Emerging contaminants in urban Soils: Characterization, sources, and environmental impacts of microplastics in southern India

Abstract

Microplastic (MP) contamination in terrestrial ecosystems, particularly urban soils, has emerged as a growing environmental concern with limited empirical data from rapidly developing regions. This study investigates the concentration, distribution, and chemical composition of microplastics (MPs) in urban soils across Chennai, India. Twenty-five soil samples were collected from diverse locations and analysed for physicochemical properties, including pH (7.0–9.8) and organic matter content (0.19 %–23.6 %). MPs underwent extraction through zinc chloride-based density separation and vacuum filtration, followed by categorization by shape and color. Fragments and fibers dominated, with white/transparent and blue/purple being the most frequent colors. Fourier-transform infrared (FTIR) spectroscopy identified polypropylene, polystyrene, and nylon as the most common polymers. MP counts ranged from 6 to 31 particles per 100 g of soil, with Sample 18 showing the highest concentration. To assess contamination levels, the Pollution Load Index (PLI) was calculated and the values ranged from 1.00 to 2.27, placing all sites within Hazard Category I, indicating low to moderate pollution. Spatial mapping indicated localized hotspots, likely driven by land use and waste disposal practices. Statistical analysis using Spearman's and Pearson's correlations revealed a significant negative relationship between MP abundance and soil organic matter (Pearson's r = −0.512, p = 0.013), while correlations with pH remained weak and statistically insignificant. Principal Component Analysis (PCA) demonstrated a strong inverse relationship between MP counts and organic matter, along with a positive association with soil pH. These variables together accounted for over 60 % of the total variance, highlighting the multifaceted influence of MPs on soil properties. This research emphasizes the increasing presence of MPs in urban environments and supports the need for ongoing monitoring and mitigation through bioremediation, adoption of biodegradable alternatives, enhanced waste infrastructure, and public engagement.