Marine Microplastic Exposure and Cancer Incidence Across U.S. Coastal Counties: A County-Level Ecological Study

Microplastics are pervasive contaminants in marine and coastal ecosystems. Although experimental and human biomonitoring studies suggest biologic plausibility for chronic health effects, population-level evidence linking environmental microplastic exposure to cancer incidence remains limited. We conducted a county-level ecological study of 255 U.S. coastal counties linking NOAA/NCEI marine microplastic exposure data with NCI/CDC State Cancer Profiles cancer incidence estimates. Counties were categorized by mean marine microplastic concentration as low, medium, or high exposure. Outcomes included incidence rates per 100,000 population for colorectal, lung, pancreatic, liver and intrahepatic bile duct, esophageal, kidney, thyroid, breast, prostate, and cervical cancers. Poisson regression was used to estimate incidence rate ratios (IRRs) comparing medium- and high-exposure counties with low-exposure counties, adjusting for county-level demographic, socioeconomic, healthcare access, and geographic covariates. Among 255 coastal counties, 53 (20.8%) had low exposure, 36 (14.1%) medium exposure, and 166 (65.1%) high exposure. High-exposure counties were more frequently located along the Atlantic and Gulf coasts and had a lower median household income, higher poverty, and higher uninsured rates than low-exposure counties. In adjusted models, higher microplastic exposure was not associated with a broad or consistent increase in cancer incidence across sites. For pancreatic cancer, the IRR comparing high- with low-exposure counties was 1.18 (95% CI 0.99–1.26), with no statistically significant overall association across exposure categories (p = 0.09). Marine microplastic exposure was geographically and socioeconomically patterned across U.S. coastal counties, but current county-level exposure metrics did not reveal a consistent population-level cancer signal. Improved exposure assessment and longitudinal individual-level studies are needed.