Hydrochemical fingerprints of karst underground river systems impacted by urbanization in Guiyang, Southwest China.

Karst groundwater plays an irreplaceable role in the formation and development of urban areas, and land-use and land-cover change (LUCC) and the input of pollutants during the urbanization process would pose potential environmental risks to underground rivers. We analysed the relationship between urbanization processes and underground river hydrochemistry over nearly 35 years in Guiyang city, southwest of China, it was found that concentrations of various cations and anions, as well as total dissolved solids (TDS), gradually increased with the urbanization process, with significant fluctuations during the rapid urbanization periods. The Hydrochemical Facies Evolution Diagram (HFED) clearly showed the influence of urbanization on the hydrochemistry of the underground rivers. The ion ratios of γMg2+/γCa2+-γHCO3-, γNa+/γCl-, Ca2+/Mg2+-Ca2+ or Mg2+/Σ cations, HCO3-/SO42--HCO3- or SO42-/Σ anions revealed two distinct phases in the hydrochemical evolution of the underground river system, highly consistent with the urbanization process. Before the rapid urbanization, acid deposition and agricultural activities affected the hydrochemistry, with HCO3-Ca·Mg and HCO3·SO4-Ca·Mg as the dominant types controlled by limestone and dolomite dissolution in water-rock interactions. As acid deposition diminished, the input of SO42- from urban sewage compensated for the reduced impact, but the increased impermeable surfaces reduced the infiltration of atmospheric precipitation, leading to a reduced dissolution of dolomite minerals in water-rock interactions, resulting in a decrease in Mg2+ and a change in the hydrochemical type. The hydrochemical type evolved from a single HCO3·SO4-Ca·Mg type and HCO3-Ca·Mg type to multiple types, such as HCO3·Cl-Ca, HCO3·SO4-Ca, HCO3-Ca, and HCO3·SO4-Ca·Mg, and was highly unstable. With changes in land use, the proportions of various cations and anions in the hydrochemistry changed, especially NH4+, NO3-, SO42-, Na+, and Cl-, which were more sensitive to human activities. This study indicated the impact of urbanization on the hydrochemistry of the underground river system, with the input of SO42- from human activities and the increase in paved surfaces due to urbanization collectively altering the hydrochemical types of the underground river system. The rapid response of karst underground river system hydrochemistry indicates a potential impact on groundwater system by urbanization that should not be ignored.

Formation of Sb2O3 microcrystals by Rhodotorula mucilaginosa.

Antimony (Sb) pollution seriously endangers ecological environment and human health. Microbial induced mineralization can effectively convert metal ions into more stable and less soluble crystalline minerals by extracellular polymeric substance (EPS). In this study, an efficient Sb-resistant Rhodotorula mucilaginosa (R. mucilaginosa) was screened, which can resist 41 mM Sb(III) and directly transform Sb(III) into Sb2O3 microcrystals by EPS. The removal efficiency of R. mucilaginosa for 22 mM Sb(III) reached 70% by converting Sb(III) to Sb2O3. The components of supernatants as well as the effects of supernatants and pH on Sb(III) mineralization verified that inducible and non-inducible extracellular protein/polysaccharide biomacromolecules play important roles in the morphologies and sizes control of Sb2O3 formed by R. mucilaginosa respectively. Sb2O3 microcrystals with different morphologies and sizes can be prepared by the regulation of inducible and non-inducible extracellular biomacromolecules secreted by R. mucilaginosa. This is the first time to identify that R. mucilaginosa can remove Sb(III) by transforming Sb(III) into Sb2O3 microcrystals under the control of EPS. This study contributes to our understanding for Sb(III) biomineralization mechanisms and provides strategies for the remediation of Sb-contaminated environment.

Characterization of Dissolved Organic Matter from Agricultural and Livestock Effluents: Implications for Water Quality Monitoring.

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 ß: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).

Distribution, source, water quality and health risk assessment of dissolved heavy metals in major rivers in Wuhan, China.

Heavy metals are released into the water system through various natural processes and anthropogenic activities, thus indirectly or directly endangering human health. The distribution, source, water quality and health risk assessment of dissolved heavy metals (V, Mn, Fe, Co, Ni, Zn, As, Mo, Sb) in major rivers in Wuhan were analyzed by correlation analysis (CA), principal component analysis (PCA), heavy metal pollution index (HPI), hazard index (HI) and carcinogenic risk (CR). The results showed that the spatial variability of heavy metal contents was pronounced. PCA and CA results indicated that natural sources controlled Mn, Fe, Co, Ni and Mo, and industrial emissions were the dominant factor for V, Zn and Sb, while As was mainly from the mixed input of urban and agricultural activities. According to the heavy metal pollution index (HPI, ranging from 23.74 to 184.0) analysis, it should be noted that As and Sb contribute most of the HPI values. The health risk assessment using HI and CR showed that V and Sb might have a potential non-carcinogenic risk and As might have a potential carcinogenic risk to adults and children in the study area (CR value exceeded target risk 10-4). At the same time, it was worth noting that As might have a potential non-carcinogenic risk for children around QLR (HI value exceeded the threshold value 1). The secular variation of As and Sb should be monitor in high-risk areas. The results of this study can provide important data for improving water resources management efficiency and heavy metal pollution prevention in Wuhan.

Bacterial community change and antibiotic resistance promotion after exposure to sulfadiazine and the role of UV/H2O2-GAC treatment.

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/H2O2-GAC DWDSs, were used to deliver sand filtered water, GAC filtered water, and UV/H2O2-GAC treated water, respectively. UV/H2O2-GAC filtration can remove the dissolved organic matter effectively, which resulted in the lowest bacterial diversity, biomass and ARGs in effluents and biofilm of DWDSs. When sulfadiazine was added to the sand filtered water, the dehydrogenase concentration and bacterial activity of bacterial community increased in effluents and biofilm of different DWDSs, inducing more extracellular polymeric substances (EPS) production. The proteins increasement percentage was 26.9%, 11.7% and 19.1% in biofilm of three DWDSs, respectively. And the proteins increased to 830.30 ± 20.56 µg cm-2, 687.04 ± 18.65 µg cm-2 and 586.07 ± 16.24 µg cm-2, respectively. The increase of EPS promoted biofilm formation and increased the chlorine-resistance capability of bacteria. Therefore, the relative abundance of Clostridium_sensu_stricto_1 increased to 12.22%, 10.41% and 0.33% in biofilm of the three DWDSs, respectively. Candidatus_Odyssella also increased in the effluents and biofilm of the three DWDSs. These antibiotic resistance bacteria increase in DWDSs also induced the ARGs promotion, including sul1, sul2, sul3, mexA and class 1 integrons (int1). However, UV/H2O2-GAC filtration induced the lowest increase of dehydrogenase and EPS production through sulfadiazine removal efficiently, resulting in the least bacterial community change and ARGs promotion in UV/H2O2-GAC DWDSs.

Fluorine enrichment of vegetables and soil around an abandoned aluminium plant and its risk to human health.

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.

[Temporal Response of Subterranean Karst Stream Hydrochemistry to Urbanization].

The hydrochemical responses of underground rivers to urbanization were studied using a 25-year groundwater observation dataset and remote sensing. We found that as urbanization progresses, the mineralization degree of underground rivers gradually increases; time-series data for dominant hydrochemical indicators changed from HCO3·SO4-Ca·Mg during the dry season and HCO3-Ca·Mg during flood season to HCO3·Cl-Ca, HCO3·SO4-Ca, HCO3-Ca, and HCO3·SO4-Ca·Mg. Influenced by surface precipitation input, the groundwater chemistry of underground rivers varies greatly during the dry season and the flood season. Prior to urbanization,[Mg2+]/[Ca2+] and[HCO3-]/[SO42-] molar ratios are affected by water-rock interactions, agricultural activities, and acid rain infiltration, the average values of which were 0.86 and 29.34, respectively. After urbanization, agricultural activities and the contribution from acid rain decreased gradually. During the periods 1990-1995, 1996-2010, and 2011-2015, the main sensitive geochemical cations were Ca2+, Mg2+, Na+, and NH4+, and the main anions were HCO3-, HCO3-, and SO42-, and Cl-. The hydrochemical response of underground rivers to urbanization was characterized by clear temporal phases.

[Study on geochemical susceptivity of groundwater system in representative karstic regions].

We investigated geochemical susceptivity of groundwater in representative karst groundwater system. The results indicated that Ca2+ and Mg2+, correlative the average values of geochemical susceptivity index (GSI) were 0.73 and 0.19; HCO3- and SO4(2-), interrelated the average values of geochemical susceptivity index were 0.92 and 0.37, are the principal cations and anions in karstic groundwater system, respectively. And the major elements are obviously characterized by the geochemical susceptivity. The rank order of geochemical susceptivity for major elements in study region is HCO3- > Ca2+ > SO4(2+) > Mg2+ > Cl- > Na+ > NO3- > K+. The susceptive regions of groundwater system were zoned by the geochemical susceptivity index of HCO3- (GSI(HCO3-)), which classified as GSI(HCO3-) < 0.5 is low-susceptivity zone, 0.5 < GSI(HCO3-) < 1 is moderate-susceptivity zone and GSI(HCO3-) > 1 is high-susceptivity zone, respectively. The groundwater systems in high-susceptivity zone may become as a collected and genetic room for pollutants. Furthermore, both continual or active exchange and mutual recharge between surface water and groundwater in high-susceptivity zones might induce intersectant pollution and serious cycle.

Adsorption of mercury on laterite from Guizhou Province, China.

The adsorption behaviors of Hg(II) on laterite from Guizhou Province, China, were studied and the adsorption mechanism was discussed. The results showed that different mineral compositons in the laterite will cause differences in the adsorption capacity of laterite to Hg(II). Illite and non-crystalloids are the main contributors to enhancing the adsorption capacity of laterite to Hg(II). The pH of the solution is an important factor affecting the adsorption of Hg(II) on laterite. The alkalescent environment (pH 7-9) is favorable to the adsorption of Hg(II). The amount of adsorbed Hg(II) increases with increasing pH. When the pH reaches a certain value, the amount of the adsorbed Hg(II) will reach the maximum level. The amount of adsorbed Hg(II) decreases with increasing pH. The optimal pHs of laterite and kaolinite are 9 and 8, respectively. The optimal initial concentrations of Hg(II) on laterite and kaolinite are 250 and 200 microg/ml, respectively. The adsorption isotherms were described by the Langmuir model. The adsorption of Hg(II) on laterite is a quick process while that of Hg(II) on kaolinite is a slow reaction. Laterite from Guizhou Province is a promising environmental material which can be used in the removal of Hg(II) from wastewater.