Due to its low cost, durability, and versatility, the invention of plastic revolutionized the entire globe. Plastics are engineered polymers that are used in a wide range of human applications and have become an indispensable element of our daily life (Hammer et al., 2012). Since the early part of use, the contamination of our environment by micro plastic has also begun. Studies on plastic pollution in the marine environment began in the late 1970s (Carpenter and Smith, 1972); since then, research on plastic contamination has increased, with major studies focusing on aquatic environments such as lakes, rivers, and deep-sea sediments (Carpenter and Smith, 1972; Cózar et al., 2014; Eerkes-Medrano et al., 2015).
Plastics which are less than 5mm are termed a micro plastic (Thompson et al., 2009; NOAA 2015) categorized into primary and secondary based on their origin. Primary micro plastics are intently manufactured in the size of less than 5mm have a varied use in the field of medicine, textile and cosmetic industry (Fendall and Sewell, 2009; Eriksen et al., 2013; Bergmann, et al., 2015).
Secondary micro plastics are produced as a result of the degradation of larger plastics (Thompson et al., 2009), and both types enter the ecosystem solely through domestic and industrial discharge. Due to prolonged exposure to sunlight and climate, micro plastic fibres originating from land-based activities disintegrated quickly (Cooper and Corcoran, 2010). Plastics' low recycling rate contributes significantly to the emergence of micro plastics. Micro plastics pose a risk to the aquatic environment because of their long residence duration, the possibility of biota ingesting them, and the emission of harmful components during degradation.
Microplastics enter the food chain of higher organisms through phytoplankton in both the marine and fresh water environments (Moore et al. 2002). Micro plastic has made its way into soils, groundwater via percolation, rivers via discharge, and fish and molluscan tissues due to its tiny size (A.L.Lusher et al., 2012; Anika Ballent, et al., 2016; Naidu et al., 2018). According to a Central Pollution Control Board (CPCB) survey conducted in 2015 across 60 cities in India, 15,342 tonnes of plastic waste is generated per day, of which 60% is recycled and the rest is landfilled (Aryan et al., 2018).
The factors affecting the distribution of the micro plastics are density, shape (fibers, fragments and pellets), size, (Eerkes-Medrano et al., 2015) wind, geostrophic circulation and water flux (Law et al., 2010; Ballent et al., 2012; Turra et al., 2014). The aim of this research is to assess the distribution of microplastics in surface water and sediment in Chennai's Cooum River.
Cooum is a non-perennial river that originates at a dam in Kesavaram, which is about 48 kilometers west of Chennai. During the monsoon season, the excess water from the cooum tank is the primary source of water in that river. Agriculture dominated the banks of the Cooum in its upper reaches, but as it neared the Vanagram, the river began to be polluted by the discharge of domestic and industrial waste and the flow of the river is almost nil in the city limits. It flows through Kanchipuram, Thiruvallur, and Chennai districts for approximately 68 kilometers before entering the sea, Bay of Bengal.