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There is growing concern about the impact of agricultural practices on water quality. The loss of nutrients such as nitrogen and phosphorous through agricultural runoff poses a potential risk of water quality degradation. However, it is unclear how dissolved organic matter (DOM) composition is associated with pollution levels in water bodies. To address this, we conducted a cross-year investigation to reveal the nature of DOM and its relationship to water quality in agricultural effluents (AEs) and livestock effluents (LEs). We discovered that DOM fluorescence components of AEs were mainly from autochthonous and terrestrial sources, while in LEs it was primarily from autochthonous sources. LEs showed a higher β:α and biological index (BIX) than AEs, indicating that LEs had higher biological activity. Compared to the LEs, DOM in AEs exhibited a higher humification index (HIX), illustrating that DOM was more humic and aromatic. Overall, our results suggest that the BIX and fluorescence index (FI) were best suited for the characterization of water bodies impacted by LEs and AEs. Excitation–emission matrix spectroscopy and parallel factor (EEMs-PARAFAC) analysis showed that DOM in AEs was mainly a humic-like material (~64%) and in LEs was mainly protein-like (~68%). Tryptophan-like compounds (C1) were made more abundant in AEs because of the breakdown of aquatic vegetation. The microbial activity enhanced protein-like substances (C1 and C2) in LEs. Our study revealed a positive correlation between five-day biochemical oxygen demand (BOD5) concentrations and tyrosine-like substance components, suggesting that fluorescence peak B may be a good predictor of water quality affected by anthropogenic activities. For both LEs and AEs, our results suggest that peak D may be a reliable water quality surrogate for total phosphorus (TP).

The effects of granular activated carbon (GAC) and UV/H2O2-GAC filtration on the bacterial community and opportunistic pathogens (OPs) in simulated drinking water systems were investigated in this study. The results indicated that GAC filtration and UV/H2O2-GAC filtration enhanced the dissolved organic carbon (DOC) and assimilable organic carbon (AOC) removal efficiency in the influents of drinking water distribution systems (DWDSs) by the removal of tryptophan-like proteins, fulvic acid-like, and humic acid-like compounds, compared with sand filtration (SF). The lower organic matter concentration reduced the diversity and richness of the bacterial community, inducing the production of lower extracellular polymeric substances (EPS) in these two DWDSs. EPSs with a lower content of proteins led to less bacterial attachment onto particles to form particle-associated bacteria, and adsorption onto the surface of pipes to form biofilms. This process induced a lower chlorine-resistance capability of the bacteria in water and biofilm in DWDSs. The relative abundance of Legionella at the genus level was 0.93%, 0.29%, and 0.13% in the biofilms of SF DWDSs, GAC DWDSs, and UV/H2O2-GAC DWDSs, respectively. Mycobacteria and Pseudomonas showed the same changes as Legionella. The quantitative polymerase chain reaction (qPCR) results also suggested that the number of Legionella pneumophila, Mycobacteria avium, and Pseudomonas aeruginosa were lower in the effluents and biofilms of GAC DWDSs and UV/H2O2-GAC DWDSs. Therefore, GAC filtration can be used to control OPs growth in DWDSs, and UV/H2O2 can improve the efficiency of GAC filtration, especially with the 48 h distribution in DWDSs.

The effects of disinfectants and particles on the occurrence of different bacteria, including total coliforms, heterotrophic plate count (HPC), different opportunistic pathogens (OPs) and amoeba hosts, were investigated in drinking water distribution systems (DWDSs) from five drinking water treatment plants. Total coliforms were not detected in all samples. HPCs were all below 500 CFU mL−1 when the free chlorine residual was higher than 0.05 mg L−1 and the total chlorine residual was higher than 0.35 mg L−1. HPC showed a good relationship with different OPs. Limiting HPC could also control OPs growth in DWDSs. However, Legionella spp., Pseudomonas aeruginosa and Hartmannella vermiformis were 100% positively detected, and Mycobacterium spp. and Legionella pneumophila were more than 90% positively detected in all samples, and pose a health risk to people. Maintaining the free chlorine residual at 0.15–0.20 mg L−1, and the total chlorine residual at 0.35–0.50 mg L−1 can control the OPs growth in DWDSs very well. However, apart from enhancing disinfectant residual concentration, controlling the particle number can also limit OPs growth. This investigation suggests that the particle number should be controlled below 300 in order to control Mycobacterium avium, Legionella pneumophila, and Acanthamoeba spp. growth. The corresponding turbidity should be controlled at 0.25–0.35 NTU. Therefore, there may be a trade-off in the selection of disinfectant residuals or particles to control the OPs growth in DWDSs.

In the process of electrolytic aluminium production, a large amount of fluoride is deposited into the surrounding environment. The growth of crops within these areas creates a state of high stress in plants that can easily result in excessive fluorine enrichment in agricultural products, which in turn poses a health threat to humans via the food chain. However, it is not clear what the degree of influence is or how long the impacts of fluorides in soil and agricultural products last for. In this study, 122 vegetable species and 36 surface soil samples were collected within 10 km of an aluminium plant that had been abandoned for five years. The single factor index and the geological accumulation index methods were used to evaluate the degree of fluorine pollution in vegetables and soil within the study area. The hazard index and the hazard quotient were used to assess vegetable and soil health risks, respectively. The results showed that the fluorine content of 89.26% of agricultural products exceeded the Chinese Maximum Levels of Contaminants in Foods and was higher than in other regions, indicating that the emissions of fluoride from the aluminium plant still had a significant effect on fluorine accumulation in vegetables. The total fluorine (Ft) content in the surrounding surface soil (average value 1328.32 mg kg−1) was similar to the soil fluorine background in the nearby uncontaminated settlement area, but the soil water-soluble fluorine (Fw) was very high, indicating that the fluorine pollutants emitted from the aluminium plant had gradually been diluted by the high background of the original soil, but the solubility of these pollutants was higher (average 15.00 mg kg−1) and would continue to threaten the safety of agricultural products in this region. Within 1 km of the abandoned aluminium plant, the degree of fluorine enrichment in vegetables, and Ft and Fw in soil were significantly higher than other ranges, indicating that this was the main fluoride deposit area. Based on the HI and HQ evaluation, vegetables and ground dust around the aluminium plant still had high non-carcinogenic risks for children, even though it has been abandoned for more than five years.

Effects of sulfadiazine on bacterial community and antibiotic resistance genes (ARGs) in drinking water distribution systems (DWDSs) were investigated in this study. Three DWDSs, including sand filtered (SF) DWDSs, granular active carbon (GAC) filtration DWDSs, and UV/H

In the process of electrolytic aluminium production, a large amount of fluoride is deposited into the surrounding environment. The growth of crops within these areas creates a state of high stress in plants that can easily result in excessive fluorine enrichment in agricultural products, which in turn poses a health threat to humans via the food chain. However, it is not clear what the degree of influence is or how long the impacts of fluorides in soil and agricultural products last for. In this study, 122 vegetable species and 36 surface soil samples were collected within 10 km of an aluminium plant that had been abandoned for five years. The single factor index and the geological accumulation index methods were used to evaluate the degree of fluorine pollution in vegetables and soil within the study area. The hazard index and the hazard quotient were used to assess vegetable and soil health risks, respectively. The results showed that the fluorine content of 89.26% of agricultural products exceeded the Chinese Maximum Levels of Contaminants in Foods and was higher than in other regions, indicating that the emissions of fluoride from the aluminium plant still had a significant effect on fluorine accumulation in vegetables. The total fluorine (F

In order to study the influence mechanism of HCO3− on the fluoride removal by AlCl3 and Al13, the residual fluoride concentration, residual aluminum concentration and pH value in coagulation effluent were measured at different HCO3− concentrations. Electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) was used to analyze the aluminum species in the supernatant after coagulation, and the flocs collected were analyzed by nuclear magnetic resonance (NMR) and X-ray photoelectron spectra (XPS). The results show that AlCl3 is used as a coagulant, when the concentration of HCO3− increases from 100 mg/L to 300 mg/L, Al3+ and HCO3− are double hydrolyzed to form Al(OH)3 alum flower after adding AlCl3, and the removal rate of fluoride rapidly increases from 9.55 % to 78.0 %. When the concentration of HCO3− increases from 300 mg/L to 1000 mg/L, the precipitation of Al(OH)3 will gradually dissolve to form Al(OH)4− and the removal rate of fluoride drops from 78.0 % to 56.2 %. When Al13 is used as a coagulant, with the increase of HCO3− from 100 mg/L to 1000 mg/L, its double hydrolysis with Al-F complexes is enhanced, resulting in the formed Al6F2, Al7F2 and Al9F3 gradually dissociate, and the removal rate of fluorine decreases from 78.8 % to 59.4 %.

Fifty-seven shallow groundwater samples were collected from Guiyang karst basin, China, to analyze the aqueous rare-earth elements in low-water seasons and it is shown that the total amount of rare-earth elements (ΣREE) in karst groundwater is exceedingly low compared with that in carbonate rocks or weathering crusts of carbonate rocks, and ranges from 0.01 to 0.43, from 0.03 to 0.27, from 0.03 to 0.19 and from 0.05 to 1.38 μg·L−1 for dolomite, dolomitic & limestone, limestone and clastic rock aquifer, respectively. Both distributions and contents of rare-earth elements (REE) in karst groundwater reflect the lithology of host rocks or weathering crusts of carbonate rocks through which groundwater flows. The chondrite-normalized patterns show a non-flat profile with higher enrichment of slightly light rare-earth elements (LREE) than heavy rare-earth elements (HREE), prominent fractionation between LREE and HREE, negative Ce anomalies and negative or positive Eu anomalies. There is more obvious fractionation between LREE and HREE in groundwater than that in carbonate rocks and their weathering crusts due to high contents of HCO3− and PH in groundwater. In shallow karst groundwater, REE(CO3)n2n−3 (n=1 and 2) is the main inorganic species of REE. But for a clastic rock aquifer, both REESO4+ and REECO3+ are the main inorganic species of REE. Species of REE in groundwater is closely associated with the hydrochemical type of groundwater which is predominated by the lithology of host rocks, groundwater-rock interaction and weathering-pedogenesis of carbonate rocks.