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Objectives: Colorectal cancer (CRC) is a major health problem with high incidence and mortality rates worldwide. The increased incidence of CRC in Taiwan may be associated with environmental contaminants such as polycyclic aromatic hydrocarbons (PAHs), nitrate, and nitrite. Accordingly, in this study, the relationship between these contaminants and CRC was investigated. Methods: Paired plasma and tumor tissues of CRC patients were obtained from the Tissue Bank at Kaohsiung Chang Gung Memorial Hospital. The samples were extracted and analyzed using enzyme-linked immunosorbent assay and gas chromatography-tandem mass spectrometry for detecting the concentrations of nitrate/nitrite and 16 types of PAHs, respectively, at the Super Micro Mass Research & Technology Center, Cheng Shiu University. Results: Nitrite and the 16 types of PAHs were undetectable in the plasma; thus, only nitrate was selected for further investigation. The data indicated that the plasma levels of nitrate were not significantly different between the CRC and control groups. Notably, the average levels of nitrate in tumor tissues were significantly higher than the average plasma levels, but the nitrate levels in paired plasma and tumor tissues did not show a significant correlation. Moreover, no significant difference in the nitrate levels of plasma and tumor tissues was found in patients with different tumor stages. Conclusions: In this pilot study, no significant correlation was found between the nitrate levels in plasma and tumors of CRC patients, which could be caused by the smaller study cohort. However, the result is a potentially valuable reference for further research. [ABSTRACT FROM AUTHOR]