The application of Schweizer's reagent with FTIR imaging spectroscopic solutions for microplastics advanced analysis of feces samples

The content, characteristics, and distribution of microplastics (MP) in feces samples are crucial for the investigation of human exposure and health risks. Feces, being rich in cellulose, is a particularly complex matrix for MP analysis. Numerous studies of microplastics in different matrices show how to remove organic matter from samples, but there are very few studies on the removal of cellulose. In this study, an efficient protocol for the digestion of children’s feces was developed and optimized as a combination of the innovative cellulose removal treatment of samples with previously known alkaline/oxidation treatments. To remove the cellulose, 40 mL of Schweizer's reagent was added for every 600 mg of dry sample for 40 mins. After that, the samples were passed through a 20 µm mesh sieve and washed with ultra-pure water. Samples were then subjected to alkaline digestion using 10% KOH for 24 hours at 40°C, followed by oxidative digestion using 30 mL of 15% hydrogen peroxide for 16 hours. MP content was determined in 14 feces samples from the Croatian region of Dalmatia, of which 7 samples contained MP. The number of MP ranged from 0 to 5, corresponding to concentrations between 1.18 and 7.25 particles per gram of sample. Among the detected polymers, polyethylene was the most prevalent (56% of particles) and the most dominant particle shape was fragment (68.75%). In comparison to alternative methods used for MP analysis in human feces, tour method efficiently remove cellulose and allow digestion of the matrix in a cost-effective and time efficient manner, allowing subsequent analysis by microFTIR.