Seasonal distribution, source apportionment and risk exposure of microplastic contaminants along the Muttukadu backwater estuary, Tamil Nadu, India

Microplastics pose a severe threat to ecosystems, human health, and aquatic life, and are a major global contributor to water contamination. Despite this, the impact of microplastics in estuaries, where freshwater meets saltwater, has received insufficient attention. This study investigates the characteristics, distribution, risks, and sources of microplastics in the Muttukadu backwater estuary, a vital ecosystem in Tamil Nadu, India. The results show that the average abundance of microplastics in water (2.75 ± 1.80 items/m³) and sediments (3.15 ± 1.81 items/kg) was higher during the wet season (November) than the dry season (March) (1.95 ± 1.63 items/m³ in water and 2.55 ± 2.25 items/kg in sediments). The dominant forms of microplastics found were fragments (60 %) and fibers (30 %), primarily blue (27 %), black (25 %), and red (20 %) in color, and measuring 500–1000 μm in size (50 %). FTIR analysis identified five polymers, with Polyamide being the most abundant, followed by Polypropylene, Polyethylene, Polystyrene, and Low-Density Polyethylene. Source apportionment studies, combining morphological identification and chemical composition of microplastics, revealed single-use plastics, boating, and fishing practices as major contributors to microplastic contamination. An ecological risk index, assessing the potential harm of microplastics to the environment, indicated a medium to high-risk category for the estuarine environment. This study provides valuable insights and actionable recommendations for stakeholders to establish effective mitigation measures, including waste reduction policies, public awareness campaigns, and regular monitoring and cleanup efforts, ultimately reducing microplastic pollution and protecting the estuarine environment.