SCALABLE, RESOURCE-EFFICIENT, ALL-GLASS APPROACH FOR MICROPLASTIC EXTRACTION FROM CLAYS, SANDS, AND SOILS

The extraction of microplastics from environmental samples, particularly those comprising complex sediments rich in clays and organic materials, presents significant methodological challenges. Traditional extraction methods struggle to effectively separate microplastics from such matrices, leading to contaminated filters that hinder microscopic observation and analysis. This research introduces an innovative all-glass method utilizing zinc chloride (ZnCl₂) for density separation. ZnCl₂ was selected for its effectiveness in recovering a broad range of plastic densities, coupled with its reusability. Our method effectively separates microplastics from clay-rich sediments with organic matter, accommodating samples from a few grams up to 500 grams using inexpensive materials.

Samples tested included four types of clays, four types of sands, and twelve different soils. Microplastic standards included seven types of new and three types of weathered particles. They ranged from 63-2000μm and included various shapes: spherical, squares, triangles, rectangles, and irregular plates. The approach involved putting a soil sample with microplastics standards and a glass stirring rod, in a beaker. This was placed in a glass tray and ZnCl₂ added to nearly fill the beaker. Sediments were agitated by alternating directions of the glass rod. Density separation of plastic particles was effective minutes after stirring, however 24 to 36 hours of settling give optimal results for clays and organics. After settling ZnCl₂ was added to the beakers to overflow and recover floating particles. Any number of samples could be processed simultaneously. Recovery was assessed by counting particles directly and recovered on filters and by comparing multiple extractions. The addition of HCl ensures the removal of ZnCl₂ residues, enhancing sample clarity. For all seven commercial plastic types, recovery was 99% for clays and sands, and 96% for soils.

This method was developed to overcome problems in extracting microplastics from complex shoreline sediments of the Salton Sea. This systematic approach offers a scalable, efficient, and environmentally friendly alternative to existing techniques, facilitating cleaner sample extraction and opening new avenues for investigating microplastic pollution in challenging environments.