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In groundwater environments, the interaction between microbial communities and the hydrogeochemical parameters have been investigated extensively in the past years. However, little is known whether the maximum contamination level (MCL) is a threshold value that dictates the microbial composition. In this study, we analyzed 10 groundwater samples for their nitrate, nitrite, COD and sulfate concentrations, and characterized their microbial compositions using 16 S rRNA based high-throughput sequencing methods. All the 10 samples had oxygen demands higher than the corresponding MCL of China (10 mg L−1); moreover, 4 out of 10 samples also had nitrate concentrations higher than the corresponding MCL, which indicated that the groundwater quality was negatively impacted by anthropogenic activities. Comparing the microbial composition of groundwater that had higher-than-MCL nitrate concentrations to those that had lower-than-MCL nitrate concentrations, no significant differences were detected in communities' richness and diversity. However, the non-metric multi-dimensional analysis suggested that the 4 groundwater samples whose nitrate concentration exceed MCL are distinctly different from those of the rest 6 samples, indicating that MCL does have a significant impact on microbial structures. Pearson's correlation analysis suggested that none of the four analyzed hydrochemical parameters had significant impact on microbial communities' richness and diversity; however, at the genus level, the correlation results suggested that JG3 0-KM -CM45 , Sphingomonas and Rhodococcus are closely correlated with nitrate concentration. The findings of this study deepened our understanding with respect to the relationships between the environmental quality indices and the microbial compositions of groundwater. • Impact of higher-than-MCL nitrate on microbial communities' structure were examined • No significant differences were found in richness and diversity • NMDS revealed higher-than-MCL NO3 led to distinct groundwater microbial community • JG-30-KM-CM45, Sphingomonas and Rhodococcus closely related with NO3 concentration [ABSTRACT FROM AUTHOR]

Atmospheric amines have attracted increasing attention due to their significant impact on new particle formation, particle hygroscopicity and particle optical properties. In this study, four low-molecule-weight amines were detected from PM 2.5 filter samples collected at an urban site of Pearl River Delta (PRD) region of China in 2018 autumn. During the campaign, the mass concentrations of ambient particulate methylamine (MA, CH 3 NH 2), dimethylamine (DMA, (CH 3) 2 NH), trimethylamine (TMA, (CH 3) 3 N), and diethylamine (DEA, (C 2 H 5) 2 NH) were quantified at daily or 12-h resolution using an optimized Ion Chromatograph (IC) method. The total measured amine concentration was 297 ± 209 ng/m3, which can account for 0.76 ± 0.33% of PM 2.5 mass concentrations. The particulate amines in PRD urban area were dominated by MA (243 ± 179 ng/m3), accounting for over 80% of total amines, then followed by DMA (49 ± 30 ng/m3, 16.5%), TMA (4 ± 2 ng/m3) and DEA (1 ± 1 ng/m3). Based on the correlation analysis, MA and DMA mainly presented as nitrate and sulfate salts. We speculate the amines tend to react with gas-phase HNO 3 or particle-phase nitrate to form particulate amine salts via local process in Guangzhou. As the relative humidity (RH) increased, enhanced partitioning of amine towards the particle phase was observed. Using approach of multiple linear regression, 71% of the particulate amines in PRD urban site could be explained by acid-base process and the rest by primary emissions from combustion sources (29%). • Particulate amines in urban PRD were quantified using an optimized IC method. • Methylamine was the most abundant amine, followed by dimethylamine. • Methylamine and dimethylamine mainly presented as nitrate and sulfate salts. • Enhanced RH facilitated the partitioning of amine towards particle phase. • Acid-base process dominated the amine formation, the left by combustion source. [ABSTRACT FROM AUTHOR]