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
Nesheim, O.N. 2002. Toxicity of pesticides. UF/IFAS EDIS Document PI-13. http://edis.ifas.ufl.edu/PI008.
Reigart, J.R. and J.R. Roberts. 1999. Recognition and management of pesticide poisonings, 5th ed. United States Environmental Protection Agency Publication EPA-735-R-98-003.
Crop Protection Handbook. 2005. vol. 91. Willoughby, Ohio: Meister Publishing Co. http://www.meistermedia.com/publications/meisterpro-crop-protection-handbook/ [3 April 2013].
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 |
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). |
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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. |
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Footnotes
This document is PI-50, one of a series of the Agronomy Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date June 2005. Reviewed August 2008 and April 2011. Visit the EDIS website at http://edis.ifas.ufl.edu.
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.
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