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Publication #PI-50

Pesticide Toxicity Profile: Organophosphate Pesticides1

Frederick M. Fishel2

This document provides a general overview of human toxicity, a listing of laboratory animal and wildlife toxicities, and a cross-reference of chemical, common, and trade names of many organophosphate pesticides registered for use in Florida.

General

Organophosphates are some of the most widely used pesticides in the world. They are used in agriculture, homes, gardens, and veterinary practices, replacing the same uses as the organochlorines, many of which have been banned for years. In general, they are not persistent in the environment as they break down quickly. Because of their relatively fast rate of degradation, they have been a suitable replacement for the more persistent organochlorines.

Toxicity

Some of the early organophosphates were developed as nerve poisons for human warfare. The organophosphates recommended for non-residential uses are relatively toxic to vertebrate organisms. Their primary mode of action on insects and other animals is by phosphorylation of the acetylcholinesterase enzyme. This enzyme is necessary for controlling nerve impulse transmission between nerve fibers. A loss of this enzyme function results in an accumulation of acetylcholine, which causes unregulated nervous impulses. Higher levels of acetylcholine result in sensory and behavioral disturbances, incoordination, and depressed motor function. Symptoms of acute poisoning develop during or after exposure, within minutes to hours, depending on method of contact. Inhalation exposure results in the fastest appearance of symptoms, followed by the gastrointestinal route, and then the dermal (skin) route. Some of the early symptoms include headache, nausea, dizziness, sweating, and salivation. Symptoms such as muscle twitching, weakening, vomiting, abdominal cramps, and diarrhea all indicate a worsening condition. Recovery from organophosphate exposure depends upon generation of new enzyme. Mammalian toxicities for organophosphate pesticides are shown in Table 1. Table 2 lists the toxicities to wildlife by the common name of the organophosphate. Table 3 provides a cross-listing of many of the trade names that these products are registered and sold by in Florida.

Additional Information

Nesheim, O.N., F.M. Fishel, and M. Mossler. 2002. Toxicity of Pesticides. Gainesville: University of Florida Institute of Food and Agricultural Sciences. https://edis.ifas.ufl.edu/pi008

Reigart, J.R. and J.R. Roberts. 2013. "Recognition and Management of Pesticide Poisonings." (6th ed.) United States Environmental Protection Agency Publication EPA-735K-13001.

Tables

Table 1. 

Organophosphate mammalian toxicities (mg/kg of body weight).

Common name

Rat oral LD50

Rabbit dermal LD50

Acephate

1,030–1,447

>10,250

Chlorpyrifos

96–270

2,000

Diazinon

1,250

2,020

Dimethoate

235

400

Disulfoton

2–12

3.6–15.9

Ethoprop

61.5

2.4

Malathion

5,500

>2,000

Methamidophos

13 (female only)

122

Methidathion

25–44

200

Naled

191

360

Oxydemeton-methyl

50

1,350

Phorate

2–4

20–30 (guinea pig)

Phosmet

147–316

>4,640

Profenofos

358

472

Table 2. 

Organophosphate wildlife toxicity ranges.

Common name

Bird acute oral LD50 (mg/kg)*

Fish LC50 (ppm)**

Bee

Acephate

MT

PNT

HT

Chlorpyrifos

HT

HT

HT

Diazinon

HT

HT

HT

Dimethoate

HT

MT

HT

Disulfoton (Di-Syston S)

HT

MT

HT

Ethoprop

HT

HT

Malathion

MT

HT

HT

Methamidophos

HT

ST

T

Methidathion

Not available

VHT

HT

Naled

MT

HT

HT

Oxydemeton-methyl

MT to PNT

ST

T

Phorate

VHT

ST

MT

Phosmet

ST

HT

HT

Profenofos

Not available

VHT

Not available

*Bird LD50: PNT = >2,000; ST = 501–2,000; MT = 51–500; HT = 10–50; VHT = <10.

**Fish LC50: PNT = >100; ST = 10–100; MT = 1–10; HT = 0.1–1; VHT = <0.1.

Bee: HT = highly toxic (kills upon contact as well as residues); MT = moderately toxic (kills if applied over bees); PNT = relatively nontoxic (relatively few precautions necessary).

Table 3. 

Cross-reference list of common, trade and chemical names of organophosphates.

Common name

Trade names*

Chemical name

Acephate

Acephate®, Orthene®,

O,S-dimethyl acetylphosphoroamidothioate

Chlorpyrifos

Chlorpyrifos®, Govern®, Lorsban®, Nufos®, Warhawk®, Whirlwind®

O,O-diethyl O-(3,5,6-trichloro-2-pyridinyl) phosphorothioate

Diazinon

Diazinon®

O,O-diethyl O-(2-isopropyl-6-methyl-4-pyrimidinyl) phosphorothioate

Dimethoate

Dimethoate®, Cygon®

O,O-dimethyl S-methylcarbamoylmethyl phosphorodithioate

Disulfoton

Di-Syston®

O,O-diethyl S-[2-(ethylthio)ethyl] phosphorodithoate

Ethoprop

Mocap®

O-ethyl S,S-dipropyl phosphorodithioate

Malathion

Fyfanon®, Malathion®

Diethyl (dimethoxythiophosphorylthio)succinate

Methamidophos

Monitor®

O,S-Dimethyl phosphoramidothioate

Methidathion

Supracide®

S-2,3-dihydro-5-methoxy-2-oxo-1,3,4-thiadiazol-3-ylmethyl O,O-dimethyl phosphorodithioate

Naled

Dibrom®

1,2-dibromo-2,2-dichloroethyl dimethyl phosphate

Oxydemeton-methyl

MSR®

S-[2-(Ethylsulfinyl)ethy]O,O-dimethyl phosphorothioate

Phorate

Phorate®, Thimet®

O,O-Diethyl S-[(ethylthio)methyl] phosphorodithioate

Phosmet

Imidan®

S-[(1,3-dihydro-1,3-dioxo-2H-isoindol-

2-yl)methyl] O,O-dimethyl phosphorothioate

Profenofos

Curacron®

O-4-bromo-2-chlorophenyl O-ethyl S-propyl phosphorothioate

*Does not include manufacturers' prepackaged mixtures.

Footnotes

1.

This document is PI-50, one of a series of the Agronomy Department, UF/IFAS Extension. Original publication date June 2005. Revised February 2014 and March 2017. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Frederick M. Fishel, professor, Agronomy Department, and director, Pesticide Information Office; UF/IFAS Extension, Gainesville, FL 32611.

The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition. Use pesticides safely. Read and follow directions on the manufacturer's label.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.