Groundwater antibiotics contamination in an alluvial-pluvial fan, North China Plain: Occurrence, sources, and risk assessment.

Antibiotics in groundwater have received widespread concern because high levels of them harm aquatic ecosystems and human health. This study aims to investigate the concentration, distribution, ecological and human health risks as well as potential sources of antibiotics in groundwater in the Hutuo River alluvial-pluvial fan, North China Plain. A total of 84 groundwater samples and nine surface water samples were collected, and 35 antibiotics were analyzed using ultra-performance liquid chromatography-tandem mass spectrometry. The results indicated that 12 antibiotics were detected in surface water with the total concentrations ranging from 5.33 ng/L to 64.73 ng/L. Macrolides were the primary category of antibiotics with a detection frequency of 77.8% (mean concentration: 9.14 ng/L). By contrast, in shallow granular aquifers (<150 m), 23 antibiotics were detected and the total concentrations of them ranged from below the method detection limit to 465.26 ng/L (detection frequency: 39.7%). Quinolones were the largest contributor of antibiotics with detection frequency and mean concentration of 32.1% and 12.66 ng/L, respectively. And ciprofloxacin and ofloxacin were the two preponderant individual antibiotics. The mean concentration of groundwater antibiotics in peri-urban areas was approximately 1.7-4.9 times that in other land use types. Livestock manure was the predominant source of antibiotics in groundwater. Erythromycin, sulfametoxydiazine, ofloxacin, and cinoxacin exhibited medium ecological risks to aquatic organisms. All antibiotics posed no risks to human health. The findings of this study provide valuable insights into the occurrence and management of antibiotic contamination in the groundwater in the Hutuo River alluvial-pluvial fan.

The bioaccessibility and fractionation of arsenic in anoxic soils as a function of stabilization using low-cost Fe/Al-based materials: A long-term experiment.

Arsenic (As)-contaminated soils occur widely worldwide. In the present study, three low-cost Fe/Al-based materials, including red soil (RS), sponge iron filter (SIF) and Al-based water treatment sludge (WTS), were applied as amendments to remediate As-contaminated soils under anoxic conditions. After 180 d of incubation, the proportion of the sum of nonspecifically absorbed As (F1) and specifically absorbed As (F2) to the total As was reduced by 6%, 52% and 13% with 5% of RS, SIF and WTS addition, respectively, compared to the control soil (31%). The results showed that among the three amendments, SIF was the most effective at decreasing As bioaccessibility in soils. Compared with RS and WTS, SIF intensified the decrease of labile fractions and the increase of unlabile fractions, and the redistribution of the amorphous oxide-bound fraction (F3) and crystalline hydrous oxide-bound fraction (F4) occurred in the SIF-amended soil. Moreover, the As stabilization processes were divided into two stages in the control and RS-amended soil, while the processes were divided into three stages in both SIF- and WTS-treated soil. The As stabilization processes in all treated soils were characterized by the transformation of labile fractions into more immobilizable fractions, except for F4 transforming into F3 in the first stage in SIF-amended soil. Correspondingly, inner-surface complexation and occlusion within Fe/Al hydroxides were the common driving mechanisms for the transformation of As fractions. Therefore, taking into consideration the results of this study, SIF could be a more promising alternative than the other two materials to passivate As in anoxic soils.

Large scale occurrence of aluminium-rich shallow groundwater in the Pearl River Delta after the rapid urbanization: Co-effects of anthropogenic and geogenic factors.

Aluminium(Al)-rich (> 0.2 mg/L) groundwater has received more concerns because of its harmful to human beings. Origins of large-scale occurrence on Al-rich groundwater in urbanized areas such as the Pearl River Delta (PRD) are still little known. The current work was conducted to investigate spatial distribution of Al-rich groundwater in the PRD, and to discuss its origins in various aquifers. For that, 265 groundwater samples and 15 river water samples were collected, and 21 hydrochemical parameters including Al were analyzed by using conventional analytical procedures. The results showed that groundwater Al concentrations were up to 22.64 mg/L, and Al-rich groundwater occurred in 15% of the area occupied by the PRD. Al-rich groundwater in the coastal-alluvial aquifer was about 2 times those in alluvial-proluvial and fissured aquifers, whereas the karst aquifer was absent. In the coastal-alluvial aquifer, Al-rich groundwater in the peri-urban area was 2 or more times those in urbanized and agricultural areas, whereas the remaining area was absent. By contrast, in the alluvial-proluvial aquifer, Al-rich groundwater in the remaining area was 1.5-3.5 times that in other areas; in the fissured aquifer, the distribution of Al-rich groundwater was independent of land-use types. The infiltration of wastewater from township enterprises was main anthropogenic source for Al-rich groundwater in urbanized and peri-urban areas, whereas irrigation of Al-rich river water was the main one in the agricultural area. Naturally dissolution of Al-rich minerals in soils/rocks, triggered by both of pH decrease resulted from nitrification of contaminated ammonium (e.g., sewage leakage, the use of nitrogen fertilizer) and acid deposition, was the main geogenic source for Al-rich groundwater in the PRD. The contribution of anthropogenic sources to Al-rich groundwater in the coastal-alluvial aquifer was more than that in alluvial-proluvial and fissured aquifers, whereas the contribution of geogenic sources was opposite. In conclusion, the discharge of township enterprises wastewater and ammonium-rich sewage, the emission of nitrogen-containing gas, and the use of nitrogen fertilizer should be preferentially limited to decrease the occurrence of Al-rich groundwater in urbanized areas such as the PRD.

Assessing natural background levels of geogenic contaminants in groundwater of an urbanized delta through removal of groundwaters impacted by anthropogenic inputs: New insights into driving factors.

Knowledge on driving forces controlling natural background levels (NBLs) of geogenic contaminants (GCs) in groundwater of coastal urbanized areas are still limited because of complex hydrogeological conditions and anthropogenic activities. This study assesses NBLs of two GCs including arsenic (As) and manganese (Mn) in four groundwater units of the Pearl River Delta (PRD) with large scale urbanization by using a preselection method composed of the chloride/bromide mass ratio versus chloride concentration and the oxidation capacity with the combination of Grubbs' test. More importantly, driving factors controlling NBLs of As/Mn in groundwater of the PRD are discussed. Results showed that groundwater As/Mn concentrations in residual datasets were independent of land-use types, while those in original datasets in different land-use types were distinct because of various human activities, indicating that the used preselection method in this study is valid for NBLs-As/Mn assessment in groundwater of the PRD. NBL-As in coastal-alluvial aquifers was >6 times that in other groundwater units. NBL-Mn in coastal-alluvial aquifers was 1.4 times that in alluvial-proluvial aquifers, and both were >4 times that in other two groundwater units. High NBLs-As/Mn in coastal-alluvial aquifers is mainly attributed to reduction of FeMn oxyhydr(oxides) induced by mineralization of organic matter in Quaternary sediments. Elevated pH also contributes higher NBL-As in coastal-alluvial aquifers. By contrast, higher NBL-Mn in alluvial-proluvial aquifers than in other two groundwater units mainly ascribes to reduction of FeMn oxyhydr(oxides) in Quaternary sediments triggered by irrigation of reducing river waters. In addition, more occurrence of As/Mn-rich sediments and the infiltration of As/Mn-rich river water are also important factors for high NBLs-As/Mn in coastal-alluvial aquifers. This study shows that revealing natural driving factors of GCs-rich groundwater in coastal urbanized areas on the basis of identification of contaminated groundwaters via the used preselection methods is acceptable.

A sharp contrasting occurrence of iron-rich groundwater in the Pearl River Delta during the past dozen years (2006-2018): The genesis and mitigation effect.

Fe-rich (>0.3 mg/L) groundwater is generally present in areas where organic matter-rich fluvial, lacustrine, or marine sedimentary environments occur. The Pearl River Delta (PRD) that marine sediments is common, where a large scale of Fe-rich groundwater was distributed but disappearing in recent decade. This study aims to investigate the change of Fe-rich groundwater in the PRD, and to discuss the genesis controlling Fe-rich groundwater in the PRD during the past dozen years. A total of 399 and 155 groundwater samples were collected and analyzed at 2006 and 2018, respectively. Results showed that Fe-rich groundwater of the PRD was from 19.3% at 2006 dropped to 1.3% at 2018. Fe-rich groundwater in coastal-alluvial aquifers was more than 2 times that in other aquifers at 2006. Both of anthropogenic and geogenic sources were contributed to the widely distribution of Fe-rich groundwater in the PRD at 2006. The infiltration of industrial wastewater and the irrigation of Fe-rich surface water were the major anthropogenic driving forces for the occurrence of Fe-rich groundwater in the PRD at 2006. The reductive dissolution of Fe minerals in aquifer sediments, associated with the degradation of organic matter in marine sediments and the sewage infiltration, was the main driving force for the enrichment of groundwater Fe in coastal-alluvial aquifers at 2006. The intrusion of sewage triggering the reductive dissolution of Fe minerals in terrestrial sediments and the reductive dissolution of Fe minerals in carbon-rich rocks induced by sewage leakages were the major driving forces for the occurrence of Fe-rich groundwater in alluvial-proluvial and fissured aquifers at 2006. All these driving forces were weaker or even not work at 2018 because of the large decrease of untreated wastewater discharge in the PRD during 2006-2018. Therefore, limiting untreated wastewater discharge is the first choice to improve the groundwater quality in urbanized areas.

The Aging Process of Cadmium in Paddy Soils under Intermittent Irrigation with Acid Water: A Short-Term Simulation Experiment.

Cadmium (Cd)-contaminated paddy soils are a big concern. However, the effect of irrigation with acid water on the migration and transformation of Cd and the effect of alternating redox conditions caused by intermittent irrigation on Cd aging processes in different depths of paddy soils are unclear. This study revealed Cd fractionation and aging in a Cd-contaminated paddy soil under four irrigation periods with acid water and four drainage periods, by applying a soil columns experiment and a sequential extraction procedure. The results showed that the dynamic changes of soil pH, oxidation reduction potential (ORP), iron (Fe) oxides and dissolved organic carbon (DOC) throughout the intermittent irrigation affected the transformation of Cd fractions. After 32 days, the proportion of exchangeable Cd (F1) to the total Cd decreased with a reduction of 24.4% and 20.1% at the topsoil and the subsoil, respectively. The labile fractions of Cd decreased, and the more immobilizable fractions of Cd increased in the different depths of soils due to the aging process. Additionally, the redistribution of the Fe and Mn oxide-bound Cd (F3) and organic matter and secondary-sulfide-bound Cd (F4) occurred at different depths of soils during the incubation time. Overall, the bioaccessibility of Cd in the subsoil was higher than that in the topsoil, which was likely due to the leaching and accumulation of soluble Cd in the deep soil. In addition, the aging processes in different depths of soils were divided into three stages, which can be mainly described as the transformation of F1 into F3 and F4.

Distributions, origins, and health-risk assessment of nitrate in groundwater in typical alluvial-pluvial fans, North China Plain.

High concentration of nitrate (NO3-) in groundwater is a major concern because of its complex origin and harmful effects on human health. This study aims to investigate the distributions of nitrate in various aquifers and in areas with different land use types in alluvial-pluvial fans in North China Plain, to identify dominant sources and factors using hydrochemical data and principal component analysis, and to conduct health-risk assessment of groundwater nitrate using the models recommended by USEPA. Results show that approximately 76.1% groundwater in fissured aquifers showed high-NO3- (> 50 mg/L), and was 2.7 times of that in granular aquifers. In fissured aquifers, the proportion of high-NO3- groundwater (PHNG-WHO) in peri-urban areas was more than 1.3 times of those in other areas. Similarly, in shallow granular aquifers, the PHNG-WHO in peri-urban areas was also higher than that in other areas. By contrast, in deep granular aquifers, the PHNG-WHO in urbanized areas was 2.8 and 5.2 times of that in peri-urban areas and farmland, respectively. High NO3- levels in both granular and fissured aquifers originated mainly from domestic sewage and animal waste, and fertilizers are also important sources of NO3- in fissured aquifers. Intensive groundwater exploitation aggravated nitrate contamination because more thickness of vadose zones resulting from over-exploitation is in favor of nitrification. Risk assessment of groundwater nitrate indicated about 43.3%, 45.6%, and 54.2% of the groundwater samples showed unacceptable non-carcinogenic risk to adult males, adult females, and children, respectively. The proportion of samples with health risks had a significant positive correlation with the urbanization level. Our study indicates that several effective measures for pollution prevention, such as strengthening sewage treatment and prohibiting groundwater over-exploitation, must be adopted so as to ensure the sustainable management of groundwater and the safety of drinking water.

Identification of Groundwater Contamination in a Rapidly Urbanized Area on a Regional Scale: A New Approach of Multi-Hydrochemical Evidences.

Efficient identification of groundwater contamination is a major issue in the context of groundwater use and protection. This study used a new approach of multi-hydrochemical indicators, including the Cl-Br mass ratio, the hydrochemical facies, and the concentrations of nitrate, phosphate, organic contaminants, and Pb in groundwater to identify groundwater contamination in the Pearl River Delta (PRD) where there is large scale urbanization. In addition, the main factors resulting in groundwater contamination in the PRD were also discussed by using socioeconomic data and principal component analysis. Approximately 60% of groundwater sites in the PRD were identified to be contaminated according to the above six indicators. Contaminated groundwaters commonly occur in porous and fissured aquifers but rarely in karst aquifers. Groundwater contamination in porous aquifers is positively correlated with the urbanization level. Similarly, in fissured aquifers, the proportions of contaminated groundwater in urbanized and peri-urban areas were approximately two times that in non-urbanized areas. Groundwater contamination in the PRD was mainly attributed to the infiltration of wastewater from township-village enterprises on a regional scale. In addition, livestock waste was also an important source of groundwater contamination in the PRD. Therefore, in the future, the supervision of the wastewater discharge of township-village enterprises and the waste discharge of livestock should be strengthened to protect against groundwater contamination in the PRD.