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Contaminant transport and fate in freshwater systems – Integrating the fields of geochemistry, geomorphology and nanotechnology

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Abstract

This special issue of the Groundwater for Sustainable Development “Contaminant Transport and Fate in Freshwater Systems – Integrating the fields of geochemistry, geomorphology and nanotechnology” provides an update of the current knowledge on the sources, pathways, and movement of anthropogenic and geogenic contaminants in the environment, the holistic interactions between biotic and abiotic components of the ecosystem, and the avant-garde technologies as innovative strategies for environmental management. We aims to provide a future platform for interaction and collaborative efforts between different workers in the scientific field. As this issue highlights the three keywords: hydro-geochemistry, geomorphology and nanotechnology; therefore, it will facilitate a unique amalgamation of pure as well as applied scientific ideas. Therefore, this combined effort will be much more beneficial and will lead to great developments in the near future. This will result in a better understanding of the background processes and the factors controlling the contamination process and therefore contribute to the development of more efficient and sustainable technologies and management options. This issue also has the broader purposes to influence the policymakers which in turn may lead to greater investments and research grants in the fields covered by the said volume, which can ultimately lead to more quality research in these fields.

Introduction

Groundwater is one of the precious sources of natural freshwater which is extensively used by human beings for centuries in multiple sectors starting from domestic, agricultural sources to industrial activities. Around, 2 billion people across the globe solely depend on ground and surface water resources in direct or indirect ways for their day to day activities and crop production purposes (Hughes et al., 2012). It is quite noteworthy that the present era of high population growth, rapid urbanization and climate change, rainfall intensity has become too unpredictable to adequately protect and manage freshwater systems. Groundwater geology, subsurface drainage, aquifer geology and other geographical features act as a driver in determining the quality of available water. The groundwater chemistry is quite complex and governed by different hydrogeochemical processes like dissolution, precipitation, oxidation-reduction, ion exchange, adsorption etc. The diverse geomorphological characteristics like lithological variations and hydrogeochemical interactions govern the abundance of arsenic, fluoride, nitrate, and salinity in the groundwater (Curtis et al., 2009). It is indeed a grave concern that millions of inhabitants around the globe (mostly in underdeveloped and developing countries) live near the metal/metal(loid) contaminated areas most commonly arsenic affected ones. These contaminants are considered as carcinogens and causing potential threats to agricultural productivity, ecological diversity, and human health. The situation is getting much worse with the appearances of contaminants of emerging concern (CECs) along with legacy pollutants. A detailed study conducted by (Ashton et al., 2004) and (Kolpin et al., 2002) highlighted the rapid occurrences of CECs in the range from ppb to ppm level. In another study, (Hughes et al., 2012) reported the hazardous prevalence of nearly > 180 pharmaceutical products in rivers, lakes and other aquatic bodies around the world with a maximum concentration examined for some special group of antibiotics. In addition, nowadays there are increasing appearances of illicit drugs, antimicrobials, and other preservatives in the surface water with the rapid usage of personal care products. The long-term effects of such CECs stemming mostly from their synergistic effects in the aquatic environment show a clear influence of geogenic sources which control the hydrogeochemistry of organic and inorganic pollutants. It is, therefore, a dire necessity to insight into the occurrence, fate and ecological impacts of such potentially toxic chemicals on the ecosystem in the era of “Anthropocene”.

The fate and transport of contaminants is the vital hydrogeochemical process of great environmental significance as it results in greater understanding of the background processes and the factors controlling the contamination process and therefore contribute to the development of more efficient and sustainable technologies and management options. Organic compounds make their pathways in the groundwater regime as non-miscible phrase liquid that consists of dissolved solutes or suspended chemical components. It is considered to be a potential mass transfer process which changes with respect to time and is associated with concentration gradients and appears as soluble or volatile mass constituents of non-miscible phrase to subsurface liquid or solid phases. The actual concentrations of solutes in contaminant plumes are variable under different physicochemical parameters like diffusion, sorption, microbial degradation, hydrodynamic dispersion, advective flow etc (Chen et al., 2018a, Chen et al., 2018b, Sun et al., 1999). Although it has been found that advection-dispersion theory and related hydrodynamic parameters have a great impact on the contaminants distribution and dispersion through different mediums like fractured, porous and tortuous pathways. In addition, organic contaminants may have some influences from the subsurface microbial environment and many mathematical models have been proposed for determining the microbial growth rates and kinetics (Kantar et al., 2009). The previous researchers have shown that migration and subsequent degradation of contaminants are controlled by multiphase flow processes which include dissolution and volatilization. Basically, a movement through a porous medium is governed by multiple fluid phases which in turn depends on capillary forces along with macro and microscale capillary fringes. Therefore cleaning up of the aquifer with a facile and eco-friendly approach is the need of the hour topic for research in current and past centuries.

There are many remediation approaches that have already been taken by the researchers to deal with intense contaminants plume depending on plume density, surface heterogeneity and existence period of plumes (Curtis et al., 2009). (Sun et al., 1999) (Sleep et al., 2000) have demonstrated the usefulness of in-situ methods over ex-situ methods of remediation in a series of hydrogeochemical experiments. Additionally, a group of researchers (Fox et al., 2012, Stoliker et al., 2013) has shown the usefulness of vapor extraction, stream injection, solubilization and microemulsions, chemical oxidations and integral pumping methods for controlling downstream contaminant mass flux. In their study, they have calculated the involvement of geomorphological and other external factors like pore geometry, flow instabilities, permeability which are the driving forces for mass discharges across a downstream plane (Cui et al., 2017). The geostatistical approaches including geospatial, Bayesian, Monte-Carlo-simulation, Multilevel sampling, Fast Fourier transformation functions are commonly employed for describing uncertainty in mass discharges and aerobic/anaerobic transformation, nitrate reduction and transformation processes (Prigiobbe and Bryant, 2014, Singer et al., 2013). (Chen et al., 2018b, Chen et al., 2018a) have demonstrated the laboratory small-scale bioreactor study for explaining the anoxic conditions and related microbial processes. The role of terminal electron acceptors, the occurrence of methanogenesis, diverse biophysical-chemical parameters, contaminants plume and metabolite formations lead to the mass balance study of contaminants under different conceptual model. This is vital for making the roadmap of natural attenuation of contaminants in the dissolved state. The slow and fast release of contaminants has been well explained by different dispersion models (Fickian vs non-Fickian) considering aqueous phase solubility as the active stage of remediation which contradicts high-cost removal processes for contaminants resulting from long residence timings in aquifers (Bearup et al., 2012, Li and Kaplan, 2012).

Any pollution management plan requires an understanding of the source to sink journey of the contaminants. This volume focuses on the transport and the ultimate fate of the pollutants in the freshwater system. Special emphasis will be given on understanding the underlying hydrogeochemistry of the contaminants, emerging pollutants (EPs), and surface water-groundwater interaction including the impact of surface water pollution on groundwater under different environmental and geomorphological conditions. Novel techniques like nanotechnology for designing management and remediation options for tackling the problems of freshwater contamination will be another highlighted aspect of this special issue of the journal. Therefore, it will also help to create a great awareness among the scientific community, policy makers and common people as a whole.

Section snippets

Layout of the special issue

Sustainability is the core focus of the journal, therefore the goal of this special issue is to highlight the problems of freshwater contamination as well as sustainable management options for this resource. The scope of this issue will, however, be much greater as it aims to understand the dynamics of surface water-groundwater contaminant interaction under different environmental conditions across the world. This issue also has the potential to influence the policy makers which in turn may

Conclusion

This special volume articles highlight on some of the latest issues affecting the surface and groundwater systems, including nutrients, geogenic contaminants as well as the emerging pollutants (EPs), which are new chemicals without regulatory status as there is no proper database concerning their environmental impact and at the same time their implications on human health is poorly understood. We are expecting that discussions embedded in this special issue will be truly international in its

Acknowledgements

This special issue would not have been possible without the support of Asia Pacific Network (APN) (http://www.apn-gcr.org) Grant Number CRRP2016-06MY-Kumar under the agies of which ISSUE-2018 was organized and selected work has been put in as this special issue. We acknowledge the cooperation of Indian Institute of Technology IIT-Gandhinagar, Kanazawa University, Japan, University of Ruhuna, Sri Lanka, the University of Tokyo, Japan and WARI program of DST. We would like to express our sincere

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