SEASONAL VARIATION OF MICROPLASTICS ABUNDANCE AND CHARACTERISTICS IN LANDFILL SOIL AT AN INTEGRATED WASTE MANAGEMENT FACILITY

Abstract

This study examines the seasonal variation in the abundance and characteristics of microplastics in soil from a landfill site at an integrated waste management facility in Lampang Province, Thailand. Soil samples were collected during wet and dry seasons, and waste composition analysis was conducted to classify plastic waste into seven types. Microplastics were isolated using wet peroxide oxidation and density separation, characterized by fluorescence microscopy, and identified using Fourier Transform Infrared Spectroscopy (FTIR). Results showed that plastic waste comprised an average of 20.19 ± 2.20% of total waste, with low-density polyethylene (LDPE) being predominant in both wet (71.57%) and dry (68.20%) seasons. Microplastic abundance was significantly higher in the dry season (1,013.33 ± 220.30 particles/kg) compared to the wet season (413.33 ± 151.44 particles/kg). Fragments were the dominant morphology, accounting for 63.46% and 85.71% in wet and dry seasons, respectively, with a statistically significant difference between seasons. The major polymer types identified were polypropylene (PP), polyethylene terephthalate (PET), and polystyrene (PS), with significantly different distributions between seasons. Notably, despite LDPE being the most abundant plastic waste type (> 68%), no LDPE or high-density polyethylene (HDPE) microplastics were detected in soil samples, suggesting differential degradation rates among polymer types. These findings highlight that seasonal variation plays a crucial role in influencing microplastic accumulation and distribution in landfill soil, with dry season conditions favoring both enhanced photodegradation of plastics and reduced leaching of microplastics from surface soil. The study provides baseline data for developing season-specific waste management strategies to mitigate microplastic pollution from landfill sites.