Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:6:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 6 (pt 1/5)
Character Range: 2523903–2526873

6                   Heptachlor

6.1              General
Several comprehensive reviews of heptachlor in the environment and its toxicity to humans are available and should be consulted for more detailed information (ATSDR 2007; WHO 1984; WHO 2006). The following provides a summary of the key aspects of heptachlor that are relevant to the derivation of a soil HIL.

Heptachlor is a polychlorinated cyclodiene insecticide that was produced and distributed from the early 1950s to the 1980s under several trade names including Heptagran®, Basaklor®, Drinox®, Soleptax®, Termide®, and Velsicol 104® (ATSDR 2007). Pure heptachlor is a white powder that smells similar to mothballs. The less pure grade commercial insecticide is tan in colour. Heptachlor is stable in light and air and does not burn easily or explode. It does not dissolve readily in water but is soluble in organic solutions (WHO 1984; ATSDR 2007).

Heptachlor is a broad-spectrum insecticide that was distributed commercially in Australia until the mid-1990s to protect against household pests such as termites. Its use in the agricultural industry to control insects in soil and seed crops was withdrawn in the late 1970s and early 1980s (NHMRC 2011). Heptachlor is a manufactured chemical and does not occur naturally. It should be noted that heptachlor is also a component of the pesticide chlordane (approximately 10%) (ATSDR 2007).

6.2              Previous HIL
The derivation of the previous HIL (HIL A = 10 mg/kg) for heptachlor is presented by Di Marco (1993) and NEPC (1999). In summary, the HIL was derived on the basis of the following:
    * Background intakes were considered in the derivation of the current HIL with the intakes from food, water and ambient air considered to comprise 40% of the adopted ADI.
    * An ADI of 0.0001 mg/kg/day, referenced from the JMPR, was considered. An additional factor of 3 was used because of the uncertainties associated with the bioavailability estimates adopted and exposure levels in the future.
    * Dermal absorption of organochlorine pesticides was considered to be 5%.
    * Oral bioavailability of organochlorine pesticides was considered to be 10%.
    * Based on intakes derived from soil (ingestion, dermal absorption and dust inhalation), an HIL of 10 mg/kg was calculated.

6.3              Significance of Exposure Pathways

6.3.1         Oral Bioavailability
Insufficient data is available to adequately define the bioavailability of heptachlor 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
Insufficient data is available on the dermal absorption of heptachlor from soil. Hence the default values of 0.1 (10%) suggested by US EPA (1995) for pesticides has been adopted in the derivation of HILs.

6.3.3         Inhalation of Dust
Heptachlor