Research Paper

A straightforward protocol for extracting microplastics from freshwater sediment with high organic content

¹ University of São Paulo, Institute of Biosciences, Department of Ecology, São Paulo, SP, Brazil
² University of São Paulo, Institute of Chemistry, Department of Fundamental Chemistry São Paulo, SP, Brazil

^* Corresponding author: queiroz@ib.usp.br; barbara.rani-borges@usp.br

Received: 4 December 2024
Accepted: 5 February 2025

Abstract

Extracting microplastics from sediment is critical in assessing pollution in freshwater environments. However, this process can be particularly challenging for clayey sediments with a significant organic matter content. This study proposes a simplified method for extracting microplastics from organic-rich clayey sediments and a complete protocol for sediment processing. To evaluate the extraction method, calcined clayey sediment was artificially enriched with varying organic content (20, 40, and 60%). Known quantities of plastic particles with distinct characteristics and compositions (PET, HDPE, PP, PE, and PS) were introduced into these artificial organic sediments, mixed with a saline solution, centrifuged, and then assessed the recovery rate. The recovery rate exceeded 83% for the five selected plastic types. Additionally, the method minimized particle loss by reducing the number of transfers between containers, a common issue in other microplastic extraction protocols. Based on the efficiency of the extraction method, we proposed and applied a protocol for environmental samples. The protocol comprises five key steps: (1) drying sediment samples, (2) density separation, (3) filtering, (4) digestion of organic matter, and (5) visual analysis. This protocol extracted a wide variety of microplastics with diverse shapes, colors, sizes, and polymeric compositions. These results demonstrate that the proposed protocol is both straightforward and effective in extracting plastic particles commonly found in clayey sediments of freshwater systems. Moreover, the protocol employs inexpensive, readily available, and environmentally friendly reagents, making it a more sustainable alternative to other methodologies for extracting microplastics from environmental matrices.