A review of plastic contamination in mud crabs (Scylla spp.): occurrence, characteristics, toxicological effect, and future direction

Plastic pollution has become a critical environmental issue in coastal and estuarine ecosystems, raising concerns about its impact on ecologically and economically important crustaceans such as mud crabs (Scylla spp.). This review synthesizes current research on the occurrence, characteristics, and toxicological effects of plastic contamination in mud crabs. A systematic literature search identified 15 relevant studies published between 2022 and 2025, including 13 that reported the presence of plastics in mud crabs and 2 that examined physiological impacts. Microplastics were the predominant size class, primarily in the gastrointestinal tract, followed by the gills and hepatopancreas. Fragments and fibers were the most common shapes observed, while blue, transparent, and black were the dominant colors. Twelve polymer types have been documented, with polyethylene (PE) and polypropylene (PP) most frequently reported, reflecting their widespread use and prevalence in mangrove and estuarine environments. Plastic abundance varies substantially across regions, species, and tissue types. Toxicological evidence indicates that microplastics tend to accumulate in various fish tissues, particularly in the digestive and respiratory organs, leading to oxidative stress, altered antioxidant enzyme activity, and DNA damage. Despite these emerging findings, substantial knowledge gaps persist, including the absence of data on muscle contamination, limited comparisons between wild and farmed crabs, lack of sex-based assessments, and minimal understanding of impacts on early developmental stages. This review highlights the urgent need for standardized methodologies and comprehensive ecotoxicological studies to improve understanding of plastic exposure pathways, physiological responses, and the broader ecological and food-safety implications for Scylla spp. populations.