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Assessment of Weathering of Microplastics: A Case Study on River Kadambrayar
Summary
A multi-year study of the Kadambrayar River near a waste dump in Kerala, India found heavily weathered microplastics with cracked, pitted surfaces, confirming long residence times and ongoing fragmentation into even smaller nanoplastic particles. Weathered microplastics are more chemically reactive and harder to detect, meaning pollution near dumping sites poses a compounding and evolving risk to nearby water supplies.
Microplastic pollution in aquatic environments is a growing concern with serious implications on human health. This study investigates the weathering of microplastics in the Kadambrayar River, located near the Brahmapuram waste dumping site in Kochi, Kerala. Water samples were collected from various locations along the river Kadambrayar during pre-monsoon season and post-monsoon season from 2019 to 2022. Sediment samples were collected from 15 stations and topsoil samples were collected from 18 locations in the vicinity of the river. It was observed that the highest number of microplastics in both the topsoil and sediment samples were near the open dumping site. The major polymers identified include Polyethylene, Polypropylene, Polystyrene, Synthetic fibres, and the prominent colour is white or colourless. Analysing the microplastic, it was found that the residence time of these microplastics was high and the surface had cracks and degradation, which shows that the microplastic had undergone weathering. The SEM analysis of the weathered microplastics showed the presence of cracks and pits on the surface, which indicated that the microplastics had a high residence time. To assess the weathering of microplastics, both natural and UV-C exposure experiments were carried out. The results of the study indicate that the weathered microplastics also retained their size (3–4 mm) and have the affinity to get degraded into smaller nano particles. In the experiments, the physical degradation was more prominent in Nylon than Polyethylene and Polypropylene. However, even with minor changes, the peaks in the spectra had changes and shifts. By oxidation and hydrolysis process, the chemical weathering was observed. The results indicate that weathering of microplastics in the aquatic environment is a slow process, and that the microplastics has a high residence time in water, which further increases the weathering exposure. The study thus indicates that the Brahmapuram dumping site is a significant source of microplastic pollution in the Kadambrayar River and the high residence time in sediment along with the ability of microplastics to act as carriers to pollutants like heavy metals raises serious concerns.