Toxicity end-points and MOS Residential applicator exposure

Public Health Significance of Urban Pests 523

14.8.3.3. Residential bystander exposures

The general assumptions made for residential bystander exposures are as follows. • The average BW of an adult is 70 kg. • The average BW of a toddler is 15 kg. • The highest label rate for each use pattern was applied. • Exposures were secondary, except for indoor foggers. For residential bystander exposure, four scenarios were assessed to take into account pos- sible exposures of adults and children after applying pyrethrins: 1. dermal transfer and incidental oral ingestion after pet treatments 2. inhalation exposure 3. incidental oral exposure during and after indoor space-spray or fogging treatments 4. dermal exposure for all use patterns.

14.8.3.4. Scenarios

14.8.3.4.1. Scenario 1: child exposure to pet treatments The assumptions made for post-application spray treatments of pets were as follows. • One half of a 473.5-ml spray container is used to treat each animal. • The transferable residue TR from a treated pet is assumed to be 20 of the maximum application rate for sprays. • The SA of a treated 15 kg dog is 6000cm 2 EPA, 1993. • The SEF is 50 50 of the dislodged residue of pyrethrins extracted from the fingers by saliva. • The SA of a hand put in a mouth is 20cm 2 . • The Freq of hand-to-mouth events is one per day. The daily incidental oral dose was given by the following expression: TR x SEF x SAhands x Freq. The MOS is given by the following expression: Short-term Oral NOAEL 20mgkgdayDaily Oral Dose mgkgday. An AEL equal to 100 was used. The MOS calculated for this route of exposure was greater than 300, which meant this route of exposure was not considered to be of concern. Pesticides: risks and hazards 522

14.8.3. Residential exposures to pyrethrins

Pyrethrins are insecticides that interact with sodium channels, disrupting the transmis- sion of impulses along the axons. In 2006, the EPA completed a comprehensive assess- ment of exposure to pyrethrins and the risk they posed EPA, 2006b. The use patterns most common in indoor environments for control of pests were crack-and-crevice or spot applications, general surface treatments, and indoor fogging. Pyrethrins applied in homes have a very short residual life and secondary exposure scenarios were unlikely. Inhalation is the primary route of exposure and neurotoxicity is the adverse effect common to all exposure routes. EPA SOPs EPA, 1997a and PHED data were used in these evaluations. However, uncertainties in the assessment arose due to a lack of data on some consumer applicator habits and children’s exposure to pesticides. Registrant task forces performed residential studies that measured these exposures, thus enabling the EPA to perform more refined exposure and risk assessments. Due to the availability of these data, an AEL below 1000 could be used. AELs equal to 100 for residential exposures and to 300 for incidental oral exposure were adopted. Therefore, if the MOS calculated as MOS = NOAELDaily Dose was greater than 100 or 300, respectively, the exposure was acceptable.

14.8.3.1. Toxicity end-points and MOS

Due to the short life of pyrethrins, only short-term exposures were evaluated. Dermal exposure was not considered a significant exposure route, but toxicity end-points were identified for the inhalation and oral routes of exposure. T he oral NOAEL was 20mgkgday, while the inhalation NOAEL was 7.67mgkgday. As already noted, neurotoxicity is the toxic effect. An AEL of 300 10 x 10 x 3 for oral incidental exposure was selected because a developmental neurotoxicity study was not available to fully cha- racterize exposure to children. An AEL of 100 was selected for inhalation exposures, because toxicity and exposure were well characterized from the data available.

14.8.3.2. Residential applicator exposure

The assessment of residential applicator exposure evaluated the following application methods: aerosol cans, dusts, handheld wand sprayers and handheld trigger sprayers. The general assumptions made were as follows. • The maximum application rate was 0.1 kg pyrethrins per 92.90 m 2 . • Only inhalation exposures were assessed, because dermal and oral exposures were assu- med to be insignificant. Exposure was assumed to occur at the time of application. The inhalation MOS was calculated as NOAELInhalation Dose in mgkgday, and the AEL equalled 100. The calculated MOSs exceeded the AEL of 100. Thus, consumer applicator exposure to pyrethrins did not exceed the level of concern and were considered to be acceptable for details on the range of MOS values, see EPA, 2006b. Public Health Significance of Urban Pests 525 The daily oral dose in mgday is given by the expression: ISR x HTE x SEF x SA x Freq x EDBW. The MOS is given by the expression: Short-term Oral NOAEL 20 mgkgdayDaily Oral Dose. An AEL of 300 was used. In this assessment, hand-to-mouth transfer from treated surfaces did not present a risk of concern as the MOS was greater than 300. 14.8.3.4.4. Scenario 4: dermal exposure from applications of pyrethrins Dermal risk assessments were not required for pyrethrins, due to negligible dermal absorption and dermal toxicity. A 21-day dermal toxicity study in rabbits showed no sys- temic or dermal toxicity at the limit dose of 1000 mgkgday. Also, a human dermal pene- tration study showed absorption was less than 0.22. For pyrethrins, the comparative risk from the use patterns can be described as follows: Inhalation Incidental Oral Ingestion Dermal Exposures. T he dermal exposure presents the lowest risk and inhalation exposure the highest. However, inhalation risks are higher for children than for adults. Also, residues on pets treated with pyrethrins for control of pests present little risk to children and adults.

14.8.4. Summary of examples of residential risk assessments