Acute dermal toxicity study of new, used and laboratory aged aircraft engine oils

There is little data available on toxicity levels of used aircraft engine oils relative to their unused (new) versions. This study was conducted to determine if new engine oils and their used versions have the potential to induce dermal irritation. Twelve male New Zealand White rabbits (Oryctolagus cuniculus, 19 weeks old) were used to determine the acute dermal toxicity potential of four aircraft turbine oils including MIL-PRF-7808 Grades 3 and 4 and MIL-PRF-23699 Grade 5 High Thermal Stability (HTS) and a Grade 5 experimental aircraft engine oil in their unused and used or laboratory stressed states. Five fur-free test sites (6 cm² each) located lateral to the midline of the back were treated with two undiluted (0.5 ml) new engine oils and their used versions. The fifth site received reverse osmosis deionized (RODI) water as a control. Each treatment was repeated 3 times (3 rabbits/oil type). Each oil was tested under both semi-occluded and occluded conditions. The 4 h exposure was followed by gauze plus wrappings removal, and gentle cleaning of sites prior to scoring for erythema and edema at 0.5-1, 24, 48 and 72 h post exposure based on Draize (1959). E-collars were placed on each animal for at least 72 h to prevent ingestion of the test substance and/or gauze and wrappings and/or disturbance of site recovery. Additional observations were made on days 7, 10 and 14 to determine recovery. Exposure to both used and new oils produced dermal irritation consisting of no more than very slight to well-defined erythema and very slight edema. The calculated Primary Dermal Irritation Index (PDII) indicated that all the oils were slightly irritating (means ranged from 0.42 to 1.08). Although the PDII values for new oils and their used versions were not significantly different from each other, they were all statistically higher (p < 0.05) than those obtained for the control regardless of the type of occlusion binding applied. The used oils under semi-occlusion conditions yielded larger size effects (Cohen's d) relative to their unused versions suggesting an enhancement in irritation when the oil is aging. Grade 4 in the used state yielded the largest size effect which was d = 5.9 versus 2.6 for its unused version. The slight dermal irritation resulting from four hours of exposure to oils raises concerns about the magnitude of impact related to prolonged and/or repeated exposure.