Microplastic Footprint in the Larval Cases of Caddisflies (Trichoptera) for Tracing the Sources of Microplastics in Freshwater Bodies

Microplastic (MP) analysis in various environmental media currently faces significant challenges due to the complex and transportable nature of these materials. This study employed Fourier-transform infrared spectroscopy (FTIR) to investigate the presence of MPs in caddisfly larval cases, which incorporate vegetative fragments, sediment grains, and MP particles as building materials. The analysis of MPs in 2049 caddisfly larval cases revealed a total of 7553 items, resulting in an average of 3.7 items/case. The lowest recorded rate was 0.8 items/case, while the highest reached 18.2 items/case. Fiber MPs comprised 39.2% of the total, followed by fragment MPs at 30.8% and spherical MPs at 30%. Among the colors analyzed, blue MPs were the most prevalent, accounting for 36.6%, with white/transparent MPs at 22.1% and red MPs at 14.1%. MPs smaller than 100 µm were the most common, accounting for 37%, followed by MPs in the 100–250 µm range at 23.9%, larger than 500 µm at 22.3%, and those between 250 and 500 µm at 15.8%. Cellulose acetate was discovered to be the most abundant MP among different polymer types, followed by cellulose acetate butyrate, polyethylene terephthalate, poly(vinyl propionate), poly(ethylene glycol), poly(acrylonitrile-co-butadiene), cellulose propionate, hydroxyethyl cellulose, polyvinyl alcohol, glycerol triacetate, polystyrene, and poly(propylene glycol) methacrylate. These findings show the existence of MP in biotic components of these ecosystems, which has implications for aquatic biota health and freshwater quality, particularly in places influenced by human activity.