Sources and pollution path identification of PAHs in karst aquifers: an example from Liulin karst water system, northern China

Temporal hydrogeochemical evolution of surface water and groundwater in a karst system discharging into a continental-type Ramsar site in the Huasteca Potosina, Mexico

Ecosystems such as wetlands have karst groundwater as their primary source of preserving their services and functions. Karst systems are complex hydrogeological systems that are difficult to study because of their complicated functioning mechanism, which requires an interdisciplinary effort based on hydrodynamic assessment and characterization of the hydrogeology of the system. The study area is the Ramsar wetland Ciénaga de Tamasopo (Mexico), which is dependent on the discharge of karst groundwater that is affected by water extraction of extensive sugarcane agriculture and is also the main water source for the rural towns. Hydrogeochemical and isotopic tools further suggest that at least two distinct sources contribute to the groundwater composition in the Ciénaga de Tamasopo basin. One corresponds to meteoric water recharging the aquifer through karst structures of the El Abra Fm. and Tamasopo Fm. inferring a local flow with an isotopic composition of δ18O (- 4.75 to - 4.20‰) and δ2H (- 29.12 to - 23.86‰). The second is associated with regional-intermediate flow, indicating that the water has an enrichment of heavy δ18O (- 6.90 to - 6.65‰) and δ2H (- 41.37 to - 40.41‰) isotopes circulating in the Guaxcamá Fm. EC and temperature variations were evaluated, determining that the EC tends to increase in the rainy season because of the mixing of local and intermediate flows and that there is evidence of temperature increase. The chemical analysis identified the dominant processes in this karst system as dissolution-precipitation of calcite, dolomite, and gypsum by water-rock interaction, mixing, and evaporation. This study facilitated the development of a conceptual model for understanding groundwater movement in warm and sub-humid climate karst systems.

Novel insights into PAHs accumulation and multi-method characterization of interaction between groundwater and surface water in middle Yangtze River: Hydrochemistry, isotope hydrology and fractionation effect

To meet the challenge of water quality protection and management in the middle Yangtze River and understand the accumulation mechanism of PAHs in aquatic complexity systems, caused by hydro-chemical changes, anthropogenic and geological activities, and intensive surface water-groundwater interaction, a comprehensive study is urgently needed. The study investigated the pollution levels, potential sources, accumulation mechanism, and groundwater- surface water interaction of polycyclic aromatic hydrocarbons (PAHs) in wet and dry seasons of the middle Yangtze River. There was no significant difference of PAHs accumulation between wet and dry seasons of the middle Yangtze River. PAHs occurrence in the middle Yangtze River was dominated by the input of tributary. Phenanthrene and Naphthalene were still the dominant species of PAHs. Coal combustion (CC) and biomass burning (BB) were the major contributor for the PAHs occurrence. However, the CC apportionment concentration increased by 6.18 ng·L-1 from wet to dry season, suggesting higher density of coal consumption in dry season. The potential mechanism of PAHs occurrence was demonstrated by the mantel test and structural equation model (SEM). Results revealed that the pollution of the middle Yangtze River could be mainly affected by primary emission in wet and dry seasons due to the significant positive effect between eutrophication levels and PAHs pollution sources. Meanwhile, the difference in redox conditions could directly affect the fate of pollutants (including the valence state transformation of nitrogen and phosphorus). The stronger interaction of groundwater and surface water in dry season was presented by hydrochemistry and isotope hydrology (δ18O and δ2H). The similar result was also evidenced by fractionation effect of PAHs, because more similar behaviors of characteristic pollutants were observed in dry season. Consequently, PAHs can be considered as an effective geochemical tracer and further expanded their toxic effects through the surface water-groundwater interaction.

A mechanistic study on the interaction effects between legacy and pollutants of emerging concern: A case study with B[a]P and diclofenac

To study the intricate toxicological mechanisms triggered by exposure to mixed pollutants, we exposed zebrafish embryos to legacy and emerging pollutants through binary mixtures of benzo[a]pyrene (B[a]P) and diclofenac (DFC). The combination of next-generation transcriptomics and toxicopathology disclosed instances where exposure to mixtures did not attain the expected sum of acute effects of individual toxicants, indicating potential antagonism. Despite overall higher mortality in DFC treatments, the same antagonistic trend was noted in genotoxicity and molecular pathways related to RNA turnover, cell proliferation, apoptosis and cell-cycle control. The formation of oedemas in the heart cavity and yolk sac can be an adverse outcome (AO) resulting from exposure to DFC isolated or combined, whose potential key events (KEs) may involve cell cycle arrest and apoptosis via p53 and MAPK pathways. From the findings it can be hypothesised that, rather than genotoxicity, the molecular initiating event (MIE) maybe inflammation triggered by oxidative stress. Nonetheless, the exact role of ROS in the process needs further clarification. Impaired eye function by action of DFC and B[a]P combined may be another AO, in the case caused by ocular degeneration following the suppression of biologic processes and molecular functions involved in eye development and its functionalities, possibly linked to hindered regulation of the expression of hsf4 and cryaa. Altogether, toxicopathology suggests predominance of antagonistic effects, but its integration with mechanism suggests that interactions between DFC and B[a]P in environmentally-relevant concentrations that may lead to hindrance of key functions such as the control of inflammation and cell cycle. These outcomes suggest potentially severe implications for health and survival, in case of prolonged chronic exposure to combined toxicants.

Comparing roles of multiple contamination indicators in tracing groundwater pollution nearby a typical municipal solid waste (MSW) landfill

Groundwater pollution resulting from leachate leakage at landfill sites has garnered significant attention. Investigating the migration of pollutants from these landfills to adjacent groundwater is crucial for understanding the diffusion patterns and extent of contamination. It is imperative to develop cost-effective yet highly efficient tracer techniques to aid landfill operators in monitoring groundwater contamination stemming from their operations. The primary objective of this research was to compare the roles of conservative tracers sodium (Na+) and chloride (Cl-), and conventional pollutants permanganate oxidation (CODMn), ammonium nitrogen (NH4 +-N), lead (Pb), and zinc (Zn) in assessing pollution levels from municipal solid waste landfills to groundwater. For this purpose, a typical municipal solid landfill was selected to investigate the origin of Cl-, groundwater quality, and spatiotemporal variations of multiple contaminations. Geochemistry analyses revealed that Na-Cl and Ca-HCO3 were the dominant groundwater type in this study and landfill was the primary source of Cl- in groundwater, with an average contribution of 78 %. Groundwater in proximity to the landfill (5#, 2#, 22#, 23#) exhibited elevated concentrations of Na+ (15.6-914.0 mg/L), Cl- (8.9-1352.0 mg/L), CODMn (0.54-95.9 mg/L), and NH4 +-N (0.33-49.0 mg/L), yet demonstrated reduced levels of Pb (0.2-391.0 μg/L) and Zn (2.0-112.8 μg/L). In contrast, groundwater located at a considerable distance from the landfill (13#, 18#, 15#, 26#) displayed the inverse trend, with relatively low concentration of Na+ (3.2-8.5 mg/L), Cl- (0.1-0.7 mg/L), CODMn (0.28-4.78 mg/L), and NH4 +-N (0.03-0.52 mg/L), but increased levels of Pb (1.2-483.0 μg/L) and Zn (1.6-357.0 μg/L). The primary determinant of groundwater quality near the landfill was NH4 +-N, with the highest pollution index (Pi) of 492.85, whereas Pb was the predominant factor affecting water quality in areas distant from the landfill, with the highest pollution index (Pi) of 10.9. While no discernible seasonal variation was detected for all pollutants, spatial variation can be observed that pollution levels decreased progressively with increasing distance from the landfill, a trend particularly corroborated by the conservative Cl- and Na+ measurements. This research suggests that conservative ions, such as Cl- and Na+, exhibit superior efficacy in tracing the pollution range from municipal solid landfills to groundwater. Therefore, monitoring these conservative ions in groundwater can yield a more precise understanding of the extent of groundwater contamination originated from landfills.

The variations of heavy metals sources varied their aggregated concentration and health risk in sediments of karst rivers - A case study in Liujiang River Basin, Southwest China

The sources and health risk variation of heavy metals (HMs) in sediments of Liujiang River Basin were investigated seasonally to clear the control of HMs contamination in karst rivers. The results revealed the exogenous input of HMs should be more prominent in wet season, due to the higher concentration and EF values. PMF identified HMs were mainly from natural, mining and industrial sources. The input of exogenous HMs were influenced by mining and industrial sources in wet season, but primarily by industrial sources in dry season. HI values were overall below 1, suggesting the relatively low non-carcinogenic risk. The TCR values of HMs were generally beyond 10-6, particularly those of As and Cr even exceeded 10-4 for children, which expressed a high carcinogenic risk. The sources components of As and Cr suggested preventing the migration of mining contaminants and limiting industrial emission should be essential to Liujiang River Basin.

Glyphosate spraying exacerbates nitrogen and phosphorus loss in karst slope farmland

Glyphosate herbicide is an indispensable material in agricultural production. In order to explore the potential environmental effects of glyphosate application in karst slope farmland, this paper used a variable slope steel tank to simulate the surface microtopography and underground pore structure characteristics of karst slope farmland, and combined with artificial rainfall experiments to explore the migration path of glyphosate in karst slope farmland and the impact of spraying glyphosate on soil nitrogen and phosphorus loss. The results showed that under the condition of heavy rain, glyphosate in karst slope farmland was mainly transported and diffused by surface runoff, supplemented by underground runoff; secondly, in different hydrological paths, glyphosate directly affected the content of nitrogen and phosphorus in runoff, and all showed extremely significant positive correlation (p < 0.001). In addition, rainfall conditions such as rainfall intensity, rainfall duration, and runoff affected the content of nitrogen and phosphorus in runoff to varying degrees. In conclusion, the application of glyphosate significantly increased the content of nitrogen and phosphorus in different runoff and accelerated the loss of nitrogen and phosphorus from soil, which not only led to soil degradation, but also threatened the safety of aquatic ecosystem. Therefore, in the prevention and control of agricultural non-point source pollution, the threat of glyphosate to the surrounding aquatic ecosystem cannot be ignored, especially in karst areas with frequent rainstorms and serious water erosion, long-term monitoring and risk assessment of glyphosate are needed.

A hydrochemical and isotopic approach for source identification and health risk assessment of groundwater arsenic pollution in the central Yinchuan basin

Arsenic contamination of groundwater is becoming a major global issue as it can severely affect the safety of drinking water and human health. In this paper, 448 water samples were investigated to study the spatiotemporal distribution, source identification and human health risk of groundwater arsenic pollution in the central Yinchuan basin by applying a hydrochemical and isotopic approach. The results showed that arsenic concentrations in groundwater ranged from 0.7 μg/L to 26 μg/L with a mean of 2.19 μg/L, and 5.9% of samples were above 5 μg/L, indicating the arsenic pollution of groundwater in the study area. High arsenic groundwater was mainly distributed in the northern and eastern areas along the Yellow river. The main hydrochemistry type of high arsenic groundwater was HCO3·SO4-Na·Mg, and the dissolution of arsenic-bearing minerals in sediment, irrigation water infiltration and aquifer recharge from the Yellow river were the main sources of arsenic in groundwater. The arsenic enrichment was dominantly controlled by the TMn redox reaction and the competitive adsorption of HCO3-, and the influence of anthropogenic activities was limited. The health risk assessment suggested that the carcinogenic risk of As for children and adults greatly exceeded the acceptable risk threshold of 1E-6, displaying a high carcer risk, while the non-carcinogenic risks of As, F-, TFe, TMn and NO3- in 2019 were largely higher than the acceptable risk threshold (HQ > 1). The present study provides insight into the occurrence, hydrochemical processes and potential health risk of arsenic pollution in groundwater.

The distribution, sources and health risk of polycyclic aromatic hydrocarbons (PAHs) in sediments of Liujiang River Basin: A field study in typical karstic river

The accumulation of PAHs in sediments of Liujiang River Basin were investigated to disclose the sources, input processes and toxicity risk of PAHs in a typical karstic river. The results revealed the concentrations of ∑₁₅PAHs are ranging from 111.97 to 593.39 ng/g, most of which are centralized in upstream and midstream of Liujiang River. Positive Matrix Factorization identified PAHs are mainly from the mixed combustion of oil and coal, biomass combustion and oil products leaking. Redundancy analysis manifested mixed accumulation should be the main approach of PAHs that inputting sediment. The values of RQ_NCs and RQ_MPCs suggested the moderate contamination of PAHs. The higher HQ and ILCR indicated the ingestion of PAHs are the main way to impact public health, while children should be more susceptible to PAHs. The values of HQ and ILCR indicated the overall low non-carcinogenic risk of PAHs, but relatively high carcinogenic risk of PAHs.

Distribution, sources, and ecological risk assessment of polycyclic aromatic hydrocarbons in surface water in the coal mining area of northern Shaanxi, China

This study investigated the spatial distribution, pollution source, and ecological risk of polycyclic aromatic hydrocarbons (PAHs) in the Kuye River, which is a typical river in the mining area of China, 16 priority PAHs were quantitatively detected at 59 sampling sites by high-performance liquid chromatography-diode array detector-fluorescence detector. The results showed that the ∑PAHs concentrations in the Kuye River were in the range of 50.06-278.16 ng/L. The PAHs monomer concentrations were in the range 0-121.22 ng/L, of which chrysene had the highest average concentration (36.58 ng/L), followed by benzo[a]anthracene and phenanthrene. In addition, the 4-ring PAHs showed the highest relative abundance in the 59 samples, ranging from 38.59 to 70.85%. Moreover, the highest concentrations of PAHs were mainly observed in coal mining, industrial, and densely populated areas. On the other hand, according to the diagnostic ratios and positive matrix factorization (PMF) analysis, it can be concluded that coking/petroleum sources, coal combustion, vehicle emission, and fuel-wood combustion contributed to the PAHs concentrations in the Kuye River by 37.91%, 36.31%, 13.93%, and 11.85%, respectively. In addition, the results of the ecological risk assessment indicated that benzo[a]anthracene had a high ecological risk. Among the 59 sampling sites, only 12 belong to low ecological risk areas, and others were at medium to high ecological risks. The current study provides data support and a theoretical basis to effectively manage pollution sources and ecological environment treatment in mining areas.

Pollution simulation and remediation strategy of a zinc smelting site based on multi-source information

Contaminated sites pose a significant risk to human health and the regional environment. A comprehensive study was dedicated to improving the understanding of the contamination condition of a smelting site by integrating multi-source information through 3D visualization techniques. The results showed that 3D visualization reveals excellent potential for application in the environmental studies to finely depict contamination in soils and establish relationships with geological features, hydrological conditions, and sources of contamination. The contamination plume model revealed that the soil environment at the site was seriously threatened by toxic metals, and dominated by multi-metal contamination, with contamination soil volume ranked as Cd > As > Pb> Zn > Hg. The stratigraphic model revealed the heterogeneous geological conditions of the site and identified the mixed fill layer as the primary remediation soil layer. The permeability model revealed that soil permeability significantly influenced contamination dispersion and contributed to delineate the contamination boundary accurately. The ecological hazard model targeted the high ecological hazard area and determined the high hazard contribution of Cd and Hg in the site soil. The outcomes can be directly applied to actual site remediation and provide a reference for the contaminated sites evaluation and restoration in the future.

Spatial and Temporal Evolution of Groundwater Chemistry of Baotu Karst Water System at Northern China

Karst water quality degradation has been a challenge for domestic and industrial water supplies worldwide. To reveal the possible factors response for karst water quality degradation, Baotu karst spring system is studied as an representative example. In this study, a hydrogeochemical investigation and mathematical, statistical, and geochemical modeling was conducted together to identify the major hydrochemical processes involved in the degradation process. It is found that the karst water is normally fresh, neutral-to-slightly alkaline, with calcium and magnesium as the predominant cations, and bicarbonate and sulfate as the predominant anions. The abnormally high chloride (95.05 mg/L) and nitrate concentrations (148.4 mg/L) give clues to the potential source of contamination in some karst water. The main hydrochemical facies of karst water are HCO3-Ca and HCO3 × SO4-Ca, accounting for 76% of water samples. The water hydrochemistry is controlled mainly by the dissolution of carbonate minerals (calcite, dolomite), followed by the dissolution of silicate and gypsum. The dissolution of calcite and dolomite mostly happens in the recharge area. In the discharge area, the karst water is basically in equilibrium with calcite. The negative SI value of gypsum represents that the water–gypsum interaction is dominated by dissolution along the whole flow path. Cation exchange is observed in the karst water in the indirect recharge area. Along the flow path, the contents of chloride, sulfate, nitrate, and TDS (Total dissolved solids, abbreviated TDS, indicates how many milligrams of dissolved solids are dissolved in one liter of water) vary significantly, which is mostly affected by pollution from human industrial and agricultural activities. The concentrations of major ions were maintained at a low level (<20 mg/L) in the 1960s in karst water. The fast elevation of the parameter values has occurred in the past two decades. The temporal elevation of some pollutants in karst water suggest that global changes (acid rain) and human activity (such as overusing fertilizer) are main factors resulting in the degradation of karst water quality in the study area. The results of this paper provide invaluable information for the management and protection of karst water resources in the urban and rural areas.

Comparison of naphthalene removal performance using H2O2, sodium percarbonate and calcium peroxide oxidants activated by ferrous ions and degradation mechanism

The presence of polycyclic aromatic hydrocarbons (PAHs) in groundwater is making a great threat to human health in the world which has received an increasing environmental concern. Among various Fenton oxidation processes, 97.6%, 92.1% and 89.4% naphthalene (NaP) removals were observed using hydrogen peroxide (H₂O₂), sodium percarbonate (SPC) and calcium peroxide (CP) as oxidants activated by Fe(II) in ultrapure water tests, respectively. While, the inhibitory effect on NaP degradation caused by the weak alkaline solution pH and the presence of HCO₃^- in actual groundwater could be compensated by doubling dosages of oxidants and Fe(II) to different extent. 98.0%, 49.8% and 11.5% of NaP were degraded by using H₂O₂, SPC and CP, respectively, strongly suggesting the best H₂O₂ performance among them. It was observed that 83.3% and 9.6% inhibition on NaP degradation in H₂O₂/Fe(II)/NaP system occurred in the presence of isopropyl alcohol and chloroform, confirming that both hydroxyl radical (HO) and superoxide anion radical () contributed to NaP degradation in Fenton process and HO was the prominent radical. The presence of HO was further demonstrated by electro-spin resonance spectrometer analysis. The identification of transformation products of NaP revealed that hydroxylation and ring rupture were the main NaP degradation pathways.

Oil impact on the environment and aquatic organisms on the coasts of the states of Alagoas and Sergipe, Brazil - A preliminary evaluation

The oil spill off the coast of the Brazilian Northeast region is one of the most significant global events regarding contamination and environmental impact in recent years. This work evaluates the effects of oil spills on the Northeast coasts between Alagoas and Sergipe states from October 2019 to January 2020. Analysis of some sampling points of seawater revealed the presence of Hg, Cd, Pb, and Cu in levels above the maximum concentration limits established by the Brazilian legislation. For water quality parameters, phosphorus, nitrite, and turbidity showed statistically different values. However, the chromatographic profiles of oil obtained from different beaches were quite similar. Seawater, fishes, and massunins (bivalve) presented the main polycyclic aromatic hydrocarbons: naphthalene, phenanthrene, fluoranthene, fluorene, and acenaphthalene. Therefore, the concentration of organic and inorganic contaminants determined in different environmental locations served as a subsidy to assess the effect of the preliminary oil spill on the Brazilian coast.