Conversion of microplastics to flocs during estuarine mixing the Aras River with the Caspian Sea

Microplastics originated from various sources are carried by rivers into oceans, seas and lakes. In the last few years, the accumulation of microplastic particles in marine environments has been on the increase which causes irreversible damages to flora, fauna and human health. One of the most considerable processes in an estuary is the flocculation process. The flocculation process converts pollutants to flocs or greater particles. In the present study, the conversion of microplastics to flocs during estuarine mixing of the Aras River water and the Caspian Sea water is investigated for the first time. The results clearly show that a huge percentage of microplastics (99.95%) are converted to greater particles (> 5mm) due to the flocculation process. The maximum flocculation rate of microplastics (47.37%) is observed at the salinity of 0.25 ppt. Moreover, 35.71% of microplastics are flocculated at the salinity of 29 ppt. Salinity enhances the flocculation of microplastics.