Airborne microplastics distribution in indoor and outdoor environments of a rapidly growing city in South India

Microplastics (MPs) are ubiquitous, persistent pollutants that are harmful to human and reported in various environmental compartments like air, water, soil and biota. Owing to its hydrophobicity, MPs can adsorb chemicals like plasticizers, additives and flame retardants that can impart oxidative stress when inhaled. In this study, the MPs concentration in particulate matter (PM) was investigated for Tiruchirappalli, a rapidly growing city in Tamil Nadu. The study focuses on the PM bound MPs in outdoor and indoor environments through the collection of active PM₁₀ samples and atmospheric depositions, respectively. The results showed that PM₁₀ concentration at the monitoring sites were in the range of 28.17±6.4 μg/m³ to 43.67±6.3 μg/m³. The MPs in PM samples were extracted and viewed under Fluorescence microscope using Nile Red staining. The results indicated only a little difference in MP concentration among the monitoring sites (30.27±13.6 particles/m³ at residential area (L1) and 32.69±7.27 particles/m³ at industrial area (L2)). It was noteworthy that majority of MPs identified in PM₁₀ samples were fragments and only a few fibres were noticed. This indicated the prevalence of MPs formed from degradation of plastic debris. The mean size of MPs was estimated to be 2.75 μm, showing the aerodynamic nature of the MPs in smaller sizes. MPs were found to be more prevalent in indoor atmospheric depositions (L1: 666 particles/m²/day; L2:727 particles/m²/day) than outdoor air. This study emphasizes the need for comprehensive understanding of the characteristics and sources of indoor and outdoor MPs so that appropriate mitigation strategies can be formulated.