Multiphase chemistry of chlorine is coupled into a 3D regional air quality model (CMAQv5.0.1) to investigate the impacts on the atmospheric oxidation capacity, ozone (O₃), as well as fine particulate matter (PM₂.₅) and its major components over the Yangtze River Delta (YRD) region. The developed model has significantly improved the simulated hydrochloric acid (HCl), particulate chloride (PCl), and hydroxyl (OH) and hydroperoxyl (HO₂) radicals. O₃ is enhanced in the high chlorine emission regions by up to 4% and depleted in the rest of the region. PM₂.₅ is enhanced by 2–6%, mostly due to the increases in PCl, ammonium, organic aerosols, and sulfate. Nitrate exhibits inhomogeneous variations, by up to 8% increase in Shanghai and 2–5% decrease in most of the domain. Radicals show different responses to the inclusion of the multiphase chlorine chemistry during the daytime and nighttime. Both OH and HO₂ are increased throughout the day, while nitrate radicals (NO₃) and organic peroxy radicals (RO₂) show an opposite pattern during the daytime and nighttime. Higher HCl and PCl emissions can further enhance the atmospheric oxidation capacity, O₃, and PM₂.₅. Therefore, the anthropogenic chlorine emission inventory must be carefully evaluated and constrained.

Biodegradation is responsible for most contaminant removal in plumes of organic compounds and is fastest at the plume fringe where microbial cell numbers and activity are highest. As the plume migrates from the source, groundwater containing the contaminants and planktonic microbial community encounters uncontaminated substrata on which an attached community subsequently develops. While attached microbial communities are important for biodegradation, the time needed for their establishment, their relationship with the planktonic community and the processes controlling their development are not well understood. We compare the dynamics of development of attached microbial communities on sterile substrata in the field and laboratory microcosms, sampled simultaneously at intervals over two years. We show that attached microbial cell numbers increased rapidly and stabilised after similar periods of incubation (∼100 days) in both field and microcosm experiments. These timescales were similar even though variation in the contaminant source evident in the field was absent in microcosm studies, implying that this period was an emergent property of the attached microbial community. 16S rRNA gene sequencing showed that attached and planktonic communities differed markedly, with many attached organisms strongly preferring attachment. Successional processes were evident, both in community diversity indices and from community network analysis. Community development was governed by both deterministic and stochastic processes and was related to the predilection of community members for different lifestyles and the geochemical environment.

Twenty-five years after the first look at polycyclic aromatic compounds (PACs) in Canada, this article presents current knowledge on Canadian PAC emission sources. The analysis is based on national inventories (the National Pollutant Release Inventory (NPRI) and the Air Pollutant Emissions Inventory (APEI)), an analysis of Canadian forest fires, and several air quality model-ready emissions inventories. Nationally, forest fires continue to dominate PAC emissions in Canada, however there is uncertainty in these estimates. Though forest fire data show a steady average in the total annual area burned historically, an upward trend has developed recently. Non-industrial sources (home firewood burning, mobile sources) are estimated to be the second largest contributor (∼6-8 times lower than forest fires) and show moderate decreases (25%–65%) in the last decades. Industrial point sources (aluminum production, iron/steel manufacturing) are yet a smaller contributor and have seen considerable reductions (90% +) in recent decades. Fugitive emissions from other industrial sources (e.g. disposals by the non-conventional oil extraction and wastewater sectors, respectively) remain a gap in our understanding of total PAC emissions in Canada. Emerging concerns about previously unrecognized sources such as coal tar-sealed pavement run-off, climate change are discussed elsewhere in this special issue. Results affirm that observations at the annual/national scale are not always reflective of regional/local or finer temporal scales. When determining which sources contribute most to human and ecosystem exposure in various contexts, examination at regional and local scales is needed. There is uncertainty overall in emissions data stemming in part from various accuracy issues, limitations in the scope of the various inventories, and inventory gaps, among others.

This study characterizes the impacts of transported peat-forest (PF) burning smoke on an urban environment and evaluates associated source burning conditions based on carbon properties of PM₂.₅ at the receptor site. We developed and validated a three-step classification that enables systematic and more rapid identification of PF smoke impacts on a tropical urban environment with diverse emissions and complex atmospheric processes. This approach was used to characterize over 300 daily PM₂.₅ data collected during 2011–2013, 2015 and 2019 in Singapore. A levoglucosan concentration of ≥0.1 μg/m³ criterion indicates dominant impacts of transported PF smoke on urban fine aerosols. This approach can be used in other ambient environments for practical and location-dependent applications. Organic carbon (OC) concentrations (as OC indicator) can be an alternate to levoglucosan for assessing smoke impacts on urban environments. Applying the OC concentration indicator identifies smoke impacts on ∼80% of daily samples in 2019 and shows an accuracy of 51–86% for hourly evaluation. Following the systematic identification of urban PM₂.₅ predominantly affected by PF smoke in 2011–2013, 2015 and 2019, we assessed the concentration ratio of char-EC/soot-EC as an indicator of smoldering- or flaming-dominated burning emissions. When under the influence of transported PF smoke, the mean concentration ratio of char-EC to soot-EC in urban PM₂.₅ decreased by >70% from 8.2 in 2011 to 2.3 in 2015 but increased to 3.8 in 2019 (p < 0.05). The reversed trend with a 65% increase from 2015 to 2019 shows stronger smoldering relative to flaming, indicating a higher level of soil moisture at smoke origins, possibly associated with rewetting and revegetating peatlands since 2016.

Cadmium (Cd) contamination in soil and crops caused by mining activities has become a prevalent concern in the world. Given that different crops have varying Cd bioaccumulation factors, crops with low Cd bioaccumulation abilities can be selected for the safe usage of Cd -contaminated lands. This study aimed to investigate Cd contamination in soil and crops and the influencing factors of soil Cd activity in a tin mining area (TMA) and control area (CA) and to put forward suggestions for the safe usage of farmlands by developing prediction models of Cd content in different crop grains. We collected 72 and 40 pairs of rice and maize grain samples, respectively, along with their rhizosphere soil samples and 6176 topsoil samples. The results showed that compared with the CA, the Cd pollution was more severe in the cultivated soil and crop grains around TMA. Furthermore, rice has a strong ability to transport Cd from soil to grains, whereas maize has a poor Cd uptake ability. The total organic carbon, CaO, pH, and Mn in soil play key roles in the transfer of Cd from soil to crop grains. Using these parameters and Cd concentration in soil, two sets of accurate Cd prediction models were developed for maize and rice. Based on the Cd concentration in the topsoil and predicted Cd concentration in crop grains, the safe utilization scheme of farmland was proposed. The proportions of priority protection, safe exploitation, planting adjustment, and strict control were 72.59%, 22.77%, 3.16%, and 1.48% in the TMA, respectively. The values reached 80.51% (priority protection), 19.12% (safe exploitation), 0.37% (planting adjustment), and 0% (strict control) in the CA. Thus, given the difference between Cd accumulation in rice and maize, adjustment of planting crops in contaminated farmlands can be applied to maximize the use of farmland resources.

To explore the performance of Streptomyces pactum (Act12) alone (A) and jointly with sulfur (SA) in the phytoextraction practice of potentially toxic elements (PTEs) (Cd and Zn), as well as their effects on soil chemical properties and microbial community composition, this paper selected potherb mustard (Brassica juncea, Coss.) as the test plant to assess the feedback of soil-plant ecosystems. Metal uptake values in lone Act12 treatments were higher than that of Act12 + sulfur treatments, and showed dose dependent with Act12 due to the higher biomass production. According to the biochemical analyses of rhizosphere soils, Act12 inoculation significantly increased urease (20.4%) and dehydrogenase (58.5%) while reducing alkaline phosphatase (68.0%) activity. The production of soil organic acids was, in descending order, formic acid > oxalic acid > malic acid > propionic acid and indicated a stimulated variation under treatments (SA > A > control). High-throughput sequencing revealed that bacterial community compositions were consistent in both phylum and genus taxonomies, while the final overall proportions were modified. The populations of the predominant phyla Proteobacteria and Bacteroidetes increased after sulfur application. The contribution of Act12 to the relative abundance of microbiota was minor compared to sulfur. Based on a redundancy analysis, soil chemical properties are the drivers of microbial activities and the main contributor to plant growth. Our results suggested Act12 inoculation may be part of an effective strategy enhancing phytoremediation of PTE-contaminated soils through chemical and biotic processes, and provided important implications for sustainable land utilization and crop production.

Dioxybenzone is widely used in cosmetics and personal care products and frequently detected in multiple environmental media and human samples. However, the current understanding of the metabolic susceptibility of dioxybenzone and the potential endocrine disruption through its metabolites in mimicking human estrogens remains largely unclear. Here we investigated the in vitro metabolism of dioxybenzone, detected the residue of metabolites in rats, and determined the estrogenic disrupting effects of these metabolites toward estrogen receptor α (ERα). In vitro metabolism revealed two major metabolites from dioxybenzone, i.e., M1 through the demethylation of methoxy moiety and M2 through hydroxylation of aromatic carbon. M1 and M2 were both rapidly detected in rat plasma upon exposure to dioxybenzone, which were then distributed into organs of rats in the order of livers > kidneys > uteri > ovaries. The 100 ns molecular dynamics simulation revealed that M1 and M2 formed hydrogen bond to residue Leu387 and Glu353, respectively, on ERα ligand binding domain, leading to a reduced binding free energy. M1 and M2 also significantly induced estrogenic effect in comparison to dioxybenzone as validated by the recombinant ERα yeast two-hybrid assay and uterotrophic assay. Overall, our study revealed the potential of metabolic activation of dioxybenzone to induce estrogenic disrupting effects, suggesting the need for incorporating metabolic evaluation into the health risk assessment of benzophenones and their structurally similar analogs.

The oxidative potential (OP) of atmospheric fine particulate matter (PM₂.₅) has been linked to organic content, which includes polycyclic aromatic hydrocarbons (PAHs). The OP of 135 individual PAHs (including six subclasses) was measured using the dithiolthreitol (DTT) consumption assay. The DTT assay results were used to compute the concentration of each PAH needed to consume 50% of the DTT concentration in the assay (DTT₅₀), and the reduction potential of the PAHs (ΔGᵣₓₙ). Computed reduction potential results were found to match literature reduction potential values (r² = 0.97), while DTT₅₀ results had no correlations with the computed ΔGᵣₓₙ values (r² < 0.1). The GINI equality index was used to assess the electron distribution across the surface of unreacted and reacted PAHs. GINI values correlated with ΔGᵣₓₙ in UPAH, HPAH, and OHPAH subclasses, as well as with all 135 PAHs in this study but did not correlate with DTT₅₀, indicating that electron dispersion is linked to thermodynamic reactions and structural differences in PAHs, but not linked to the OP of PAHs. Three ambient PM₂.₅ filters extracts were measured in the DTT assay, alongside mixtures of analytical standards prepared to match PAH concentrations in the filter extracts to test if the OP follows an additive model of toxicity. The additive prediction model did not accurately predict the DTT consumption in the assay for any of the prepared standard mixtures or ambient PM₂.₅ filter extracts, indicating a much more complex model of toxicity for the OP of PAHs in ambient PM₂.₅. This study combined computed molecular properties with toxicologically relevant assay results to probe the OP of anthropogenically driven portions of ambient PM₂.₅, and results in a better understanding of the complexity of ambient PM₂.₅ OP.

Coking is a substantial source of carbonaceous aerosols in China, but the emission characteristics and pollution levels of coking-produced organic carbon (OC) and elemental carbon (EC) remain unknown, causing considerable uncertainty in emission estimates. In this study, the emission factors of OC (EFOC) and EC (EFEC) of typical coking plants in Shanxi, China, were measured. The measured EFEC and EFOC from fugitive emissions (7.43 and 9.54 g/t) were significantly higher than those from flue gas (1.67 and 3.71 g/t). The technological conditions of coke production affect the emissions of OC and EC. For example, the total emissions from coke plants that use 3.2-m-high coke ovens were greater than those from plants that use 4.3- and 6-m-high ovens. The EFOC and EFEC for plants conducting stamp charging were considerably higher than those for plants using top charging. The stable carbon isotopes of total carbon (δ¹³CTC), OC (δ¹³COC), and EC (δ¹³CEC) for fly ash during coking were −23.74‰ to −24.17‰, −23.32‰ to −23.87‰, and −23.84‰ to −24.14‰, respectively, and no clear isotopic fractionation was found during coke production. Different EC/OC ratios from different emission pathways and the carbon isotope signature of coke production should be considered when investigating the sources of carbonaceous aerosols. The total estimated EC and OC emissions from coke production in China were 3.93 and 5.72 Gg in 2017, and Shanxi, Hebei, and Shaanxi made the largest contributions.

Cd accumulation in paddy soils and its subsequent transfer to the food chain are widespread environmental issues, which has been extensively investigated in China. However, most studies focused on regional scales and these results may not be applicable to present the Cd contamination status in soil-rice ecosystems at a national scale. Therefore, based on collected data from China’s rice cultivation dominated regions, this study provides the Cd pollution level of paddy soils and rice grains in China. Results indicates that the Yangtze River basin, especially Hunan, required more attention due to the elevated Cd concentrations in soil-rice ecosystems. Moreover, this review summarizes the significant natural and anthropogenic sources, transport and accumulation mechanism as well as the influencing factors of Cd in soil-rice ecosystems. The wide occurrence of Cd contamination in paddy soils derived primarily from mining activities, intensive application of phosphates fertilizers and e-waste. Physicochemical characteristics of soil, soil microorganisms, temperature as well as the physiological features of rice plants all contribute to Cd accumulation in rice grains, which can be controlled to mitigate Cd accumulation in rice grains. This review will provide a scientific reference for Cd pollution control and management with respect to paddy field ecosystems in China and other countries.