Temephos

TRADE OR OTHER NAMES

Trade names for products containing the compound include Abat, Abate, Abathion, Biothion, Bithion, Difennthos, Ecopro, Nimitox, and Swebate. The compound may also be found in mixed formulations with other insecticides including trichlorfon.

INTRODUCTION

Temephos is an non-systemic organophosphorus insecticide used to control mosquito, midge and black fly larvae. It is used in lakes, ponds and wetlands. It also may be used to control fleas on dogs and cats and to control lice on humans. Temephos is a General Use Pesticide.

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

Temephos containing products are moderately toxic compounds that carry the signal word WARNING on their labels despite the relatively high LD50 of the technical compound. This is due to the high toxicity of xylene, one of the components (or carriers) found in many of the trade products. This Pesticide Information Profile is oriented to the toxicity of the technical product temephos and not the different trade products unless specifically noted. Typical of other organophosphate insecticides, temephos inhibits the action of the group of enzymes called cholinesterases. Specific types of these enzymes are found throughout the body including the nervous system, the brain, and the blood stream. Symptoms of acute exposure are also similar to other organophosphates and may include nausea, salivation, headache, loss of muscle coordination, and difficulty breathing (1). However, humans ingested 256 mg/kg for five days and 64 mg/kg for four months without any symptoms or detectable effects on blood enzyme activity (1). At the higher dose the volunteers in the study all refused to take the dose any longer because of the obnoxious taste.
In other mammals, temephos produces signs and symptoms typical of cholinesterase inhibition at moderate levels of exposure (500 mg/kg). Death does not occur unless very large doses of the compound are administered. The LD50 of temephos ranges from 2,000 to 13,000 mg/kg for rats (2) and is 4,700 mg/kg for mice. The LD50 for a 2% powder formulation of temephos in dogs and cats is greater than 5,000 mg/kg for both species.
Temephos is nearly four times more toxic when used in combination with the insecticide malathion. Its toxicity is relatively unaffected when used in combination with 23 other organophosphate insecticides (3).

CHRONIC TOXICITY

Rats fed temephos at low doses (below 12.5 mg/kg) for a month had no compound induced changes in blood and brain cholinesterase activity. At the next higher feeding level (25 mg/kg), the rats experienced some weight loss and changes in the enzyme activity in the blood and the brain. When fed much higher amounts of the compound for three months, all of the surviving rats experienced a complete inhibition of blood cholinesterase activity (3). Rats exposed to very low amounts of the compound for three months experienced a depression in their cholinesterase activity at and above 0.3 mg/kg. A similar pattern of toxic effects at lower concentrations over longer periods of time have been observed in the dog as well. Thus, while the LD50 values for acute toxicity indicate that the compound is relatively non-toxic or only slightly toxic, the compound has the potential to cause significant toxic effects (depression of the activity of the enzyme cholinesterase in the blood and the brain) to mammals at low concentrations over long periods of time.
Temephos was used in cisterns and other potable water sources in some locations in the United States and in the West Indies for the control of mosquito larvae. Subsequent tests on the residents that had used the water sources showed no observable effects in the exposed individuals. No indication of the total dose or levels of exposure with time were available.

Reproductive Effects

Neither of two separate studies of rats fed small amounts of temephos showed any reproductive difficulties in the test animals. The maximum dose (25 mg/kg) had no effect on the number of litters, litter size, or variability in the young and produced no congenital defects in the offspring. The concentration of temephos in the diet of the test animals was, however, sufficient to produce cholinesterase inhibition and some toxic symptoms (3). Low oral doses of temephos of up to 2.5 mg/kg administered in feed over a year and a half caused no reproductive effects in sheep or in their offspring (3).

Teratogenic Effects

There were no birth defects noted in the offspring of pregnant rabbits fed low doses of temephos (time interval not noted). The two separate studies utilized different formulations of temephos, a 2% formulation and a 90% formulation. In both studies, maternal toxicity and depression of cholinesterase activity occurred during the study (7). These two tests, though negative, do not provide enough information to assess the potential teratogenic risk to humans at low levels of exposure to temephos.

Mutagenic Effects

The potential of the commercial product containing temephos (Abate) to cause mutations was tested on several strains of bacteria. Though the conclusion of the study was that the compound was not mutagenic, weakly mutagenic effects were noted in one of the strains. Additional tests on rabbits and on other strains of bacteria have shown the compound to be non- mutagenic.

Carcinogenic Effects

Only one study of the carcinogenic potential of temephos has been conducted with rats. The rats were fed small amounts of the compound over a two year interval. No tumors or cancer related changes were noted in the test animals at the highest dose used (15 mg/kg). During the study the rats experienced a reduction in liver weight at the lowest dose of 0.5 mg/kg. More information is needed to make firm conclusions about the carcinogenic potential of temephos in humans.

Organ Toxicity

As noted under carcinogenicity, a reduction in liver weights was noted in a study on rats fed very small amounts of temephos over a two-year period. In another study some minor pathological changes were noted in the liver at a low dose of 10 mg/kg. No adverse effects in the liver were noted at lower doses of 1 mg/kg (3). No other effects on organs have been reported.

Fate in Humans and Animals

In general, organophosphate insecticides are readily absorbed through the lungs, skin, and digestive tract (1). A single oral dose of temephos reached peak concentration in the bloodstream of rats between five and ten hours after it was administered. Some of the compound was also found in the digestive tract and some in fat. In mammals, elimination of the compound is mainly in feces and urine. Most of the eliminated compound is the unchanged parent compound though other breakdown products have been detected in the urine and feces. No studies of the absorption and breakdown of temephos in humans were found.

ECOLOGICAL EFFECTS

Tests with various wildlife species indicate that the compound is highly toxic to some organisms and moderately toxic to other species. The LD50 of temephos ranges from 18.9 mg/kg for the California quail to 240 mg/kg for the chukar partridge. Most of the bird species had an LD50 within the 35 mg/kg to 85 mg/kg range indicating a compound that is moderately to highly toxic to avian species. Species tested include the house sparrow, mallard ducks, red- winged blackbird and rock doves. Mallards fed diets containing moderate amounts of temephos showed no changes in reproduction except in the frequency of egg laying (4). Temephos shows a wide range of toxicity to aquatic organisms. The most sensitive species of fish is the rainbow trout with a temephos LD50 ranging from 0.16 to 3.49 mg/kg (1). Other LD50 values for temephos are coho salmon (0.35 mg/kg), largemouth bass (1.44 mg/kg), channel catfish (3.23 to 10 mg/kg), bluegill sunfish (1.44 to 21.8 mg/kg), and Atlantic salmon (6.7 mg/kg to 21 mg/kg).
Freshwater aquatic invertebrates such as amphipods are very highly susceptible to temephos as are some marine invertebrates such as mysids (8). The LD50 of temephos for Gammarus lacustris is 0.08 mg/kg. Because the compound is an insecticide and is used effectively to control the aquatic larval stages of mosquitos, black flies and midges, its highly toxic nature to these organisms is not surprising. The product Abate 4E is highly toxic to the saltwater species, the pink shrimp (LD50 0.005 mg/l) and the Eastern oyster (LD50 0.019 mg/l) (6). The compound is nearly non-toxic to the bull frog with an LD50 of greater than 2000 mg/kg. Temephos is highly toxic to bees.
Temephos has the potential to accumulate in aquatic organisms. The bluegill sunfish accumulated 2,300 times the concentration present in the water. Nearly 75% of the compound was eliminated from the fish after exposure ended (6).

ENVIRONMENTAL FATE

There is only a minimal amount of information available about the fate and behavior of temephos in the environment. Current evidence suggests that the compound has a low persistence in the environment. Weekly application of temephos at twice the normal application rates on pond water resulted in the rapid disappearance of the compound from the water and from the sediments (2). At even higher application rates to pond water there were still only traces of the compound detected one week after application. Temephos was sprayed over an intertidal mangrove community in Florida. Between 15% and 70% of the sprayed amount reaching the leaf surface entered the water below the trees. Additional amounts were washed into the water during rainfall. Pesticide residues were detected in the water two hours but not four hours after application, indicating a very short persistence in the water. However, in simulated tide pools the compound persisted for up to four days. It also persisted in oysters for two days after application (8).

PHYSICAL PROPERTIES AND GUIDELINES

Exposure Guidelines:

NOEL (rat):	0.3 mg/kg (cholinesterase inhibitions)
RfD:	NA
ADI:	NA
MCL:	NA
HA:	NA
TLV:	10 mg/m3

Physical Properties:

Common Name:	temephos
CAS #:	3383-96-8
Chemical name:	O,O'-(thiodi-4,1-phenylene)O,O,O'O'-tetramethylphosphorothioate
Chemical class:	organophosphate
Solubility in water:	0.03 mg/l at 25 degrees C
Solubility in solvents:	Soluble in common organic solvents. Insoluble in hexane and methylcyclohexane
Melting point:	30 - 30.5 degrees C
Vapor pressure:	NA
Partition coefficient:	NA

BASIC MANUFACTURER

American Cyanamid Co.
One Cyanamid Plaza
Wayne, New Jersey 07470
Telephone: 210-831-2000
Emergency: 210-831-2000

Review by Basic Manufacturer:

Comments solicited: June, 1993
Comments received:

REFERENCES

1. Hazardous Substance Data Base. 1993. TOXNET. National Library of Medicine. Bathesda, MD.
2. Smith, G.J. 1993. Toxicology and Pesticide Use in relation to Wildlife: Organophosphorous and Carbamate Compounds. U.S. Department of the Interior. C.K. Smoley. Boca Raton, FL.
3. Gallo, M.A. and N.J. Lawryk. 1991. Organic Phosphorous Pesticides. In Handbook of Pesticide Toxicology, Volume 2, Classes of Pesticides. Wayland J. Hayes and Edward R. Laws (eds.). Academic Press Inc., NY.
4. Franson, J.C. and J.W. Spann. 1983. Effects of Dietary ABATE on Reproductive Success, Duckling Survival, Behavior, and Clinical Pathology in Game-Farm Mallards . Archives of Environmental Contamination and Toxicology 12:529-534.
5. Farm Chemicals Handbook. 1992. Meister Publishing Co. Willoughby, OH.
6. Communication between American Cyanamid and US EPA Office of Pesticide Programs. Re: Temephos. July 2, 1986.
7. US Environmental Protection Agency. Office of Pesticides/HED/SACB. Tox. Oneliners. 6/18/85. Temephos #845.
8. Pierce, R.H., R.B. Brown, K.R. Hardman, M.S. Henry, C.L. Palmer, T.W. Miller and G. Witcherman. 1989. Fate and Toxicity of Temephos Applied to an Intertidal mangrove Community. Journal of the American Mosquito Control Association. December 5 (4): 569-578.