Pathway-specific microplastic dynamics in a Himalayan urban lake, India: insights on how continuous rainfall transforms microplastic characteristics and risk

Abstract

Microplastic (MP) pollution in freshwater systems has emerged as a pressing environmental concern, yet our efforts on prioritizing key pathways remain obscure. One of the promising approaches to reduce MP emissions is identifying key pathways to reduce their emissions at the source. To this end, we investigated how major MP pathways like stormwater runoff, wastewater treatment plants (WWTPs), littering zones, and laundry facilities show distinct MP characteristics in response to continuous rainfall in a highly urbanized lake. Our findings spotlighted WWTPs as persistent MP hotspots, with continuous rainfall substantially increasing MP abundance near stormwater outfalls. Fibers were dominant near WWTP and laundry sites, while stormwater and littering sites were dominated by fragments, signifying pathway-specific characteristics. Black particles were observed only near stormwater outlets and confirmed as rubber derived from tire and road wear abrasion. Continuous rainfall also affected the chemical profiles, particularly near stormwater outlets, resulting in the appearance of new polymers like polyurethane (PU), acrylonitrile butadiene styrene (ABS), and polyvinyl chloride (PVC). Furthermore, diversity indices also proved the transformative nature of continuous rainfall in reshaping MP community composition, highlighting the complexity of MP pollution dynamics. The risk assessment identified stormwater and WWTP pathways as significant contributors to MP-related toxicity. Overall, the findings showed how extreme weather events like continuous rainfall play a critical role in changing MP dynamics in freshwater systems and spotlighted key pathways and the need for targeted interventions, especially improving stormwater management and wastewater treatment to mitigate MP pollution.