This different paper talks about this approach and its limitations: https://www.mdpi.com/2673-8929/1/2/16
"Prior to Pyr-GC/MS analysis, environmental samples undergo purification steps to isolate MP from the environmental matrix. However, this purification is not complete, and several organic and mineral constituents survive these treatment steps, especially in complex matrices such as sediments or soils. Hurley et al. [15] reported that the efficiency of removing organic matter from soil varied from 34% to 108% depending on the used reagent (H2O2, Fenton’s reagent, NaOH, KOH). These remaining particles will hamper the characterization and quantification of MP particles through Pyr-GC/MS. Upon thermal cracking, the polymers release pyrolysis products of lower molecular weight. Some of these products are defined as indicator compounds when they allow the detection of targeted polymers. However, some constituents of the remaining natural organic matter may release the same pyrolysis products as the targeted polymers [15,16,17,18], hence a potential MP overestimation. The identification of pyrolysis products that are specific to the targeted polymers is therefore necessary."
Sounds like the detection methods and methodology for microplastics are evolving. It is plausible that the amounts are materially over estimated.
Another thing that seems implausible is the increase between 2016 and 2024? "our finding that total plastics mass concentration in brains increased over 50% in the past 8 years.". 50% in 8 years! Is the world really that different in terms of plastic exposure 2024 vs. 2016. Unless something has fundamentally changed with the food supply in this period how can this be possible? Plastic production is increasing (https://www.statista.com/statistics/282732/global-production...) but for a 50% increase in this period something would have to have fundamentally changed with exposure routes in this period.