Occurrence and Polymer Types of Microplastics from Surface Sediments of Molawin Watershed of the Makiling Forest Reserve, Los Baños, Laguna, Philippines

Abstract

Microplastic pollution is an emerging topic in environmental science. However, information about its prevalence in the freshwater ecosystems is still scarce. This study quantified and identified microplastic form and polymer types from surface sediments of the Molawin River. Sediment samples were collected from the upstream, midstream, and downstream stations of the river. Isolation of microplastics was performed through a modified granulometric approach, density separation, and filtration. Stereoscopic microscopy and Fourier-transform infrared spectroscopy (FTIR) were conducted to quantify and describe microplastics and identify the polymer types based on the infrared spectrum of absorption, respectively. The highest concentration of microplastics was found in the downstream station, with an average number of 97±12 items/100 g and 47.33±11.39 items/100 g sediment dry weight in the bank and channel, respectively. The isolated microplastics were dominated by ≥100 to ≤200 μm size range. Based on stereoscopic microscopy, microfragments and microfibers were the most common microplastic type, while polyethylene (PE) and polypropylene (PP) were the polymer types identified based on FTIR analyses. This study revealed the presence of microplastics and confirmed the microplastics polymers present in the Molawin Watershed of Makiling Forest Reserve.