Due to high population density, anthropogenic activities and waste disposal have negatively affected artificial lakes in urban areas. The lakes capacity for auto-depuration is limited since it is affected by overwhelming anthropogenic pollution; thus, they have the potential to act as reservoirs for antibiotic resistance genes (ARGs). In this study, we examined three urban artificial freshwater lakes in Nanjing to determine the abundance of sulfonamide and tetracycline resistance genes. Concerning water quality, the three lakes were found to be highly eutrophic, owing to their high levels of Total Nitrogen (TN), Phosphorous (TP), and Chlorophyll a (Chla). The average abundance of sulfonamide resistance genes detected in the three urban lakes was 42.446 log10 gene copies/100 mL, which was lower than the average abundance of tetracycline resistance genes (68.207 log10 gene copies/100 mL). Analysis by ANOVA revealed that all ARGs, except sul3, showed significant differences, probably due to varied anthropogenic influences in lakes. Pearson correlation and principal component analyses were performed to explore the correlation between ARGs, water quality markers, and heavy metals to understand the co-selection and drivers of ARGs propagation. tetM showed no correlation with any water quality markers, whereas Chla showed a positive correlation with all ARGs except tetM. tetM was the only gene that was unaffected by TN, TP, and Chla. The tet genes also showed strong associations with each other except tetM, especially tetA, tetQ, and tetG. The co-selection results between most heavy metals and ARGs were insignificant (p>0.05), with tetM being the most sensitive to the effects of heavy metals and Arsenic (As) having the strongest effect on sul3 and tet genes. The results from this study provide basic but archival information that TN, Chla and As, might be directly or indirectly involved in the dissemination of certain sulfonamide and tetracycline ARGs in freshwater environments.

Freshwater environments are vulnerable to emerging contaminants such as Antibiotic resistance genes (ARGs), and their occurrence is gaining more attention. However, the occurrence of ARGs along with potential pathogens is less explored. The current study aimed to evaluate the abundance of ARGs and explore bacterial communities for the presence of potential bacterial pathogens in water samples collected from a tributary to the Yangtze River in Nanjing. Twelve physico-chemical parameters were analyzed, followed by quantifying 10 ARGs targeting sulfonamide (sul1, sul2), tetracycline (tetG, tetM, tetQ), erythromycin (ermB), vancomycin (vanA, vanR), and streptomycin (strA, strB) using real-time PCR and bacterial diversity characterization using high-throughput 16S rRNA sequencing. The results indicated poor water quality and high-level eutrophication in most sampling locations. sul1, sul2, and strB were dominant in the study area with average concentrations of 6.8, 7.1, and 6.5 Log10 gene copies/100mL, respectively. Proteobacteria, Cyanobacteria, Bacteroidetes, and Actinobacteria were the main phyla detected in the study area, and genus-level analysis revealed the presence of eight potential pathogenic and ten fecal-associated bacterial genera at several locations in the study area. The distance-based Redundancy analysis indicated that total phosphorus, electrical conductivity, dissolved oxygen, total dissolved solids, ammonium-N (NH4+-N), and chlorophyll a had significantly influenced the bacterial community composition in the monitored locations. Correlation analysis demonstrated that water temperature, pH, NH4+-N, and total organic carbon were positively correlated with sul2, tetG, and vanR genes, indicating that these environmental parameters significantly affected the ARGs distribution pattern. Overall, our results provide valuable information regarding the occurrence of ARGs and potential bacterial pathogens in the study area; however, their co-existence highlights increased human health risks.

In the last decade, Chinese megacities have undergone rapid and massive urbanisation that resulted in rising PM2.5 levels in megacities, which forced the government to implement stricter air quality guidelines to combat it. This study investigates the effectiveness of the five-year (2013–2017) air combat plan in reducing PM2.5 in these megacities since they have achieved a certain level of urbanisation. The findings show that annual concentrations of PM2.5 exceeded the World Health Organization (WHO) guideline value, and eight out of ten cities exceeded the national ambient air quality standard (NAAQS) guideline value. Although, on an annual level, a consistent downward trend was observed for PM2.5 values among all cities starting from 2013, indicating positive policy feedback from guidelines. The cumulative rate of change in PM2.5 concentrations from 2013 to 2019 indicated that the highest magnitude of the decrease occurred in Beijing and Chengdu (-59%). The Environmental Kuznets curve was observed for PM2.5 with GDP and Industrial SO2 emission. A negative relationship was observed between PM2.5 and secondary industry share, while the contrary was observed between PM2.5 and Industrial NO2 emissions. Our data indicated that stricter sanctions and emission policies are needed to lower the PM2.5 values in most of these megacities.

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