Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 1/5)
Character Range: 2613513–2616603

3                   MCPA, MCPB and Mecoprop

3.1              General
The following information on MCPA (4-chloro-2-methylphenoxyacetic acid), MCPB (4-(2-methyl-4-chlorophenoxy)butyric acid) and mecoprop (also referenced as MCPP) are grouped together as they are structurally similar chlorophenoxy herbicides.

While limited data is available, reviews of these compounds in the environment and their toxicity to humans are available and should be consulted for more detailed information not presented in this summary (WHO 2011; HSDB 2010). The following provides a summary of the key aspects of these compounds that are relevant to the derivation of a soil HIL.

In their pure form the three compounds are white crystalline solids, though technical grade products can be white to light brown crystal powders or liquids. The compounds are often formulated as salts (e.g. potassium or diethylamine salts) or esters (e.g. iso-octyl esters). The three compounds are the active ingredients in post emergence herbicides used to control annual and perennial weeds in agricultural, commercial/industrial and domestic environments. In Australia all three compounds are registered for agricultural application on wheat, barley, oats, sorghum, rice, linseed, peas, grass pastures, turf, clover, corn/maize and oilseed poppies, and for the home garden to control broadleaf weeds (WHO 2011).

3.2              Previous HIL
No previous HIL is available for MCPA, MCPB or mecoprop (NEPC 1999).

3.3              Significance of Exposure Pathways

3.3.1         Oral Bioavailability
Insufficient data is available to adequately define the bioavailability of MCPA, MCPB or mecoprop, 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.

3.3.2         Dermal absorption
Insufficient data is available on the dermal absorption of MCPA, MCPB or mecoprop 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.

3.3.3         Inhalation of Dust
MCPA, MCPB and mecoprop are 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.

3.3.4         Plant Uptake
Most chlorophenoxy herbicides are toxic to plants and, as such, will be phytotoxic to almost all broadleaf crops including tomatoes, grapes and fruit trees well before plant uptake into edible portions of fruit and vegetable crops is of significance. Hence the uptake of these compounds into home-grown produce has not been considered in the derivation of HIL A.

Note that the phytotoxic effects of these compounds may need to be addressed on a site-specific basis if detected in soil.

3.3.5         Intakes from Other Sources – Background
Limited data is