S-Methoprene 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
Methoprene (CAS 40596-69-8; 41205-06-5; 65733-16-6; 65733-17-7, depending on the isomer) is an insect growth regulator which mimics juvenile hormones and prevents metamorphosis of larvae. It was introduced by Zoecon (now Sandoz) (Tomlin 1994). Its IUPAC name is isopropyl (E,E)-(RS)-11-methoxy-3,7,11-trimethyldodeca-2,4-dienoate.
Its formula is C19H34O3 and molecular weight is 310.5. It is only slightly soluble in water (1.4 mg/L) and has a log Kow of 5.2.
Uses and environmental fate
Methoprene is most commonly used to control Diptera (e.g. flies and mosquitos) and other insect pests in public areas, stored goods, food preparation areas, mushroom sheds, on flowers and crops and on animals (Tomlin 1994). In Australia, it is commonly used for mosquito larvae control where its environmental risk appears to be much less than temephos (Mortimer & Chapman 1995). Methoprene is stable in water and sensitive to ultraviolet (UV) light.
Freshwater fish: four species, 96-hour LC50, 1010 to 121,000 µg/L. 30-day NOEC (growth), P. promelas, 48 µg/L.
Freshwater crustacean: two species, 48 to 72-hour LC50, 20 to 300 µg/L.
Freshwater molluscs: one species, 48-hour LC50, 10,600 µg/L.
Marine fish: one species, 96-hour LC50, 125,000 µg/L.
Marine crustaceans: three species, 48 to 96-hour LC50, 1950 to 2150 µg/L for Gammarus aequicauda; 3300 to 5820 µg/L for Australian Heloecius cordiformis; 246,000 µg/L for Australian Trypaea sp. (shrimp).
Australian and New Zealand data
Data for the two Australian marine estuarine crustaceans are given above.
Factors that modify toxicity
No data were available.
A freshwater low reliability trigger value of 0.2 µg/L was calculated for S-methoprene using an assessment factor (AF) of 100. A marine low reliability trigger value of 20 µg/L was calculated for S-methoprene using an AF of 100 (low algal toxicity is expected). These figures 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.
Mortimer MR & Chapman HF 1995. Acute toxic effects of (S)-methoprene and temephos to some Australian non-target aquatic crustacean species. Australasian Journal of Ecotoxicology 1, 107-112.
Tomlin C 1994. The pesticide manual: A world compendium. 10th edn, British Crop Protection Council & Royal Society of Chemistry, Bath, UK.