2025 Volume 5 Pages 107-118
Hexavalent chromium (Cr(VI)) is a hazardous substance but has been used in various industrial applications. Consequently, it has caused severe environmental pollution in many regions worldwide. One notable site of concern is the final landfill of a former chemical factory located approximately 8 km east of central Tokyo, where high concentrations of Cr(VI) leach into the public sewage system and the surrounding environment. Rainfall plays an important role in the transport of substances in the environment; however, its specific effects on Cr(VI) behavior within this area remain unclear. To elucidate the effect of rainfall on the outflow of Cr(VI) from the former chemical factory site, we examined the relationship between Cr(VI) concentration, pH, redox potential (Eh), and antecedent dry hours in stagnant water samples collected from a rainwater inlet, after classifying the data based on the presence or absence of rainfall within a defined preceding time frame. The results revealed a strong positive correlation between Cr(VI) concentration and pH in samples collected after rainfall, thereby proving that rainfall accelerates Cr(VI) outflow. This phenomenon likely occurs because the hexavalent chromium slag, a potential source of contamination, is a highly alkaline material. Additionally, the rainfall-induced Cr(VI) outflow peaked approximately 6–24 hours following the rainfall event. This finding was supported by the relationships among the 4 factors mentioned above. The combination of low Eh values and high Cr(VI) concentrations in the water samples appears to result from a decline in Eh and accumulation of Cr(VI) in the groundwater during antecedent dry periods. This study highlights the importance of reinforcing pollution control measures, particularly during the critical 24 h window following rainfall. Further quantitative studies are needed to develop effective countermeasures to better understand Cr(VI) behavior, considering hourly rainfall patterns.
