restore) is of paramount importance in solving these Gordian knots. This review essentially concentrates on latest advancements in the field of ‘simultaneous waste reduction and energy production’ technologies. The waste-to-energy approaches (thermal and biochemical) for energy production from the agricultural residues are comprehensively discussed in terms environmental, techno-economic, and policy analysis. The review will assess the loopholes in order to come up with more sophisticated technologies that are not only eco-friendly and cost-effective, but also socially viable. The waste-to-energy nexus as a paradigm for sustainable development of restoring waste is critically discussed considering future advancement plans and agendas of the policy-makers.

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.