Microplastics in the rivers of Gujarat (India) to the Arabian Sea: assessment of the sources, distribution, and associated environmental risk

Abstract

Microplastics (MPs) have become a notable concern and are released into the environment through the disposal or fragmentation of large plastics. Rivers have been the major pathways for MPs present in the oceans, which significantly affects the marine environment. In this study, water samples were collected from the upper stream and downstream of the Damanganga and Tapi rivers across different sites in the state of Gujarat, India, for exploration of MP contamination. Additionally, samples were collected from Dumas Beach to detect the presence of MPs. Microplastics were extracted from the samples through sieving, density separation, and wet peroxide oxidation techniques, and were subsequently analyzed using μ-FTIR (micro-Fourier transform infrared spectroscopy), optical microscopy, pyrolysis gas chromatography-mass spectrometry (Py-GCMS) and scanning electron microscopy (SEM). The concentration of MPs was also quantified from each stretch of the Damanganga and Tapi rivers as well as Dumas Beach. Findings revealed that the Damanganga showed a higher concentration (3.53 particles/L) of MPs compared with the others. Further, optical microscopy and μ-FTIR analysis confirmed the presence of MPs such as polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), polyethylene (PE), and polymethyl methacrylate (PMMA). Pyrolysis products of PP, PS, and polyamide (PA) were detected from Py-GCMS studies. Additionally, SEM images revealed that MPs were subjected to weathering, oxidation, and atmospheric deposition over the years. The study additionally confirmed the flux of MPs in both rivers and the beach due to anthropogenic and industrial effects. Risk assessment of MPs was performed using the pollutant loading index (PLI), which indicated that the overall MP pollution in the studied sites was marginal. Nevertheless, the PLI scores revealed that Damanganga was the most prone to MP pollution among the three study sites.

Keywords: environmental samples; freshwater and coastal pollution; microplastics types; risk assessment; sampling.