Temephos in freshwater and marine water

​Toxicant default guideline values for protecting aquatic ecosystems

October 2000

Description of chemical

Organophosphorus pesticides are derivatives of phosphoric, phosphonic, phosphorothioic, or phosphonothioic acids, comprising many chemicals with a wide range of uses (WHO 1986). They exert their acute effects in insects, fish, birds and mammals by inhibiting the acetylcholinesterase (AChE) enzyme, but may also have a direct toxic effect (WHO 1986).

Temephos (CAS 3383-96-8) is a non-systemic phosphorothioate insecticide introduced by American Cyanamid Co. Its IUPAC name is O,O,O¹,O¹-tetramethyl O,O¹-thiodi-p-phenylene bis(phosphorothioate), formula is C₁₆H₂₀O₆P₂S₃ and molecular weight is 466.5. It has low solubility in water (0.03 mg/L at 25°C) and its log K_ow is 4.91 (Tomlin 1994). The current analytical practical quantitation limit (PQL) for temephos in water is 0.1 µg/L (NSW EPA 2000).

Uses and environmental fate

Temephos is used primarily for control of mosquito larvae and biting midges in public health and agriculture as well as for controlling fleas on pets and lice on humans (Tomlin 1994). Its use on aquatic waterways is restricted in Australia and New Zealand due to its high toxicity.

Temephos does not persist for long in soil and water, and it has a half-life of a few weeks. The main route of breakdown is microbial metabolism. Temephos adsorbs strongly to sediment but tends to bioaccumulate. Residues in salt marsh snail Melampus bidentatus correlated with population declines (Fitzpatrick & Sutherland 1978). In 1984, temephos was associated with a major kill of migratory wading birds in Lake Forrestdale WA, when it was applied for midge control in a shallow drying lake (J Holland pers. comm. 1997). Temephos has the potential to bioaccumulate with BCF in Lepomis macrochirus up to 2300. However, it is rapidly depurated after initial exposure (Kamrin 1997).

Factors that affect toxicity

Formulations of temephos are often more toxic than the technical material.

Aquatic toxicology

Freshwater fish: 21 species, 48 to 96-hour LC50, 160 to 22,750 µg/L. A figure for Gambusia holbrooki of 4.1 µg/L was not accepted. Oncorhynchus mykiss was most sensitive, and Channa gachua and Heteropneustes fossilis, least sensitive.

Freshwater crustaceans: one species, Gammarus lacustris, 96-hour LC50 of 80 to 640 µg/L.

Freshwater insects: eight species, 48 to 96-hour LC50, 0.09 to 5.6 µg/L for mosquito larvae (four species), 8 µg/L (Berosus sp.) to 216 µg/L for other insects.
Marine fish: eight species, 48 to 96-hour LC50, 23 (Mugil carinatus) to 11,400 µg/L. M. cephalus and Fundulus heteroclitus had LC50s ≤40 µg/L; eel Anguilla japonica (7500 µg/L) and Macropodus cupanus were least sensitive.

Marine crustaceans: nine species, 48 to 96-hour LC50, 1 (Penaeus japonicus) to 4100 µg/L. Five species of shrimp and prawns were most sensitive (1 to 45 µg/L), while Caridina denticulata was less sensitive (320 µg/L). Crabs (two species) were least sensitive (3000 to 4100 µg/L). Pierce et al. (2000) measured 96-hour LOECs for survival of first moult larvae of two species of salt marsh crabs between 15 to 20 µg/L and NOECs between 7 to 12 µg/L.

Marine insect: Berosus sp. (beetle) tested under marine conditions gave a 72-hour LC50 of 8 µg/L.

Marine molluscs: two species, 72 to 96-hour LC50, 8600 to 58,000 µg/L.

Marine annelids: one species, 72-hour LC50, 1500 µg/L.

Australian and New Zealand data

Less sensitive figures for the crabs Heloecius cordiformis (3000 µg/L) and Mictyris longicarpus (4100 µg/L) were from Brisbane estuarine systems.

Factors affecting toxicity

Toxicity of temephos did not change significantly with changes in pH, hardness or animal size (Johnson & Finley 1980).

Guideline

It was not considered appropriate to include data on mosquitoes in guideline calculations, given that they are the target species for temephos. Although a freshwater trigger value (low reliability) could be derived by applying an assessment factor (AF) of 100, it was preferred to adopt the marine figure, which was quite similar.

References

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.

Fitzpatrick G & Sutherland DJ 1978. Effects of organophosphorous insecticides (Abate) and chlorpyrifos (Dursban) on populations of the salt-marsh snail Melanapus bidentatus. Marine Biology 46, 23-28.

Johnson WW & Finley MT 1980. Handbook of acute toxicity of chemicals to fish and aquatic invertebrates. US Department of the Interior, Fish and Wildlife Service, No 137, Washington DC.

Kamrin MA 1997. Pesticide profiles: Toxicity environmental impact and fate. CRC Press, Lewis Publishers, Boca Raton Fl.

NSW EPA 2000. Analytical Chemistry Section, Table of Trigger Values 20 March 2000, LD33/11, Lidcombe, NSW.

Tomlin C 1994. The pesticide manual: A world compendium. 10th edn, British Crop Protection Council & Royal Society of Chemistry, Bath, UK.

WHO 1986. Environmental health criteria 63. Organophosphorus insecticides: A general introduction. World Health Organization, Geneva.