Researchers from the Indian Institute of Science (IISc), Bengaluru, and Vellore Institute of Technology (VIT), Vellore, have detected microplastics in groundwater drawn from deep borewells in the hard rock regions of eastern Karnataka.
The study is among the first to document microplastics in deep hard-rock aquifers in India, expanding the scope of concern beyond surface water and coastal regions.
Published in the journal Current Science, the study noted the presence of microplastic particles in drinking water sourced from borewells tapping aquifers located 60 to over 100 metres below the surface. These aquifers, formed within ancient granites and gneisses, were previously considered relatively protected from surface contamination and have been the primary source of drinking water in large parts of rural India.
Researchers collected groundwater samples from 25 borewells across 18 rural locations in eastern Karnataka over two sampling phases conducted in November 2024 and February 2025. The results showed that microplastics were present in a majority of the samples, with concentrations reaching up to three particles per litre.
Nearly 94% of the detected particles were between 20 micrometres and 1,000 micrometres in size, making them small enough to pass through natural rock fractures and potentially enter drinking water systems.
The study, "Occurrence of microplastics in groundwater used for drinking in hard rock aquifers of Eastern Karnataka," identified a range of commonly used plastic polymers, including low-density polyethylene (LDPE), high-density polyethylene (HDPE), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), and polyamide (PA).
Interestingly, polyvinyl chloride (PVC)—widely used in borewell pipes—was not detected in the samples, suggesting either limited degradation or lower mobility of this material in subsurface environments.
Microscopic analysis revealed that the particles occur as fragments, fibres, and elongated prisms—shapes that may aid their transport through these confined pathways. Their varied colours and textures indicate differing levels of weathering, likely caused by prolonged exposure to sunlight and environmental conditions before entering the subsurface.
The study, conducted by R. Srinivasan, S. A. Pandit, and G. Gowrisankar from the Divecha Centre for Climate Change, IISc, Bengaluru, and R. Devananth and S. Mahenthiran from the School of Civil Engineering, VIT, Vellore, warned that the aquifers in this region are largely unconfined, allowing contaminants from the surface to percolate downward over time.
The presence of microplastics is largely linked to human activity in rural areas, with researchers identifying multiple sources such as the improper disposal of household plastic waste like carry bags and multilayered packaging.
Other sources included the extensive use of plastics in agriculture, including irrigation systems, mulch films, and storage materials; plastic components used in inland fishing; and routine practices such as washing clothes and livestock near water sources.
Many of these materials degrade over time into smaller particles, which can infiltrate soil and eventually reach groundwater.
The types of plastics detected in the study closely matched those commonly used in rural domestic and agricultural settings, reinforcing the link between surface waste and subsurface contamination.
One of the key observations of the study was the variability in microplastic presence across locations and sampling periods. Even at the same site, the number and type of particles detected changed over time, reflecting the dynamic nature of groundwater systems.
For instance, some borewells that showed no contamination in the first sampling phase recorded microplastics in the second. In other cases, both the quantity and composition of particles differed between sampling rounds.
The researchers also found that larger sample volumes yielded more representative results. While one-litre samples typically showed one to three particles, 20-litre samples revealed a wider diversity and higher counts of microplastics, suggesting that smaller samples may underestimate contamination levels.
The study findings reflect the broader global context of rising plastic pollution. According to the United Nations Environment Programme, over 400 million tonnes of plastic are produced annually, much of which eventually enters natural ecosystems.
However, the contribution of drinking water to this exposure remains uncertain. Based on the observed concentrations, the researchers estimated that individuals in the studied regions may ingest around 1,100 microplastic particles annually through groundwater consumption.
At present, this level is not considered immediately alarming. Moreover, many villages use reverse osmosis (RO) systems, which are capable of filtering out microplastic particles from drinking water.
Despite the relatively low concentrations observed, the study underscores the need for caution. The presence of microplastics at such depths indicates that contamination pathways are more extensive than previously understood, cautioned the researchers.
They warned that without effective plastic waste management, especially in rural areas, the levels of microplastics in groundwater could rise over time.
As reliance on groundwater continues to grow, particularly in water-stressed regions, ensuring its safety becomes critical. The findings serve as an early warning, stating that in the absence of timely intervention, what is currently a low-level contamination could evolve into a more serious public health and environmental issue.
