Microplastics (MPs), as emerging environmental pollutants of the 21st century, have raised serious global health concerns due to their persistence, microscopic size, and widespread distribution across terrestrial, aquatic, and atmospheric ecosystems. These extremely small particles, ranging in size from 1 μm–5 mm, can enter the human body through drinking water, food, and contaminated air, and may accumulate in organs such as the intestine, stomach, and liver. Recent studies indicate that MPs induce oxidative stress, chronic inflammation, disruption of the intestinal barrier, and gut microbiota dysbiosis—mechanisms that collectively promote DNA damage, genomic instability, and carcinogenesis. Moreover, MPs act as vectors for carcinogenic compounds including heavy metals and persistent organic pollutants (POPs and PAHs), amplifying their toxic and mutagenic potential. This review article aims to critically summarize recent findings on the biological interactions between microplastics and the human gastrointestinal tract, focusing on their possible role in the development of gastric, colorectal, and hepatic cancers. Accumulating experimental and in vivo evidence supports a possible link between microplastic exposure and gastrointestinal cancers, particularly colorectal, gastric, and hepatic malignancies. Nevertheless, the absence of standardized toxicity assessment protocols and physiologically relevant exposure models hampers accurate risk evaluation. Hence, interdisciplinary research and global plastic pollution control policies are urgently needed to elucidate the carcinogenic potential of MPs and safeguard human health.
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