Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:7:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 7 (pt 1/4)
Character Range: 2666783–2669844

7                   Bifenthrin

7.1              General
Several comprehensive reviews of bifenthrin in the environment and its toxicity to humans are available and should be consulted for more detailed information not presented in this summary (ATSDR 2003; US EPA 1999; Fecko 1999; Taylor & Di Marco 2003). The following provides a summary of the key aspects of bifenthrin that are relevant to the derivation of a soil HIL.

Bifenthrin is the common name for the compound (2-methyl-1, 1-biphenyl-3-y1)-methyl-3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethylcyclopropanecarboxylate. It is referred to as a 'third generation' synthetic pyrethroid insecticide and is known to be more stable and persistent in the environment and have a greater insecticidal activity than previously synthesized pyrethroid compounds (Taylor & Di Marco 2003). Pure bifenthrin is a crystalline or waxy solid which is off-white to pale tan in colour.

Bifenthrin is used in the agricultural industry to control insects in a number of crops and to protect stored grains. It is also used in domestic and commercial settings as a barrier to repel or kill insects such as termites (Taylor & Di Marco 2003).

7.2              Previous HIL
No previous HIL is available for bifenthrin (NEPC 1999). It is noted, however, that review of bifenthrin by Taylor & Di Marco (2003) derived a soil investigation level (residential) of 300 mg/kg on the basis of a threshold toxicity reference value of 0.01 mg/kg/day (noted to be derived from the Therapeutic Goods Administration), 100% oral bioavailability, soil ingestion only, and an assumption that exposures from soil contribute (by default) 20% of the reference value.

7.3              Significance of Exposure Pathways

7.3.1         Oral Bioavailability
Insufficient data is available to adequately define the bioavailability of bifenthrin, 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.

7.3.2         Dermal absorption
Insufficient data is available on the dermal absorption of bifenthrin from soil. Hence the default value of 0.1 (10%) suggested by US EPA (1995) for pesticides has been adopted in the derivation of HILs.

It is noted that review by ATSDR (2003) considered the limited human and animal data associated with dermal application of pyrethroids. Dermal absorption values in the range of 0.5% to 1.8% were identified. Hence the adoption of 10% is considered conservative.

7.3.3         Inhalation of Dust
Bifenthrin 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.

7.3.4         Plant Uptake
Limited information is available on the potential for plant uptake of bifenthrin. ATSDR (2003)