| Details: |
The unceasing release of plastic debris into the freshwater systems from different anthropogenic sources is a globally escalating problem due to its degradation into Microplastics (MP). MPs have caught the attention of the global scientific community due to their properties like the smaller size, high surface area to volume ratio and surface charge. These properties make MPs toxic and the potential vectors for co-contaminants like metal ions in the freshwater systems. The synergistic toxicological effects of both MPs and metal ions on many aquatic species are well known; hence, their quantitative and qualitative assessment in freshwater systems with remediation is requisite. In this study, MP distribution and characterization assessment was done across the Mahanadi River in Eastern central India. Significant number concentrations of the MPs were found across all the locations along the river, ranging from 337-1333 MP/m3, 17-69 MPs/Kg and 0.4-3 MPs/Fish, in sediment, water and fish samples, respectively. The prominent colours found in the samples from all locations were black and blue, with abundant sizes of <1 mm in all the sample types. The dominance of <1mm size fraction potentially indicated high weathering and disintegration of the large plastic debris. The presence of filament, fragment and film-shaped MPs profusely with Polypropylene (PP), Polyethylene (PE) and Polyethylene-terephthalate (PET) polymers in dominance potentially highlights the contamination from different anthropogenic sources. MP Pollution index studies revealed that all the sampling sites lie in polymer load index (PLI) Category I with <10 range concentrations. The Polymer Hazard and Polymer risk assessment studies indicated a high threat with calculated values for maximum locations in Risk category V. The MP concentrations measured from all sample types manifested an increased MP load towards the sink of the river. After completing, the assessment studies, we also explored the simultaneous removal of microplastics (different functionality and size) and metal ions (Ni2+, Cd2+, AsO43-, CrO42-) from water using nano-Zerovalent iron-loaded Biochar synthesized from sugarcane bagasse. Column and batch sorption experiments demonstrated an efficient removal of carboxylate-modified Nanoplastics (NPs) of size 0.5 µm (〖 q〗_max = 90.3 mg/g), followed by Cd2+ and CrO42- ions (〖 q〗_max=44.0 and 87.8 mg/g), respectively. The pseudo-second-order kinetic and Sip’s isotherm models are the best-fitted kinetic and isotherm models. The synthesized material worked efficiently in variable pH (4-8) and ionic strength (1-20 mM) with >90% removal. Electrostatic attraction, complexation and pore retention are the potential mechanisms for removing NPs. In contrast, reduction co-precipitation along with electrostatic attraction are the potential mechanisms for removing metal ions. The synthesized material successfully removed the target contaminants simultaneously from different types of water (Textile effluent, Wastewater and River water) with significant efficacy, reflecting its broad applicability in realistic environmental conditions, including freshwater ecosystems. |