Safety Assessment of Air-Ultrafine Bubbles Measured, Transported, and Stored According to ISO Standards for Dermal, Ocular, and Oral Applications

Fine bubbles (FBs), which are microscopic bubbles with a particle size less than 100 μm, have been increasingly utilized in industrial fields. They have been widely adopted across various industries including agriculture, fisheries, and cleaning. Furthermore, FBs are negatively charged colloids that can encapsulate various gases, leading to their potential use in the medical field. However, information on the biological safety of ultrafine bubbles (UFBs) remains limited. In particular, no safety evaluations of UFBs have been reported using internationally standardized protocols. Therefore, this study comprehensively evaluated the biological safety of air-UFB water that was measured, transported, and stored according to International Organization for Standardization (ISO) standards. To this end, in vitro skin irritation and eye irritation tests, as well as an in vivo 28-d repeated-dose oral toxicity test, were conducted in accordance with international protocols. The results of both in vitro tests showed that UFB water was classified as "Not classified" under the United Nations Globally Harmonized System of Classification and Labelling of Chemicals and was considered non-irritating and not seriously damaging to the skin or the eyes. Similarly, the abnormal changes attributable to the administration of UFB water were not observed in blood biochemistry and hematology tests, organ weights and histopathological evaluations on the in vivo test. These results, in which no toxicity attributable to UFBs was observed in dermal, ocular, or oral tests, support the fundamental safety of ISO-certified air-UFB water.