Bacteria are candidates for the biotransformation of environmental arsenic (As), while As metabolism in bacteria is not yet fully understood. In this study, we sequenced the genome of an As-resistant bacterium strain Stenotrophomonas maltophilia SCSIOOM isolated from the fish gut. After arsenate (As(V)) exposure, S. maltophilia transformed As(V) to organoarsenicals, along with the significant change of the expression of 40 genes, including the upregulation of arsH, arsRBC and betIBA. The heterogeneous expression of arsH and arsRBC increased As resistance of E. coli AW3110 by increasing As efflux and transformation. E. coli AW3110 (pET-betIBA) could transform inorganic As into dimethylarsinate (DMA) and nontoxic arsenobetaine (AsB), which suggested that AsB could be synthesized through the synthetic pathway of its analog-glycine betaine. In addition, the existence of arsRBC, betIBA and arsH reduced the reactive oxygen species (ROS) induced by As exposure. In total, these results demonstrated that S. maltophilia adopted an As metabolism strategy by reducing As accumulation and synthesizing less toxic As species. We first reported the production and potential synthetic pathway of AsB in bacteria, which improved our knowledge of As toxicology in microorganisms.

The homeostasis of gut immunity and microbiota are associated with the health of the gut. Dechlorane 602 (Dec 602) with food web magnification potential has been detected in daily food. People who were orally exposed to Dec 602 may encounter increased risk of health problems in the gut. In order to reveal the influence of short-term exposure of Dec 602 on gut immunity and microbiota, adult female C57BL/6 mice were administered orally with Dec 602 (low/high doses: 1.0/10.0 μg/kg body weight per day) for 7 days. Lymphocytes were examined by flow cytometry. Gut microbiota was measured by 16S rRNA gene sequencing. Results showed that fecal IgA was upregulated after exposure to the high dose of Dec 602, suggesting that there might be inflammation in the gut. Then, changes of immune cells in mesenteric lymph nodes and colonic lamina propria were examined. We found that exposure to the high dose of Dec 602 decreased the percentages of the anti-inflammatory T regulatory cells in mesenteric lymph nodes. In colonic lamina propria, the production of gut protective cytokine interleukin-22 by CD4⁺ T cells was decreased, and a decreased trend of interleukin-22 production was also observed in type 3 innate lymphoid cells in the high dose group. Furthermore, an altered microbiota composition toward inflammation in the gut was observed after exposure to Dec 602. Additionally, the altered microbiota correlated with changes of immune parameters, suggesting that there were interactions between influenced microbiota and immune parameters after exposure to Dec 602. Taken together, short-term exposure to Dec 602 induced gut immunity and microbiota perturbations, and this might be the mechanisms for Dec 602 to elicit inflammation in the gut.

Many contaminants were carried by dust, a common environment media that is easy to contact with human beings, and antibiotic resistance genes (ARGs) as an emergency pollutant also harbor in dust and pose serious threats to human health especially those carried by opportunistic pathogens because inactivation of antibiotics caused by ARGs may enhance pathogenicity. Considering there is a gap of investigation of dust ARGs, 16 S rRNA gene sequences and high-throughput quantitative PCR were employed to obtain information of microbial communities and accumulated ARGs in dust from different urban places, including the malls, hospitals, schools and parks, to investigate the distribution and influencing factors of ARGs and discover the potential hosts of ARGs in dust. Here, 9 types of ARGs such as sulfonamide, tetracycline, and beta-lactamase and 71 subtypes of ARGs like sul1, tetM-01, and drfA1 were detected in dust. ARGs had varying distribution in different public places and seasons in dust. The abundances of total ARGs, MLSB and tetracycline genes were higher in spring than summer. The diversity of ARGs was highest in malls, follow by hospitals, schools, and parks. Additionally, multi-drug resistance genes in dust were more abundant in hospitals than in schools and parks. The microbes were distinguished as the most important driving factors for ARGs in dust, followed by the mobile genetic elements (MGEs) and different places, while dust physicochemical parameters only exert a negligible impact. Notably, several opportunistic pathogens like the Streptococcus, Vibrio, and Pseudomonas were inferred as potential hosts of high-risk ARGs such as mecA, tetM-02, and tetO-01 in dust because of strongly positive co-occurrence. These results imply that dust is likely an important reservoir of ARGs. We should realize that ARGs may be harbored in some opportunistic pathogens occur in dust and endanger human health because of dust contacting to human easily.

Silver nanoparticles (AgNPs) are increasingly released into the aquatic environments because of their extensive use in consumer products and industrial applications. Some researchers have explored the toxicity of AgNPs to nitrogen (N) and carbon (C) cycles, but little is known about the role of aquatic plants in regulating the impact of AgNPs on these biogeochemical processes and related microorganisms. Here, two 90-day pot experiments were conducted to determine the effect of AgNPs on denitrification rates and greenhouse gas emissions in riparian wetland soils, with or without emergent plants (Typha minima Funck). As a comparison, the toxicity of equal concentration of AgNO₃ was also determined. The results showed that AgNPs released a great quantity of free Ag⁺, most of which was accumulated in soils, while little (less than 2%) was absorbed by plant shoots and roots. Both AgNPs and AgNO₃ could increase the soil redox potential and affect the growth and nutrient (N and phosphorus) uptake of plants. In soils with plants, there was no significant difference in denitrification rates and emissions of N₂O and CH₄ between control and AgNPs or AgNO₃ treatments at all tested concentrations (0.5, 1 and 10 mg kg⁻¹). However, low levels of AgNPs (0.5 mg kg⁻¹) significantly enhanced CO₂ emission throughout the experiment. Interestingly, in the absence of plants, a high dosage (10 mg kg⁻¹) of AgNPs generally inhibited soil denitrification and stimulated the emissions of CO₂, CH₄ and N₂O in the short-term. Meanwhile, the abundance of key denitrifying genes (nirS and nirK) was significantly increased by exposure to 10 mg kg⁻¹ AgNPs or AgNO₃. Our results suggest that emergent plants can alleviate the short-term negative effects of AgNPs on N and C cycling processes in wetland soils through different pathways.

Tire wear particles (TWPs), which are among the microplastic pollutants in the environment, can inevitably accumulate in coastal sediments. The present study comprehensively investigated the effect of pristine TWPs on bacterial community structure in coastal sediments and compared the effect of pristine TWPs and aged TWPs on nine strains of bacteria in sediments. In addition, the effect of the TWP leachate was studied with all the nine bacterial strains and the toxicity-causing substances in the leachate was investigated using Bacillus subtilis. Exposure to TWPs could lead to a shift in bacteria community and affect nitrogen metabolism in marine sediments. Aged TWPs were more toxic than pristine TWPs due to changes in particle surface characteristics. The leachate exhibited greater toxicity than TWPs as well, and Zn was identified to be the major toxicity-causing substance. The overall results of this study are important for understanding the effects of TWPs and the leachates on microorganisms in marine sediments.

The bioavailability of chromium (Cr) in soils is highly dependent on Cr fractions and soil physicochemical properties, but it is still unclear how the Cr fractions change in different soils. In this study, phytotoxicity to wheat root elongation was evaluated in different soils across China, and the kinetics of the biogeochemical processes of the added Cr(VI) were examined. After 105 days of soil Cr(VI) spiking, the added Cr(VI) causing 10% inhibition (EC₁₀) of wheat root elongation varied greatly in soils (0.92–151.12 mg kg⁻¹). The results of correlation analysis between EC₁₀ and soil properties showed that the toxicity of Cr was affected by pH, organic matter (OM), clay, cation exchange capacity (CEC), and amorphous Fe oxides. Moreover, the correlation analysis showed that wheat root elongation was more sensitive to extracted Cr(VI) than Cr(III) after 105 days of incubation. A kinetic model was established to evaluate the redox and aging-activating reactions of Cr(VI)/(III) over 105 days. The correlation analysis between the soil properties and rate constants of the model showed that the pH, clay, and amorphous Fe/Al oxides might be the key factors controlling the aging and reduction processes of Cr(VI), and the OM and CEC might greatly affect the aging process of Cr(III). This modeling study is helpful in understanding which soil properties control the transformation and toxicity of Cr in soils.

Nitrogen loss via overland flow from agricultural land use is a global threat to waterways. On-farm denitrifying woodchip bioreactors can mitigate NO₃⁻ exports by increasing denitrification capacity. However, denitrification in sub-optimal conditions releases the greenhouse gas nitrous oxide (N₂O), swapping the pollution from aquatic to atmospheric reservoirs. Here, we assess NO₃⁻-N removal and N₂O emissions from a new edge-of-field surface-flow bioreactor during ten rain events on intensive farming land. Nitrate removal rates (NRR) varied between 5.4 and 76.2 g NO₃⁻-N m⁻³ wetted woodchip d⁻¹ with a mean of 30.3 ± 7.3 g NO₃⁻-N m⁻³. The nitrate removal efficiency (NRE) was ∼73% in ideal hydrological conditions and ∼18% in non-ideal conditions. The fraction of NO₃⁻-N converted to N₂O (rN₂O) in the bioreactor was ∼3.3 fold lower than the expected 0.75% IPCC emission factor. We update the global bioreactor estimated Q₁₀ (NRR increase every 10 °C) from a recent meta-analysis with previously unavailable data to >20 °C, yielding a new global Q₁₀ factor of 3.1. Mean N₂O CO₂-eq emissions (431.9 ± 125.4 g CO₂-eq emissions day⁻¹) indicate that the bioreactor was not significantly swapping aquatic NO₃⁻ for N₂O pollution. Our estimated NO₃⁻-N removal from the bioreactor (9.9 kg NO₃⁻-N ha⁻¹ yr⁻¹) costs US$13.14 per kg NO₃⁻-N removed and represents ∼30% NO₃⁻-N removal when incorporating all flow and overflow events. Overall, edge-of-field surface-flow bioreactors seem to be a cost-effective solution to reduce NO₃⁻-N runoff with minor pollution swapping to N₂O.

Microplastics (MPs) present in non-negligible amounts in urban environments, where urban rivers serve as important transport channels for MPs. However, the footprint of MPs in urban rivers under the influence of natural and anthropogenic factors is poorly understood. This study investigated the MPs organization, stability and pollution risk before and after rainfall in the Qing River, Beijing. Rainfall potentially diluted the MPs abundance, attributed to opening of barrages and increase of flow velocity. The proportion of small-sized MPs (SMPs, 48–300 μm) decreased slightly, whereas that of normal-sized MPs (NMPs, 300–1000 μm) and large-sized MPs (LMPs, > 1000 μm) increased. However, SMPs dominantly presented in the Qing River before and after rainfall. Polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), and polystyrene (PS) were main polymers observed in the Qing River. The proportions of PET and PS decreased, while PP and PE increased after rainfall. The main types of MPs introduced by stormwater were PP and PE. The elevated MP diversity integrated index after rain suggested that rainfall enriched the sources of MPs. Rainfall reduced the stability and fragmentation of MPs owing to the introduction of large debris. NMPs and LMPs were susceptible to further fragmentation and downsizing, implying that MPs abundance in the Qing River tended to rise and SMPs might enriched. In addition, alteration of MPs fragmentation and stability reflected that the likely input source was wastewater treatment plant and atmospheric deposition before rainfall, whereas soil and road dust were possible sources after rain. The pollution risk assessment defined the MPs pollution risk of Qing River as low level and decreased after rainfall. This study demonstrated that rainfall substantially influences MPs organization in urban river and provides empirical support for MPs environmental behavior under influence of natural and anthropogenic factors.

Groundwater constitutes a major source of fresh water globally. However, it faces serious quality challenges from both conventional pollutants and contaminants of emerging concern (CECs) such as pharmaceutically active compounds (PhACs), personal care products (PCPs) and pesticides. There exists a significant knowledge gap regarding the occurrence of CECs in groundwater, especially in Africa. This study presents unique data on the concentration of fourteen PhACs, five PCPs and nine pesticides in groundwater wells in Nzoia River basin, Kenya. Generally, PCPs were the most dominant class with concentrations up to 10 μg/L (methylparaben). Anti(retro)virals, being important in the treatment of HIV/AIDS, were more prevalent among the PhACs as compared to the developed world, with concentrations up to 700 ng/L (nevirapine). In contrast, pesticides were measured at lower concentrations, the maximum being 42 ng/L (metolachlor). A basic risk assessment shows that – among the detected CECs – carbamazepine may pose medium human health risk and requires further investigation among infants and children. Point-of-use (POU) technologies are being increasingly promoted especially in the developing nations to provide drinking water solutions at the household level, but very little data is available on their performance towards CECs removal. Therefore, besides measuring CECs in groundwater, we investigated ceramic filters and solar disinfection (SODIS) as possible POU treatment options. Both techniques show potential to treat CECs in groundwater, with removal efficiencies higher than 90% obtained for 41 and 22 compounds in ceramic filters and SODIS, respectively. Moreover, for the more recalcitrant compounds (e.g. sulfadoxin), the performance is improved by up to three orders of magnitude when using TiO₂ as a photocatalyst in SODIS.