Subchronic toxicity of 222 nm ultraviolet irradiation in rats for safe human translation and application guidelines

This study investigated the long-term safety of 222 nm far-ultraviolet light, a promising technology for continuous disinfection that is believed to be safe for human exposure. To address concerns about its practical efficacy and potential long-term effects, an accelerated 90-day toxicological study was conducted on rats. The animals were exposed to graded doses of 222 nm light: high (5000 mJ/cm²/day), medium (1000 mJ/cm²/day), and low (500 mJ/cm²/day). The results were dose-dependent. The high-dose group exhibited significant adverse effects, including skin damage (inflammatory cell infiltration, thickening), systemic weight loss, and thymic atrophy. In stark contrast, the low and medium-dose groups showed no abnormal clinical symptoms, behavioral changes, or weight abnormalities throughout the entire study. Comprehensive analysis of hematological, biochemical, and histopathological indicators confirmed no toxicologically relevant changes at these lower doses. Based on these findings, the study established a No Observed Adverse Effect Level (NOAEL) of 1000 mJ/cm²/day for subchronic exposure in rats. This indicates that continuous exposure to 222 nm far-UV light at or below this dose level is not associated with any detectable adverse biological effects, supporting its potential for safe use in occupied spaces.