Application for the Reassessment of a Hazardous Substance under ...

Appendix 1:APVMA - Summary of benchmarks used in occupational riskassessments (APVMA, 2008b).“NOELs for Occupational Health & Safety Assessment―Dichlorvos products intended for professional use are most likely to be applied byPCOs [pest control operators], horticulturalists and operators of grain storage facilitiesand flour mills. Depending on pest activity, PCOs may use dichlorvos products onseveral days or daily during the working week. Repeated use of dichlorvos for treatmentof commercial and industrial buildings could result in daily exposure of buildingoccupants, given that dichlorvos has been detected in workplace atmospheres for up to afortnight after application (Schofield, 1993). Grain storage operators and avocadogrowers are more likely to be exposed on a seasonal basis, but also may be exposed onseveral days in succession. Exposure of horticulturalists would be dictated by thegrowth cycle of mushrooms or plants under cultivation, and could occur regularly onsingle days but with several days or more between uses. The most likely potential routesof exposure would be by dermal contact with the undiluted products or spray mixture,and by inhalation of dichlorvos vapour or aerosols.“Dermal NOEL for Occupational Exposure Assessment―Short-term repeat-dose toxicity studies of up to 28 days‘ duration are considered to bethe most appropriate for derivation of NOELs for occupational health and safetyassessment of product users who are exposed repeatedly. The most relevanttoxicological end-point for occupational exposure to dichlorvos is plasma ChEinhibition, as in a repeated exposure scenario, there would be scope for progressivelyincreasing inhibition of plasma ChE activity if the (less sensitive) RBC ChE inhibitionwere used as the pivotal end-point. Although repeat-dose studies via the dermal routewould be optimal for derivation of occupational health and safety NOELs, no suchstudies with dichlorvos are available. The assessment therefore must be performedusing studies undertaken by oral administration. A summary of NOELs determined inoral studies considered adequate for regulatory purposes is shown in the followingtable:Dichlorvos reassessment – application Page 269 of 436