Spatial distribution and health risk assessment for groundwater contamination from intensive pesticide use in arid areas

Unraveling the hydrogeochemical evolution and pollution sources of shallow aquifer using multivariate statistical analysis and hydrogeochemical techniques: a case study of the Quaternary aquifer in Beni Suef area, Egypt

This study integrates multivariate statistical analysis and hydrogeochemical modeling to investigate the processes controlling the groundwater composition of a shallow aquifer where increased pumping rates and anthropogenic impacts were prevalent. Eighteen groundwater samples were collected and analyzed for major elements and selected heavy metals. The data were classified on the basis of multivariate statistical analysis into three clusters: C1 (Na-Cl facies), C2 (Ca-SO₄ facies), and C3 (Ca-HCO₃ facies). The application of factor analysis gave four factors affecting the groundwater chemistry, namely the salinization factor, anthropogenic/secondary enrichment factor, the secondary and the micro-nutrient fertilizers, and the aluminum fertilizer factor. The hydrogeochemical study of the groundwater revealed that the processes controlling the groundwater chemistry in the study area are mainly affected by the groundwater occurrence either to the east or to the west of Bahr Youssef Canal. Generally, the dominant hydrogeochemical processes affecting the groundwater are silicate weathering, ion exchange, irrigation return flow, gypsum applications in soil, and evaporation. The groundwater quality evaluation shows that water quality varies from fair to excellent for drinking purposes, where the best water is located in the northern and central parts of the study area. The suitability of groundwater for irrigation was evaluated using several indices indicating that groundwater is suitable for irrigation in the northwest and western parts of the study area. As some groundwater samples lie in high salinity classes on the US Salinity diagram, it is recommended to use this water for plants with good salt tolerance under good drainage conditions. The integration between the statistical and geochemical tools helps reveal the dominant processes through data reduction and classification.

Degradation of four pesticides in five urban landscape soils: human and environmental health risk assessment

Pesticides are the most cost-effective means of pest control; however, the serious concern is about the non-target effects due to their extensive and intensive use in both agricultural and non-agricultural settings. The degradation rate constant (k) and half-life (DT₅₀) of four commonly used pesticides, glyphosate, 2,4-D, chlorothalonil and dimethoate were determined in five Australian urban landscape soils, with varying physicochemical characteristics, to assess their environmental and human health risks. The k values (day^-1) for the selected pesticides were inversely proportional to those of organic carbon (OC), silt, clay and Fe and Al oxides, and directly proportional to pH and sand content in soils. In contrast, the calculated values of DT₅₀ (days) of all the four pesticides in five soils positively correlated with OC, clay, silt and oxides of Fe and Al, whereas soil pH and sand content exhibited a negative correlation. The calculated values of environmental indices, GUS and LIX, for the selected pesticides indicate their potential portability into water bodies, affecting non-target organisms as well as food safety. The evaluation for human non-cancer risk of these pesticides, based on the calculated values of hazard quotient (HQ) and hazard index (HI), suggested that exposure of adults and children to soils, contaminated with 50% of initially applied concentrations, through ingestion, dermal and inhalation pathways might cause negligible to zero non-carcinogenic risks. The present data might help the stakeholders in applying recommended doses of pesticides in urban landscapes and regulatory bodies concerned in monitoring the overall environmental quality and implementing safeguard policies. Our study also clearly demonstrates the need for developing improved formulations and spraying technologies for pesticides to minimize human and environmental health risks.

Distribution and transport of microplastics in groundwater (Shiraz aquifer, southwest Iran)

Despite the significance of groundwater to the hydrological cycle and as a source of potable water, very little information exists on microplastics (MPs) in this environment. In the present study, MPs have been determined in ten well samples obtained from an alluvial aquifer in a semi-arid region (Shiraz, Iran) following filtration, digestion and inspection under a binocular microscope. A total of 96 MPs were identified, and concentrations ranged from 0.1 to 1.3 MP L^-1 (mean and median = 0.48 and 0.43 MP L^-1, respectively) and exhibited a complex distribution across the area that reflected differences in land use and local hydrology and geology. The majority of MPs (about 70%) were fibres of ≤ 500 μm in length, but fragments and films were present at some sites, and the dominant polymers were polystyrene, polyethylene and polyethylene terephthalate. Coupling meteorological and water table monitoring data from the regional water organization and published information on aquifer hydrology, we estimate a lag time from precipitation to water table intrusion of between one and five months and groundwater velocity flows of between 0.01 and 0.07 m d^-1. Although the extent of retardation of MPs within the pores of groundwater is unknown, by considering empirical data and theoretical predictions on particle flow through porous media in the literature we surmise that MP residence times in the aquifer are likely to range from years to decades, thereby impeding any clear means of source identification. Nevertheless, and more generally, the consumption of potable groundwater may make to a contribution to MP exposure through ingestion.

Integrated ecosystem models (soil-water) to analyze pesticide toxicity to aquatic organisms at two different temperature conditions

In order to increase the knowledge about pesticides considering the soil-water interaction, ecosystem models (mesoscosms) were used to analyze the of leachate on the immobility and feeding rate of the cladocerans, Ceriodaphnia silvestrii and D. similis and algae Raphidocelis subcapitata, at two different temperatures. Mesocosm were filled with natural soil (latosolo) that were contaminated with insecticide/acaricide Kraft 36 EC® and fungicide Score 250 EC®, using the recommended concentration for strawberry crops (10.8 g abamectin/ha and 20 g difenoconazole/ha). Pesticides were applied once (hand sprayers) and the precipitation was simulated twice a week (Days 1, 4, 8, 11, 15 and 18). The mesocosm were kept in a room with a controlled temperature (23 and 33 °C) and photoperiod (12h light/12h dark). The Kraft 36 EC® insecticide showed toxicity for both species of cladocerans tested, with effects on immobility and feeding rate, both at 23 and 33 °C. Score 250 EC® showed to be toxic only for the experiments that analyzed the immobility of C. silvestrii at 23 °C and the feeding of D. smilis at 33 °C, demonstrating that the effects are species-specific and related to the temperature at which they are tested. While for species R. subcapitata there was an effect only for mixture treatments of the pesticides analyzed at both temperatures. Thereby, zooplanktonic organisms may be at risk when exposed to this compound even after percolating in a soil column, which could lead to effects on the entire aquatic trophic chain and that temperature can influence the organism response to the contaminant.

Source identification and management of perennial contaminated groundwater seepage in the highly industrial watershed, south India

Perennial contaminated groundwater seepage is threatening the downstream ecosystem of the Kazipally Pharmaceutical industrial area located in South India. The sources of seepage are unknown for the last three decades that challenging the regulatory authorities and industries. In general, water quality monitoring and geophysical techniques are applied to identify the sources. However, these techniques may lead to ambiguous results and fail to identify the seepage sources, especially when the area is urbanized/paved, and groundwater is already contaminated with other leakage sources that have similar chemical compounds. In the present study, a novel and multidisciplinary approach were adopted that includes satellite-based Land Surface Temperature (LST) observations, field-based Electrical Resistivity Tomography (ERT), continuous Soil Electrical Conductivity (SEC) and Volumetric Soil Moisture (VSM%) measurements along with groundwater levels monitoring to identify the sources and to control the seepage. The integrated results identified that the locations with the Standard Thermal Anomaly (STA) in the range of -0.5 to -1 °C, VSM% >50%, SEC > 1.5 mS/cm, bulk resistivity < 12 Ω m with shallow groundwater levels < 3 m below ground level (bgl) are potentially contaminated perennial seepage sources. Impermeable sheet piles have been installed across the groundwater flow direction to control the seepage up to 1.5 m bgl, where groundwater frequently intercepts land surface. The quantity of dry season groundwater seepage has been declined by 79.2% after these interventions, which in turn minimized the treatment cost of 1,96,283 USD/year and improved the downstream ecosystem.

Effects of hydrogeochemical conditions on the distribution of pesticides in the karst river system

Karst aquifer systems are tended to be polluted compared to other types of aquifers because pollutants are able to enter aquifers through developed conduit systems. To identify the effects of hydrogeochemical conditions on the distribution of pesticides in a karst river system in Kaiyang, southwest China, a typical pollution mode combining intermittent infiltration with intrusion was constructed. Twelve aqueous samples were collected along the karst river, and a total of 24 pesticides were detected. The results showed that the pesticide ubiquity and the dominant organophosphate (40%) and organonitrogen pesticides (49%) were both observed. Based on the spatial distribution, the attenuation of pesticides was found in the underground conduit and surface river. The wastewater treatment plant and the rural dump were the two important point sources releasing pesticides. In addition, ten core pesticides were identified by clustering analysis and regional characteristics of three types of pesticides in Songnen Plain, North China Plain, and Southwest karst areas were also summarized. With correlation analysis between pesticides and environmental factors, the significant correlations of pesticides with ammonium ion and dissolved oxygen were found, which indicated that rapid developing urbanization and long-term agricultural practices could remarkably affect the spatial distribution of pesticides. The calculation of ecological risk quotients showed that organophosphate pesticides had the highest risk to invertebrate, followed by organonitrogen pesticides, and finally organochlorine pesticides. Invertebrates were the most vulnerable aquatic organisms. These findings fill a gap in the multiple pesticides' pollution in the karst areas of China. Graphical abstract.

Spatio-temporal distribution and ecological risk assessment of pesticides in the water resources of Abou Ali River, Northern Lebanon

The objective of this study is to assess the occurrence, spatial, and temporal distribution of forty-eight multiclass pesticides in surface and groundwater samples of the Abou Ali River, located in the North of Lebanon. A 3-year monitoring program (six batches from August 2015 to March 2017) was implemented, and thirty sampling points were selected along the river for analysis. The analysis was executed using a previously developed and optimized solid-phase micro-extraction (SPME) gas-chromatography-mass spectrometry (GC-MS) method. Statistical analysis, using Kolmogorov-Smirnov, Kruskal-Wallis, and Dunnet T3 multiple comparison tests, was applied to compare mean concentrations of pesticides between the different sampling sites and the batches taken. The pesticides that had the highest frequency of detection in the surface and groundwater samples were alachlor, α-endosulfan, and methomyl. For surface water samples, high mean concentrations were perceived for two stations in the upper stream (S5 and S7), two stations (S11 and S14) in the middle stream, and one station (S16) in the lower stream of the river. The highest mean concentrations were observed in October 2015 and August 2016, the time of the year which correlates with the period of pesticide application. Considering groundwater samples, high mean concentrations of pesticides were detected in sites G4, G9, G10, and G12 and during October 2015 and March 2016, following the rainy season. Ecotoxicological risk assessment using the risk quotient (RQ) methodology revealed high risk for five pesticides under average conditions and fourteen under extreme conditions. This study presents, for the first time, a statistical analysis showing the quantification of pesticides in the water resources of the Abou Ali River. In conclusion, it reveals the need to apply a complete pesticide monitoring program, not only for the Abou Ali River but for all the water resources in Lebanon.

Investigating Atrazine Concentrations in the Zwischenscholle Aquifer Using MODFLOW with the HYDRUS-1D Package and MT3DMS

Simulation models that describe the flow and transport processes of pesticides in soil and groundwater are important tools to analyze how surface pesticide applications influence groundwater quality. The aim of this study is to investigate whether the slow decline and the stable spatial pattern of atrazine concentrations after its ban, which were observed in a long-term monitoring study of pesticide concentrations in the Zwischenscholle aquifer (Germany), could be explained by such model simulations. Model simulations were carried out using MODFLOW model coupled with the HYDRUS-1D package and MT3DMS. The results indicate that the spatial variability in the atrazine application rate and the volume of water entering and leaving the aquifer through lateral boundaries produced variations in the spatial distribution of atrazine in the aquifer. The simulated and observed water table levels and the average annual atrazine concentrations were found to be comparable. The long-term analysis of the simulated impact of atrazine applications in the study area shows that atrazine persisted in groundwater even 20 years after its ban at an average atrazine concentration of 0.035 µg/L. These results corroborate the findings of the previous monitoring studies.

Quantitative assessment of ecological compensation for groundwater overexploitation based on emergy theory

Ecological compensation is an important economic tool for the control and management of ecological and environmental problems. The accurate assessment of the amount of compensation is the key factor in the implementation of ecological compensation schemes. However, due to the complex and various ecological and environmental problems caused by groundwater overexploitation, there is no scientific quantitative method. Emergy theory is a new method to quantitatively study the relationship between environmental resources and social economy. Based on the literature review of ecological compensation for groundwater overexploitation, this paper puts forward a new evaluation method for using emergy loss as groundwater overexploitation ecological compensation. The emergy system diagram of environmental problems caused by overexploitation of groundwater is constructed. And the calculation methods of the emergy loss of eco-environmental problems caused by groundwater overexploitation, such as land subsidence (collapse), salt water intrusion, surface runoff reduction, vegetation deterioration, and groundwater pollution, were presented, respectively. Taking Zhengzhou as an example, the total amount of ecological compensation for groundwater overexploitation in 2014 was equivalent to 853 × 10⁶ US dollars. The largest loss of land subsidence is 816 × 10⁶ US dollars, which accounts for 95.64% of the total loss. It can be seen that land subsidence is the most serious in the eco-environmental problems caused by overexploitation of groundwater in Zhengzhou.

Pesticides in the typical agricultural groundwater in Songnen plain, northeast China: occurrence, spatial distribution and health risks

Songnen plain is an important commodity grain base of China, and this is the first study on the comprehensive detection of multiple pesticides in groundwater. Based on an analytical method of 56 pesticides, 30 groundwater samples were collected and analyzed. At least 4 pesticides were detected in each sample and 32 out of 56 pesticides were detected. The average detected levels of individual pesticides were approximately 10-100 ng/L. Organophosphorus pesticides and carbamate pesticides were the dominant pesticides, and their percentage of total pesticide concentrations were 35.9% and 55.5%, respectively. Based on the spatial distribution, the characteristic of nonpoint source pollution was indicated in the whole study area except for a point source pollution with the influence of a sewage oxidation pond. Nine core pesticides and three distinct clusters of the core pesticides with various concentration patterns were revealed by cluster analysis. Linear regression identified a significant relationship between the cumulative detections and the cumulative concentrations, providing access to identify the outlying contaminant events that deviate substantially from the linear trend. A new insight for prediction of pesticide occurrence was provided by the Pearson correlation between some individual pesticide concentrations and the cumulative detections or the cumulative concentrations. According to health risk assessment, the residual pesticides posed medium risks for children and infants and approximately 90% of risks were composed of β-HCH, dimethoate, ethyl-p-nitrophenyl phenylphosphonothioate and methyl parathion. These findings contributed to establishing a database for future monitoring and control of pesticides in agricultural areas.

Integrated management of pesticides in an intensive agricultural area: a case study in Altinova, Turkey

Pesticide contamination of groundwater is a common critical problem faced by many countries due to excessive and unconscious applications. As a result of increasing concerns about pesticides, several qualitative and quantitative risk assessment models/indicators were developed and applied. In this study, a practical approach was presented for the protection of groundwater from pesticide contamination. The first phase is the assessment of the specific vulnerability of groundwater to pesticide contamination using the DRASTIC-Pesticide model. The second phase is the monitoring and assessment of groundwater quality to verify vulnerability assessment. The third phase is to assess the impacts of pesticides on the environment and human health using a commonly applied pesticide risk indicator, the environmental impact quotient (EIQ). The pilot study area (PSA) is the Altinova region at Antalya city of Turkey which exhibits intensive agricultural activities and covers an approximate surface area of 75 km². A total of 25 groundwater wells were chosen for monitoring of groundwater quality where four sessions of seasonal field measurements were conducted for 1 year. Two sessions of water quality analyses were also performed for many physical, bacteriological, and chemical parameters, including pesticides. Additionally, soil samples were analyzed, site surveys were conducted, and other relevant information (topographical, geological and meteorological characteristics, pesticide use and toxicological data sets, etc.) was gathered. The PSA was determined to have high vulnerability to contamination of groundwater, and it was verified through monitoring results. The commonly used pesticides in the PSA were ranked according to their risks to select pesticides with the least environmental impacts.

Assessment of groundwater quality and remediation in karst aquifers: A review

Karst aquifers, capable of storing and transmitting large amount of water, are the main source of drinking water in many regions worldwide. Their excessive permeability leads to an enhanced vulnerability to retain and spread the contamination accordingly. From sustainability perspective, the environmental, economic and social impacts of karst contamination on water resources management are gaining more attention. In this study, an overview of hydrogeological processes and concepts regarding groundwater flow and contaminant transport in karstic systems is presented, followed by a short discussion on surface water and groundwater interaction. Due to the complexity of karstic systems, different approaches have been developed by researchers for investigating and understanding hydrogeological processes and groundwater behavior in karst which are reviewed herein. Additionally, groundwater contamination issues and the most common and effective remediation techniques in karstic terrains are discussed. Lastly, modeling techniques and remote sensing methods, as beneficial and powerful tools for assessing groundwater flow and contaminant transport in karst terrains, are reviewed and evaluated. In each section, relevant research works conducted for Puerto Rico are discussed and some recommendations are presented to complement the ongoing hydrogeological investigations on this island.

Integrating geochemical investigations and geospatial assessment to understand the evolutionary process of hydrochemistry and groundwater quality in arid areas

Groundwater is the key for life in arid areas. Aquifer overexploitation and climatic conditions can significantly deteriorate groundwater quality. The Al-Qassim area in central Saudi Arabia is characterized by dense agricultural use and is irrigated mainly by fossil groundwater from the Saq Aquifer. Understanding the area's hydrochemistry, major factors governing groundwater quality, and alternative uses of the groundwater are the main goals of this study. Groundwater samples were collected and examined for major, minor, and trace elements. Ionic relationships, hydrochemical facies, geospatial distributions, and multivariate analyses were conducted to assess the hydrochemical processes at play. The salinity and nitrate concentrations of the Saq Aquifer's groundwater were found to increase in the outcrop areas more than the confined areas. The spatial distributions were fragmented by three main factors: (i) modern recharge by relatively brackish water, (ii) irrigation return flow in intensive farming areas, and (iii) overexploitation and draining of deep and relatively saline zones of the aquifer. Seven water types were found representing the alkaline water with a predominance of sulfate-chloride ions and earth alkaline water with a predominance of sulfate and chloride. Mixing between fresh and brackish water, dissolution of mineral phases, silicate weathering, and reverse ion exchange were recognized as the evolutionary processes, while evaporation played a minor role. Cluster analyses characterized the fresh groundwater zone, modern groundwater recharge zone, and anthropogenic influence zone. In the confined areas, nearly all the groundwater was appropriate for domestic use and irrigation. In the outcrop areas, some limitations were found due to unsuitable conditions.