Emerging contaminants in Multi-Environmental Compartments: Sources, Distribution patterns, and association with Heavy Metals

Abstract

Microplastic (MP) contamination in freshwater systems is a prevalent and persistent environmental issue, yet their occurrence and distribution remain poorly understood. This thesis examines the abundance of MPs and the factors controlling their distribution across multiple environmental compartments, including sediment, soil, surface water, and groundwater systems in the Indian subcontinent. Furthermore, the thesis explores the relationship between heavy metals and the distribution of MPs, as well as their potential interactions. The results indicate a widespread occurrence of MP pollution across all environmental media. Five main types of MPs were identified: beads/pellets, fragments, fibers, foams, and films, with beads being the predominant type. Polypropylene, polyethylene, and polystyrene were the dominant constituents of the observed MPs. The variability in MP abundance at sampling sites appears to result from factors such as the proximity of industrial establishments and human habitation, while the influence of environmental factors (e.g., water depth, grain size, total organic carbon, etc.) on MP distribution appears to be limited. Although heavy metals exhibited correlations with each other, there was a weak association between their levels and the presence of MPs in freshwater systems. SEM-EDS analysis revealed the presence of toxic elements such as Hg, Zn, Pb, Cr, Cd, Ni, and Cu on the surfaces of MPs. Additionally, the correlation between MPs and phthalates suggests the potential use of phthalates as tracers for MPs in freshwater systems. Overall, this thesis expands the baseline characterization of MPs in freshwater systems and enhances our understanding of the potential sources and factors influencing MP distribution.