Pesticide Toxicity Profile: Organophosphate Pesticides
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Pesticide Toxicity Profile: Organophosphate Pesticides

   

Pesticide Toxicity Profile: Organophosphate Pesticides1

Frederick M. Fishel2

This document provides a general overview of human toxicity, provides 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

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
Azinphos-methyl


 4


 150 - 200 (rat)
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
Fenamiphos


 10.6 - 24.8


 71.5 - 75.7
Malathion


 5,500


 >2,000
Methamidophos


 13 (female only)


 122
Methidathion


 25 - 44


 200
Methyl parathion


 6


 45
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
Azinphos-ethyl

HT

VHT

HT
Chlorpyrifos

HT

HT

HT
Diazinon

HT

HT

HT
Dimethoate

HT

MT

HT
Disulfoton (Di-Syston S)

HT

MT

HT
Ethoprop

HT

HT

---
Fenamiphos

Not available

Not available

Not available
Malathion

MT

HT

HT
Methamidophos

HT

ST

T
Methidathion

Not available

VHT

HT
Methyl parathion

Not available

ST

---
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
Azinphos-methyl


 Azinphos®, Guthion®


O,O-dimethyl S-[(4-oxo-1,2,3-benzotriazin-3(4H)-yl)methyl]phosphorodithioate
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
Fenamiphos


 Nemacur®


 Ethyl 3-methyl-4-(methylthio)phenyl (1-methylethyl)phosphoramidate
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
Methyl parathion


 Penncap-M®


 O,O-dimethyl O-(nitrophenyl) phosphorothioate
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 Pesticide Information Office, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date July 2005. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.

2. Frederick M. Fishel, Associate Professor, Agronomy Department, and Director, Pesticide Information Office; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, 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 extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.


Copyright Information

This document is copyrighted by the University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS) for the people of the State of Florida. UF/IFAS retains all rights under all conventions, but permits free reproduction by all agents and offices of the Cooperative Extension Service and the people of the State of Florida. Permission is granted to others to use these materials in part or in full for educational purposes, provided that full credit is given to the UF/IFAS, citing the publication, its source, and date of publication.