Advisory Committee on Pesticides Annual Report 2001

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Section E: UK Review Programme would rapidly dissipate and dissipation could be expected to be enhanced by the moderate volatility of chlorpyrifos-methyl. Any material that did volatilise was unlikely to be persistent in the atmosphere. Some information had been provided to show the environmental fate and behaviour of chlorpyrifos-methyl in soil, water and air should accidental exposure occur. As a precaution and in line with other products, the ACP considered that the standard warning ‘Exclude wildlife from buildings during treatment’ should appear on the product label. The ACP recommended that current approvals for chlorpyrifos-methyl should be allowed to continue. Chlorpyrifos – dog study At its meeting in July 2000 the ACP had considered a proposed acceptable daily intake (ADI) and acceptable operator exposure level (AOEL) of 0.01 mg/kg bodyweight (bw) [which was in line with that set by the Joint FAO/WHO Meeting on Pesticide Residues (JMPR)]. Although no new scientific data had become available to raise concerns about chlorpyrifos, the <strong>Committee</strong> had been concerned that the evidence underpinning the proposed ADI was not as strong as it would like to see, in particular regarding the possibility of effects on the peripheral nervous system. The <strong>Committee</strong> had therefore requested a four-week study in dogs to provide the reassurance sought. Ministers’ agreement to the ACP recommendations had not been reached. However, the company had undertaken a six-week study in dogs of the type required. 41 The new study showed that within the peripheral tissues there was no consistent inhibition of acetyl cholinesterase (AChE) activity in any tissue. Where inhibition was recorded, it was not dose-related (with the exception of the atrium in males), and in no tissue was inhibition recorded consistently in both sexes. There were no statistically significant effects in any peripheral tissue. It was concluded that the differences recorded in peripheral tissues resulted from a natural variation in AChE activity rather than treatment-related effects. Also the <strong>Committee</strong> did not consider that the inhibition in the atrium in males was a treatment-related effect. No inhibition was recorded in females, and it was considered to be biologically implausible that there would be a sex difference in the effects of chlorpyrifos which only affected atrial tissue and no other tissue.
<strong>Advisory</strong> <strong>Committee</strong> on Pesticides Annual Report 2001 Overall the ACP concluded that this study showed no marked difference in sensitivity to AChE inhibition between brain AChE and AChE in peripheral tissues. Red blood cell (RBC) AChE was significantly more sensitive. Therefore reference values based on no observed adverse effect levels (NOAELs) for inhibition of brain AChE would be expected to cover AChE in the peripheral nervous system, and reference values based on inhibition of red blood cell AChE in dogs would be conservative. The <strong>Committee</strong> thus decided that reference values for chlorpyrifos should be based on NOAELs for inhibition of brain AChE in dogs, since the results of the dog study examining peripheral tissues suggest that such reference values would also protect the peripheral nervous system. It was concluded that the ADI and AOEL for chlorpyrifos should be maintained at 0.01 mg/kg bw/day. On the basis of this reference value the <strong>Committee</strong> recommended that approvals for chlorpyrifos could continue as previously recommended. The <strong>Committee</strong> also asked that some further investigation of drench treatment with chlorpyrifos be carried out. 42 Chlorpyrifos – ornamental bulb dipping When the ACP had considered chlorpyrifos in July 2000, it had recommended, among other things, that off-label approval for use as a bulb dip should be revoked unless a suitable protocol for an operator exposure study was provided within eight weeks. However, subsequent to the ACP consideration, the off-label approval for this use expired and no further action was taken. The ACP heard that this approval had been allowed to lapse through oversight on the part of the off-label applicants and was an important use which grower groups were prepared to continue to support. The ACP noted that exposure had been estimated using the Health and Safety Executive’s (HSE’s) waterbased timber pre-treatment model based on 95 th percentile values and that estimated exposure was 130 percent of the AOEL. The <strong>Committee</strong> felt that when based on the usual 75 th percentile values, estimated exposures were likely to fall within the AOEL. The ACP recommended that the off-label approval for the use of chlorpyrifos for bulb dipping should be reinstated and that the secretariat should consider, with the off-label applicants, further refinement of the risk assessment including handling of treated bulbs and disposal of dipping solution. Note: The recommendation to reinstate the off-label approval was not a unanimous conclusion of the <strong>Committee</strong>.
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Advisory Committee on Pesticides Annual Report 2001

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