Delayed neurotoxicity of trixylenyl phosphate and a trialkyl/aryl phosphate mixture, and the modulating effect of atropine on tri-o-tolyl phosphate-induced neurotoxicity.

Two hydraulic fluids, Fyrquel EHC (trixylenyl phosphate) and Reofos 65 (trialkyl/aryl phosphate mixture), were examined for effects of organophosphorus-induced delayed neurotoxicity (OPIDN) in hens using the OECD Test Guideline (1984). Furthermore, the influence of atropine and the concentration of tri-o-tolyl phosphate (TOTP) in the oil vehicle on the development of OPIDN were investigated. For Fyrquel EHC a neurotoxic effect was demonstrated with single oral doses of 5, 10 and 15 g/kg. Reofos 65 caused no clinical neurotoxic effect after single oral doses of 5, 10 and 15 g/kg. Redosing at day 22 with Reofos 65 did not result in clinical delayed neurotoxicity, but minor histopathological changes were found in the spinal cord and peripheral nerves. Atropine 10 mg/kg im delayed the onset of OPIDN caused by TOTP 1 g/kg po without affecting the final neurotoxic effect. Dilution of TOTP in large amounts of soybean oil vehicle reduced its neurotoxic effect. In conclusion, the neurotoxic potential of the hydraulic fluids was very low. The effect of atropine and the concentration of the test compound in oil vehicle should be taken into consideration when designing experiments on OPIDN.