Microplastic isolation in biomass-laden sea-ice samples: a low-cost method for particle isolation and automated polymer analysis

Microplastic (MP; plastic particles < 5 mm) pollution is pervasive in the marine environment, generating interest in their prevalence, fate, and associated environmental threats. The diversity of MPs poses complex analytical challenges in isolating these particles from their sample medium for data analysis. Here, we present an efficient methodology for isolating suspected MPs in sea ice at high sample volumes (liters) with respect to filters being used for micro-Fourier-Transform Infrared (µFTIR) spectroscopy. Our approach is novel in that it employs sand filtration for faster sample size reduction and oxidative digestion to reduce concurrent biological matter while leaving polymers unaltered for µFTIR spectroscopy and automated polymer analysis. Demonstrated on five sea-ice cores with varying levels of biomass from the East Antarctica, we identified 369 MPs, with a mean concentration of 67.4 particles L⁻¹ (2.3 × 10⁷ μm³ L⁻¹ assuming spherical dimensions) and sample concentrations ranging from 4 to 116.4 particles L⁻¹. Fourteen polymer types were identified, including those most common in marine samples (polypropylene, polyethylene, polystyrene, polyamide). Over 80% of the isolated MPs were ≤ 1000 µm².