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

[0.625 x {(0.018 x 0.05) + (2.68 x 0.05) + (0.26 x 0.1)} x 0.3] / 70 =(0.1006 x 0.30) / 70 = 0.0302 / 70 = 0.0004 mg/kg b.w.Inhalation exposures:For the estimation of inhalation exposures APVMA (2008b) noted that as long as theoperator did not walk back through the efflux stream then the highest airborneconcentration of dichlorvos should be the use rate, 50 mg/m 3 , with a TWA of 25 mg/m 3 .The APVMA estimated the duration of exposure on the application times from themanufacturer‘s specification for the manual pressure gun (70 sec/300 m 3 ; i.e. (375/300x 70) = 87.5 seconds, (3750/300 x 70) = 875 seconds and (12500/300 x 70) = 2917seconds for the New Zealand Scenarios) for larger industrial spaces. [These valueswere rounded to 1.5, 15 and 50 minutes, equivalent to 0.025, 0.25 and 0.83 hourrespectively for the model.] The operator‘s ventilation rate was taken as 1m 3 /hour forlight activities (US EPA, 1996; Original not sighted).For 375 m 3 – inhalation exposure:= airborne concentration (TWA) [mg/m 3 ] x ventilation rate [m 3 /hr] x duration [hr]25 x 1 x 0.025 = 0.625 mg a.i./personThen accepting the inhalation absorption factor of 100%, and dividing by 70 kg b.w.,the systemic dose will be:(0.625 x 1.00) / 70 = 0.0089 mg/kg b.w.If RPE is considered to mitigate exposures, APVMA used 10% penetration of half-facerespirators; 2% penetration of full-face respirators; and, no penetration of air-hoserespirators or SCBA (Thongsinthusak et al., 1993; Original not sighted):With half-face (protection factor applied, 0.1):(25 x 1 x 0.025) / 70 = (0.625 x 0.10) / 70 = 0.0625 / 70 = 0.0009 mg/kg b.w.For 3750 m 3 – inhalation exposure:25 x 1 x 0.25 = 6.25 mg a.i./person.Then accepting the inhalation absorption factor of 100%, and dividing by 70 kg b.w.,the systemic dose will be:(6.25 x 1.00) / 70 = 0.0893 mg/kg b.wDichlorvos reassessment – application Page 358 of 436