Refined analysis of microplastics in endemic fish species from Lake Victoria using µ-FTIR and pyrolysis GC-MS

Pyrolysis–gas chromatography–mass spectrometry (Pyr-GC-MS) has evolved into one of the most powerful methods for microplastics (MPs) analysis. However, analytical challenges are still encountered whenever Pyr-GC-MS is applied to matrices with high organic matter, protein and lipid contents. In this study, a workflow integrating stereomicroscopy, micro-Fourier transform infrared (µ-FTIR) spectroscopy and Pyr-GC-MS was extended to analyse MPs in three endemic fish species ( Protopterus aethiopicus , Rastrineobola argentea and Synodontis victoriae ) from Lake Victoria. Stereomicroscopic analysis only detected MPs in the gastrointestinal tracts of P. aethiopicus and S. victoriae , with the highest mean particle numbers being 16.0 ± 7.8 and 14.7 ± 6.7 items/fish taxon, respectively. No MPs were found in whole samples of R. argentea . The microparticles were mostly blue and brown 0.3–1.9-mm fragments and filaments, which µ-FTIR analysis confirmed to be composed of nylon 66, nylon 6/66, nylon 6/10, nylon 11, polyethylene and polypropylene. Retention time locking and post-column backflush considerably reduced the cycle time and increased stability of the Pyr-GC-MS method. Nylon 66 (243 µg/g in S. victoriae ), nylon 6 (0.24–96 µg/g), polypropylene (6.4 µg/g in P. aethiopicus ), poly(ethylene terephthalate) (1.2–107 µg/g) and styrene-butadiene rubber (8.5–34.8 µg/g) were quantified. Polyethylene and poly(methyl methacrylate) were detected below their limits of quantification. To prevent false positive detection of polyethylene in the lipid-rich tissues, the evaluation focussed on C21-α,ω-alkene as a marker. Polypropylene was not detected in some samples, as it formed several discrete propylene oligomers during pyrolysis, which suppressed the yield of its target quantification marker (2,4-dimethyl-1-heptene).