1.1 Introduction
Over the decades, the ever-growing demand for agricultural, livestock, medical, and industrial products resulted in the overconsumption of water resources leading to scarcity and pollution of the water bodies. Approximately 80,000 synthetic chemicals recognized as “emerging contaminants” (since 1990) (Naidu et al., 2016) are discharged into the natural surroundings annually as a result of the wastewater release (Lapworth et al., 2012; Stuart and Lapworth, 2013; Kumar et al., 2021). “Emerging contaminants” (ECs) are a group of synthetic and natural organic chemicals that are currently not incorporated in conventional monitoring plans at the European level and can be candidates for future regulation, depending on the investigation on their (eco)toxicity, potential health consequences, and their existence in the multiple environmental compartments (Rosenfeld and Feng, 2011; Norman, 2012). Over 1,036 compounds have been distinguished as ECs by the NORMAN network and are classified into 30 classes based on their origin and kind (Dey et al., 2019). Prominent categories that are usually identified in aquifers are pharmaceuticals and personal care products (PPCPs), lifestyle compounds, plasticizers (bisphenol A (BPA)), industrial solvents, flame retardants, surfactants, benzothiazoles, polyaromatic hydrocarbon (PAHs), pesticides, food additives, and transformed products of parent organic chemical (Menon et al., 2020; Mohapatra et al., 2018, 2021; Priyanka and Mohapatra, 2020; Kumar et al., 2019 a,b). They are detected in studies at concentrations varying from μg/L to ng/L in aquatic environments, and the degree of contamination depends on the properties of both contaminants and aquifers, and the pathway through which contaminants reach groundwater. Many of these organic contaminants and their by-products are persistent and bio-accumulative in nature (Stefanakis and Becker, 2015). This chapter discusses the regularly occurring ECs in groundwater from the year 2015 across the globe and identifying the areas with the highest concentrations. Their sources, pathways, fate, and condition of the aquifer that results in contamination are reviewed. Based on this information risk assessment, methods are reported from different studies. Still, many unknown organic compounds are being discharged, and fate and toxicological studies of the identified ones are poorly understood.
1.2 Sources and pathways
Based on the conventional classification, sources of ECs are described as point or non-point sources. Point sources are characterized as the discernible, confined point that can be spatially isolated, identified like the plume with the highest concentration near the source and decreasing as drifting further away (Thomaidis et al., 2012). Point sources include wastewater discharge from different industries (such as tanneries, paper, and pulp industries, steel plants, food processing industries, industrial-scale animal feeding operations, manufacturing factories, pharmaceutical industrial), municipal wastewater treatment plant and combined sewage-stormwater overflow, healthcare facilities for animals and humans (veterinary hospitals, nursing homes, hospitals), domestic sewage, mining activities, waste disposal sites (such as landfill settings, agricultural waste pools, and industrial confinements), aquacultural activities, livestock farms, buried septic tanks, and artificial recharge from undertreated water (Lapworth et al., 2012; Stefanakis and Becker, 2015; Pal et al., 2014). Non-point sources refer to pollution from indistinct and diffused sources occurring over a larger geographical area and are difficult to demarcate. Examples include stormwater runoff; surface runoff from agrarian land, urban areas, and roads; use of biosolids and manure to the soil; diffuse aeolian deposition; leakage from urban sewer settings; and flash floods eroding landfill sites (Stuart et al., 2012; Lapworth et al., 2012). Diffuse sources are difficult to trace back to the polluter due to lower loading of contaminants compared to point sources and are more prone to attenuation (Lapworth et al., 2012). ECs introduced from different sources are summarized in Table 1.1.
Table 1.1 Different sources of ECs for groundwater | Type of emerging contaminant | Sources | References |
| Pharmaceuticals | Discarding unused and expired medicine in drainage systems and at landfill sites releases antibiotics and inflammatory drugs. Hospitals wastewater discharge of iodinated X-ray contrast media and from human excretion via waste water treatment plant (WWTP) effluents. Animal feeding operations (CAFOs) and aquaculture produce contaminants and biosolids applied to cultivated field such as veterinary antibiotics, hormones. Artificial recharge and septic tanks release ibuprofen and paracetamol. | Lapworth et al. (2012), Stuart and Lapworth (2013), Pal et al. (2014), Naidu et al. (2016) |
| Personal care products (PCPs) | Perfumes, cosmetic soaps, and lotions release musk, and fragrances like galaxolide, tonalide, nitro musk, phthalates, etc. via WWTP effluents. UV filters like benzophenone, antimicrobial agents (triclosan), and preservatives (parabens and derivatives) are released from sunscreens, moisturizers, lipsticks, and haircare products. Mosquito repellants (only <20% is absorbed by the skin) contaminate bathing water and are discharged via WWTP effluents. | |
| Lifestyle compound and food additives | Caffeine and nicotine from sewage effluent. Food additives like artificial sweeteners (like aspartame saccharine, cyclamate, and sucralose) are discharged directly from food industries, domestic sewage, livestock raising, and excreted unaltered. | |
| Industrial compounds | Perfluorinated compounds (PFCs) used in chromium plating, aviation hydraulic fluid, photography industry, semiconductor industries, and firefighting foam released via wastewater discharge. Flame retardants, plasticizers, and solvents like polychlorinated alkanes (PCAs) from industries such as plastics and textiles, and surface finishes and coatings present in WWTP effluents, combustion, and the natural breakdown of the plastic. Polychlorinated naphthalenes (PCNs) are used as dielectric fluids, engine oil additives, electroplating masking compounds, wood preservatives, and dye production. Benzothiazoles employed for corrosion inhibition, herbicides, antialgal agents, in paper and pulp industry and azo dyes, chemotherapeutics and fungicides in lumber, and leather production release via WWTP. | Walter and Santillo (2006) Clarke and Smith (2011), Pal et al. (2014) |
| Quaternary ammonium compounds (QACs) | Household usage of QACs as cationic surfactant is the chief source that enters the WWTP. Also sourced from shampoos, toilet cleansers, soaps, shaving cream, baby wipes, sunscreens, lotions, sanitizing sprays, fabric softeners, disinfectants, and spermicidal jellies. | Clarke and Smith (2011) |
| Pesticides | Pesticides are introduced in water by agricultural runoff and from industrial manufacturing of pesticides, spraying of insecticides in urban households, and atmospheric deposition. | Stuart et al. (2012) Pal et al. (2014) |
Pathways include both direct and indirect passages of contamination in groundwater. Direct passages include leakages from point sources, permeation of chemicals applied to the soil and landfill sites, artificial recharge, and indirectly from groundwater-surface water (GW-SW) interaction. The route favored will depend upon the physicochemical properties of the contaminant in the environment, such as its solubility in water (Lapworth et al., 2012; Stuart et al., 2012). For example, plasticizers with low molecular weight have high mobility and easily diffuse to the environment (Yan et al., 2010). Organic manure widely used in agricultural fields liberates pharmaceutical residues, which may infiltrate and pollutes groundwater directly or indirectly through surface water contamination during runoff. The movement of contaminants occurs through the soil zone, the unsaturated zone, and the saturated zone in a well-entrenched way. Recharging activities through rainwater and roof runoff can also contaminate groundwater (Bucheli et al., 1998, Patel et al., 2019).
The presence of some compounds, i.e., carbamazepine, sulfamethoxazole, benzophenone, 5-methyl-1H-benzotriazole, N, N-diethyl-meta-toluamide (DEET), and tributyl phosphate, after soil-aquifer passage, suggests that these compounds can reach subsurface under recharge conditions (Mohapatra et al., 2021). Insufficient removal of estrogenic steroids during wastewater t...
