Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:4:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 4 (pt 1/4)
Character Range: 2625437–2628428

4                   Picloram

4.1              General
Limited data is available on picloram, however reviews of this compound in the environment and its toxicity to humans are available and should be consulted for more detailed information not presented in this summary (Health Canada 1988; US EPA 1995a; OEHHA 1997). The following provides a summary of the key aspects of picloram that are relevant to the derivation of a soil HIL.

Picloram is a member of the pyridine carboxylic acid group and is manufactured in a number of forms. Picloram acid is only manufactured as an intermediate product in the production of herbicides whereas the amine salt, potassium salt and ester derivatives of picloram are produced as commercial herbicides. Technical grade picloram acid is an off-white to brown powder. It is slightly soluble in water and the amine and potassium salt derivatives are highly soluble. The ester derivative, however, is insoluble in water (US EPA 1995a).

Picloram acid and its derivatives have been used since the 1960s as a systemic herbicide to control woody plants and broadleaf weeds in rights of way, forestry, rangeland and pasture. In Australia, picloram derivatives are used to control weeds in winter cereals and linseed crops and to control a number of environmental and noxious weeds (APVMA 2009).

Picloram products are commonly contaminated with hexachlorobenzene (HCB). The presence of HCB in picloram affects the assessment of toxicity in a number of studies. Limited data is available for picloram alone. Available data also show that picloram is synergistic with several common herbicides (in particular 2,4-D, atrazine and alachlor) with respect to its toxicity to mammals and fish (NCAP 1998).

4.2              Previous HIL
No previous HIL is available for picloram (NEPC 1999).

4.3              Significance of Exposure Pathways

4.3.1         Oral Bioavailability
Insufficient data is available to adequately define the bioavailability of picloram, 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.

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

4.3.3         Inhalation of Dust
Picloram 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.

4.3.4         Plant Uptake
Most carboxylic herbicides are toxic to plants and, as such, will be phytotoxic to almost all broadleaf crops including tomatoes, grapes and fruit trees well before