WORLD HEALTH ORGANIZATION FOOD AND AGRICULTURE
ORGANIZATION
ORGANISATION MONDIALE DE LA SANTE ORGANISATION POUR L'ALIMENTATION
ET L'AGRICULTURE
VBC/DS/77.23
ORIGINAL: ENGLISH
DATA SHEETS ON PESTICIDES No. 23
December 1976
FENTHION
It must be noted that the issue of a Data Sheet for a
particular pesticide does not imply endorsement of the pesticide by
WHO or FAO for any particular use, or exclude its use for other
purposes not stated. While the information provided is believed to
be accurate according to data available at the time when the sheet
was compiled, neither WHO nor FAO are responsible for any errors or
omissions, or any consequences therefrom.
The issue of this document does Ce document ne constitue pas une
not constitute formal publication. Il ne doit faire
publication. It should not be l'objet d'aucun compte rendu ou
reviewed, abstracted or quoted résumé ni d'aucune citation sans
without the agreement of the l'autorisation de l'Organisation
Food and Agriculture des Nations Unies pour
Organization of the United l'Alimentation et l'Agriculture
Nations or of the World Health ou de l'Organisation Mondiale de
Organization. la Santé.
Part 1 - General Information
CLASSIFICATION:
Primary use: Insecticide
Secondary use: Avicide, Acaricide
Chemical group: Organophosphorus compound
Data sheet No. 23
Date issued: December 1976
1.1 COMMON NAME: FENTHION (ISO)
1.1.1 Identity:
dimethyl 3-methyl-4-methylthiophenyl phosphorothionate.
1.1.2
Synonyms Local synonyms
Baytex
Lebaycid
Queletox
Tignvon
OMS-2
1.2 SYNOPSIS
An organophosphorus insecticide of moderate mammalian toxicity which
may be absorbed through the skin, from the gastrointestinal tract
and by inhalation. It is active upon metabolism into the more toxic
oxygen analogue. Symptoms after acute poisoning tend to be
prolonged.
1.3 SELECTED PROPERTIES
1.3.1 Physical characteristics
When pure, colourless, almost odourless liquid of boiling point 87°C
at 0.01 mm Hg. The technical material is 95-98% pure, a brown oily
liquid with a weak garlic odour.
1.3.2 Solubility
Water at 20°C, 54-56 ppm, readily soluble in most organic materials
and glyceride oils.
1.3.3 Stability
It is stable up to 160°C and is resistant to light and alkaline
hydrolysis.
1.3.4 Vapour pressure (volatility)
4 x 10-5 mm Hg at 20°C. It has a low vapour pressure but is
slightly volatile
1.4 AGRICULTURE, HORTICULTURE AND FORESTRY
1.4.1 Common formulations
Fogging concentrates between 40% and 60%: wettable powders 25% to
40%; emulsifiable concentrates 50%; dusts 3%; ultra low volume
application 1000 g per litre.
1.4.2 Pests mainly controlled
Used as a contact and stomach insecticide and is highly persistent.
Effective against fruit flies, leaf hoppers, cereal bugs, weaver
birds, animal parasites, mites, aphids, codling moth.
1.4.3 Use pattern
Used preharvest on sugar cane, rice, field corn, beets, pome and
stone fruit, citrus fruits, pistachio, cotton at rates up to
2 kg/ha. Active matter - also on olives, coffee, cocoa, vegetables,
vines and corn at rates up to 1 kg/ha.
1.4.4 Unintended effects
Not phytotoxic if used at the recommended dose rates. Applications
are not likely to give rise to contamination of food.
1.5 PUBLIC HEALTH PROGRAMMES
Mainly as larvicide in mosquito control. Not recommended for
residual indoor application due to rather high mammalian toxicity.
1.6 HOUSEHOLD USE
Not recommended for indoor use.
Part 2 - Toxicology and risks
2.1 TOXICOLOGY-MAMMALS
2.1.1 Absorption route
Absorbed by the intact skin as well as by inhalation and from the
gastro-intestinal tract.
2.1.2 Mode of action
Cholinesterase inhibition after conversion into the more toxic
oxygen analogue in the body.
2.1.3 Excretion
In rats 86% of an oral dose is eliminated in seven days (urine 45%
and faeces 40%). Metabolites include the sulfone and sulfoxide of
both the parent compound and its oxygen analogue.
2.1.4 Toxicity, single dose
Oral LD50 rat (M) 215 mg/kg Dermal LD50 rat (M) 330 mg/kg
(F) 245 mg/kg rat (F) 330 mg/kg
Dermal LD50 rabbit (M) 150 mg/kg
Most susceptible species
Calf - oral LD50 approximately 40 mg/kg
2.1.5 Toxicity, repeated doses
Oral
Rats of both sexes were given repeated oral doses of 10, 25, 50 and
100 mg/kg for five days. No deaths were observed at 10 and 25 mg/kg.
One out of four animals died at 50 mg/kg and all died at 100 mg/kg.
Fasciculations were observed after a single dose of 25 mg/kg.
Daily oral doses of 25 mg/kg for 75 days, six days a week to 30 rats
killed 12 animals. Daily administration of 30 mg/kg five days a week
for 13 weeks to male rats gave a 30% mortality and 80-90% reduction
of cholinesterase activity. Cholinesterase recovery was slow, up to
40 days.
Inhalation
Female rats tolerated a daily one-hour inhalation exposure to
fenthion of 0.163 mg/l for 30 days with inhibition of cholinesterase
but no deaths. At 0.415 mg/l, all animals died within 10 days.
Dermal
Dermal administration of fenthion at 14.5 and 25 mg/kg for 60 days
to rats resulted in 40% mortality in the higher dosed group. Blood
cholinesterase activity was reduced to 20% of normal in the lower
group. The five-day repeated dermal LD50 has been given as
73 mg/kg/day to rats (total dose 365 mg/kg).
Cumulation of compound
Fenthion is not cumulative to any marked degree. However,
cholinesterase recovery is slow after inhibition by this compound.
Cumulation of effect
Repeated exposure may produce cumulative effect on cholinesterase.
2.1.6 Dietary studies
Short-term
Male and female rats were fed fenthion at dietary levels of 0.25,
0.50, 2.5 and 5.0 mg/kg for three months. Reduction of erythrocyte
cholinesterase activity was observed at all dose levels. At the
lowest level, 0.25 mg/kg, the inhibition, approximately 10-20%, was
not progressive with time. Mortalities were observed in the females
at 5.0 mg/kg, the animals died manifesting muscarinic and nicotinic
effects. Histological examination revealed reduced spermatogenesis
in the testis and atrophic prostate glands at the highest feeding
levels (2.5 and 5.0 mg/kg).
Long-term
Six groups of 25 males and 25 female rats were fed for one year
on diets of 2, 3, 5, 25 and 100 ppm fenthion. Survival of male rats
at 25 ppm was slightly decreased and cholinesterase activity was
reduced at the 5 ppm level and above with only those animals at 2
and 3 ppm showing no adverse enzyme effects. Haemosiderosis was
evident in the spleen of the rats at the 100 ppm level.
2.1.7 Supplementary studies of toxicity
Carcinogenicity
No information available.
Teratogenicity
A three generation study in rats at 3.15 and 75 ppm involving two
litters per generation produced no adverse effects on rat
reproduction. Only slight growth depression was observed at the
highest dietary level.
Neurotoxicity
No neurological disruption in hens was observed when fenthion was
administered orally as a single dose of 25 mg/kg and at up to
100 ppm in the diet for 30 days.
2.1.8 Modifications of toxicity
Fenthion potentiates the acute intraperitoneal toxicity of malathion
dioxathion and coumaphos in rats. The greatest - almost threefold -
potentiation was with coumaphos. Reduction of cholinesterase
activity was also potentiated by a combination of fenthion and
coumaphos when fed to dogs.
2.2 TOXICOLOGY-MAN
2.2.1 Absorption
Ingestion has proved to be the important cause of severe poisoning
with this compound. It may also be absorbed through the skin and by
inhalation of dust particles.
2.2.2 Dangerous doses
Single: not known.
Repeated: not known.
2.2.3 Observations on occuptionally exposed workers
Fenthion has been widely used in many parts of the world for control
of household pests and mosquitos. Twenty-seven out of 28 workers who
sprayed fenthion as residual indoor application for 15 days in a
malaria control operational trial without taking adequate
precautions, demonstrated various degrees of poisoning. These
included headache, vertigo, blurred vision, muscle and abdominal
pains, cramps, diarrhoea and prolonged vomiting. Very severe
reduction of whole blood cholinesterase activity was observed, and
it was still reduced a month after the end of spraying. However, in
a second smaller spraying operation when precautions were more
stringent, only one out of 12 men showed mild symptoms.
In mosquito larviciding operations, dermal exposure was found to
average 3.6 mg/h with both power and hard sprayers and 12.3 mg/h
using a granular formulation dispersed by hand. Some workers showed
some plasma cholinesterase depression but in no case was erythrocyte
cholinesterase depressed.
2.2.4 Observations on exposure of the General population
No information available.
2.2.5 Observations of volunteers
No information available.
2.2.6 Reported mishaps
Apart from the incident when applied in a trial as a residual indoor
insecticide, most incidents have been from ingestion of quantities
of fenthion. In these separate incidents there has been recovery
although the patients were suffering from severe poisoning (one was
comatose and cyanosed at presentation). However, extensive treatment
with pralidoxime, atropine, artificial respiration, and in one case
endotracheal intubation, were necessary. In these cases the acute
effects were prolonged; in one case, recovery took 30 days.
2.3 TOXICITY TO NON-MAMMALIAN SPECIES
2.3.1 Fish
Information being obtained.
2.3.2 Birds
Harmful.
2.3.3 Other species
Information being obtained.
Part 3 - For regulatory authorities
RECOMMENDATIONS ON REGULATION OF COMPOUND
3.1 RECOMMENDED RESTRICTIONS ON AVAILABILITY
(For definition of categories, see introduction.)
Liquid formulations above 10%, category 3. All others, category 4.
Solid formulations above 10%, category 4. All others, category 5.
3.2 TRANSPORTATION AND STORAGE
All formulations
United Nations Classification 6.1.
Should be transported or stored in clearly labelled rigid and
leakproof containers, under lock and key, secure from access by
unauthorized persons and children. No food or drink should be
transported or stored in the same compartment.
3.3 HANDLING
Formulations in categories 3 and 4
Full protective clothing should be used by those handling the
compound. Adequate facilities should be available at all times
during handling and should be close to the site of handling. Eating,
drinking and smoking should be prohibited during handling and before
washing after handling.
Formulations in category 5
No facilities other than those needed for handling of any chemical
may be required.
3.4 DISPOSAL AND/OR DECONTAMINATION OF CONTAINER
Containers must either be burned or crushed and buried below
topsoil. Care must be taken to avoid subsequent contamination of
water sources. Decontamination of containers in order to use them
for other purposes should not be permitted.
3.5 SELECTION, TRAINING AND MEDICAL SUPERVISION OF WORKERS
Formulations in categories 3 and 4
Pre-employment medical examination of workers necessary. Workers
suffering from active hepatic or renal disease should be excluded
from contact. Pre-employment and periodic plasma and erythrocyte
cholinesterase determinations for workers desirable. Special account
should be taken of the workers' mental ability to comprehend and
follow instructions. Training of workers in techniques to avoid
contact essential.
Formulations in category 5
No special cholinesterase monitoring of workers necessary. Warning
of workers to minimize contact essential.
3.6 ADDITIONAL REGULATIONS RECOMMENDED IF DISTRIBUTED BY AIRCRAFT
All formulations
Pilots and loaders should have special training in application
methods and recognition of early symptoms of poisoning and must wear
a suitable respirator. Use of flagmen not recommended. Flagmen, if
used, should wear overalls and be located away from the dropping
zone.
3.7 LABELLING
Formulations in categories 3 and 4
Minimum cautionary statement
Fenthion is an organophosphorus compound which inhibits
cholinesterase. It is poisonous if swallowed. It may be absorbed
through the skin or inhaled as dusts or mists. Avoid skin contact;
wear protective gloves, clean protective clothing and a respirator
when handling the material. Wash thoroughly with soap and water
after using. Keep the material out of reach of children, and well
away from foodstuffs, animal feed and their containers. If poisoning
occurs, call a physician. Atropine and pralidoxime are the specific
antidotes and artificial respiration may be needed.
Formulations in category 5
Minimum cautionary statement
This formulation contains fenthion, a toxic substance which is
poisonous if swallowed. Keep the material out of reach of children
and well away from foodstuffs, animal feed and their containers.
3.8 RESIDUES IN FOOD
Maximum residue limits for fenthion have been recommended by the
Joint FAO/WHO Meeting on Pesticide Residues.
Part 4 - Prevention of poisoning in man and emergency aid
4.1 PRECAUTIONS IN USE
4.1.1 General
Fenthion is an organophosphorus pesticide of moderate toxicity which
penetrates the intact skin and is also absorbed by inhalation of
dusts and from the gastrointestinal tract. Most formulations should
be handled by trained personnel wearing protective clothing.
4.1.2 Manufacture and formulation
T.L.V.
No information.
Closed system and forced ventilation may be required to reduce as
much as possible the exposure of workers to the chemical.
Formulation should not be attempted without advice from the
manufacturer.
4.1.3 Mixers and applicators
When opening the container and when mixing, protective impermeable
boots, clean overalls, gloves and respirator should be worn. Mixing,
if not mechanical, should always be carried out with a paddle of
appropriate length. When spraying tall crops or during aerial
application, a face mask should be worn as well as an impermeable
hood, clothing, boots and gloves. The applicator should avoid
working in spray mist and avoid contact with the mouth.
Particular care is needed when equipment is being washed after use.
All protective clothing should be washed immediately after use,
including the insides of gloves. Splashes must be washed immediately
from the skin or eyes with large quantities of water. Before eating,
drinking or smoking, hands and other exposed skin should be washed.
4.1.4 Other associated workers (including flagmen in aerial
operations)
Persons exposed to fenthion and associated with its application
should wear protective clothing and observe the precautions
described above in 4.1.3 under "mixers and applicators".
4.1.5 Other populations likely to be affected
With good agricultural practice subject to 4.2 below, other
populations should not be exposed to hazardous amounts of fenthion.
4.2 ENTRY OF PERSONS INTO TREATED AREAS
Unprotected persons should be kept out of treated areas for at least
one day. (Does not apply when used as a larvicide.)
4.3 SAFE DISPOSAL OF CONTAINERS AND SPILLAGES
Residues in containers should be emptied in a dilute form into a
deep pit taking care to avoid contamination of ground waters.
Decontamination of containers in order to use them for other
purposes should not be permitted. Spillage should be removed by
washing with 5% sodium hydroxide solution and then rinsing with
large quantities of water.
4.4 EMERGENCY AID
4.4.1 Early symptoms of poisoning
Early symptoms of poisoning are headache, vertigo, blurring of
vision, tightness in the chest, joint and muscle pains, abdominal
cramps, diarrhoea and repeated vomiting. Other symptoms that may
occur include insomnia, loss of appetite, weakness, slurred speech,
constriction of the pupils and generalized anxiety.
4.4.2 Treatment before person is seen by a physician if these
symptoms appear following exposure
The person should stop work immediately, remove contaminated
clothing and wash the affected skin with soap and water, if
available, and flush the area with large quantities of water. If
swallowed, vomiting should be induced if the person is conscious. In
the event of collapse, artificial respiration should be given,
bearing in mind that if mouth to mouth respiration is used, vomit
may contain toxic amounts of fenthion.
Part 5 - For medical and laboratory personnel
5.1 MEDICAL DIAGNOSIS AND TREATMENT OF CASES OF POISONING
5.1.1 General information
An organophosphorus pesticide of moderate toxicity which is absorbed
through the intact skin as well as by inhalation and from the
gastrointestinal tract. It is converted in vivo to its oxygen
analogue which is an active cholinesterase inhibitor. Continued
exposure to small amounts may inhibit blood cholinesterases to
hazard levels.
5.1.2 Symptoms and signs
Initial symptoms of poisoning may include excessive sweating,
headache, weakness, giddiness, nausea, copious and prolonged
vomiting, stomach pains, muscle and joint pains, blurred vision,
slurred speech, muscle twitching and hypersalivation. More advanced
symptoms of poisoning may include laboured respiration, cyanosis,
coma, loss of sphincter control and loss of reflexes.
5.1.3 Laboratory
The most important laboratory finding is reduction in activity of
blood cholinesterases. Direct measurement can be made of metabolites
in urine and faeces.
5.1.4 Treatment
If the pesticide has been ingested, unless the patient is vomiting,
rapid gastric lavage should be performed using 54 sodium
bicarbonate, if available. For skin contact the skin should be
washed with soap and water. If the compound has entered the eyes,
they should be washed with isotonic saline or water.
Persons without signs of respiratory inefficiency but with manifest
peripheral symptoms should be treated with 2-4 mg of atropine
sulfate and 1000-2000 mg of pralidoxime chloride or 250 mg of
toxogonin (adult dose) by slow intravenous injection. More atropine
may be given as needed. Persons with severe intoxication with
respiratory difficulties, convulsions and unconsciousness should
immediately be given atropine and a reactivator. In such severe
cases 4-6 mg of atropine sulfate should be given initially followed
by repeated doses of 2 mg at 5-10 minute intervals. The patient's
condition, including respiration, blood pressure, pulse frequency,
salivation and convulsions should be carefully observed as a guide
to further administration of atropine. If the patient is cyanotic,
artificial respiration should be given first and then atropine
sulfate.
The airways should be kept free and artifical respiration should be
applied, if required, preferably by mechanical means. If necessary,
intubation should be performed.
Contraindications are morphine, barbiturates, phenothiazine,
tranquillizers and central stimulants of all kinds.
5.1.5 Prognosis
If the acute toxic effects are survived and these may be prolonged,
and adequate artificial respiration has been given, the chances of
complete recovery are good. However, in very severe cases,
particularly if artificial respiration has been inadequate,
prolonged hypoxia may give rise to permanent brain damage.
5.1.6 References of previously reported cases
Case histories and methods of treatment can be found in:
Dean et al. (1967) So. African Med. J., 1017-1019
Von Clarmann, M. et al. (1966) Arch. Toxik., 22, 2-11
Pickering, E. N. (1966) Can. 3. Med. Tech., p. 174
5.2 SURVEILLANCE TESTS
Test Normal level* Action level*,+ Symptomatic level*
Plasma cholinesterase 100% 50% variable
Erythrocyte cholinesterase 100% 70% usually < 40%
+The level at which action has to be taken to terminate exposure of the men until
recovery of cholinesterase occurs.
*Expressed as percentage of pre-exposure activity.
5.3 LABORATORY METHODS
References only are given.
5.3.1 Detection and assay of compound
It is unlikely that unchanged fenthion will be detectable in human
tissues after exposure. Determination of the level of blood
cholinesterase is probably the most suitable method in cases of
suspected poisoning. Levels of metabolites can be measured in urine
or faeces. Most methods of residue analysis involve gas-liquid
chromatography.
Thornton, 3. S. Chemagro Corp., Research Department, Report No.
20.420 (revised 21 October, 1968)
Bowman & Beroza (1968) J. Ag. Food Chem., 16, 399-402
Additional information will be found in:
Analytical methods for pesticides, Plant Growth Regulations and Food
Additives, ed. Zweig, G., Vol. II, 1964, Academic Press
5.3.2 Other tests in cases of poisoning
Levels of cholinesterase in the blood provides the most useful
diagnosis of poisoning for methods of estimation. See:
Michel, N. O. (1969) J. Lab. Clin. Med., 34, 1566-1568
Ellman et al. (1961) Biochem. Pharmacol. I., 88-95
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