Contamination of Water: Health Risk Assessment and Treatment Strategies

By Pardeep Singh

Water containing significant amounts of inorganic and organic contaminants can have serious environmental consequences and serious health implications when ingested. Contamination of Water: Health Risk Assessment and Treatment Strategies takes an interconnected look at the various pollutants, the source of contamination, the effects of contamination on aquatic ecosystems and human health, and what the potential mitigation strategies are. This book is organized into three sections. The first section examines the sources of potential contamination. This includes considering the current scenario of heavy metal and pesticide contamination in water as well as the regions impacted due to industrialization, mining, or urbanization. The second section goes on to discuss water contamination and health risks caused by toxic elements, radiological contaminants, microplastics and nanoparticles, and pharmaceutical and personal care products. This book concludes with a section exploring efficient low-cost treatment technologies and remediation strategies that remove toxic pollutants from water. Contamination of Water incorporates both theoretical and practical information that will be useful for researchers, professors, graduate students, and professionals working on water contamination, environmental and health impacts, and the management and treatment of water resources.

• Provides practical case studies of various types and sources of contamination
• Discusses inorganic and organic contaminants and their impact on human health
• Evaluates effective water treatment and remediation technologies to remove toxins from water and minimize risk

• Language: English
• Publisher: Academic Press
• Release date: Aug 6, 2021
• ISBN: 9780128240595

Book preview

Preface

Water is the world’s most valuable natural resource. Contamination-free water is everyone’s right. Due to rampant urbanization, industrialization, and uncontrolled population growth, pressure on existing water resources (surface/groundwater) has increased. Organic or inorganic discharges into the aquatic environment from various sources increase daily. These result in reduced quantities, quality degradation, and ultimately deteriorating human health. In the current scenario, over 0.78 billion people worldwide have no access to safe drinking water, eventually deteriorating their health. Because of lack of awareness, alternative pure water sources, and lower socioeconomic standards, large world populations consume contaminated water for drinking, bathing, and cooking. In the contemporary context, fluoride (F−), nitrate (NO3−), heavy metals [As(III/V), Pb(II), Cd(II), Cr(VI/III), Hg(II), Ni(II), and Zn(II)], pesticides, and other emerging contaminants are attracting greater attention because of their harmful nature and impact on human and aquatic health, particularly when they exceed the prescribed limits.

Water pollution from domestic, municipal, mining, agriculture, and industry sources are now widely studied. Global populations drink primarily from surface and groundwater. Currently, due to consumption and dermal contact of contaminated water worldwide, several researchers focus on health risk assessment studies. Water intake with large amounts of inorganic and organic contaminants can cause serious health effects, from shortness of breath to different types of human cancers.

Human health risk assessment is the process of estimating the nature and likelihood of adverse health effects in people who may be exposed to contaminated water, now or in the future. Contaminants exceeding permitted water limits can harm natural environments and cause health problems. These assessments identify a source’s potential to introduce risk agents into the environment, estimate the number of risk agents coming into contact with human-environmental boundaries, and quantify the health effects of exposure. After primary analysis of particular contaminants and other health risk assessments, safe and potable drinking water must be provided to the community by removing those toxic pollutants from water using low-cost, efficient treatment technology. Adsorption processes among various water treatment technologies are simplest, sustainable, and acceptable. Adsorption has a flexible design and function. Nanomagnetic solid materials, with the higher surface area associated with lower particle diameters, are now the best-recommended water treatment materials with higher pollutant-removal capacity and postadsorption separation. Using functionalized solid materials with a variety of functional groups can be more efficient water treatment techniques.

Recent adsorption signs of progress reveal suitability for single and multi-component systems. Despite excellent adsorption materials, their applications have various disadvantages. Sometimes adsorptive materials should have linked photocatalytic degradation properties to complete degradable pollutants like dye and other organic pollutants. Water treatment technology also requires antimicrobial adsorption. Generally, adsorbents cannot be used to inhibit microbe growth found in water bodies usually unfit for biological pollutants. Biofilm formation also concerns the solid surface. Much has been done to improve the water treatment efficiency of adsorbents and/or find alternatives to existing adsorbents, obtain suitable materials with properties for adsorptive removal of various water pollutants, and photocatalytic degradation of degradable pollutants, inhibition of growth of infectious microbes, and postadsorption magnetic separation.

This book presents various chapters on water contamination around the different land-use areas, health risk assessment, and adsorption-based water treatment. It also includes the study of toxic metals, fluoride, ammonia, pesticides, pharmaceuticals, personal care products, microplastics and nanomaterials, and radiological contamination of water resources. It also highlights the health risk issues related to different types of inorganic and organic contaminants present in water. Chapters related to the removal of these contaminants from the water are also included.

The book will be useful for university students, teachers, and researchers, especially those working in water contaminations, hydrogeochemistry water treatment, health issues, and water resources management. It will also be useful for the NGOs working on health and water contamination issues, policymakers, and various government organizations.

Coming to the scheme of the study, the book is divided into three sections containing 39 chapters, well aligned to the specific aspects of water contamination, health risk assessment, and adsorption-based water treatment. Section A, Water Contamination, includes contamination of water resources around mining regions, fly ash dumping sites, saline lakes, and industrial areas worldwide. It also includes the study of inorganic and organic contaminants in water. Section B, Health Risk Assessment, highlights the health risk issues related to different types of inorganic and organic contaminants (i.e., toxic metals, ammonia, arsenic, radiological contaminants, microplastic, nanomaterials, pharmaceuticals, personal care products, and other emerging contaminants) present in water. Section C, Water Treatment Strategies, is based on the various treatment technologies and removal of pollutants from water.

This book is a humble attempt to address various water-related issues in all respects with the hope that it would be a significant addition to the available literature on the topic. The book’s contributors having different expertise provide a holistic literature on the topic imbibing diverse approaches and perspectives. We express our sincere gratitude to all the contributors and publishers who helped to produce a remarkable and meaningful edited volume on a very important topic.

Section A

Water contamination

Outline

Chapter 1 Contamination of water resources in the mining region

Chapter 2 Contamination of water resources in and around saline lakes

Chapter 3 Contamination of groundwater by fly ash heavy metals at landfill sites

Chapter 4 Current scenario of heavy metal contamination in water

Chapter 5 Health impacts due to fluoride contamination in water: current scenario

Chapter 6 Contamination of water resources in industrial zones

Chapter 7 Contamination of groundwater resources by pesticides

Chapter 8 Current scenario of pesticide contamination in water

Chapter 1

Contamination of water resources in the mining region

Anita Punia¹ and Saurabh Kumar Singh²,    ¹Department of Civil Engineering, Indian Institute of Technology, Guwahati, India,    ²School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, India

Abstract

Mines disturb ecological systems and are major source of environmental contamination at local and regional levels. Mines generate a huge quantity of sulfide rich waste, such as tailings and waste rocks, during the ore extraction and mineral processing. Sulfides on exposure to oxygen and water generates acid mine drainage (AMD) which leads to a decrease in pH and leaching of heavy metals from the waste. The AMD generation capacity of mine waste depends on the chemical composition of waste, extraction, or beneficiation process and climatic factors. The runoff from waste piles enriched with AMD mixes with streams and increases the load of heavy metals. The percolation of heavy metals from waste piles contaminates the groundwater and the impact is more in shallow aquifers. The abandoned mines (surface and underground) left after the extraction of ore are also major source of water contamination. Additionally, the overexploitation of water resources during dewatering and changes in land use and land cover due to mines disturbs the recharge and discharge capacity of aquifers. It leads to the degradation of water quality and changes in hydrogeochemical processes. Thus the implementation of proper waste management and treatment policies are urgently needed to save the quality and quantity of water resources in the mining regions.

Keywords

Heavy metals; mines; groundwater; surface water; source of contamination

1.1 Introduction

Mines are important for economic development of a country, but lack of proper management policies lead to environmental destruction and disturbance of ecosystem functions. The exploitation of mineral ores from earth adversely affects the quality of water resources, that is surface (Alonso et al., 2020) and groundwater (Ghezzi et al., 2019). The overexploitation of water resources for mines elevates salinity and heavy metal content in groundwater (Gomo and Vermeulen, 2013). Lack of water availability in arid and semiarid regions further intensifies the problem. Some of the merits and demerits of mines considering socioeconomic aspects are given in Table 1.1.

Table 1.1

Mines generate a huge quantity of waste in the form of overburden or waste rocks, slag, and tailings which are mainly dumped near mining sites after taking all the necessary precautions (Elouear et al., 2016; Moncur et al., 2015). The overburden rocks contain significant amount of mineral/metal, but their economic extraction is not feasible. Tailing is a waste containing processing fluids from concentrators or mills that remains after the extraction of minerals, economic metals, or mineral fuels. Tailings are stored and preserved in artificial dams following the scientific methods. Natural resources or minerals are depleting at a faster rate, but their demand is increasing continuously. It puts pressure on mining industries to extract low grade ore that further results in more tailings (Mehrabani et al., 2010). Tailings and waste rocks contain good amounts of unextracted sulfides (Punia et al., 2017) and on exposure to oxygen and water generates acid mine drainage (AMD) which is a major cause of concern for the environment (Zhu et al., 2020).

Depending upon the pH, the mine drainage could be AMD or neutral mine drainage. In the presence of neutralizing materials, the pH is maintained in neutral range, that is, between pH 6 and 9 (Nordstrom et al., 2015). The pH of AMD is also observed negative (González et al., 2020). The produced sulfuric acid dissolves elements from minerals and intensifies the mobilization of heavy metals into the environment. AMD accelerates the dissolution of minerals, and the acid formed by sulfide oxidation is neutralized by the dissolution of carbonates and weathering of silicate minerals (Santelli et al., 2001). It releases heavy metals from host rocks and contaminates the environment. Heavy metals leached from mine waste mixes with nearby streams and increases their concentration (Ferreira da Silva et al., 2015).

It is important to understand the sources of heavy metals in the mining region, migration pathways of heavy metals, and remediation methodologies to mitigate the impacts of mines. The objectives of the chapter are to discuss the (1) sources of heavy metals in the mining region, (2) impacts of water contamination on vegetation and human, and (3) available remediation methods to mitigate the impacts.

1.2 Sources of contamination

Identifying the source of heavy metal is essential for better implementation of management policies and strategies during the active phase of the mine, and application of remediation technologies after the closure of the mine. In mining regions, mine workings and waste (tailings, waste rocks and slag) are a major source of heavy metal contamination (Fig. 1.1). However, geogenic sources of heavy metals in the surface water are also observed in the mining region at metalliferous Louisa Mine at Glendinning, Scotland (Mbadugha et al., 2020). Mobility of heavy metals in waste and soil depends on source (anthropogenic and geogenic) of contamination (Punia and Siddaiah, 2019). Hierarchical cluster analysis and principle component analysis are frequently used methodologies for the identification of source of contamination (Eang et al., 2018).

Figure 1.1 In mining regions, mine workings and waste (tailings, waste rocks and slag) are major source of heavy metal contamination.

1.2.1 Mining area

Huge number of mines are active and abandoned worldwide and details of a few of them are given in Table 1.2. Excavation of minerals and ores from host rocks expose sulfides to oxygen and water leading to AMD formation. Oxidation of pyrite majorly generates AMD and is summarized in Eqs. (1.1)– (1.4).

(1.1)

(1.2)

(1.3)

(1.4)

Table 1.2

The active or abandoned mine workings are a major polluter of groundwater and significantly influence hydrogeochemistry and hydrogeochemical processes in the nearby vicinity (Nordstrom, 2011; Gomo and Vermeulen, 2013; Bozaua et al., 2017). Both metallic and nonmetallic mines influence the hydrogeochemical processes or composition of groundwater, in addition to local geology and climatic factors. The concentration of SO4²− in groundwater is a reliable indicator of mining pollution and enhance the dissolution of Ca²+ and Mg²+ enriched carbonates and silicates on exposure of AMD (Kim et al., 2017). Mining pollution also elevates electrical conductivity (EC) and salinity of lakes with large surface areas in the near vicinity and impacts the aquatic ecosystem (Leppänen et al., 2019).

Mines are also active in the sensitive ecosystems of subarctic regions. Kittilä gold mine, Finland, is contaminating the Seurujoki River and measured contaminates are within the maximum permissible limits but are 4–16 times higher than the other high altitude river water (Yaraghi et al., 2020). The continuous monitoring of EC detects the sudden impact of mines on water quality, as the ionic concentrations at higher altitudes are low. Similarly, lake sediments of Courageous Lake Greenstone Belt, Canada, has an elevated concentration of As due to operation of two high-grade and low-tonnage historical gold mines (Tundra Mine and Salmita Mine). The Arctic region is sensitive to climate change and metalloids present in the sediments are susceptible to remobilization with climate warming. The climate change increases the load of metalloids in the high altitude lakes sediments (Miller et al., 2019).

1.2.1.1 Active and abandoned mines

Mines contaminate water resources during the active phase and even after the closure. Heavy metal concentration in water may be of geogenic origin, but active mining activities increase their level of concentration (Bokar et al., 2020). Extensive extraction of ore increases the extent of sulfide exposure to environment. In the case of active mines, fresh material is continuously exposed during mineral excavation leading to oxidation of sulfides (Calmels et al., 2007). The fresh material generates more AMD compared to old material. In contrast, dewatering of pit water reduces the oxidation of sulfides to some extent during active phase of mining.

Ancient mines (active in 18th and 19th century) released heavy metals from waste heaps and contaminated fluvial systems in recent times (Kincey et al., 2018; Clement et al., 2017); although the released quantity of heavy metals is not as high as from recent mines (Martin, 2019). However, the degradation of water quality due to past or historical mines is reported in different parts of the world, namely Italy (Cidu et al., 2009), United Kingdom (Beane et al., 2016), Slovakia (Hiller et al., 2012), China (Qin et al., 2019a), Spain (Olías et al., 2019), South Korea (Park and Choi, 2013), Portugal (Ferreira da Silva et al., 2015), Nigeria (Adamu et al., 2015), Morocco (Moyé et al., 2017), and Turkey (Gemici et al., 2009).

Restoration of a disturbed ecosystem in a mining region is a challenging task due to lack of money and manpower. The failure of enforcement of environmental regulations during post closure of mines results in heavy metal contamination of water (Tarras-Wahlberg and Nguyen, 2008). The reconstruction of environmental impacts due to historical mines using tree rings (Rodrigueza et al., 2018) and scale chemistry of aquatic organisms (Cobelo-García et al., 2017) is helpful in understanding the degradation of environment in ancient times.

1.2.1.2 Metallic and nonmetallic

Percolation of rainwater dissolves minerals in the flow path, and rock water interaction or mineral composition of parent rocks control the geochemical evolution of groundwater (Phan et al., 2018). The soil formed from the carbonate rocks have the capability to neutralize acid generated from sulfides (Favas et al., 2016). However, the elevated sulfate content overcomes the neutralization capacity of carbonates and increases heavy metals concentration in groundwater (Qin et al., 2019b). The heavy metals are abundant in groundwater at circum-neutral pH buffering caused by calcium and magnesium carbonates in the vicinity of metallic mines (Hiller et al., 2012). The metallic mines present in a karst aquifer are sources of heavy metals in the groundwater (Wen et al., 2016) and it is observed that the silicified limestone is a source of Sr, S, and Sb in natural water (Wen et al., 2016). The abundance of carbonates increases alkalinity and low concentration of heavy metals in a karst aquifer is observed irrespective of the presence of metallic mines (Pavoni et al., 2018). Carbonate neutralizes acidity, but the interaction of mines with groundwater degrades water quality and increases the content of SO4²− and heavy metals (Cidu et al., 2009).

In nonmetallic mines, AMD from coal mines is well known for heavy metal contamination of water resources downstream (Dutta et al., 2020; González-Martínez et al., 2019; Wright et al., 2018; Gammons et al., 2013). Coal is a nonrenewable energy resource used for electricity generation and energy production in the industrial sector. High demand of coal accelerates heavy metal pollution, as coal mines are also a source of pyrites. Waste generated from limestone mines have acid neutralization capacity. The limestone quarry is known for calcite dissolution, which increases Ca²+ and HCO3− content in groundwater (Eang et al., 2018). Calcite dissolution neutralizes the released acidity from sulfide oxidation.

1.2.1.3 Surface and underground mines

The depth of the mine depends on the availability of ore, that is, in surface mines ore is present near the upper surface of earth, and in underground mines ore is present deep into the earth. Surface mines majorly affect the forest cover and upper surface of earth during ore excavation. After the completion of the ore excavation process, surface mine pits that are left abandoned intercept with groundwater and cause heavy metal contamination via AMD formation. Rainwater infiltration leads to a drop in pH, and dissolves pyrite and calcite in the initial stages of the mine and generates AMD (Labus and Lutyńska, 2017).

It is well known that mining adversely transforms land use and land cover (LULC) patterns (Popelková and Mulková, 2019; Redondo-Vega et al., 2017) due to extensive deforestation (Sonter et al., 2017). Additionally, overexploitation of groundwater resources decreases availability of water for vegetation in the mining area (Liu et al., 2019). Depth of groundwater and vegetation cover depends on each other in arid and semiarid regions (Yang et al., 2019). Changes in agricultural patterns due to reduced water availability decreases soil moisture content and vegetation cover leading to changes in the LULC pattern (Popelková and Mulková, 2018). LULC change also affects the quality of soil, water, and biota (Duraisamy et al., 2018; Delelegn et al., 2017; Schilling et al., 2008), so it is important to assess the nature and magnitude of mining impacts at the landscape level. Both mining and land-use changes contribute to the release of heavy metals into the environment (Luo et al., 2020).

1.2.2 Mine waste

Industrialization and increased population put pressure on the mining industry to extract low quality ore. The extraction of low-grade ore increases the production of mining waste. Lack of availability of land for disposal of mining waste is one of the major concern. The disposal of mining waste in open environment enhances the probability of heavy metals leaching. The fine particles of waste material are transported to distant locations through wind and runoff (Kim et al., 2011). By limiting the availability of oxygen to mine waste, we can reduce the mobility of heavy metals for short durations (Kaasalainen et al., 2019). The variation in oxygen and water content at different parts of the dumps results in nonuniform oxidation of pyrite (Shahhosseini et al., 2020).

The waste storage facilities are usually located in the close vicinity of mines to save transportation costs. Waste from metallurgical processing, that is, tailings (Abraham and Susan, 2017) and slag (Ashelford and Gore, 2020), and waste during the mineral excavation, that is, waste rocks (Martin et al., 2019), are the potential source of heavy metal contamination. Lack of proper disposal of mining waste and an incomplete smelting process would lead to contamination of toxic pollutants into the local environment (Yan et al., 2019).

1.2.2.1 Tailings

Tailing dams and ponds are significant sources of heavy metals and contaminate neighboring water resources. The concentration of heavy metals (Co, Cu, Zn, and Cd) are of 1–2 orders of high magnitude in groundwater near a tailings storage facility than in background groundwater in the arid district of the Black swan nickel sulfide mine north-east Kalgoorlie (Western Australia) (Xie et al., 2010). Similarly, heavy metal (As, Cd, Pb, and Zn) concentration in surface water resources near the tailing pond of Dabaoshan mine, a polymetallic mine, South China, are 2–100 times higher than Chinese standard surface water during rainy season indicating unsuitability for irrigation (Luo et al., 2020).

The runoff passing along the corners or edges of tailings is also responsible for the load of seepage, in addition to water flows over the upper surface (Kim et al., 2020). Thus covering of tailings from all the sides and implementation of barrier/impermeable layer is important to prevent the oxidation. Runoff transports fine particles of tailings to streams. The sediments of river flowing in the downstream of tailings are enriched in heavy metals posing the potential ecological risk (Bouzekri et al., 2019).

Designing of a tailing dam is a major challenge faced by the management authorities. Tailing dam failures spill huge quantities of waste into the neighboring areas. Contamination of streams, rivers, and groundwater in the downstream due to spillage and dam breaks is reported widely across the world (Liu et al., 2020; Glotov et al., 2018). Another major problem with tailings is the upward migration of mobile heavy metals in dried condition and forms efflorescent salts or evaporative secondary minerals on the upper surface of tailings dam (Buzatu et al., 2016). These salts are enriched in heavy metals (Khorasanipour and Eslami, 2014) and carried away with runoff to water resources.

1.2.2.2 Waste rocks

The upper surface of earth is removed during excavation of minerals and ores, generating waste rocks. Under the influence of high precipitation and temperature, waste rocks generate AMD and contaminate water resources. The excavated rocks are used for refilling abandoned open pit mines after the closure. Groundwater and surface water resources show decreases in concentration of heavy metals in the initial phase of backfilling, but show signs of ongoing oxidation of waste rock sulfides or production of AMD despite dry cover (Villain et al., 2013). The refilling improves nutrient capability of the upper soil and reduces their environmental contamination potential. The contamination of surface water by waste piles is more in the absence of remediation measures such as revegetation, soil covering, leaching ponds, and construction of retaining walls (Yan et al., 2019).

Waste rocks contain high concentrations of heavy metals even after a long time, and gradually contaminate the environment and ecosystem through weathering and erosion (Perlatti et al., 2021). Fine particles of waste rock with a low content of carbonates produce acid drainage with a high content of heavy metals while coarser fractions of waste rocks with a high content of carbonates remain neutral for many years, indicating the role of particle size in drainage chemistry (Vriens et al., 2019).

1.2.2.3 Slag

Slag is a waste left after the metallurgical process. It is considered inert material and safe for the environment, but high concentrations of heavy metals in slag is a potential source of contamination. It is observed that Sb-enriched drainage from the slag heap of an abandoned mine (active between 1880 and 1980) of Su Suergiu (Sardinia, Italy) contaminates surface water resources in the downstream (Cidu et al., 2013). The concentration of Sb concentration reaches up to 1500 μg/L and contaminates the Flumendosa River several kilometers downstream of the mine area.

1.2.3 Mine water

Due to the extensive extraction of minerals, the depth of a mine pit reaches groundwater level and develops a cone of depression affecting the water quality (Su et al., 2020). The extensive pumping required for dewatering to keep mine workings dry for the extraction process and it depletes groundwater level and water quality. Once the pumping stops, the mine pit fills with the groundwater known as groundwater rebound (Gandy and Younger, 2007). Excessive pumping forms precipitates from the primary sulfides or waste, and these precipitates dissolve metals on contact with water posing a risk to public supplies (Cidu et al., 2001). The mine water also discharges heavy metals into neighboring surface water resources (Banks et al., 1997). The mine water geothermal power plants are sustainable renewable sources of energy. The mine water from an abandoned coal mine of Spain is technically and economically feasible to provide energy to 17,000 households (Menéndez et al., 2020). The thermal bands of satellite images could identify potential sources of geothermal energy from the abandoned mine (Joshi and Punia, 2019).

Low pH of mine water dissolves cationic metalloids including rare earth elements (REEs). The abandoned mines filled with water are the potential sources of heavy metal contamination for groundwater resources (Newman et al., 2020) as the depth of abandoned mine pit is close to groundwater. REE is abundant in abandoned mine water and could be recovered by sorption/desorption, adsorption, bioaccumulation, and precipitation processes (Royer-Lavallée et al., 2020).

The pit cut of abandoned mines filled with the rainfall runoff and groundwater seepage forms mine pit lakes and contaminates the down gradient stream and groundwater (Newman et al., 2020). The accidental spills from the underground and abandoned open pits is also reported across the world (Olías et al., 2019; Taylor and Little, 2013), similar to spill from a tailings dam. Spill from an abandoned pit lake of the La Zarza mine (Spain) increases the elemental concentration (Fe and As) about 450 times higher in the Odiel River (Olías et al., 2019). The accidental spill from the abandoned mines causes adverse impact on the environment and human health (Hudson-Edwards, 2016).

1.3 Pathways of contamination

The contamination of water resources in mining regions basically follows two pathways (1) AMD discharge into the surface water through runoff or wind dispersal of fine waste particles and (2) by percolating or dissolution of minerals by AMD or leaching of heavy metals into the groundwater (Fig. 1.2).

Figure 1.2 .Water resource contamination in mining regions basically follows two pathways (1) AMD discharge into the surface water through runoff or wind dispersal of fine waste particles and (2) by percolating or dissolution of minerals by AMD or leaching of heavy metals into the groundwater.

1.3.1 Contamination of surface water resources

Surface water resources located in close proximity of mining waste and mine workings are at high risk of exposure (Gray and Eppinger, 2012). The runoff flowing from the mining waste and mine working drains into surface water resources during intense precipitation (Cidu et al., 2012; Jarvis et al., 2006). The efflorescent salts or secondary minerals form on the upper surface of mining waste during the dry season and dissolves in contact with rainwater (Nieva et al., 2018) contaminating streams and lakes.

Another important pathway is aerial dispersal of fine particles of mining waste. The strong winds carry fine particles of mining waste to distant locations, and contaminates soil and surface water resources (Žibret et al., 2018; Brotons et al., 2010). The phenomenon is more prominent in arid and semiarid areas with low vegetation cover. In wet regions, the surface water resources are dominantly contaminated through runoff and in the arid/semiarid region by aerial dispersal.

1.3.2 Contamination of groundwater resources

The chemical composition of groundwater is controlled by geology, rock–water interaction, depth of groundwater level, climatic factors, and other hydrogeochemical process (Mazhar and Sarfaraz, 2020; Valenzuela-Diaz et al., 2020; Verma et al., 2019). Infiltration of rainwater significantly influences the groundwater quality in the downstream of tailings. The values of EC and heavy metals observed high in the rainy season compared to the dry season confirming the increase in ionic concentration (Cánovas et al., 2016b; Cheong et al., 2012). In groundwater, the hydrological responses are complex to study compared to surface water resources due to lack of information regarding the flow path and acidic weathering of host rocks which mobilizes elements (Cánovas et al., 2016a).

Weathering, ion exchange, precipitation, and evaporation are major processes in controlling the hydrogeochemistry (Mahaqi et al., 2020). The heavy metal concentration was observed high in soil surrounding the mining area, and under the influence of intense precipitation heavy metals leach into groundwater. The fractures and fissions present in parent rocks also play a significant role in the permeability and contamination of groundwater in the downstream of mines (Moyé et al., 2017).

The shallow aquifers are easily contaminated by mines compared to deep aquifers. In shallow aquifers also, two contamination zones, that is, low and high metal (antimony) concentrations are observed at the Xikuangshang Mine area (in Hunan province, China) exceeding China’s national drinking water quality guidelines (Hao et al., 2020). Dissolution of carbonate minerals control groundwater chemical composition in low Sb content. In case of high content, two mechanisms, that is, ion-exchange interaction and dissolution of carbonate and silicate minerals, influences the chemical composition. The infiltration of rainwater dissolves minerals from parent rocks and impacts the hydrogeochemistry of groundwater (Neiva et al., 2019). The seasonal variation of AMD controls heavy metal concentration in water resources (González et al., 2020). Precipitation of sulfate salts during dry season and the dissolution in rainy season controls the fluxes of heavy metals in the aquifer (Cánovas et al., 2016a). The secondary iron minerals formed in AMD are natural scavengers of trace elements through the mechanism of adsorption and precipitation processes (Parviainen et al., 2015). Secondary iron minerals are formed at different pH such as jarosite at pH<3, schwertmannite between pH 3-–4, and goethite at neutral pH (Bigham and Nordstrom, 2000).

1.4 Impacts of mines on vegetation and humans

1.4.1 Vegetation

Water quality assessment is an important step to ensure safe consumption using water quality and pollution indices (Santana et al., 2020; Adamu et al., 2015). Surface and groundwater contaminated by mines and mining waste (tailings, slag, and waste rocks) (Zhou et al., 2016) is used for irrigation and drinking purposes at many places. Heavy metals get accumulated in edible products such as food grains, vegetables, and fruits on irrigation with contaminated water. Consumption of contaminated food grains is also potential cause of bioaccumulation of heavy metals in human body. Water is found unsuitable for the irrigation purposes in neighboring locations of metallic or nonmetallic mines (Sahoo and Khaoash, 2020). The continuous use of contaminated water results in the accumulation of heavy metals in plants. To assess water quality for irrigation purposes, many indexing models namely sodium adsorption ratio (SAR), sodium percentage (Na%), residual sodium carbonate (RSC), Kelly’s ratio (KR) and permeability index (PI) are used worldwide (Richards, 1954; Kelly, 1963; Szabolcs and Darab, 1964; Ramesh and Elango, 2011; Singh et al., 2012) [Eqs. (1.5)–(1.9)].

(1.5)

(1.6)

(1.7)

(1.8)

(1.9)

High concentration of heavy metals are observed in plants and vegetables grown in the vicinity of mines (Dan-Badjo et al., 2019; Cidu et al., 2013). However, at some places the concentration of heavy metals in water are high, but heavy metals (Cu, Zn, and Cd) concentration are within the permissible limit in plants (green been, green walnut, mushroom, cucumber, tomato, potato, green pepper, cherry, walnut, garlic, and corn) (Avkopashvili et al., 2017). Plants having high heavy metal accumulation capacity could be used for the revegetation of contaminated sites in mining regions (Ashraf et al., 2011).

Apart from heavy metal contamination, the salinity of groundwater increases due to overexploitation and elevated ionic concentration in the mining region (Su et al., 2020) which adversely effects the growth of plants. The dust material from mines deposit on leaves leading to the accumulation of heavy metals in plants (Cidu et al., 2013). Accumulation of high concentration of heavy metals in plants grown in the mining region is a major concern for human health (Dan-Badjo et al., 2019).

1.4.2 Human health

High concentrations of heavy metals in soil, ground, and surface water lead to health risk to humans via direct consumption or dermal contact (Park and Choi, 2013). The rate of heavy metals intake via various pathways from highest to lowest probability is: soil inhalation as dust>crop ingestion>groundwater ingestion>soil ingestion>soil contact (Park and Choi, 2013). National or international agencies such as the World Health Organization set permissible limits for heavy metal concentration in water used for consumption by the public. Mines elevate heavy metal concentration in domestic water supply, exceeding the permissible limits (Abraham and Susan, 2017). Risk assessment is the estimation of probable risk using magnitude, frequency, and duration of human exposure on consuming heavy metal-contaminated water.

Health impacts caused by heavy metals could be categorized as carcinogenic or noncarcinogenic. Average daily dose (ADD), hazard quotient (HQ), and hazard index (HI) values predicate the possible health impacts in human beings on consuming the contaminated water (USEPA, 2009, 2001). ADD is calculated using the mean concentration of heavy metals, daily intake, exposure duration and frequency, average time of exposure, and body weight of a person as parameters [Eq. (1.10)].

(1.10)

where, ADD is average daily dose (mg/kg/day), C is mean concentration (mg/L) of heavy metal, ED is exposure duration, EF is exposure frequency, IR is water intake rate, BW is average body weight, AT is average time and RfD (reference dose). HQ and/or HI values exceeding 1 indicates potential noncarcinogenic effects on health as a result of exposure [Eqs. (1.11)–(1.12)], while HQ and/or HI<1 means health risks to consumers are unlikely.

(1.11)

(1.12)

Heavy metal-contaminated water resources in the vicinity of mines are a potential source of carcinogenic and noncarcinogenic health impacts, specifically more in children than adults (Lu et al., 2019; Rehman et al., 2018). The high concentration of Hg and Pb could cause noncarcinogenic health risks and the value of HQ is observed greater than 1 near abandoned barite mines of south-eastern Nigeria indicating a high probability of health risk (Adamu et al., 2015).

1.5 Remediation methods

Heavy metal content in AMD shows long term seasonal fluctuation, so continuous monitoring is recommended before designing the remediation system (Caraballo et al., 2016). Extraction of available minerals from waste should be promoted to reduce the size of dumps. Recently, the extraction of REE along with some critical elements is found feasible from acid mine leachate from a coal preparation plant through sequential precipitation methods by controlling the pH using chemicals such as 10 M HNO3, oxalic acid, and Na2S (Zhang and Honaker, 2020). In the remediation technologies, the particle size of aerosol from mines should be considered a priority as finer fractions contain more heavy metals and are more prone to inhalation and ingestion (Kim et al., 2011).

Proper and scientific implementation of remediation technologies require high economic investments and manpower. The major problem in treating AMD is the cost of neutralizing material and complications in chemical reaction. The application of naturally available materials like marl, sandstone, calcareous crust (García-Valero et al., 2020), and limestone (Luo et al., 2020) are recommended to solve the problem of AMD. The treatment of mine water with lime needs a real time monitoring for titratable acidity to balance the pH and dose of neutralizing agent (Qin et al., 2019b).

Neutralization of AMD using limestone is a well known method, and the reaction between AMD and nano particles of limestone are potential sorbents for hazardous elemental contaminants from mine water (Dutta et al., 2020). Calcium carbonate, calcium oxides, and hydroxides are found to be an attractive method for remediation of tailings (Kastyuchik et al., 2016). Tailings amended with cement or magnesium oxides are more buffered against the re-acidification compared to tailings amended with chicken eggshell residue, commercial calcitic limestone, and commercial dolomitic limestone (Kastyuchik et al., 2016). AMD neutralization efficiency or adsorption capacity of limestone increases after modification with sodium chloride, sodium hydroxide, and sodium carbonate (Iakovleva et al., 2015).

Phytoremediation is a sustainable and economically viable solution to mitigate the environmental impacts of mine water and waste. The water usage capacity of some trees (Eucalyptus and Pinus species) are high; specifically Eucalyptus plantations, as a biodrainage option, reduces the water ingression into mine workings (Dennis et al., 2020). The major hindrance in having a plantation on the contaminated sites is the presence of high contents of toxic heavy metals. The accumulation of heavy metals retards the growth of plants and leads to death. In phytoremediation, the heavy metals are extracted from contaminated water and accumulate in different parts of plants, that is, shoots, roots, or leaves. The amendments improving the texture and phosphorus content are recommended before phytocapping (Karaca et al., 2018) and phytoremediation (Kasowska et al., 2018). Harvesting and disposal of plants is a major concern as, on decomposition heavy metals again enter into the environment.

Revegetation of mining waste dumps or heaps reduces the dispersion of contaminated materials into water resources. Pistacia lentiscus grows normally on Sb contaminated soil at the Su Suergiu mine (Sardinia, Italy) suggesting its possible use for the revegetation of Sb-rich heaps (Cidu et al., 2014). It further demands more studies for the identification of different plant species for mitigation purposes. The remediation processes by phytoremediation with macrophytes decreases the heavy metal concentration in soil and water but are not enough for the rehabilitation of area (Antunes et al., 2016). The reclaimed ore processing sites are also found to be a potential contamination source (Khaska et al., 2018) and, hence, implementation of a proper remediation method is recommended.

Reforestation of abandoned mines is a sustainable way to reduce the environmental impacts. Reforestation of mining land and waste heaps of coal, lignite, and sulfur mines are successfully achieved in Poland (Pietrzykowski and Krzaklewski, 2018). Soil formation is initiated from waste heaps at Turów and Bełchatów after the reclamation, following the method of acid neutralization and a plantation of grass and legumine vegetation. Similarly, in eastern Kentucky, USA, reforestation of mine land started during 1996–97 and the lands are converted into forest ecosystems. It is observed that the spoil preparation or compaction in the initial stages of reclamation plays an important role in reforestation. The loose spoil heaps resulted in higher survival and larger trees of all species even after the two decades of establishments (Dement et al., 2020).

1.6 Summary

Mines are well known for disturbing the ecosystem process and as a cause of pollution. Mines contaminate water resources via two processes, that is, pollution and degradation of natural resources. Mines located in different corners of the world are causing contamination of water and currently, contamination of water at higher altitudes is also a major concern. Surface water bodies located at higher altitudes are prone to climate change and the increase in temperature due to global warming mobilizes the heavy metals in sediments. Additionally, degradation of natural resources such as water resources, forest cover, and soil for mines results in LULC which disturbs recharge/discharge capacity of aquifers degrading the quantity and quality of water.

Heavy metal concentration exceeds prescribed permissible limits in drinking water at a majority of places neighboring the mines. Use of heavy metal-contaminated water for irrigation and drinking purposes lead to health hazards. The implementation of phytoremediation technologies is highly recommended. Acid neutralization and restoration of an abandoned mine to a natural ecosystem is costly and needs manpower. The application of locally available cheap material such as chicken eggshell residue, agricultural and kitchen waste for the acid neutralization is recommended. Thus the implementation of proper waste management and treatment policies are urgently needed to save the quality and quantity of water resources in the mining regions.

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