A method for microplastic extraction from ornithogenic soils

Organic rich samples require digestion prior to extracting microplastics for spectroscopic analyses. However, it can be challenging to fully digest samples containing high amounts and multiple types of organic matter without causing degradation or complete loss of the targeted polymers. Ornithogenic soils contain algae, feathers, chitinous krill, and lipid rich guano which may be difficult to fully break down using single-step digestion methods. We investigated suitable methods for microplastic extraction from ornithogenic soils by carrying out a combination of oxidative (Fenton's reagent, H₂O₂, NaClO, and alkaline (10% KOH) digestion methods. The optimal method was a three-step digestion method using NaClO, 10% KOH, and 30% H₂O₂ at temperatures of ≤40 °C. The organic material present was sufficiently digested without comprising microplastic identification. Reference microplastic (100-5000 μm) recoveries ranged from 96 to 100% for spiked ornithogenic soils and 92-98% for procedural blanks. This three-step digestion method is recommended for organic rich guano and ornithogenic soil samples where microplastic extraction would not be possible otherwise. • Organic matter in the ornithogenic soil samples was successfully digested using NaClO, 10% KOH, and 30% H₂O₂. • Microplastic extractions were completed in five days.