Efficient Schweizer’s reagent-based protocol for microplastic extraction from fecal samples: Toward standardized human biomonitoring

Abstract

Reliable methods for the isolation of microplastics (MPs) from human feces are essential for advancing exposure and health risk assessment. However, the cellulose-rich fecal matrix is analytically very challenging. This study evaluated two different pre-treatments in protocols for MPs isolation from fecal samples. Protocol A, involved pre-treatment with a urea/thiourea/KOH (UTS) solution, followed by a comprehensive four-step digestion process (acidic, enzymatic, alkaline, and oxidative digestion) and Protocol B, involved Schweizer’s reagent (copper(II) hydroxide in ammonium hydroxide, SR) for pre-treatment, followed by the same four digestion steps. The protocol based on SR pre-treatment was further optimized. The developed protocol achieved >99.8% removal of biological matrix and a 98 ± 3% recovery rate across five polymer standards, without interfering with polymer identification by µ-FTIR. The method was successfully applied to children’s stool samples, detecting MPs in 7 of 14 cases with concentrations ranging from 1.18 to 7.25 items g−¹ feces. The size of the detected MPs ranged from 40 to 300 μm. Polyethylene was the dominant polymer (56%), and fragments represented the main morphology (69%). Compared to conventional digestion workflows, the SR-based approach offers clear advantages in efficiency, reproducibility, and cost, making it well-suited for routine application in clinical and environmental health laboratories. By facilitating standardization in fecal MP analysis, this method may provide a practical tool for large-scale biomonitoring studies. Building on its established use in ASTM D8333 for water and wastewater, this is the first application of SR to cellulose-rich biological matrices