Fenthion (Insecticide):

Summary Information
Classification Chemicals / Complex Chemical Agents/ Chemical:
Alternative Names Chemical name: O,O-dimethyl O-4-methylthio-m-tolyl phosphorothiaote (W180.Feb02.WNV2) 
  • Formerly called DMTP. 
  • Baycid; Baytex; Entex; Lebayeid; Queletox; Spotten; Talodex; Tiguvon; Lebaycid; O,O-dimethyl-O-[4-(methylthio)-m-tolyl] phosphorothioate; Lebaycid(R); O,O-dimethyl O-(4-methylmercapto-3-methylphenyl) thionophosphate; O,O-dimethyl O-(3-methyl-4-methylthiophenyl) thiophosphate; O,O-dimethyl O-(4-methylthio-3-methylphenyl) thiophosphate; Phosphorothioic acid O,O-dimethyl O-[3-methyl-4-(methylthio)phenyl]ester; phosphorothioic acid O,O-dimethyl O-(4-methylthio)-m-tolyl ester; b 29493; bay 29493; bayer 9007; bayer 29493; bayer s-1752; m-cresol, 4-(methylthio)-, O-ester with O,O-dimethyl phosphorothioate; O,O-dimethyl O-4-(methylmercapto)-3-methylphenyl phosphorothioate; O,O-dimethyl O-3-methyl-4-methylthiophenyl phosphorothioate; DMTP; MPP; OMS 2; S 1752; spotton; Mosquitocide 700; Rid-a-Bird; BX-1; BX-2; Cresol, 4-(methylthio)-, O-ester with O,O-dimethyl phosphorothioate; Dimethyl (3-methyl-4-(methylthio)phenyl) phosphorothionate; Dimethyl methylthiotolyl phosphorothioate; Dimethyl O-((4-methylmercapto)-3-methylphenyl)thionophosphate; Dimethyl O-(3-methyl-4-(methylthio)phenyl) thiophosphate; Dimethyl O-(4-(methylthio)-m-tolyl) phosphorothioate; Mercaptofos; Thiophos; 4-Methylmercapto-3-methylphenyl dimethyl thiophosphate (W324.Oct01.WNV1)
  • O,O-Dimethyl O-[3-methyl-4-(methylthio)phenyl] phosphorothioate. (W325.May01.WNV1)
  • Finest (AGRO-SAN Chemicals Industry and Trade Inc.); Fenchem (Chemet Chemicals Ltd.); Prestig (Hektas Ticaret T.A.S.); Korfen (Koruma Tarim A.S.); Libersan (Kuang Hwa Chemical Co., Ltd.). (W325.May01.WNV1)
Chemical Formulation Fenthion is available in dust, emulsifiable concentrate, granular, liquid concentrate, spray concentrate, ULV, and wettable powder formulations. (W180.Feb02.WNV2, W325.May01.WNV1)
Chemical Formula C10H15O3PS2 (W324.Oct01.WNV1)
Chemical Structure fen.jpg (3447 bytes)


An organophosphate compound.

Molecular Weight 278.33 (W180.Feb02.WNV2); 278.32046 (W324.Oct01.WNV1).
  • Pure: colorless oily liquid. 
  • Technical grade: yellow or brown oily liquid with a weak garlic odour.

(W180.Feb02.WNV2, W324.Oct01.WNV1, W325.May01.WNV1)

Physical Properties
  • Melting point: 7.5C. (W324.Oct01.WNV1, W325.May01.WNV1)
  • Boiling point: 87C at 0.01 mm Hg. (W324.Oct01.WNV1); 87C at 1.4 Pa (W325.May01.WNV1)
  • Density: 1.25 at 20C. (W324.Oct01.WNV1, W325.May01.WNV1)
  • Vapour pressure: 0.37 mPa at 20C. (W325.May01.WNV1)
  • Solubility in water: 0.0055 g/100 ml. (W324.Oct01.WNV1)
  • Other solubilities: Very readily soluble in dichloromethane, toluene. Readily soluble in 2-propanol. Soluble in n -hexane. (W325.May01.WNV1)
Chemical Actions  Fenthion is an organophosphate compound. These compounds act as an inhibitors of cholinesterase enzymes, which are involved in normal transmission of nerve impulses within the nervous system. (B36.39.w39)
Chemical Uses Insecticide and acaricide. (W324.Oct01.WNV1)
  • Fenthion is a contact and stomach organophosphate insecticide used against many sucking, biting pests, especially fruit flies, stem borers, mosquitoes, and Eurygaster cereal bugs, also other insects in fruit, grapes, olives, vegetables, cotton, tea, sugarcane, rice, etc. (W180.Feb02.WNV2, W325.May01.WNV1)

In mosquitoes, fenthion is toxic to both the adult and immature forms (larvae). (W180.Feb02.WNV2)

  • Once used extensively in the U.S. for controlling intestinal worms, fenthion no longer has FDA approval due to poisoning deaths. (W180.Feb02.WNV2)
  • While it is effective as an insecticide, it is also moderately toxic to mammals, and highly toxic to birds.
    • Based on its high toxicity to birds, fenthion is used in various parts of the world for weaver bird control. Pest control operators have used it to control pigeons around public buildings, as well. For bird control, use is made of fenthion's contact action and its ready absorption through the skin. It is applied as a paste to roosting areas when utilized for such purposes. (W180.Feb02.WNV2)
Toxicity Rating Fenthion is a moderately toxic compound in EPA toxicity class II. (W180.Feb02.WNV2, W325.May01.WNV1)

 It is classified by the U.S. Environmental Protection Agency (EPA) as a Restricted Use Pesticide (RUP) due to the special handling warranted by its toxicity. All bird control products, as well as non-domestic, non-granular formulations of 70% and greater are RUPs. RUPs may be purchased and used only by trained certified applicators. Fenthion may not be used on food crops in the USA. Labels for products containing fenthion must bear the Signal Word "WARNING". (W180.Feb02.WNV2)

  • Acute toxicity:
    • Moderately toxic via the oral route, with reported oral LD50 values of 180 to 298 mg/kg in rats (Laboratory rat (Rattus norvegicus - Brown rat)), 150 mg/kg in rabbits (Oryctolagus cuniculus - European rabbit (Domestic rabbit)), and 88 to 145 mg/kg in mice (Mus domesticus - Laboratory mouse). 
    • Moderately toxic via the dermal route as well, with reported dermal LD50 values of 330 to 1000 mg/kg in rats, and 500 mg/kg in mice. 
    • Slightly toxic via inhalation with a reported 1-hour airborne LC50 for fenthion in rats of 2.4 to 3.0 mg/L. 
    • Acute effects of fenthion are similar to those caused by other organophosphates, but may take somewhat longer to develop.
    • Fenthion is of sufficiently low toxicity it has been investigated as an agent against insect parasites in animals (e.g., dogs (Canis familiaris - Domestic dog)).
    • Symptoms of acute exposure to organophosphate or cholinesterase-inhibiting compounds may include the following: numbness, tingling sensations, incoordination, headache, dizziness, tremor, nausea, abdominal cramps, sweating, blurred vision, difficulty breathing or respiratory depression, and slow heartbeat. Very high doses may result in unconsciousness, incontinence, and convulsions or fatality. 


  • Chronic toxicity:
    • In rats, 12.5 mg/kg/day caused weight loss and 85% inhibition of normal brain cholinesterase activity within 4 weeks.
      • Much less severe, but still detectable decreases were noticeable at doses of 2.5 mg/kg/day. 
    • Repeated or prolonged exposure to organophosphates may result in the same effects as acute exposure, including the delayed symptoms. 
    • There was no evidence of weight loss or decreased food consumption in dogs that were given dietary doses of 1.25 mg/kg/day for 1 year. 
    • In Nigerian sprayers, those not wearing protective clothing while spraying showed decreased whole-blood cholinesterase activity. 
    • Veterinary clinic workers who did not use skin protection when applying a 20% topical application to dogs experienced symptoms ranging from tingling and numbness of the hands and feet to generalized weakness and shooting pains. 
    • Other possible effects are similar to those caused by the other organophosphates. 


  • Reproductive effects:
    • Single injections of 40 or 80 mg/kg of fenthion into the abdominal cavities of pregnant female mice caused poisoning in the developing fetuses, particularly when administered on days 10 to 12 of gestation. 
    • Fetuses were injured primarily by dosages that caused toxicity in the maternal mouse. 
    • No influence was seen on reproduction in other three-generation studies of mice. 
    • These data indicate that reproductive effects are unlikely in humans. 


  • Teratogenic effects:
    • Some reduction in fetal weight occurred, but no defects were found in mice that were given intraperitoneal doses of up to 80 mg/kg of fenthion in single-day or 3-day periods during the period of gestation in which organs are formed. 
    • No teratogenic effects were seen in five generations of mice that drank water containing 60 mg/L fenthion. 
    • Other tests on mice and rats did not show teratogenic effects from fenthion. 
    • These data indicate that fenthion is not teratogenic. 


  • Mutagenic effects:
    • Tests on mice did not show mutagenic effects from fenthion. 
    • Available data are insufficient to draw a conclusion regarding the mutagenicity of the compound.


  • Carcinogenic effects:
    • One carcinogenicity test on fenthion indicated that this insecticide may be a carcinogen in male mice. However, no carcinogenic effects were observed in other 2-year feeding studies of rats and mice. 
    • Available data are insufficient to draw conclusions regarding the carcinogenicity of fenthion.


  • Organ toxicity:
    • Animal tests and human use experience have identified that target organs affected by fenthion exposure include the central nervous system, peripheral nervous system, and the heart. (W180.Feb02.WNV2)
  • Fate in humans and animals:
    • In animals, fenthion is quickly absorbed into the bloodstream through the digestive tract, lungs, and skin, and is systemically distributed. 
    • Fenthion is eliminated through the urine and the feces. 
    • A single dose of the insecticide has prolonged action, suggesting that much of it is stored in body fat and later released for metabolism.
      • Fenthion and its metabolites were found in the fat of steers slaughtered 3 days after dermal application of fenthion. 
    • When cows (Bos taurus - Domestic cattle) were given a dermal application of 9 mg of fenthion per kilogram, 45 to 55% of the dose was excreted in the urine, 2.0 to 2.5% in the feces, and 1.5 to 2.0% was recovered in the milk. 


Environmental Persistence
  • Breakdown in soil and groundwater: Fenthion has moderate persistence in soil, with an average field half-life of 34 days under most conditions. In soil, residues of fenthion may persist for approximately 4 to 6 weeks. (W180.Feb02.WNV2)
    • It adsorbs fairly strongly to soil particles, and so is not likely to move (or leach) through the soil. (W180.Feb02.WNV2)
  • Breakdown in water: In one study of its persistence in water, 50% of applied fenthion remained in river water 2 weeks later, while 10% remained after 4 weeks. (W180.Feb02.WNV2)
    • It is more rapidly degraded under alkaline conditions. (W180.Feb02.WNV2)
  • Breakdown in vegetation: Fenthion is phytotoxic (or harmful to plants) to American linden, Hawthorn and sugar maple trees, and to certain rose varieties. It is not considered phytotoxic when used at recommended rates, although injury has occurred in certain varieties of apples and cotton. 
    • Plant foliage should not be sprayed when temperatures exceed 90 F. 
    • Only about 10% of applied fenthion remained on rice plants after 6 hours. Almost half of the activity was found in the rice bran, 6.5% was in the husk, and 14.7% was in polished rice. 
    • Water soluble metabolites were found 14 days after fenthion application to rice plants.


Effects on Non-target Species
  • Effects on birds (Aves - Birds (Class)): 
    • Fenthion is very highly to highly toxic to birds: reported LD50 values for various species range from less than 4 mg/kg in bobwhite quail to 26 mg/kg in ducks. Birds which showed acute LD50 values within this interval were California quail, Japanese quail, Canada geese (Branta canadensis - Canada goose), finches, starlings (Sturnus vulgaris - Common starling), sparrows, mallards (Anas platyrhynchos - Mallard), mourning doves (Zenaida macroura - Mourning dove), and chukar partridges. (W180.Feb02.WNV2)
    • Acute symptoms of fenthion poisoning in birds include tearing of the eyes, foamy salivation, lack of movement, tremors, congestion of the windpipe, lack of coordination in walking, and an abnormally rapid rate of breathing or difficult breathing. 
    • Chickens (Gallus gallus domesticus - Domestic chicken (Phasianidae - Grouse, Turkeys, Pheasants, Partridges, etc. (Family))) developed leg weakness when they were fed 25 mg/kg doses of fenthion. The acute oral LD50 in poultry is 15 to 30 mg/kg. 
    • The approximate dietary LC50 values (over an unspecified number of days) for fenthion are: Japanese quail, 130 ppm; pheasant (Phasianus colchicus - Common pheasant), 200 ppm; bobwhite quail 30 ppm, and mallard, 230 ppm.
    • After administration of 0.5 mg/kg/day for 30 days, the eggs laid by surviving mallards had markedly reduced fertility.


  • Effects on aquatic organisms:
    • Fenthion is moderately toxic to fish with reported 96-hour LC50 values of 9.3 mg/L in rainbow trout, 1.33 mg/L in brown trout, 1.32 mg/L in coho salmon, 1.16 mg/L in carp, 1.54 mg/L in largemouth bass, 1.38 mg/L in bluegill, 1.65 mg/L in yellow perch, 2.40 mg/L in fathead minnow, and 3.40 mg/L in goldfish. 
    • Brown bullheads were not affected by the insecticide when it was applied to a California refuge at 0.01 pounds per acre.
    • Fenthion may be very highly toxic to some freshwater aquatic invertebrates.


  • Effects on other organisms:
    • Fenthion is toxic to bees. (W180.Feb02.WNV2)

Management Techniques

(USA Contacts for Managing WNV Disease)

(Further Reading)
Click image for full contents list of ELECTRONIC LIBRARY

Authors Debra Bourne (V.w5)
Referee Suzanne I. Boardman (V.w6); Becki Lawson (V.w26)

Return to Top of Page