Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:2:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 2 (pt 1/5)
Character Range: 2600899–2603960

2                   2,4-D

2.1              General
2,4-D is the common name for the chlorophenoxy herbicide 2,4-dichlophenoxy acetic acid.

Several comprehensive reviews of 2,4-D in the environment and its toxicity to humans are available and should be consulted for more detailed information not presented in this summary (APVMA 2006; WHO 1984; WHO 1987). The following provides a summary of the key aspects of 2,4-D that are relevant to the derivation of a soil HIL.

The herbicide is also formulated as an amine salt, alkali metal salt and ester derivative of 2,4-D (WHO 1984). Pure 2,4-D is a white to off-white crystalline powder with a slight phenolic odour (APVMA 2006). The commercial grade herbicide is often combined with solvents or surfactants and sold as granules, dust, emulsions and liquid concentrates (WHO 1984). 2,4-D is slightly soluble in water whereas the amine and alkali metal salt derivatives are highly soluble. The ester derivate is insoluble in water (WHO 1984). 2,4-D esters with short chain alcohols are highly volatile whereas 2,4-D and its salt and amine derivatives have a low volatility (APVMA 2006).

Some chlorinated by-products produced during manufacture of 2,4-D and its derivatives such as 2,7- dichlorodibenzo-p-dioxin, 1,3,6,8- and 1,3,7,9-tetrachlorodibenzo-p-dioxins and 1,3,7-trichlorodibenzo-p-dioxin have been associated with enhanced toxicity findings (WHO 1984).

2,4-D and its derivatives are systemic herbicides commonly used in Australia to control broadleaf and aquatic weeds (NHMRC 2004). At least 122 separate products containing these compounds were registered in Australia in 2003 (APVMA 2006). They were registered to control weeds in agricultural crops such as cereals, sugar cane and rice and in pastures and turf. 2,4-D herbicides were also applied at very low application rates to citrus and pears to reduce premature fruit drop and increase fruit storage life (WHO 1984; APVMA 2006). In addition, 2,4-D is used to increase the proportion of medium-sized potato tubers and the intensity of colour in red-skinned varieties (APVMA 2006). In 2006, the Australian Pesticides and Veterinary Medicines Authority conducted a review of the environmental fate and ecotoxicity of volatile 2,4-D esters and concluded that the registration of these compounds should be suspended (APVMA 2006). This review process is ongoing and the APVMA website (www.apvma.gov.au) should be checked for any updates on which products are currently registered.

2.2              Previous HIL
No previous HIL is available for 2,4-D (NEPC 1999).

2.3              Significance of Exposure Pathways

2.3.1         Oral Bioavailability
Insufficient data is available to adequately define the bioavailability of 2,4-D, 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.

2.3.2         Dermal absorption
A dermal absorption value of 0.05 (5%) is available from US EPA (2004) based