Microplastic Polymer Mass Fractions in Marine Bivalves: From Isolation to Hazard Risk

Microplastics (MPs) are a ubiquitous marine pollutant, and their presence in bivalves is receiving increasing attention due to the associated risks to human health. The steps of pretreatment, detection, and quantification in the analysis of MPs depend on the type of polymer. Research on MPs is challenging because of the varying characteristics of these materials, such as the size, shape, and polymer type. Consequently, there are no standardized methods for their collection, separation, identification, or quantification. This review specifically examines the available bivalve digestion steps, focusing on efficient and time-reducing methods, such as the microwave-assisted (MAW) procedure and its advantages. Recent achievements in the application of pyrolysis gas chromatography-mass spectrometry (Pyr-GC-MS) are presented for the profiling of polymer mass-related microplastics data in marine bivalves. Here, we provide an overview of the abundance, properties, and polymer types of MPs in bivalve species, highlighting the polymer mass fractions. To date, the available mass-based concentrations have revealed nine types of MPs-polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polystyrene (PS), polymethyl methacrylate (PMMA), polyamide 66 (PA66), polycarbonate (PC), and polyamide 6 (PA6)-with PE, PP, and PVC being the most common. The total MP levels in bivalves were at ppm levels, ranging from 0.26 µg/g to 36.4 µg/g wet weight. The risk of human ingestion of MPs was assessed through the consumption of bivalves as seafood. The overall potential human health risk value (H) for marine bivalves was classified within the moderate to high hazard category.