Detecting microplastics in feces of pig fed former food products

Former food products (FFPs) are authorized feedstuffs. However, there is presence of plastic packaging remnants in feed made from FFPs. Such contaminants, especially microplastics (MPs), can occur in biological matrices like feces. Thus, we aimed to test the efficiency of the selected method for MP sampling, digestion, and extraction in pig feces. The 36 fecal samples were collected from growing-finishing pigs fed a control diet or diets containing 30% sugary FFPs or 30% salty FFPs (n=12 per group). Feces were collected from rectum, placed in aluminum bags to avoid contamination, and 3 sets of 3 g feces were obtained from random spots in each fecal sample. Then, 25 mL 30% H2O2 was added to feces at room temperature for a week to digest organic matter. The 3 extra samples were spiked with blue polypropylene pieces to check if the digestion process may change plastic’s appearance. For density separation, 100 mL saturated NaCl solution (D=1.2 g/cm3) was added to the samples that were filtered after overnight settling. Treated feces were inspected under a stereomicroscope to detect plastic remnants. Suspected particles were placed in a petri dish to be analyzed by the Fourier transform infrared spectroscopy for material confirmation. Plastic’s appearance was not changed by H2O2 digestion. However, it was not able to detect any MPs from collected feces with the chosen method as the original packaging contamination in FFPs was low and MPs’ presence was diluted by FFPs’ inclusion level. Hence, further studies are needed to test different methods, develop a standard protocol for fecal MP extraction, and seek markers to trace the fate of MPs in animals.