A method for the characterisation of microplastics in sludge.

Area of Science:

• Environmental Science
• Analytical Chemistry

Background:

• Microplastics (MPs) are increasingly detected in ecosystems, with wastewater sludge being a major reservoir.
• Wastewater treatment processes can remove 80-90% of MPs, but accurate quantification in sludge is lacking for effective management.

Purpose of the Study:

• To validate a rapid method for quantifying microplastics in sludge.
• To assess the accuracy and precision of the method across different microplastic sizes and concentrations.

Main Methods:

• Recovery tests using spiked low-density polyethylene (LDPE) fragments (sizes 5-0.15 mm).
• Sludge samples were freeze-dried, sieved, purified using Fenton's reagent, visually sorted, and analyzed by FTIR.
• Quantification was performed by fragment number and weight.

Main Results:

• Recoveries based on fragment number were quantitative (80-100%) across all tested sizes and initial quantities.
• Recoveries by weight consistently exceeded 100% due to retained materials adhering to LDPE fragments.
• Attached residues caused weight overestimation by up to 33% for the smallest fraction (500-150 μm).

Conclusions:

• The validated method provides accurate and precise microplastic quantification in sludge when assessed by fragment count.
• Weight-based quantification requires careful consideration of interfering residues, which can lead to overestimation.
• Further refinement may be needed to address residue interference for precise weight-based microplastic analysis in sludge.