Impact of mineral particles on the fate of tiny plastic debris in the riverine environment

Choudhary, Aniket Dnyaneshwar (2025) Impact of mineral particles on the fate of tiny plastic debris in the riverine environment. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Aniket Dnyaneshwar Choudhary (19IP019)) 19IP019.pdf - Submitted Version Restricted to Repository staff only Download (9MB)

Abstract

Globally growing plastic production and its mismanagement are significant concerns due to its high durability, versatility, and robustness, leading to massive plastic accumulation in the riverine and subsurface environments. The tremendous plastic waste load in the environment around the globe has been reported as the novel emerging contaminants in different sizes i.e., microplastics (MPs, <5 mm) or nanoplastics (NPs, <1μm) are omnipresent and currently a critical topic of discussion considering their ecological consequences. However, micro-nanoplastics (MNPs) distribution, bioavailability, fate and transport in the environment remain understudied. The current thesis offers a comprehensive overview of MNPs in the aquatic environments, starting with their assessment and characterisation in freshwater systems. Further, to better understand the MNPs accumulation in the environment, it is imperative to advance our knowledge of MNPs environmental fate and how it is linked with existing abundant minerals and varying geochemical conditions. Keeping this in mind, we investigated the interaction of NPs with abundantly occurring mineral weathering sequences under varying environmental parameters. Additionally, considering realistic scenario where minerals are often exists as organo-mineral complexes (OMCs), we have thoroughly studied OMCs interaction with NPs, providing detailed insights on fate and transport of NPs in the environments. We have adopted an interdisciplinary approach to studying NPs to bring novel insight into their interaction with the aquatic environmental components. Rivers, which serve as essential links between terrestrial and marine ecosystems, are increasingly burdened by MNPs contamination, which seriously threatens aquatic species and human health. The escalating problem of plastic pollution in India prompted us to investigate the MNPs abundance along the complete stretch of River Godavari, the longest river system in peninsular India. The first objective represents a first effort to estimate MPs abundance in the Godavari River's water, sediments and fish. Polymer and ecological risk indices suggested that most sampling locations fall in the extremely high-risk category. Examined MPs in edible (flesh+skin) and inedible parts (GIT and gills) of seven different fish species showed a higher average MPs abundance in edible parts than gills and GIT. This suggests that removing gills and GIT from fish doesn’t eliminate the consumer’s risk of MPs intake. Current work highlights the extent of MNPs accumulation in riverine systems, providing essential data on the ecological risk associated with the MNPs, further study demands detailed understanding of MNPs behaviour in aqueous environments to delineate their fate and enhanced toxicity. Therefore, a detailed understanding of NPs interaction with environmental colloids is of extreme scientific and societal significance. Further objectives of the thesis focused on NPs interaction with minerals of the freshwater weathering sequence with varying geochemical parameters, which is crucial for understanding major components that govern the fate and transport of NPs in the freshwater water system. We created different weathering sequences of the most abundant silicate (Feldspar- Gibbsite- Kaolinite), iron oxide minerals (Magnetite- Maghemite- Hematite), and Manganese minerals (Manganite- Pyrolusite- Bixbyite) and observed their interaction with NPs and transport behavior under varying environmental conditions. Mechanistic insights highlighting relevant environmental scenarios were gained through bimodal charge distribution analysis, sedimentation kinetics, batch and column retention tests and detailed spectroscopic characterisation. Results revealed drastic alteration in NPs interactions with mineral colloids as they weather and transform to new secondary minerals, leading to varied retention and transport in subsurface columns. The study provides a fundamental base and understanding of the impact of mineral colloids weathering on NPs fate and environmental transport. Colloidal mineral particles are omnipresent and often associated with organic matter and form organo-mineral complexes (OMCs) exhibiting different reactivity than their pure mineral phase. In the final objective, we studied the influence of ferrihydrite and its weathered product, goethite and their corresponding organo-mineral complexes (OMCs), i.e., organo-ferrihydrite and organo-goethite, on NPs fate and transport under varying environmental conditions. Results revealed drastic alteration in NPs interactions with minerals and compared to their corresponding organo-mineral complexes, leading to varied NPs retention and transport in aqueous and subsurface media. The study provides a fundamental base and understanding on the impact of minerals and OMCs on NPs fate and transport in the environment.

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