Mirex in freshwater and marine water
Toxicant default guideline values for protecting aquatic ecosystems
Extracted from Section 8.3.7 ‘Detailed descriptions of chemicals’ of the ANZECC & ARMCANZ (2000) guidelines.
The default guideline values (previously known as ‘trigger values’) and associated information in this technical brief should be used in accordance with the detailed guidance provided in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality.
Description of chemical
Most organochlorine pesticides have been phased out of use in recent years, mainly because of their residual properties and potential for bioaccumulation. The guideline trigger values stated are for toxicity only and need to be adjusted for bioaccumulation where appropriate. Where the statistical distribution method was used, figures quoted are the 95% protection levels, usually applicable to slightly to moderately disturbed systems although 99% protection figures are recommended for chemicals that bioaccumulate.
Mirex (CAS 2385-85-5) is a cyclodiene organochlorine pesticide. Its chemical name is dodecachloropentacyclo[5,3,O2,6,O3,9,O4,8]decane, formula is C10Cl12 and molecular weight 546.
Uses and environmental fate
Mirex has only two registered uses in Australia, against termites in northern Australia (NRA 1997a).
The toxicity of mirex was high to moderate for a small range of species.
Freshwater crustaceans: two species, 96-hour LC50 or EC50 (immobilisation), of 510 and 2000 µg/L. A 24-hour LC50 was reported for a Macrobrachium sp. of 104 µg/L.
Freshwater insects: one species, (Dineutus americanus), 72-hour EC50 (immobilisation) 40 µg/L. A 24-hour EC50 (immobilisation) of 160 µg/L was reported for Gerris remigis (note that, for other less sensitive species, test durations < 96 hours were not sufficient to reach incipient toxicity).
Freshwater hydra: one species, 96-hour LC50 4100 µg/L.
A low reliability freshwater trigger value of 0.04 µg/L was derived for mirex using an assessment factor (AF) of 1000. This can also be used as an interim working level for marine systems. Mirex bioaccumulates strongly. These figures have not taken this into account and would need to be adjusted for bioaccumulation.
ANZECC & ARMCANZ 2000. Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra.
NRA 1997a. Database extraction of selected pesticides: Registered uses in Australia, National Registration Authority, July 1997, Canberra.