19.1 Introduction

Arsenic (As) pollution has been recognized as one of the most significant environmental contaminants because of multiple anthropogenic activities, and numerous institutions have reported regarding its toxicity and remediation including various industries, environmental groups as well as the general public (Alka et al. 2021). It is the 20th highest metalloid found naturally in the earth crust and is generally recognized for causing adversity on human and marine animals (Yin et al. 2017). Moreover, World Health Organization (WHO) has classified arsenic (As) as Class I carcinogen, as it is closely associated with the cancerization of numerous organs including skin, bladder, lung and kidney (Lindsay and Maathius 2017). Most of the As related concerns arise from anthropogenic activities and resultant contamination leads millions of individuals to life menacing situations by drinking the poisoned water as well as consuming the foods produced on As contaminated soils. Its contamination has been noted as the 21st century devastation by several researchers and scientific authorities (Hare et al. 2019; da Silva et al. 2019). Arsenic exists in nature in numerous oxidation states i.e., 3−, 0, 3+ and 5+ as well as in many organic and inorganic forms (Palma-Lara et al. 2020) due to different reasons i.e., human and microbial activities as well as volcanic eruption, rock weathering (Villaescusa and Bollinger 2008; Verma et al. 2018), mining, consumption of agrochemicals (fertilizers and pesticides) and fuel consumption. Its exposure to human beings occurs via numerous pathways including air, water, food and soil (Khan et al. 2020), the exposure pathways vary region wise, and depend highly on the geological compositions of the aquifers as well as activities of residents such as drinking groundwater (Liang et al. 2016; Alam et al. 2016) or ingesting the As contaminated fish and shellfish (Liang et al. 2011). Based on the recommendations given by the WHO, the permissible limit of As in drinking water is 10 μg L−1 (Tariq et al. 2019; Zacarías-Estrada et al. 2020). Generally, people suffer from As contamination via food as well as drinking water (Lindberg et al. 2006; Kabiraj et al. 2022). Its accumulation in the soil and water leads to serious health hazards in humans (Verma et al. 2018; Abad-Valle et al. 2018). In recent times, health concerns related to As exposure have gained considerable attention in different countries (Singh et al. 2015a, b; Osuna-Martínez et al. 2020). Various epidemiological studies have reported the adverse impacts of chronic As exposure to different body systems e.g., reproductive system, respiratory system, circulatory system and immune system (Jain and Ali 2000). Nearly, 13 million people in Pakistan belonging to 27 major districts are susceptible to As contamination due to the consumption of contaminated water for drinking, and more threats are being observed by those populations residing along the Indus river (Rabbani et al. 2017; Ali et al. 2019). The As contamination may arise naturally or anthropogenically (Smedley 2008; Farooq et al. 2016). In Chakwal and Jhelum cities (Punjab province), geothermal sources and coal mining activities contribute towards As contamination whereas, in Tharparkar district (Sindh), complicated geological structure as well as arid climate result in As contamination in the ground water via favoring the reductive dissolution of minerals containing As (Brahman et al. 2013).

19.1.1 Arsenic (As) in Soil–Water System

Various countries of the world, including China, Bangladesh, USA and India, have reported dangerous levels of As in drinking water and consequent human exposure (Hoover et al. 2017; Li et al. 2018; Wasserman et al. 2018; Chatterjee et al. 2018). On a global scale, reports about the natural contamination of drinking water with As are available for more than 70 countries, and majority of these countries lie in the South Asian to Southeast Asian regions (Ravenscroft et al. 2011). Several biogeochemical processes (adsorption/desorption, volatilization, methylation/demethylation, or precipitation) caused either microbially/algally or chemically, may accelerate As mobilisation, resulting in a massive increase in As content in water bodies (Drewniak and Sklodowska 2013). The concentration of As in water varies from one water to the next, as various researchers have discovered. Welch et al. (1988) found that the concentration of As in the ocean is between 0.15 and 6 g L−1, but Chapell et al. (2001) found it to be between 1–2 g L−1. The freshwater As concentrations can vary from 100–1000 μg L−1 of water (Mandal and Suzuki 2002; Barringer and Reilly 2013). Similar to other countries, Pakistan is also facing the issue of water scarcity as well as contamination in the available water supply (Ali et al. 2019). Rehman et al. (2019) performed a systematic field study to investigate the drinking water for total As concentrations, its organic (monomethylarsonic acid and dimethylarsenic acid) and inorganic species (arsenate and arsenite) in the KPK province of Pakistan. They reported total As concentrations ranged from 1.2 to 23 times in 28% of samples collected from Dera Ismail Khan and Lakki Marwat, exceeding WHO standards for drinking water and inorganic As species. Most of the Pakistan’s area is located in the arid to semi-arid climate where the average annual rainfall is below 200 mm and the availability of groundwater is scarce (Salma et al. 2012; Alamgir et al. 2016). Alarming levels of As in the ground as well as surface water resources of Pakistan have been found (PSQCA 2017). Major groundwater resources of Pakistan include the irrigated areas of Indus basin. Since most of the Pakistani people use ground water for drinking as well as other household purposes, As contamination of ground water renders more than 50 million people at higher risks of poisoning (Podgorski et al. 2017).

The mineralogical characteristics of the aquifer contribute greatly towards the concentration of As in ground water which can release As upon weathering. The extent of weathering is regulated by the physical and chemical characteristics of the groundwater as it is essential for aquifer weathering. Geothermal activity can sometimes contribute to As pollution in ground water because oxidized forms of As may be found in groundwater in many regions of the world, it is clear that the processes of As dissolution are not caused by the reduction of As-rich iron minerals, but rather by the oxidation of As-rich materials (Sarkar and Paul 2016). Because As comprises, alongside other elements such as antimony (Sb), boron (B), selenium (Se), lithium (Li) and mercury (Hg) comprises a distinct group that does not fit easily within the network of common rock minerals (Barringer and Reilly 2013). The As is the most problematic oxyanion forming element that is easily available over a broad range of redox circumstances without getting immobilized.

19.2 Remediation Measures

19.2.1 Physicochemical Methods

Incessant consumption of As-rich ground water leads to various kinds of chronic diseases i.e., keratosis, pigmentation, black-foot disease, nausea and cancer as well where inorganic As compounds are relatively more lethal as compared to the inorganic compounds. Among the organic compounds, methylated arsenic acids are believed to have demonstrated carcinogenic effects in humans. In this regard, scientists as well as researchers are exploring new ways to alleviate this issue. Several measures have been undergone for treating the As contamination such as activated carbon (C), via chemicals, reverse osmosis as well as nanomaterials via adsorption, etc. (Sarkar and Paul 2016). The conventional As remedial measures are mainly the physicochemical techniques. Adsorption, coagulation-precipitation, membrane filtration, ion exchange, reverse osmosis, and permeable reactive techniques are only a few examples. Every treatment technique uses the adsorption, coagulation-precipitation and oxidation–reduction principles, followed by filtering. Prior to treating the aqueous As, a pre-oxidation process is generally preferred as As (III) species usually prevail at drinking water pH and cannot be easily removed as compared to the As (V) species (Malik et al. 2009) and for this purpose, different methods such as aeration, ozonation, oxidation is frequently carried by using potassium permanganate or hydrogen peroxide, UV rays or chlorination (Litter et al. 2010).

19.2.1.1 Coagulation-Precipitation and Filtration

Coagulation followed by flocculation has been found useful for the effective extraction of As (particularly arsenite) from soil–water system (Ge et al. 2020). It does not require the comprehensive pre-treatment, preparation of the wastewater or use of non-manufactured chemicals (Cheng et al. 1994). Rather, the pre-requisite for the process include pre-oxidation and pH corrections. Transformation of dissolved As to globules occurs after adding the cationic coagulants, which nullify the negative charges present on the surface of colloidal particles. Resultantly, colloids accumulate into larger sized particles followed by their precipitation into flocs which are easily isolated by filtration. This method in turn, improves the quality of the water by allowing the separation of suspended particles, poisonous compounds along with As (Mohanty 2017; Wang et al. 2021a, 2021b, 2021c). Ferric chloride and alum have been long accepted as efficient chemical coagulants for removing As (Inam et al. 2021). It is a simple, straightforward, and successful approach for separating charged particles from liquids including the formation of a stable colloidal particle for floc accumulation and resultantly, extraction is preferred. Uniform incorporation of the coagulant into the As contaminated water is desirable for achieving maximum As extraction efficacy. Water insoluble As substances such as arsenate are removed by the resultant gelatinous precipitates (Mohindru et al. 2017). Important coagulants include titanium sulfate, zirconium (IV) chloride, titanium (III)/titanium (IV) chloride, titanium (IV) oxy-chloride and zirconium (IV) oxychloride etc.

19.2.1.2 Adsorption

Adsorption is a useful process for decreasing the arsenic concentration from the environment (Gulledge and O'Connor 1993). Using the activated C is costly as there are recovery issues which limits its use in the developing nations (Ochedi et al. 2020; Rodríguez-Romero et al., 2020).Which has increased the demand for low cost efficient adsorbing materials, with greater adsorption abilities as well as commercial availability (Kumar et al. 2013; Subburaj and Kumar 2020; Sivaranjanee and Kumar 2021). Guan et al. (2012) reported the removal of natural as well as inorganic As by using the titanium dioxide (TiO2) and related products. To date, photocatalytic oxidation of arsenite to arsenate as well as chemisorption of As (organic and inorganic) seems to be the focus of As extraction methods involving TiO2. Moreover, Fe-based nanoparticles have shown higher potential for As adsorption particularly at pH close to neutral. Most fascinating attribute of the Fe based nanomaterials is the extent of ease in their magnetism-based removal from the faded medium (Nikić et al., 2020). Similarly, biochar is a safe, cost-limiting and long-lasting and has shown phenomenal potential to remove toxic substances from water including As. However, revival of biochar and As recovery from biochar are still a mystery which needs to be resolved before the extensive application of biochar for the remedial purpose. It is indeed very critical to implement the most suited technique for post adsorption processing of used biochar (Amen et al. 2020).

In contrast to the conventional sorbent materials, modern synthetic materials i.e., graphene oxide, organic metal frameworks, nanotubes and related materials have shown great tendency to replace traditional materials owing to their tremendous As removal potential as demonstrated by improved reuse and higher partitioning co-efficient (Liu et al. 2020a, 2020b). Similarly, another form of dual hydroxide, hydrotalcites, has proved to be an effective adsorbent material for the smooth recovery of As contaminated water. However, determination of remaining arsenite intensity in the optimum solution after using hydrotalcites still remains challenging and demands further attention (Dias and Fontes 2020).

19.2.1.3 Membrane Based Remedial Methods

Membranes based methods for the extraction of arsenic has replaced other conventional techniques as they do not generate solid by-products unlike in other methods (Kartinen and Martin 1995). Membranes possess distinctive surface morphology such as permeability, pore size, harshness, hydrophobicity, width, segregation and harshness on account of their physicochemical attributes. They should reveal following properties (a) chemical and mechanical opposition, (b) long reliability, (c) high specificity and permeability and (d) low price. Moreover, all the membrane comprising technologies generate a concentrated stream from where, the ions are restored (Moreira et al. 2020). Membrane based procedures encompass several ways to reduce As. The As species are too small to pass through the membrane hence, ultrafiltration and microfiltration may not allow for the immediate removal. Govindappa et al. (2022) developed a novel polymer inclusion membrane (PIM) for the extraction of arsenic (As) from water. The PIM is among one of the best substituents to solvent extraction process with additional advantages such as considerably less solvent, extractant, economical and cost-effective even for large scale industrial processes. They concluded that the developed PIM permitted the transport of As (V) at higher concentrations for different natural waters spiked with 100 mg L−1 As (V). Moreover, they confirmed that low-cost novel PIM device can be used in metal industries to extract arsenate from contaminated water with greater efficacy. Nano filtration membranes and Reverse osmosis (RO) have also been reported to separate As species from groundwater in numerous working conditions. Nanofiltration is typically used for removing the divalent cations however, it can also remove As (III) and As (V) species predominantly by size omission (Siddique et al., 2020; Worou et al., 2021).

19.2.1.4 Ion Exchange

Ions exchange phenomenon involves the active replacement of electrostatically held ions on the solid phase by the ions present in the solution phase having uniform charge (Katsoyiannis and Zouboulis 2006) and used to remove various pollutants including arsenic (As). It is used to lessen the hardness of water and to extract different contaminants i.e., chromate, selenite, arsenate and nitrite anions in the waste water. Regularly synthesized resins are used and waste water passes from them recycling and reinforcing the exchanges ions (Al-Jubouri and Holmes 2020). Ion exchange predominantly remove arsenate from the waste water owing to the presence of negative charge (Jadhav et al. 2015). Total dissolved solids (TDS) interfere with the efficacy of As removal during the exchange process (Jadhav et al. 2015). Specific ion exchange resins have been recommended by the U.S. Environmental Protection Agency (EPA) particularly chloride ions for As removal. Factors determining the efficiency of ion exchange resins induced As removal are type of resins, total dissolved salts (TDS), arsenic concentration, high sulfate salts and competing ions (Sarkar and Paul 2016). Limited reports exist in literature regarding the use of ion exchange for As removal (Dong 2019).

19.2.1.5 Electrokinetic Technique

The Electrokinetic approach is a promising, effective and emerging technology for removing the free pollutants from soil (Li et al. 2020a, 2020b). It implies the removal mechanism comprising the movement as well as transport of various pollutants in the soil under the influence of an electric field such as electromigration, electrophoresis, electroosmotic flow and water electrolysis (Xu et al. 2019). Electrokinetic method for the removal of arsenic (As) has also been evaluated (Weng et al. 2009; Yang et al. 2016). The approach faces limitation during the As removal because it is difficult to be treated in its dissolved phase however, its efficiency can be remarkably enhanced and it can be made economically viable by coupling with other removal techniques (Li et al. 2020a, 2020b). Yuan and Chiang (2007) performed a study, where they used an electrokinetic process coupled with a permeable reaction barrier (PRB) in a soil matrix to remove As. Moreover, the efficacy of electrokinetic technique can also be significantly improved by combining with a permeable reactive barrier such as activated carbon (Zhao et al. 2016), hydrous ferric hydroxide (Yuan and Chiang 2007), carbon nanotubes, atomizing slag (Chung and Lee 2007). A brief summary of the As-remediation efficacy of different physiochemical approaches used by researchers has been illustrated in Table 19.1. The physicochemical methods have several limitations which hinder their excessive application on a larger scale such as generation of toxic sludge, high operational and maintenance cost, decreased efficiency under natural conditions and operational difficulties, etc. (Srivastava and Dwivedi 2015). In contrast to that, bioremediation does not involve such limitations and can be used for the efficient removal of As from the environment (Rahman and Singh 2020). Various researchers have reported the beneficial impacts of using various bioremediation approaches for As removal i.e., phytoremediation (Yang et al. 2018), remediation using bacterial species (Taran et al. 2019), phytobial remediation approach involving the application of biological agents (bacteria and plants) in integration with genetic engineering techniques (Irshad et al. 2020; Moens et al. 2020; Banerjee et al. 2020), fungal bioremediation (Tripathi et al. 2020), phytosuction separation approach (PS-S; Arita and Katoh 2018) and biosorption by using microbial cells (Podder and Majumder 2018), etc. Despite the ongoing extensive research, bioremediation of As is still limited to laboratory or pilot scale trials and its practical and field implications still require laborious and recurrent scientific researches.

Table 19.1 Summary of various physicochemical techniques to remove arsenic from different medium
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19.2.2 Bioremediation Approaches

19.2.2.1 Phytoremediation

Phytoremediation has gained much importance as an important, promising, cost-effective and eco friendly technique for As clean up from the contaminated environments (Budzyńska et al. 2017; Lei et al. 2018). Many researchers have found that As hyperaccumulators provide most effective, eco-friendly and low-cost solution for bioremediation via the bioaccumulation of As within the plant body (Kofroňová et al. 2019), phytovolatilization (Guarino et al. 2020) and phytoextraction (Lei et al. 2018). Phytoremediation is a green technology which employs plants for the cleaning process and is a cost-effective and environment friendly approach. There are two types of approaches which are commonly used for the remediation of contaminants from soils as well as wetlands i.e., natural and induced phytoremediation (Niazi et al. 2016). The use of genetically modified plants (GMOs) has also been proposed recently however, GMOs are currently facing the issue of restrictive legislation (Rahman et al. 2016). However, the phytoremediation process also bears some limitations in terms of climatic and geographic distributions as well as relative biomass content (Irshad et al. 2021). Moreover, different factors affect the efficiency of phytoremediation process. For example, pH is an important factor determining the solubility of different ions as well as their interactions. Similar is the case for As where increased soil pH lessens the solubility of arsenite and increases the solubility of arsenate. Hence, a reduction in pH will uplift the phytoavailability of arsenite (Fresno et al. 2016). Similarly, humic substances in the soil can adsorb arsenite on their surface, where maximum adsorption capacity is demonstrated at pH 5.5. The roots mediated oxidation and reduction of As owing to the pH alterations perform a keen part in As immobilization. So, the remediation of As is a multifactorial strategy where the optimization of each factor is inevitable to maximize the removal efficiency (Duan and Zhu 2018).

Another limitation of the phytoremediation is the sensitivity of the used plants towards soil chemical conditions as well as the level of As contamination (Yang et al. 2018). So, there is a need to explore an efficient, economical and practical solution. Moreover, the safe disposal of the harvested biomass after the completion of phytoremediation is also an issue (Irshad et al. 2021). In addition, there is a need to use the integrated approaches to enhance the phytoremediation efficiency such as microbe-assisted phytoremediation and phytosuction separation techniques. Various scientists have also emphasized on the combined application of microorganisms and plants to accelerate the phytoremediation process.

19.2.2.2 Microbial Based Bioremediation

19.2.2.2.1 Bacteria

Bacteria use different mechanisms to mobilize, transform or bioremediate the As such as biosorption (Saba et al. 2019), redox reactions (Zhang et al. 2016; Bhakat et al. 2019), volatilization and methylation (Zhang et al. 2014), etc. Many As-resistant bacteria that can withstand elevated concentrations of As have been potentially used for the bioremediation of As from soil–water systems. Several systems exist in bacteria which aid in overcoming As toxicities such as arsenate (ars system), arsenite oxidation system (aio), anaerobic arsenate respiration system (arr) and arsenic methylation system (arsM). There could be multiple As resistance system operating in a single bacterium however, the most common is the ars system (Kumar et al. 2021). Saba et al. (2019) investigated the efficiency of extracellular polymeric substances (EPS) producing bacterial species for As bioremediation and correlated it with the EPS production potential of the bacteria. The EPS are complex high molecular weight substances that are released by microorganisms. They concluded that the presence of large number of polyanionic functional groups on the bacterial EPS can sequester As via covalent or electrostatic interactions. Bacterial mediated oxidation of As is mainly related to the catalytic activity of As (III) oxidase (periplasmic enzyme) and it is a major detoxification process usually carried out by the heterotrophic As-oxidizing bacteria (Rahman and Hassler 2014). Several prokaryotes have demonstrated the potential of As oxidation such as Agrobacterium, Pseudomonas and Alcaligenes (Ghosh et al. 2015). Biswas and Sarkar (2019) isolated two-gram positive bacteria from shallow aquifers and tested their As tolerance. One of the specie was found to be able to withstand 70 mM of arsenite and the other was tolerant against 1000 mM of arsenate. Both the strains exhibited tremendous potential to convert As (III) to less toxic As (V) from As enriched media. They reported that the As oxidizing bacteria can perform a keen role in the subsurface As transformation that can help in designing future bioremediation strategy. At the same time, some bacterial strains also cause the reduction of arsenic (Jebelli et al. 2017; Rios-Valenciana et al. 2020) and thereby, facilitate the transfer of As in the above-ground plant parts. The reduced form, As (III) predominates in the soil as compared to the oxidized form (As, V) as plant’s ability to uptake As (III) depends on the competition with phosphate present in the soil which makes it difficult for the plant to remediate it (Alka et al. 2020).

Many bacterial species also use As (III) oxidase or As (V) reductase enzymes thereby, use As compounds as electron acceptors/donors and get their energy by metabolizing them (Rhine et al. 2007). Due to alarming increase in the As contamination, transgenic bacteria using genetic engineering techniques can also be used for ensuring As bioremediation. Various studies have evidenced regarding the effectiveness of using transgenic bacteria possessing the target genes responsible for increased As methylation as well as detoxification (Huang et al. 2015; Prum et al. 2018; Vezza et al. 2020). This strategy has also contributed towards decreased translocation followed by accumulation of As in food crops (Chen et al. 2013).

19.2.2.2.2 Yeast and Fungi

Myco-remediation (using fungi to remediate contaminants) has emerged as one of the most promising and cost-effective approach for As detoxification (Tripathi et al. 2015) in plants and their beneficial role regarding the plant growth and survival under stressed conditions. Fungi have been extensively known for their widespread metabolic competence and the ability of their cell wall to bind metal (loid) ions owing to the presence of amino group and polysaccharides. Hence, isolation followed by enumeration of As tolerant fungal species from the contaminated sites could provide an inside into the fungal mediated As bioremediation (Singh et al. 2015a, b). Until now, numerous fungal species have been isolated from As contaminated sites such as Trichoderma, Aspergillus, Fusarium and Penicillium etc. (Caporale et al. 2014; Zeng et al. 2015; Govarthanan et al. 2018). The adaptation of fungi towards the contaminated sites might be due to their high surface area to volume ratio and different mechanisms of metal detoxification (Kapoor et al. 1999; Tripathi et al. 2020). Biomethylation of As by fungi via the enzyme based conversion of As into the volatile as well as non-volatile species and by using the S-adenosylmethionine and thiols offer a keen role in its biogeochemical cycling and detoxification. Govarthanan et al. (2019) examined the metal mineralization potential of calcite, microbially induced precipitate using Trichoderma in remediating the As contaminated soils. The fungus was found to tolerate 500 mg L−1 of As. The effect of three different factors on the bio-mineralization of As was checked i.e., CaCl2 concentration, urea concentration and the pH. Their results revealed the formation of metal-carbonates by the Trichoderma species and carbonate fraction of As was found to be uplifted by 46% in the bioremediated site as compared to the control (35.5%). The X-ray diffraction indicated the potential of calcite precipitate in bioremediating the As contaminated soil. They concluded that microbially induced calcite can have promising effects on the remediation of As from the contaminated sites.

Yeast is a unicellular fungus that can proliferate easily and are able to adapt to various environmental niches (Mukherjee and Sen 2015). They also exhibit the bioremediation capacity against certain contaminants (Khan et al. 2016; Ilyas and Rehman 2018). Bobrowicz et al. (1997) reported the presence of fragment of 4.2 kb on the chromosome XVI and its contribution in conferring resistance against sodium arsenate (7 mM). They further explained that in yeasts, three genes are present in a continuous manner (ACR1, ACR2 and ACR3) which exhibit resistance against arsenic compounds. Two proteins are present in the As-ATPase efflux pump namely ArsA and ArsB, in which ArsA possesses the catalytic activity and ArsB has inner membrane protein (Rosen et al. 1988). Similarly, another protein, ArsC displays reductase activity and transforms As (V) to As (III), which is then, released to the outer environment through As efflux pump (Sher and Rehman 2019). Verma et al. (2019) assessed the potential application of yeast as a plant growth promoting agent to stimulate rice growth. Under As stress, the transgenic yeast species Saccharomyces cerevisiae harboring the WaarsM gene demonstrated an increased As methylation followed by volatilization activity under As stress. Moreover, the rice seedling coated with yeast showed high seedling vigor index in comparison with the control. They concluded that As volatilization form the contaminated sites is possible with the help of yeast and it could be effectively used as an instrumental agent for reducing As contents from the soil water system.

19.2.2.2.3 Algal Bioremediation

Few reports are also available regarding the As methylation by algae (Jia et al. 2015) which uses several detoxification pathways for As (Upadhyay et al. 2018) and hence, convert As (III) into less toxic and mess mobile form As (V) (Jia et al. 2013). The cell wall of algae possesses several functional groups i.e., carbonyl, hydroxyl (-OH), carboxyl (-COOH), thiol (-SH) and amino which possess the tendency to adsorb metal(loid)s including the As oxyanions from water (Wang et al. 2015). Many algal species can cause a rapid absorption of As from the aqueous media and hence, plays a key role in its detoxification (Jiang et al. 2011). Among these species, red algae (Gracilaria, Porphyra and Ceramium), brown algae (Dictyopteris, Eisenia and Cystoseira), green algae (Ulva and Caulerpa) and seagrass (Zostera) have exhibited tremendous capacity to adsorb As with the maximum adsorption capacity (1.3 ± 0.1 mg g−1) achieved by sea grass and red alga (Ceramium; Pennesi et al. 2012). In algae, the biotransformation of As starts with the uptake of As (V), which is then, reduced to As (III) followed by subsequent formation of methylated species (Wang et al. 2015). Earlier studies have reported about the phosphate independent uptake of As (V) by algae which further depicted that more As (V) uptake pathways prevail in algae in addition to As uptake via the phosphate channels (Duncan et al. 2014). The As transformation pathways in algae are influenced by different factors such as concentration and species of As, composition of the growth medium (Wurl et al. 2013), pH, temperature, Eh (Murray et al. 2003), duration of light exposure as well as intensity (Zhang et al. 2013) etc. Moreover, phosphate presence in water is of critical importance as it can also affect As uptake by algae. Algal mediated As sorption has a tremendous potential in As bioremediation in aquatic system due to its environment friendly nature and high removal efficiency (Hussain et al. 2021).

19.2.2.2.4 Phytobial Remediation

This approach uses the plant microbe interactions and assists the phytoremediation process and thereby, plays a critical role in the plant survival, growth and development under contaminated sites. It helps the plants by conferring stress resistance, favoring nutrient acquisition and supplying different phytohormones (Kaur et al. 2018). Remediation by exploiting the plant–microbe interactions for As removal has been extensively reported in the literature (Liang et al. 2019; Irshad et al. 2020). Few reports are available where the As remediation by the plants was increased in presence of transgenic bacteria that were harboring As degradation genes. However, this treatment still faces certain limitations in lieu of the efficacious application of transgenic bacterial strains (Liu et al. 2019). Irshad et al. (2020) investigated the symbiotic relationship between indigenous Bacillus specie and As-hyperaccumulator named Vallisneria denseserrulata to remove As. They found that the native bacterial specie was able to excrete higher quantities of EPS, siderophore and indole acetic acid (IAA) and thereby, reduced As toxicity to the plants. The synergetic relationship exhibited more As uptake and removal potential. They further reported that the As detoxification was attributed to the presence of various carboxyl, amide, hydroxyl and thiol groups as well as the prevalence of an As metabolizing process in the plant leaves.

19.2.2.2.5 Phytosuction Separation

Phytosuction separation (PS-S) is a relatively modern technique for reducing the heavy metals or metalloids concentration from the soil. Current method involves two soil types: a planting soil without any metal(loid) followed by a heavy metal(loid) contaminated base soil present in the bottom and these soils are separated by an immobilizing material. In the As remediation study, ferrihydrite has been used as an immobilization material. Plants are grown on the planted soil and irrigation water is applied as recommended. In response to the applied irrigation, plant roots suck the water which then take up the dissolved heavy metal(loid) present in the bottom soil due to water suction effect of the roots, and the contaminant is held by the above lying immobilization material (Katoh et al. 2016). Arita and Katoh (2018) used ferrihydrite as an immobilization material and applied in the As contaminated soil. They compared the efficiency of PS-S system with that of phytoextraction (PE). Their results indicated that PS-S system holds greater tendency to remove As than PE and its efficiency increases with an increase in the depth of the soil (even less than 0.5 cm soil layer), indicating the efficacy of PS-S system in the shallow soil layers. Nearly 38% of the As was removed from the soil which was observed to be 54% more than PE technique. Positive growth regulating microbes might improve the effectiveness of this technique by facilitating the supply of proper nutrients towards the plants. It has also been shown that the metal(loids) existing particularly in the form of oxyanions are more prone to be removed by the PS-S system as compared to those existing as cations. This technique has also shown promising results during the phytoremediation of lead (Pb) and antimony (Sb) with removal efficiencies ranging from 8–25 and 69–533 times respectively as compared to the phytoextraction process. Main factors during the smooth running of the OS-S system are mobility of the target metal(loids) under consideration.

19.2.2.2.6 Arsenotrophy

Despite its toxicity, As is also used by several microbial species to harvest their metabolic energy needs rather then its detoxification. Their metabolic activities comprise As oxidation as well as reduction via electron transfer for using it as food or respiration (Amend et al. 2014). The process is termed as arsenotrophy (Oremlan et al. 2009) and the related microbes are termed as arsenotrophs (Stuckey et al. 2015) which are known for their tremendous role in the biogeochemical cycling of As. During the arsenotrophy process, microbes solubilize the As from sediments followed by the reductive transformation of As (V) to As (III). The exposition of microbial processes determines their effectiveness to remove As from the contaminated sites. They are known to stimulate the oxidation of different organic compounds such as lactate, acetate, malate, pyruvate, ethanol and glycerol by reducing As in anaerobic conditions (Stolz and Oremland 1999; Anand et al. 2022). Moreover, arsenotrophy has been termed as redox reactions of As related to the phototrophic or respiratory processes via the transfer of electrons to/from As for energy (Silver and Phung 2005). Three different types of enzymes are responsible for catalyzing this process in prokaryotes viz. AioA, ArxA and ArrA (Andres and Bertin 2016). Most of the arsenotrophic pathways have been identified in chemoautotrophs however, anoxygenic photosynthesis, a light dependent pathway involving As (III) as an electron donor was first identified in Ectothiorhodospira species (Budinoff and Hollibaugh 2008). Various researchers have reported regarding the microbially mediated arsenotrophic reactions of As transformation. Uhrynowski et al. (2017) used an indigenous arsenotrophic bacterium Aeromonas sp. and investigated its transformation potential for As. They reported that Aeromonas is a facultative anaerobe which can utilize arsenate as a substrate to carry out its respiration and lactate, citrate and acetate as electron donor. The introduced strain exhibited considerable resistance against As and other heavy metals and the As reduction was observed to be initiated after 24 h. The strain exhibited increased production of biofilm which was found to be responsible for the entrapment of dissolved arsenic species as well as other toxic elements. In addition, several studies have evidenced about the enrichment of As contaminated groundwater with numerous arsenotrophic bacteria (Sanyal et al. 2016) Table 19.2.

Table 19.2 Summary of different bioremediation techniques for As removal from soil–water system
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19.3 Concluding Remarks

The problem of arsenic contamination has dramatically increased in the recent times owing to the enhanced global pollution. Different limitations related to the conventional physicochemical approaches imply that in the present times, bioremediation approaches are the most widely accepted, eco-friendly and sustainable techniques to tackle As contamination. With advancements and further experimentations, more perfection and practical outcomes are expected. However, few things need to be addressed to proceed with clear understandings. More comprehensive knowledge is required to clearly understand the mechanisms of bacterial mediated As oxidation. Advancements in the use of transgenic organisms (plants or microbes) can discover new interventions in using As for the bio-energy systems and microbial fuel cells applications. Moreover, the fate of the harvested plants after the successful completion of phytoremediation (phytoextraction) process is still a challenge. Pyrolysis, bio-gasification and composting could assist in this regard. In addition, cost–benefit analysis is a pre-requisite for the successful implementation of the bioremediation process on a larger scale.