Microplastics in Indian freshwater systems – is an anthropogenic influence measurable?

Microplastics are detected in most environmental compartments and hence receive a great deal of attention, especially in aquatic environments where rivers act as pathways for microplastics. Currently, a particularly high input of microplastics through Asian rivers is assumed predominantly by modelling data, while field measurements are scanty.

Three rivers in South India were considered for this purpose to focus on their microplastic loads. The emphasis was on the comparison of microplastic concentrations in urban and rural rivers to identify if the anthropogenic influence control the loads. While two rivers in the megacity Chennai (Tamil Nadu) were found to have an average microplastic concentration of 0.4 microplastic particles/L, a rural river near Munnar (Kerala) had an average concentration of 0.2 microplastic particles/L. The results show higher loads in the urban area with a high anthropogenic influence by wastewater discharges and waste disposal through high number of residents dumping directly by the river. Fibres were the predominant shape (64.13%), black was the predominant particle colour (44.80%) and polyethylene and polyprolyene were the predominant polymers (each 46.67%) detected within the identified particles of all samples.

Rough estimates of annual microplastic discharge from the Adyar River (Chennai) into the Bay of Bengal are found to be as high as 11.6 trillion microplastic particles. This study, which is one of the first baseline studies for microplastic loads in South Indian streams, should be complemented with further environmental sampling during pre-monsoon, monsoon and post-monsoon seasons to get more detailed information on the storage and transportation of fluvial microplastics and to understand the seasonal effect on the river flow characteristics as well as the fate of microplastics.