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

5POST-APPLICATION OR RE-ENTRY WORKER EXPOSURES & RISK ASSESSMENT5.1 Only a limited number of the proposed use scenarios for dichlorvos gaveacceptable risks, based on modelled estimates of exposure to operators.5.2 The routes of exposure during post-application activities are analogous to thosefor the operator, i.e. dermal and inhalation. However, the sources are different:foliage, soil and dust may contribute as treated surfaces cause pesticide residues tobe transferred to the skin.5.4 Most maintenance activities include frequent contact with the foliage of the crop.Therefore, dermal exposure is considered to be the most important exposure routeduring these re-entry activities. The amount of resulting exposure (for a certainactivity) depends on the amount of residue on foliage, the intensity of contact withthe foliage and the duration of contact.5.5 The length of time between possible applications (7 days) was long enough, giventhe dissipation rates for dichlorvos (see below), to treat the applications separatelyand not cumulatively, i.e. complete dissipation is assumed between applications 7days apart.5.6 Studies indicate that delays between application and handling can significantlyreduce the extent of dermal exposure as only about 5% of applied dichlorvosremains on the leaf surfaces after 20 minutes, while about 50% was volatilisedand 45% absorbed by the plant (Casida et al., 1962 in WHO/IPCS, 1971).5.7 Inhalation exposure may potentially occur from residual vapour and airborneaerosols. Movement of the crop may also result in inhalation exposure toaerosol/vapour as well as dust during re-entry activities.Re-entry into treated outdoor cropsDermal Exposures:Dislodgeable foliar residue (DFR)5.8 The amount of residue on foliage depends on several factors, for example, theapplication rate, targeting and retention of spray, crop type and the amount offoliage (leaf area index). Moreover, dissipation of residues on crop foliage overtime depends on the physical and chemical properties of the applied activesubstance as well as on environmental conditions. Where experimentallydetermined dislodgeable foliar residue data are not available, a worse caseassessment of the initial DFR (DFR0), in a first tier assessment, assumes 3micrograms of active substance/square centimetre of foliage/per kg a.s.applied/hectare (UK CRD, 2008a).5.9 However, some experimental data on dichlorvos is available. Only 5% of a 0.1%aqueous 32 P-dichlorvos solution remained on the leaf surfaces of maize, cottonDichlorvos reassessment – application Page 309 of 436