Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:6:p2
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 6 (pt 2/6)
Character Range: 2652530–2655562

a health-based soil investigation level (residential) of 80 mg/kg on the basis of a threshold toxicity reference value of 0.003 mg/kg/day (noted to be derived from US EPA), 100% oral bioavailability, soil ingestion only, and an assumption that exposures from soil contribute (by default) 20% of the reference value.

6.3              Significance of Exposure Pathways

6.3.1         Oral Bioavailability
Insufficient data is available to adequately define the bioavailability of chlorpyrifos, hence a default approach of assuming 100% oral bioavailability has been adopted in the derivation of an HIL. It is noted that a site-specific assessment of bioavailability can be undertaken where required.

6.3.2         Dermal absorption
Limited data is available on dermal absorption of chlorpyrifos. Review by APVMA (2009) identified that in acute animal studies, dermal absorption has been shown to be low. In human volunteers, dermal absorption was estimated to be 1.35% of the applied dose (NRAAVC 2000). Dermal absorption of chlorpyrifos in soil (not in solution) is expected to be lower. The assessment of occupational exposures by NRAAVC (2000), as confirmed by APVMA (2009), has adopted a dermal absorption value of 3%. This has been adopted in the derivation of HILs.

6.3.3         Inhalation of Dust
The inhalation exposure pathway is expected to be of significance during and immediately after the application of products containing the product. In these cases chlorpyrifos may be present in the vapour phase as well as sorbed to particulates (ATSDR 1997). An Australian study by Beard et al. (1995) demonstrated that airborne exposures to pesticides in the community can be substantial and are largely related to residential use of pesticides rather than agricultural applications. These issues should be considered on a site-by-site basis.

For the assessment of chlorpyrifos as a soil contaminant (no product application considered), the compound is not considered sufficiently volatile to be of significance and inhalation exposures associated with particulates outdoors and indoors are expected to be of less significance than ingestion of soil. While likely to be negligible, potential inhalation exposures associated with dust have been considered in the HIL derived.

6.3.4         Plant Uptake
Information relating to the potential for plant uptake of chlorpyrifos is mixed. ATSDR (1997) notes that some research has shown that only very small levels of chlorpyrifos are taken up by plant roots, translocated, or metabolised by plant tissues. However, other researchers have found that soil-applied doses of chlorpyrifos are transported to foliage. APVMA (2009) notes that absorption and translocation of foliar deposits of chlorpyrifos is very low, with the bulk dissipating through volatilisation. Absorption by roots from the soil is also poor. This is further supported by studies presented by JMPR (1972) that show that the uptake of chlorpyrifos or its degradation products is insignificant through the foliage