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

Children’s incidental ingestion of soil (US EPA, 2006b)6.8 The approach used to calculate doses that are attributable to soil ingestion is:Where:ADOD = (AR x DF) x F x IgR x SDF / BWADOD = oral dose on day of application (mg/kg b.w./day)AR = application rate (mg/cm 2 ) [Note: this value has been modified by the DFvalues used in the first 3 equations to reflect these spray drift situations, and notdirect turf applications.]F = fraction or residue retained on uppermost 1 cm of soil (%) (note: this is anadjustment from surface area to volume)SDF = soil density factor -- volume of soil (cm 3 ) per microgram of soil;IgR = ingestion rate of soil (mg/day)BW = body weight (kg)Assumptions:F - fraction or residue retained on uppermost 1 cm of soil is 100 percent based onsoil incorporation into top 1 cm of soil after application (1.0/cm)SDF = soil density factor -- volume of soil (cm 3 ) per gram of soil; to weight 6.7 x10 -4 cm 3 /mg soil)IgR - ingestion rate of soil is 100 mg/dayBW - body weight of a toddler is 15 kg6.9 These models have been applied to two potential New Zealand use patterns: boomspraying at 0.6 mg/ml (Scenarios 1-4); and, air assisted spraying at 1.026 mg/ml(Scenarios 5 & 6; 7 & 8). Applications in passionfruit (Scenarios 7 & 8) arestated to be carried out with knapsack sprayers, and as the target is high-level thedrift fallout value (DF) for air assisted spraying (10%) had been used rather thanground boom value (1%). This approach is likely to be extremely precautionary.6.10 No New Zealand monitoring studies of airborne dichlorvos at application sites areavailable to estimate possible public exposure, or modify the default assumptionsof these models. However, some relevant experimental data from Casida et al. ondichlorvos dissipation are available, and these are discussed above in Section 5.5% of a 0.1% aqueous 32 P-dichlorvos solution remained on the leaf surfaces ofmaize, cotton and peas 20 minutes after application, while about 50% wasvolatilised and 45% absorbed by the plant (Casida et al., 1962 in WHO/IPCS,1971; APVMA, 2008b). In which case, the TTR turf transferable residue factor inthe UK CRD equations, which is set at 5% (the US EPA default value) needs to bemodified to reflect that the Casida et al. data indicates that only 5% is availablefor transfer, while the TTR suggests only 5% of the available remaining residueon the foliage is actually transferred. See Appendix 6 and Table XX.6.11 For non-cancer (or toxicological endpoints with thresholds) risks, the estimatedexposures to dichlorvos are compared to the AOEL (0.0014 mg/kg b.w./day) toDichlorvos reassessment – application Page 335 of 436