Dicofol 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 systemsalthough 99% protection figures are recommended for chemicals that bioaccumulate.
Dicofol (CAS 115-32-2) also known as Kelthane® has IUPAC name of 2,2,2-trichloro-1,1-bis(4-chlorophenyl)ethanol, formula of C14H9Cl5O and molecular weight of 370.5. It is soluble in water only to 0.8 mg/L at 25°C and has a log Kow of 4.3. It is one of the few organochlorine pesticides still in use in Australia.
Uses and environmental fate
Dicofol is used as a non-systemic acaricide (miticide) in a variety of fruits, vegetables, cotton, tobacco and ornamentals. It has almost 120 registered uses in Australia (NRA 1997a).
Dicofol has a similar basic structure to DDT but the aliphatic OH group provides an active site for more rapid degradation. It is slowly degraded in acid media (DT50 of 85 days) but degrades rapidly in alkaline conditions (DT50 of 3 to 4 days at pH7 and only 26 minutes at pH 9) (Tomlin 1994). The 2,4'-isomer is hydrolysed more rapidly. It is also degraded by light, to the dichlorobenzophenone (Tomlin 1994).
Dicofol has high to moderate toxicity to most test species. Its toxicity is less, however, than many other organochlorine pesticides.
Freshwater fish: 13 spp, 48 to 96-hour LC50, 53 to 4400 µg/L. An outlying figure of 25,000 µg/L was also reported for Anguilla japonica (AQUIRE 1994) well above the water solubility. Oncorhynchus clarki and Salvelinus fontinalis were most sensitive. Tomlin (1994) reported a ‘life cycle no observed effect concentration (NOEC)’ for fathead minnow, Pimephales promelas, of 4.5 µg/L and for Oncorhynchus mykiss (ELS) of 4 4 µg/L. This could not be assessed.
Freshwater crustaceans: no data available. Tomlin (1994) reported a 48-hour EC50 figure of 140 µg/L to Daphnia magna, which could not be assessed.
Freshwater insects: 1 sp, Pteronarcys californica, 96-hour LC50, 650 µg/L.
Freshwater molluscs: 4 spp, 48-hour LC50, 1400 to 5600 µg/L, above the water solubility.
Marine fish: no data available.
Marine crustaceans: 3 spp, 48 to 96-hour LC50, 138 to 1380 µg/L.
A freshwater low reliability trigger value of 0.5 µg/L. was derived for dicofol using the assessment factor (AF) method with a factor of 100.
Even less marine data were available but a marine low reliability trigger value of 0.1 µg/L was derived using a factor of 1000. These should only be used as indicative interim working levels.
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.
Tomlin C 1994. The pesticide manual: A world compendium. 10th edn, British Crop Protection Council & Royal Society of Chemistry, Bath, UK.