A hybrid method for identifying and counting microplastics in environmental sediment samples has been devised by researchers from the U.S. Environmental Protection Agency and University of Rhode Island.

Microplastic particles are first extracted by shaking a sample of sediment in a salty solution. Since plastic is less dense than sediment, microplastic particles initially float while sediment sinks, allowing for the separation of plastic from sediment. Raman spectrometry is then applied to analyze and identify the plastic particle constituents.

The approach was used to examine sediment samples from Narragansett Bay, Rhode Island. Analysis ofSource: Michaela A. Cashman et al. samples from seven sites revealed 38 different types of plastic, with cellulose acetate identified as the most abundant type. Other microplastic polymers found included polyester, polypropylene, methyl cellulose, polyurethane, polystyrene, polyethylene, ethyl cellulose, and polyvinyl chloride.

One study site had extremely high microplastic content at 4.6 million pieces of plastic per 100 g sample, most of which was cellulose acetate. The other six sites had 40 to 293 pieces of a variety of types of plastic per 100 g sample, considered a more typical range of microplastic quantity and polymer type.

The variation found in both the type of plastic and quantity of microplastic particles underscores the variability of microplastics throughout the global environment and the need for improved analytical and monitoring methods.

The hybrid method described in Marine Pollution Bulletin can help render microplastics research more standardized and accessible.