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Environmental contaminants are defined as substances introduced into the environment, either naturally or anthropogenically, that pose potentialharm to living organisms and ecosystems (Masindi and Muedi, 2018).These contaminants include a diverse range of pollutants, such as chemicalagents, biological contaminants and physical pollutants (Ahmed et al.,2021). Understanding these contaminants and their toxicity is of paramountimportance, given their profound implications on human health, biodiversityand the overall functioning of ecosystems (Samuel et al., 2023).Environmental contaminations are pervasive in nature and originated fromdiverse sources. Industrial activities are major contributors, releasing heavymetals, organic solvents, and particulate matter into air, water and soil(Williams, 2019). Similarly, agricultural practices contribute to contaminationthrough excessive use of fertilizers and pesticides, which often runoff intoaquatic systems, causing eutrophication and harming aquatic life (Zahoor and Mushtaq, 2023). Urbanization and improper waste management have alsointensified the problem with plastics and emerging contaminants finding theirway into ecosystems (Singh et al., 2022). Even natural events like volcaniceruptions and forest fires contribute to environmental contamination, thoughtheir impacts are often localized and episodic compared to the persistent andwidespread pollution caused by human activities (Ernst, 2012).The study of environmental contaminants and their toxic effects is of vitalimportance for several reasons in today’s context of escalating global pollution(Hussain and Reza, 2023). First, it provides insights into the health risks posedto humans and wildlife (Pereira et al., 2015). Many contaminants, such as lead,mercury and polychlorinated biphenyls (PCBs), are known to have chronic andacute toxic effects on biological systems, affecting neurological, reproductivand immune functions (Priyadarshanee et al., 2022). These substances interactwith biological systems in complex ways, often leading to adverse outcomessuch as bioaccumulation, oxidative stress, endocrine disruption and ecologicalimbalances (Satkar et al., 2024). Heavy metals like lead and mercury are known to accumulate in organisms and disrupt critical biological functions,while synthetic chemicals like bisphenol A (BPA) can interfere with hormonalsystems, resulting in reproductive and developmental issues (Pan et al., 2024).Such impacts underscore the need to understand how these substances interactwith living organisms, identify their exposure thresholds and mechanisms oftoxicity to formulate strategies for risk assessment and mitigation (Kumar andSingh, 2023).

1. Introduction Bioremediation is a process that utilizes biological agents, such asmicroorganisms, to eliminate pollutants, making it a natural and efficientmethod for environmental cleanup. This approach is considered cost-effectiveas it transforms harmful pollutants into less toxic substances through microbialdegradation or detoxification. Currently, many developing nations areprioritizing industrial growth, urbanization, and the use of agrochemicals inagriculture, which has heightened the importance of bioremediation and drawnsignificant attention to this practice. As a sustainable solution, bioremediationoffers a way to restore healthier ecosystems by removing pollutants from theenvironment (Fig. 1).

1. Introduction One of the foremost environmental challenges the world faces today is airpollution. As industrialisation, urbanisation, and transportation continueunabated, harmful substance levels in the atmosphere have becomealarmingly high (Thanvisitthpon et al., 2024). This general contamination inthe air is not just a serious risk to humanity but also harms ecosystems whilcontributing to global climate change. Controlling airpollution has becomea critical necessity at this stage, with the need for innovative solutions inthis respect. Bioremediation is one of the innovative solutions, where certainmicroorganisms break down or neutralise pollutants in the air.

1. Introduction Agro-industrial waste plays a crucial role in bioremediation, the process of usingbiological organisms to remove or neutralize pollutants from contaminatedenvironments (Garg, 2020). With the rise of industrialization and agriculturalactivities, there’s a corresponding increase in waste production. However,these waste materials, often rich in organic compounds, can be repurposedas valuable resources as mentioned in scientific studies (Sahota and Sharma,2020; Yadav et al., 2022).

1. Introduction 1.1. The Growing Problem of Pesticide Pollution Pesticides are used in very great amounts in agricultural production for theprotection of crops against pests, diseases and weeds. They are also veryinstrumental in boosting agricultural productivity by ensuring food securityand preventing losses that may be caused by outbreaks of pests (Popp et al.,2013). However, the extensive use of pesticides has generally resulted in hugeenvironmental concerns. Improperlymanaged pesticide residues may remainin soil, water and even air for many years and create severe ecological andhealth hazards in the long run (Zhang et al., 2024). This widespread existenceof pesticides in the environment has raised a serious alarm concerning theiradverse impacts on biodiversity, soil fertility and quality of water, furtherbioaccumulation in the food chain that affects wildlife and human populations(Aktar et al., 2009).

1. Introduction Bioremediation is an environmentally friendly process that uses numerousdifferent microbes (e.g., fungi & bacteria), green plants, or combinations of them to weaken and detoxify dangerous pollutants in a sequential orsuccessional manner. The pollutant composites are converted by biologicalorganisms through a response that takes place as part of their metabolicprocesses. They convert poisonous pollutants into carbon dioxide (CO2) andwater (H2O), microbial biomass, and other products that are less poisonous.The organic wastes are biologically degraded under controlled, harmless, andsafe condition into inoffensive products below the admissible limits establishedby supervisory authorities.

1. Introduction Metals pollution in water particularly in wastewater has become a center ofconcern due to social changes such as industrialization and urban development(Blaszczak-Boxe et al., 2023). It is in this context that most of the conventionalwastewater treatment fails to remove the heavy metals in question satisfactorilyand that there is a pressing need for new ideas that would be sustainable. Thischapter aims to discuss algal bioremediation as an environmentally suitableprocess for the decontamination of wastewater containing toxic metals.

1. Introduction The world’s ecosystem is facing significant challenges because of risingpopulations, more urbanization, and industrialization (Juwarkar et al.,2014). Significant environmental contamination has been caused by moderncivilizations, industrialization, population increase, intensive agriculturalpractices, human activities, and technological advancement (Lalevic et al.,2016).

1. Introduction In recent decades, environmental contamination has emerged as a seriousthreat to our modern society. The relentless growth of urbanization andindustrialization leads to the ever-increasing production of hazardouschemicals. Safe disposal of these hazardous materials is crucial, as releasingthem into an already strained environment has severe consequences. Theexponential rise in human activity is directly related to the alarming risein local and global pollution levels, which severely disturbs the balance ofecosystems. Industrial activities, in particular, are a major source of highlyhazardous chemicals such as dyes, pigments, and aromatic compounds,which pose a serious threat to the environment. In India, the textile industry, amajor force driving the country’s economic growth, also ranks asthsecondlargestpolluter. The printing, finishing, and dyeing processes used in textileproduction generate significant waste (Dubey et al., 2018). Dyes, a majorsource of pollution in this industry, are syntheticand complex in structure. Thiscomplexity makes them poorly soluble in water, hindering biodegradation andposing a long-term environmental concern. The global textile industry utilizesa wide range of dyes, with estimates indicating over 100,000 commerciallyavailable options. The worldwide production of these dyes is estimated to be700,000 tons per year (Al-Tohamy et al., 2020). However, dye contaminationis a major challenge in this industry. Studies indicate that during synthesisand dyeing processes, a significant portion, ranging from 10% to 15% of thetotal dyestuffs used ends up released into global water bodies (Leal et al.,2020). A significant portion of textile dyes, ranging from 2% to 20%, aredirectly released into water reservoirs through wastewater effluents. This is

1. Introduction Dyes are compounds after addition to a substrate, for a moment give it a colorthrough a process that modifies the colored substance’s crystal structure (Bafanaet al., 2011). Such varieties of compounds with significant coloring capacityare widely employed in the textile, pharmaceutical, food, photographic, andpaper industries (Zollinger et al., 1987). Dyes can adhere to suitable surfacesthrough methods such as dissolving, forming covalent bonds, complexing withsalts or metals, physically adsorbing, or being mechanically retained (Kirkand Othmer, 2004). The chemical structure and application of dyes determine their classification. The dye color is produced by a collection of atoms calledchromophores. Chromophore centres, which are responsible for color, consistof various functional groups like azo, anthraquinone,methine, nitro, arylmethane, carbonyl, and others. Additionally, substituents that either donateor withdraw electrons to enhance or create the color of these chromophoresare called auxochromes. Common examples of auxochromes include amine,carboxyl, sulfonate, and hydroxyl groups. There are three methods for dyingtextile materials: batch, continuous, and semi-continuous. Thekind of materialincluding yarn, fabric, fiber, clothing, and fabric structure as well as the generalfiber size of the dye lot, type, and quality standards of the dyed fabric, all playa role in determining the dyeing method used. Among these techniques, theprocess called the batch procedure is the most frequently employed for dyeingtextile materials. (Ogugbue et al., 2011).

1. Introduction Oil spills are defined as the unintentional release of liquid petroleum hydrocarbons into the environment, predominantly impacting marine ecosystems. This form of pollution, often caused by human activities, can also occur onterrestrial landscapes. Spills typically result from the discharge of crude oilfrom sources such as tankers, offshore platforms, drilling rigs, and wells, aswell as from refined petroleum products like gasoline and diesel (Smith etal., 2019). While such incidents are primarily accidental, they may arise fromvarious circumstances, including inadequate storage or poor maintenance,leading tocontainerleaks. Historically, one of the earliest documented oil spillsoccurred in 1907 in Batum, a region then part of the Russian Empire (moderndayBatumi, Georgia). This incident, involving a collision between an oil-ladenship and another vessel in the Black Sea, marked the beginning of recorded oilspill events, though historical records from that time remain limited (Johnsonet al., 2021). The consequences of oil spills are profound, affecting both theenvironment and the economy. On the ocean’s surface, oil disrupts aquaticecosystems by blocking sunlight penetration and depleting dissolved oxygenlevels, which are vital for marine life. Crude oil compromises the insulating andwaterproofing properties of fur and feathers, leading to hypothermia and deathin oil-coated birds and marine mammals. Additionally, ingesting oil can causeseveretoxicity, while damage to habitats and reproductive systems often delaysthe long-term recovery of affected species. Coastal vegetation, particularly inecosystems such as saltwater marshes and mangroves, is also highly vulnerable

1. Introduction Water is the most essential resource for life, supporting the survival of allliving beings, including humans, and playing a crucial role in food productionand economic progress. Currently, many cities around theworld are facingsignificant water shortages. About 40 % of global food production dependson irrigation, and countless industrial operations rely heavily on water. Theavailability and quality of water, whether surface or groundwater, have amajor impact on environmental health, economic development, and societagrowth. Human activities like urban expansion, population increase, industrialoutput, and climate shifts are causing a decline in water quality. As nationsdevelop, industrial activities increasingly lead to the pollution of watersources, resulting in negative consequences such as widespread disease and diminished beauty of water bodies. This pollution is a significant threat toboth the planet and its inhabitants. Higher temperatures are interfering with themetabolic processes of aquatic life, while changes in water pH create unstableconditions. Additionally, increased cloudiness in water reduces oxygen levels,affecting deep-water species and contributing to health issues for both animalsand humans. Polluted water also hinders growth and development in allliving organisms Haldar et al., 2015 and Arif et al., 2020. A study conductedby Halder et al. (2015) highlighted severe health challenges faced bylocalcommunities due to pollution in the Turag River, Dhaka, caused by thedischarge of untreated wastewater into the river. It was revealed that elevatedpH levels in the water, resulting from the use ofcaustic chemicals such assoda ash and caustic soda in industrial processes, were associated with skinirritation and sores. Dietary exposure to polluted crops and fish was found to contribute to stomach ailments, including gastric ulcers. Concerns wereraised about potential groundwater contamination through the infiltration ofindustrial waste. Microbial contamination was identified as a likely cause ofdiarrhoea and dysentery. The use of river water for bathing and laundry wasobserved to facilitate the spread of waterborne diseases. Outbreaks of yellow fever, cholera, dengue, malaria, and other epidemics were noted as prevalent inthe area. Respiratory problems and foul odours were attributed to air pollutioncaused by industrial discharge. Maternal and child health in riverbank slumsfound to be vulnerable, emphasizing the urgent need for interventions to addressthese public health concerns.Wastewater produced by industries, agriculture,and domestic activities contains high levels of nutrients, heavy metals, andchemicals, which harm the environment by polluting land, air, and water,

1. Introduction Pharmaceutical pollution has emerged as a significant global concern, raising alarms about its potential impacts on ecosystems and human health. The journey of pharmaceutical compounds from their point of use to contamination of water bodies reveals a complex and interconnected web of anthropogenic activities. From manufacturing plants to individual households, these pollutants persistently infiltrate aquatic systems, creating a growing

1. Introduction Since plastic was discovered, global plastic production for industrial scale usages has grown exponentially, causing a tremendous increase in plastic waste from a few tons in the 1950's to almost 400 million tons in 2018 (Syberg et al. 2021). Plastic is non-biodegradable and ubiquitous. Environmental degradation of plastic operates through a mechanism ofphysical fragmentation, photodegradation and microbial degradation (Wright et al., 2020), resulting in fragmentation of larger plastics into smaller plasticparticles, also called microplastics and nanoplastics (MNPs). These debris areserious environmental threats (Hartmann et al., 2019).

1. Introduction The term “plastic” is derived from the Greek word “Plasticos" whichmeans to be capable of molding into various sizes and shapes. Daily usedsynthetic plastics are categorized based on their physical and chemicalproperties, such as thermoplastic and thermosetting. (i) Thermoplastics: Astheir names suggest, thermoplastic polymers melt and turn into a plastic orrubbery state when exposed to heat. They have various numbers of polymericchains and are the most widely used plastics in day-to-day life. Examples ofthermoplastics are Polystyrene(PS), Polyvinylchloride (PVC), Polypropylene(PP), Polyethylene Terephthalate (PET), Polyethylene (PE) etc. (Massy,2017), (Sharma et al., 2017). (ii) Thermosetting polymers: As the namesuggests, they set or harden permanently when heated (Massy, 2017). Due totheirstrong crosslinked structure, they are non-recyclable polymers. Examplesinclude Polyurethanes(PUR), Phenol formaldehyde, Melamine formaldehyde,and Polyester Resin (PR) (Sharma et al., 2017). Different polymers and theirapplications are illustrated in Fig. 1.

1. Introduction Plastic pollution is a global problem that requires immediate attention due toits negative impacts on ecosystems, infrastructure, (MacLeod, M., Arp et al.2021) society, and the economy (Honingh, D. et al.,2020).In terms of absolute emissions, we find that South-eastern part of Asia, andSub-Saharan part of Africa possess the greatest quantities of plastic pollution,with India emitting the most (9.3 Mt year−1), or about one-fifth of the world'stotal plastic pollution (Joshua W. Cottom et al.). Future regulations pertaining to the manufacturer, usage, and getting ridof plastics will be influenced by the discussions for a worldwide plasticpollution treaty. A baseline with great resolution of waste flows and sourcesof plastic emissions will be useful for the stakeholders in order to identify pollution hotspots and the reasons behind them (United Nations EnvironmentProgramme). Furthermore, in addition to the production of municipal waste,the pandemic of coronavirus illness has raised the usage of disposable polymerproducts, masks, tissues, gloves, and additional personal protection equipment,which made the plastic pollution disaster worse (De-la-Torre GE et al., 2021).Wasted plastics can break down and fragment into three different sizes: 1mm to 5 mm big microplastics, 1 μm to 1 mm microplastics, and 1 nm to1 μm nano plastics, (Waller et al., 2017; De-la-Torre 2020; Atugoda et al., 2022) being exposed to ultraviolet (UV) light and other processes that causeenvironmental damage

1. Introduction to Biomedical Waste (BMW) The waste produced at different medical facilities, including hospitals,laboratories, research centers, mortuaries, and autopsy centers is considered asBiomedical Waste (BMW). Some of the BMW is hazardous whereas some arenon-hazardous in nature. Hazardous waste includes, Infectious, Pathological,Microbiological, Pharmaceutical, Chemical, Cytotoxic and Radioactive wastematerial as described by World Health Organization (Fig. 1). Healthcarepersonnel and the general public are at risk from physical, chemical, andmicrobiological effects of hazardous waste. On the other hand, the nonhazardousBMW which are not harmful, include packaging material made upof plastic & thermocol, cardboards, paper waste etc. (Capoor & Parida, 2021).

1. Introduction The environment and human health are seriously threatened by contaminants,both organic and inorganic, whose prevalence and persistence have beensteadily rising in recent years. In addition to propelling economic and scientificadvancement, the industrial revolutions of the 19th and 20th centuries have alsoled to widespread pollution (Wuana & Okieimen, 2011; Singh et al., 2013).Industrial activity has increased trace metal concentrations in the environment,with sediments acting as key sources and reservoirs for heavy metals. Thesemetals build up in soils and aquatic bodies as a result of scouring, erosion,rainfallleaching, wastewater discharge, and atmospheric deposition (AlonsoCastillo et al., 2013). Additionally, toxic contaminants like phenols, industrialeffluents, domestic wastewater, agricultural runoff, fly ash, fertilizers, andwaste from insecticides, pesticides, and pharmaceutical industries infiltratethe environment and food chain via mechanisms such as bioaccumulation,biomagnification, and bioconcentration (Arora & Bae, 2014; Azubuike et al.,2016).

1. Introduction It is the need of the hour that disposal of radioactive wastes be taken seriouslyand given appropriate attention. We house around one million gallons of liquidradioactive waste awaiting remediation at U.S. Department of Energy’s HanfordReservation alone (Parshley & McDermott, 2021). Not only the numbers are but the increasing demand of nuclear energy paves the way forgeneration of even more radioactive waste in future. The conventional methodshave certain limitations. Ion-exchange resins have reported to bedegradedunder high radiation and chemical precipitation has proven to be ineffectivein treating low concentration of radionuclides found in groundwater, posingrisk for centuries (Zhang & Liu, 2020). Remediation methods including soil