Occurrence and Interaction of Microplastics with Metal Nanoparticles as Co-contaminants in the River Ganga (India)

The current study explores MPs in sediments and water that were collected at five major cities across the Ganga River from India. The results showed that the MPs number and mass density range in sediment were found to be 17 to 36 items/kg dry weight (d.w.) and 10 to 45 mg/kg d.w. of sediments, respectively, while in the water sample, they were 380 to 684 items/1000 m3 and 143 to 340 mg/1000 m3, respectively. Overall, white color and film-shaped MPs were the major contributors in all samples. MPs of 2.5-5 mm size contributed to a greater number and mass as compared to other fractions[1]. Polyethylene and polypropylene were found to be widely distributed plastic types reflecting their high usability. We considered MPs made of polypropylene further to perform contaminant interaction studies by exposing the CeO2 nanoparticles to the pristine (P-MPs) and weathered microplastics (R-MPS). For P-MPs, the sorption capacity was as high as 12.9 mg/g, while for R-MPs, kinetic equilibrium was achieved faster and an enhanced sorption capacity (13.4 mg/g) was identified. A rise in sorption with an increase in salinity was noted while pH and humic acid exhibited a negative correlation. The observed interactions were attributed to the aggregation profile and surface charge of CeNPs and MPs. The type of aqueous matrix influenced the sorption process and the sorption capacity at equilibrium followed the trend: distilled water> synthetic freshwater> river water. The work highlights the possible MPs-aided-contaminant transport in the riverine systems attributing to the secondary water contamination[2]. Reference: Singh, N., et al., Characteristics and spatial distribution of microplastics in the lower Ganga River water and sediment. Marine Pollution Bulletin, 2021. 163. Singh, N., et al., Interaction of metal oxide nanoparticles with microplastics: Impact of weathering under riverine conditions. Water Research, 2021. 189: p. 116622.