Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:9:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 9 (pt 1/4)
Character Range: 2559265–2562261

9                   Mirex

9.1              General
Several comprehensive reviews of mirex in the environment and its toxicity to humans are available and should be consulted for more detailed information (ATSDR 1995; WHO 1984; US EPA 2003). The following provides a summary of the key aspects of mirex that are relevant to the derivation of a soil HIL.

Mirex is the common name for the compound 1,1a,2,2,3,3a,4,5,5,5a,5b,6-dodecachloroocta-hydro-1,3,4-metheno-1H-cyclobuta[c,d]pentalene. Mirex can also be used to describe an insecticide containing the compound as its active ingredient. The mirex compound is an odourless, white, crystalline solid. It is virtually insoluble in water, has a low vapour pressure and does not burn easily (WHO 1984; ATSDR 1995). Mirex is very stable and does not react with acids (sulfuric, nitric or hydrochloric), bases, chlorine or ozone (WHO 1984).

Until recently, mirex was used extensively in the Northern Territory to control giant termite populations. An exemption was granted under the Stockholm Convention for the continued use of mirex for giant termite control but the compound was completely banned in Australia in 2007 following the development of suitable alternative treatments (DEH 2006; APVMA 2007). Mirex was historically used as a pesticide to control fire ants, mostly in the south-eastern part of the United States. It was also used as a flame retardant in plastics, rubber, paint, paper and electrical goods and as a smoke generating compound when mixed with zinc oxide and aluminium (WHO 1984; ATSDR 1995).

9.2              Previous HIL
No previous HIL is available for mirex (NEPC 1999).

9.3              Significance of Exposure Pathways

9.3.1         Oral Bioavailability
Insufficient data is available to adequately define the bioavailability of mirex 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.

9.3.2         Dermal absorption
Insufficient data is available on the dermal absorption of mirex 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.

9.3.3         Inhalation of Dust
Mirex 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.

9.3.4         Plant Uptake
Mirex is noted to bioaccumulate in terrestrial plants (ATSDR 1995). Limited data shows plant uptake of mirex when applied as a pesticide, however no data is available on plant uptake from soil with residual contamination of mirex. Mirex has a high Koc value (log Koc = 3.7) and low solubility in water (ATSDR 1995), suggesting that the compound is