Ethephon was last reviewed toxicologically by the 1993 JMPR, which established an ADI of 0-0.05 mg/kg bw. At that time, the Meeting noted that ethephon is an unesterified phosphonic acid and therefore is unlikely to phosphorylate hydrolases at the serine residue. Inhibition of plasma and erythrocyte, but not brain, cholinesterase activity has however been seen in vivo. Studies of cholinesterase inhibition with pure or technical grade ethephon in vitro were not available. The Meeting considered that the effects on cholinesterase required clarification and recommended re-evaluation of the compound in 1995.
The 1995 JMPR was informed that pure ethephon, technical-grade ethephon, and six manufacturing impurities in technical-grade ethephon were each being tested for anticholinesterase activity in rat plasma and erythrocytes in vitro. The Meeting recommended re-evaluation of ethephon in 1997.
The present Meeting was informed that ethephon did not inhibit cholinesterase activity in these preparations and that an investigative research programme to address this issue was being undertaken. The Meeting recommended that the results of these studies be reviewed when they become available.
The ADI of 0-0.05 mg/kg bw was maintained. No toxicological monograph was prepared.