A new protocol to assess the microplastics in sewage sludge

Abstract

Pollution from plastics and their slow degradation are current problems that require urgent solutions. The natural degradation of plastics leads to its fragmentation, resulting not only in microplastics (MPs) but also in nanoplastics (NPs). In recent years, research and monitoring of MPs and NPs concentrations has increased. The monitoring of their concentrations in the environment, sampling sites, detection and quantification methods are not standardised due to the inherent properties of the materials and the origin of the samples, which tends to make the comparison of data between different studies difficult. In this study, we developed an H2O2-enzyme protocol for the extraction of MPs from sludge based on existing analytical methods in the literature, from sampling to quantification and detection. Our laboratory study consists of four protocols used to verify MPs recovery from doped sludge samples containing three polymers (polypropylene, polyethylene terephthalate and nylon). To emphasise the relevance of the optimal protocol, a triplicate test was performed for each of these protocols, all of them using sieve fractions between 100 and 500 μm, while isoporous polycarbonate membranes were used for the filtration of the samples. The percentage polymer distribution of H2O2-enzyme protocol was similar to the control (42% ± 8.49; 38% ± 2.83; 16% ± 11.31), with some limitations for the larger fraction. Data collection was carried out by optical visualisation and chemical identification using Fourier-transform infrared spectroscopy to record polymer spectra obtained for potential interpretation. Finally, a test was conducted to try all protocols on a real sludge from a local plant to confirm their efficiency.