Intercomparison study on commonly used methods to determine microplastics in wastewater and sludge samples

Area of Science:

• Environmental Science
• Analytical Chemistry
• Polymer Science

Background:

• Harmonized procedures for microplastic sampling, treatment, and identification are absent, hindering result comparison and effective monitoring.
• Existing microplastic analysis methods often lack validation with spiked samples, leading to uncertain recovery rates and estimations of environmental concentrations.

Purpose of the Study:

• To evaluate and compare six different microplastic analysis methods for municipal wastewater and digested sludge.
• To determine the most efficient and effective treatment procedures for microplastic quantification in environmental samples.
• To assess the impact of chosen methods on microplastic identification using micro-Raman and FTIR microscopy.

Main Methods:

• Six established microplastic analysis methods were tested on municipal wastewater and digested sludge samples.
• Samples were spiked with seven types of plastic particles and fibers to determine recovery rates.
• Evaluation included recovery rates, time efficiency, and suitability for micro-Raman and FTIR analysis.

Main Results:

• Filtration with size fractionation emerged as the optimal method for both wastewater and sludge.
• This method achieved high recovery rates for spiked microplastics: 91.4% for wastewater and 92.9% for sludge.
• Staining with Rose Bengal did not enhance microplastic recovery. Treatment impacts on spectroscopic identification were assessed.

Conclusions:

• Filtration with size fractionation provides a reliable and efficient method for microplastic analysis in wastewater and sludge.
• Standardized, validated methods are crucial for accurate microplastic monitoring and environmental concentration assessment.
• Further research should focus on method harmonization to improve data comparability in microplastic research.