Pollutants and Water Management: Resources, Strategies and Scarcity, First Edition. Edited by Pardeep Singh, Rishikesh Singh, Vipin Kumar Singh, and Rahul Bhadouria. © 2021 John Wiley & Sons Ltd. Published 2021 by John Wiley & Sons Ltd. 210 9 The Fate of Organic Pollutants and Their Microbial Degradation in Water Bodies Gurudatta Singh, Anubhuti Singh, Priyanka Singh, Reetika Shukla, Shashank Tripathi, and Virendra Kumar Mishra Institute of Environment and Sustainable Development, Banaras Hindu University, Varanasi, Uttar Pradesh, India 9.1 Introduction The past century has witnessed a dramatic increase in the production of a range of artificial organic chemicals (xenobiotic), for example, pesticides, plastics of various grades, hydrocar- bons, soaps, and detergents. These compounds trigger a series of biochemical reactions in the environment that ultimately affects all biota. Most of these chemicals are of great con- cern from a human health perspective due to their persistence, bioaccumulation capacity, and high toxicity to wildlife and human (Xing et al. 2005). A wide spectrum of hazardous organic pollutants with diverse structures originates from anthropogenic sources and con- tinuously pollutes the environment (Alaee et al. 2003; Covaci et al. 2011; Sverko et al. 2008). These organic pollutants have a hazardous impact on various components of environments, which are mostly aquatic ecosystems, i.e. water bodies. Important organic contaminants include polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), hydrocarbons (HCs), pharmaceutical compounds, dioxins, organophosphates, biochemical oxygen demand (BOD), and organometallic compounds (Connell et al. 2009). The major sources of organic pollutants of water bodies can be identified, viz. industries, municipal sewage, and agricultural activities (Figure 9.1). Further, these sources can be classified as point sources such as industrial effluent outlets, effluent discharges from domestic sewage treatment plants, and nonpoint sources, which are characterized by discharges over huge areas due to diffusive sources. For example, pesticides used in agriculture can be widespread in low but potentially hazardous concentrations, causing chronic effects (Schwarzenbach et al. 2006). Biodegradation has been defined as “the biologically catalyzed reduction in complexity of chemicals.” This can lead to the conversion of carbon, nitrogen, phosphorous, sulfur, or other elements bound within the original organic chemical to inorganic products, this is called mineralization (Mattes et al. 2010). If a compound is biologi- cally transformed into products that are either not metabolized or metabolized very slowly,