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Spatio-temporal variation of microplastics during the past four decades in a lacustrine sedimentary environment in southern India
Summary
Using sediment dating techniques, researchers traced four decades of microplastic accumulation in a tropical Indian lake, finding a steady rise from 1975 to 2010 driven by rainfall, fishing, and poor waste disposal. This historical record demonstrates that microplastic pollution is not a recent phenomenon — it has been steadily building in freshwater systems for generations.
Microplastics (MPs) have been detected in various systems, including lakes, rivers, ice sheets, soils, and biota, as well as in humans. They are also recognized as carriers of other dangerous contaminants, including persistent organic pollutants and heavy metals. This study investigated the spatial and temporal distribution of microplastics (count, shape, size, colour, and polymer composition) present in the surface and sub-surface sediments of a tropical lake (Lake Madagadakere) in south-western India. The sub-surface sediments were dated using 137Cs and 210Pb methods. Microplastics in surface sediments range from 100 to 450 particles/kg (average: 322.22 particles/kg). A steady increase in the concentration of microplastics between 1975 and 2010 was documented (150–1475 particles/kg), with a decrease from 2010 to 2016 (440–225 particles/kg). Fibres are abundant types of microplastics in both surface and subsurface sediments. The MPs in the surface sediment samples are predominantly polypropylene (PP), whereas sub-surface samples contain high-density polyethylene (HDPE) in addition to the former. A small creek joins the lake in the north-east part, which might act as a major source for microplastic influx into the lake. Rainfall, fishing activity, and inadequate plastic disposal have collectively influenced the fluctuation in microplastic concentration in the sedimentary profile over the past 43 years. The present study provides baseline data on the spatio-temporal characteristics of microplastics in lacustrine sedimentary environments in southern India, where limited data are available. It also explores the potential usage of microplastics as a stratigraphic indicator of the ‘Anthropocene’ or ‘Plasticene’.