MAFF was first alerted to the problem in early 1999 when the Advisory Committee on Pesticides (ACP), the body that advises MAFF ministers on pesticide safety, identified concerns about the possible risk of birth defects. The committee found there was a possible risk of harm to the unborn child if the mother is exposed to products containing the fungicide while working with the chemical. Test animal studies submitted by the manufacturer, concluded that tridemorph was capable of inducing abnormalities, primarily cleft palate, during the development of the rat foetus (see PN44 pp20-21).
Given the severity of the effects, the steepness of the dose response curve and the absence of a clear no observed adverse effect level (NOAEL) in the rat development study, the ACP recommended an increased safety factor in establishing the acceptable daily intake (ADI) for consumers, acute reference dose (ARfD) and admissible operator exposure level (AOEL). An ADI, AOEL and ARfD of 0.01 mg/kg (parts per million) of body weight per day were agreed based on the minimal effect of 10 mg/kg in the rat developmental study and using a 1,000 fold safety factor.
After receiving advice from the ACP, MAFF ministers announced a series of restrictions on formulation/packaging specifications and personal protective clothing.
At the same time, the committee recommended that further data were necessary to support continued approval – including an operator monitoring study.
In September 1999 the ACP considered comments from the manufacturer relating to the previous derivation of the ADI, AOEL and ARfD and its arguments supporting the use of a 100-fold safety factor. The committee rejected this opinion, and raised additional concern that the manufacturer was intending to produce a reasoned case based on existing scientific data for an operator monitoring study, rather than commission a study.
The ACP considered the manufacturer’s case to address operator exposure in November 1999. It had proposed a reduction in the safety factor to 500. The committee considered this to be unrealistic as there was no substantive evidence to support the use of a lower safety factor. The ACP therefore recommended to Ministers, in the absence of an operator monitoring study, that all approvals for products containing tridemorph should be revoked.
The latest restrictions on use do not come into force immediately. To allow for disposal of existing stocks in the supply chain, approval for use continues for a further two years.
Pesticide Safety Directorate, an executive agency of MAFF, p.s.d.information@psd.maff.gsi.gov.uk; see also Pesticide Monitor March 2000.
[This article first appeared in Pesticides News No. 48, June 2000, page 17]