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

6BYSTANDER & RESIDENT EXPOSURE & RISK ASSESSMENTBystander and resident exposure & risk assessment for outdoor usesIntroduction6.1 The main potential sources of exposure to the general public (bystander orresident) from dichlorvos (other than via food residues) is via spray drift at thetime of application or from surfaces contaminated either by spray drift or directtreatment. Bystander and resident exposures would tend to be intermittent incomparison to exposure of workers, who are handling the pesticide throughout theapplication. In addition, spray densities, and hence exposure levels drop off withdistance from spraying operations.6.2 TCL notes that any potential bystanders or residents will not be directly handlingthe substance, and they will not be wearing PPE. [Note: amateur, home users arenot considered bystanders or residents while using pesticides.]6.3 UK CRD Bystander Exposure Guidance Document (UK CRD, 2008b) givesmodels for estimating bystander exposure in three circumstances:• Exposure from spray drift at the time of application;• Exposure from inhalation of pesticide which volatilises from the crop or soilsurface after the application has been made; and• Exposure through contact with spray drift contaminated surfaces.6.4 Of these options, the Agency has advised TCL that the first two approachesshould not be used due to concerns about these models. The UK CRD model forexposure through contact with spray drift contaminated surfaces (UK CRD,2008b) is used with the addition of the US EPA model estimate of spray driftcontaminated soil/grass ingestion by young children (US EPA, 2006b).Children’s dermal exposure (UK CRD, 2008b)6.5 Systemic exposures via the dermal route were calculated using the UK CRD(2008b) default drift fallout values (1% from boom sprayers (Scenarios 1-4); 10%from air-assisted sprayers (Scenarios 5 & 6)) and the following equation:SE(d) = AR x DF x TTR x TC x H x DA / BWWhere:SE(d) = systemic exposure via the dermal routeAR = field application rate (μg/cm 2 )DF = drift fallout valueTTR = turf transferable residuesTC = transfer coefficientH = exposure duration for a typical day (hours) – this has been assumed tobe 2 hours which matches the 75th percentile for toddlers playing on grassDichlorvos reassessment – application Page 333 of 436