The link between microplastics and colorectal cancer.

Microplastics and nanoplastics (MNPLs) are known to enter the human body and accumulate within different tissues. As MNPLs have been shown to exert toxic effects in vivo, we aimed to evaluate the link between MNPLs and colorectal cancer tumorigenesis. A literature review was conducted, using Ovid MEDLINE and PubMed databases. MeSH terms "colorectal carcinoma" and "microplastic" were the foundations for the search strategy. Forty-one studies were initially identified, of which fourteen were ultimately selected for analysis. MNPLs are found within human colorectal tumors and are present at higher levels in the feces of colorectal cancer patients. The tissue sample studies however are limited by small sample sizes (n = 10 or 25), and are representative of mainly Chinese populations (five of the six human studies conducted in China). The mouse studies observed increased tumor loads and dysbiosis in mice exposed to MNPLs, and the in vitro studies observed increased reactive oxygen species (ROS) when cells were exposed to MNPLs in culture. Although the direct link between MNPLs and de novo development of colorectal cancer remains to be elucidated, these findings suggest that MNPLs can induce the molecular changes involved in tumorigenesis, and tumorigenesis itself when combined with a compromised gastrointestinal barrier. Given that barrier disruption occurs with inflammatory bowel disease, smoking, alcohol, stress, and infections, these populations may be most vulnerable to the effects of MNPLs.