Gut microbiota is of critical importance to host health. Aryl hydrocarbon receptor (AhR) is found to be closely involved in the regulation of gut microbial dynamics. However, it is still not clear how AhR signaling shapes the gut microbiota. In the present study, adult zebrafish were acutely exposed to an AhR antagonist (CH223191), an AhR agonist (polychlorinated biphenyl 126; PCB126) or their combination for 7 d. Overall intestinal health and gut microbial community were temporally monitored (1 d, 3 d and 7 d) and inter-compared among different groups. The results showed that single exposure to PCB126 significantly disrupted the overall health of intestines (i.e., neural signaling, inflammation, epithelial barrier integrity, oxidative stress). However, CH223191 failed to inhibit but enhanced the physiological toxicities of PCB126, implying the involvement of extra mechanisms rather than AhR in the regulation of intestinal physiological activities. Dysbiosis of gut microbiota was also caused by PCB126 over time as a function of sex. It is intriguing that CH223191 successfully abolished the holistic effects of dioxin on gut microbiota, which inferred that growth of gut microbes was directly controlled by AhR activation without the involvement of host feedback modulation. When coming to detailed alterations at certain taxon, both antagonistic and synergistic interactions existed between CH223191 and dioxin, depending on fish sex, exposure duration and bacterial species. Correlation analysis found that gut inflammation was positively associated with pathogenic Legionella bacteria, but was negatively associated with epithelial barrier integrity, suggesting that integral intestinal epithelial barrier can prevent the influx of pathogenic bacteria to induce inflammatory response. Overall, this study has deciphered, for the first time, the direct regulative effects of AhR activity on gut microbiota. Future research is warranted to elucidate the specific mechanisms of AhR action on certain bacterial population.

Knowledge of distribution of toxic metal in crop is essential for studying toxic metal uptake, transportation and bioaccumulation, and it is important for environmental pollution monitoring. In this study, the macro spatial distribution of chromium in rice leaves was visualized by re-heating dual-pulse laser-induced breakdown spectroscopy (DPLIBS) and chemometric methods. After the optimization of two important parameters (delay time and energy ratio) in DPLIBS, chromium prediction model was established based on global spectra. The global model achieved acceptable performance while slight overfitting for model was found because of numerous irrelevant variables. Feature variables including emissions from chromium and other elements were successfully selected by the values of regression coefficient in partial least square regression model. Best performance was achieved by using the feature variables and support vector machine, with correlation coefficient of prediction of 0.959, root mean square error of prediction of 13.4 mg/kg and residual predictive deviation of 3.6. Finally, the distribution of chromium in rice leaves was visualized with the best prediction model. The distribution image showed that chromium distributed approximately symmetrically along the vein and was likely to be accumulated in leaf apex. The preliminary results provide an approach for investigating the macro spatial distribution of elements in crops, which is important for environmental protection and food safety.

Peroxyacetyl nitrate (PAN) is an important reservoir of atmospheric nitrogen, modulating reactive nitrogen cycle and ozone (O3) formation. To understand the origins of PAN, a field measurement was conducted at Tung Chung site (TC) in suburban Hong Kong from October to November 2016. The average level of PAN was 0.63 ± 0.05 ppbv, with a maximum of 7.30 ppbv. Higher PAN/O3 ratio (0.043–0.058) was captured on episodes, i.e. when hourly maximum O3 exceeded 80 ppbv, than on non-episodes (0.01), since O3 production was less efficient than PAN when there was an elevation of precursors (i.e. volatile organic compounds (VOCs) and nitrogen oxide (NOx)). Model simulations revealed that oxidations of acetaldehyde (65.3 ± 2.3%), methylglyoxal (MGLY, 12.7 ± 1.2%) and other oxygenated VOCs (OVOCs) (8.0 ± 0.6%), and radical cycling (12.2 ± 0.8%) were the major production pathways of peroxyacetyl (PA) radical, while local PAN formation was controlled by both VOCs and nitrogen dioxide (NO2). Among all VOC species, carbonyls made the highest contribution (59%) to PAN formation, followed by aromatics (26%) and biogenic VOCs (BVOCs) (10%) through direct oxidation/decomposition. Besides, active VOCs (i.e. carbonyls, aromatics, BVOCs and alkenes/alkynes) could stimulate hydroxyl (OH) production, thus indirectly facilitating the PAN formation. Apart from primary emissions, carbonyls were also generated from oxidation of first-generation precursors, i.e., hydrocarbons, of which xylenes contributed the most to PAN production. Furthermore, PAN formation suppressed local O3 formation at a rate of 2.84 ppbv/ppbv, when NO2, OH and hydroperoxy (HO2) levels decreased and nitrogen monoxide (NO) value enhanced. Namely, O3 was reduced by 2.84 ppbv per ppbv PAN formation. Net O3 production rate was weakened (∼36%) due to PAN photochemistry, so as each individual production and loss pathway. The findings advanced our knowledge of atmospheric PAN and its impact on O3 production.

In this study, antibiotic resistance to macrolide-lincosamide-streptogramin B (MLSB) antibiotics in total microbial community in surface water in a coastal urban city was measured using a modified fluorescence in situ hybridization (FISH) technique. This FISH technique quantified the rate of antibiotic resistance to MLSB antibiotics through targeting methylation site of A2058 of 23S rRNAs resulting from expressed erythromycin ribosome methylation (erm) genes. Correlations between the rates of MLSB resistance measured by FISH and macrolide concentrations was stronger than that between the relative abundance of erm genes and macrolide concentrations, especially in residential areas where the main detected antibiotics were macrolides. These results suggest that trace levels of antibiotics in environmental waters, which was as low as 40 ng L−1, may still play important roles in the development and spread of antibiotic resistance. Additionally, methylation as a result of erm gene expression, instead of erm gene abundance, was a better indicator of selective pressure of trace level macrolides. The rates of MLSB resistance varied significantly among land use types, suggesting that anthropogenic activities are important factors to select for erm gene expression in the environment. Microbial community analysis of representative surface water samples showed that relatively high rates of MLSB resistance were observed in Alphaproteobacteria (42%), Acidobacteria (36%), Bacteroidaceae (32%), Chloroflexi (27%), and Betaproteobacteria (20.2%).

Chemical compositions of fog and rain water were measured between July 2017 and September 2018 at Sejila Mountain, southeast Tibet, where fog events frequently occurred in original fir forests at altitude 3950 m. Fog water samples were collected using a Caltech Active Strand Cloud Collector (CASCC), and rain samples were collected using a precipitation gauge. Differences were observed between fog water and rain composition for most analyzed ions. Ion abundance in fog water was Ca²⁺ > Cl⁻ > Na⁺ > SO₄²⁻ > Mg²⁺ > NH₄⁺ >K⁺ > NO₃⁻ whereas an order of Ca²⁺ > Na⁺ > Cl⁻ > Mg²⁺ > SO₄²⁻ > NO₃⁻ > K⁺ > NH₄⁺ was observed for rain water. All ion concentrations were higher in fog water than in rain water. Additionally, Ca²⁺ was the dominant cation in both fog and rain samples, accounting for more than half of all measured cations. NH₄⁺ and SO₄²⁻ concentrations were notable for being higher in fog than rain water when compared with other ions. For trace elements, Al, As, Mn and Se were the most abundant elements in fog water; only Al and As were detected in rain water. Seventy-two hour back-trajectory analysis showed that air masses during fog and/or rain events mainly came from the south of Sejila Mountain. Spearman correlation analysis and source contribution calculations indicated that both marine and terrestrial sources contributed to the observed ion concentrations. Considering the higher concentrations of NH₄⁺ and higher ratio of NH₄⁺/NO₃⁻ measured in fog than in rain, we suggest that quantification of fog nitrogen deposition and its ecological effect in this area should be given more attention.

Electron transfer capacities (ETC) of humic-like acids (HLA) and their effects on dechlorination are dependent on their redox-active properties. Aging and minerals can affect the chemical compositions and structures of HLA. However, the underlying mechanism and the impacts on the dechlorination capacities of HLA are poorly understood. We investigated how redox properties change in association with the intrinsic chemical natures and exterior minerals of the HLA extracted from landfilled solid wastes. Furthermore, the ETC of the landfill-derived HLA could be strengthened by increasing landfill age and demineralization, thereby facilitating the dechlorination of pentachlorophenol (PCP). The HLA molecules started to polymerize aromatic macromolecules during landfilling, leading to an increase in ETC and dechlorination capacities. Macromolecular HLA were dissociated to smaller molecules and exposed more aromatic and carboxyl groups when separated from minerals, which enhanced the ETC and the dechlorination abilities of the HLA. Microbial-mediated dechlorination was an effective way to degrade PCP, and almost 80% of the PCP was transformed after 40 days of demineralized HLA and Shewanella oneidensis MR-1 incubation. The demineralization and aging further facilitated the microbial-mediated PCP dechlorination. The findings provide a scientific base for improving in-situ bioremediation of chlorinated compound-contaminated soils using freshly synthesized HLA.

Surfactants are known to enhance the degradation of halogenated organics by nanoscale zerovalent iron (n-ZVI) or n-ZVI-based bimetallic particles, but the mechanism of the promotion is not well understood. In this study, we used nanoscale Ag/Fe particles (n-Ag/Fe) to degrade 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) in different surfactant solutions. The results show that the nonionic surfactant TX-100 had the best promoting effect, which might be attributed to the decrease in particle agglomeration and improvement of mass transfer efficiency after the adsorption of TX-100 on n-Ag/Fe. The distribution analysis of BDE-47 in solid and liquid phases indicates that when the concentration of TX-100 in aqueous solution was above critical micelle concentration, BDE-47 started to dissolve in the liquid phase. Thus, TX-100 micelles can enhance the mass transfer efficiency of BDE-47. However, a too high concentration of TX-100 (above 1.0 mM) would influence the promotion effect of BDE-47 degration, which might be attributed to the excessive and thicker micelles of TX-100 hindering the contact between BDE-47 and n-Ag/Fe. We also studied the degradation pathway of BDE-47 and its products, and found that surfactants did not change the degradation pathway of BDE-47.

The increasing demand for clean water resources for human consumption, is raising concerning about the sustainable worldwide provisioning. In Mexico, rivers near to high-density urbanizations are subject to irrational exploitation where polluted water is a risk for human health. Therefore, the aims of this study are to analyze water quality parameters and bacterial community dynamics to understand the relation between them, in the Apatlaco river, which presents a clear environmental perturbance. Parameters such as total coliforms, chemical oxygen demand, harness, ammonium, nitrite, nitrate, total Kjeldahl nitrogen, dissolved oxygen, total phosphorus, total dissolved solids, and temperature were analyzed in 17 sampling points along the river. The high pollution level was registered in the sampling point 10 with 480 mg/L chemical oxygen demand, 7 mg/L nitrite, 34 mg/L nitrate, 2 mg/L dissolved oxygen, and 299 mg/L of total dissolved solids. From these sites, we selected four samples for DNA extraction and performed a metagenomic analysis using a whole metagenome shotgun approach, to compare the microbial communities between polluted and non-polluted sites. In general, Proteobacteria was the most representative phylum in all sites. However, the clean water reference point was enriched with microorganism from the Limnohabitans genus, a planktonic bacterium widespread in freshwater ecosystems. Nevertheless, in the polluted sampled sites, we found a high abundance of potential opportunistic pathogen genera such as Acinetobacter, Arcobacter, and Myroides, among others. This suggests that in addition to water contamination, an imminent human health risk due to pathogenic bacteria can potentially affect a population of ∼1.6 million people dwelling nearby. These results will contribute to the knowledge regarding anthropogenic pollution on the microbial population dynamic and how they affect human health and life quality.

Marine plastic waste has become an ever-increasing environmental threat in the world’s ocean largely due to their unique properties and ubiquitous occurrence. They include diverse forms of land- and ocean-based sources of plastics and are estimated to account for up to 85% of marine debris worldwide. As secondary pollutants, marine microplastic particles (<5 mm) are derived from pellet loss and degradation of macroplastics. Up to now, several reports have proposed negative impacts of both macro-sized and micro-sized plastics on marine biota. As one of the rapidly growing economies, China is the topmost contributor of plastic waste in the world. China’s massive impact on the plastic levels of the ocean are a definite cause of concern and is developing multiple economic, environmental and biological complications. The research of plastics impact on coastal environments in China is only incipient. Here we review the available information on plastic waste, their impacts on marine biota and human health, and Chinese government policies and management initiatives. Although Chinese coastal environments (surface water, coastal sediments, water column) are affected by microplastics pollution, both from land-based and sea-based activities, their impacts on marine biota remain to be elucidated. Though national-level policies are modern and well suited for minimizing the impacts of plastic pollution, there is hardly any legislation for containment of microplastic pollution. Our objective is to review and summarize the information about the occurrence, impacts, and management of plastic pollution in the Chinese coastal environments in order to comprehend their widespread repercussions.Microplastics are increasingly being detected and quantified in Chinese coastal environments and legislation for containment of such pollution is highly recommended.