WORLD HEALTH ORGANIZATION FOOD AND AGRICULTURE
ORGANIZATION
ORGANISATION MONDIALE DE LA SANTE ORGANISATION POUR L'ALIMENTATION
ET L'AGRICULTURE
VBC/DS/75.11
ORIGINAL: ENGLISH
DATA SHEETS ON PESTICIDES No. 11
1975
PYRETHRINS
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.
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not constitute formal publication. Il ne doit faire
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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.
PYRETHRINS
Part 1 - General information
CLASSIFICATION
Primary use: insecticide
Secondary uses: insect repellent and flushing agent
Chemical group: chrysanthemumic acid ester
Data sheet No. 11
Date issued: March 1975
1.1 COMMON NAME: Pyrethrins
Identity: The term refers generally to the mixed active ingredients
as present in commercially available extracts of the pyrethrum flower,
largely Chrysanthemum cinerariaefolium. Such extracts contain 20-25%
total pyrethrins, the main active constitutents being pyrethrin I and
pyrethrin II plus smaller amounts of the related cinerins and
jasmolins. The chemical names are:
Pyrethrin I: cis 4-hydroxy-3-methyl-2(2,4-pentadienyl)-2-cyclopenten-l-
one d-trans 2,2-dimethyl-3-(2-methylpropenyl)-cyclopropanecarboxylate,
or pyrethrolone ester of d-trans chrysanthemic acid.
Pyrethrin II: cis 4-hydroxy-3-methyl-2(2,4-pentadienyl)-2-cyclopenten-
l-one d-trans 2,2-dimethyl-3-(3-methoxycarbonyl-3-methylpropenyl)-
cyclopropane-carboxylate or pyrethrolone ester of pyrethric acid.
Synonyms: Local synonyms:
Pyrethrum extract
Pyrethrum oleoresin
1.2 SYNOPSIS: A highly insecticidal extract which is of weak
mammalian toxicity. It is rapidly detoxified in the gastrointestinal
tract, and on exposure to sunlight.
1.3 SELECTED PROPERTIES
1.3.1 Physical characteristics: Pyrethrins I and II are refined to
pale non viscous liquid oleoresin solutions.
I - b.p. 170°C at 0.1 mm Hg with decomposition.
II - b.p. 200°C at 0.1 mm Hg with decomposition.
1.3.2 Solubility: Water at 20°C virtually insoluble, soluble in
hydrocarbons and many other organic solvents.
1.3.3 Stability: Rapidly oxidized and inactivated in sunlight:
decomposed by exposure to light with loss of insecticidal activity.
Rapidly hydrolysed by alkali.
1.3.4 Vapour pressure: Not known, virtually non-volatile at ambiant
temperature.
1.4 AGRICULTURE, HORTICULTURE AND FORESTRY
1.4.1 Common formulations:
0.2-0.4% dusts; 0.5-1.0% ULV sprays; 0.1-0.5% pressure packs,
emulsifiable concentrates to give 0.003%-O.015% final pyrethrins
content (high volume usage). Most formulations contain a synergist
usually piperonyl butoxide and stabilizers; UV screens are also now
being included. Also used at a low concentration, admixed with other
insecticides as a "flushing" agent.
1.4.2 Susceptible pests
Effective against a wide range of agricultural, horticultural and
forest pests, including sawfly larvae, lepidopterous caterpillars,
leafhopers, aphids, beetles, and thrips. Particularly useful where
rapid "knockdown" paralysis is required, less effective in killing the
target pest unless synergised.
1.4.3 Use pattern
As pre-harvest treatment, applied just before harvest on growing bush
and vine fruits, deciduous fruits and nuts, forage crops and
vegetables, ornamentals.
Spray or dust formulations are used on freshly picked fruits and
vegetables in the field, in storage and in processing plants. Widely
used as sprays or dusts directly on commodities, for protection of
dried fruit, tree-nuts, grains, oil seeds and animal feeds during
storage. Applied as repellant to the outside of bags containing stored
cereals, cocoa, etc. Aerosols and sprays are used for treating food-
handling, processing and storage premises, agricultural premises and
households. Used as spray for control of ectoparasites of livestock
(including dairy and meat cattle) and poultry. Also used for control
of blowfly during fish drying.
1.4.4 Unintended effects
Pyrethrins are toxic to cold-blooded animals: avoid contamination of
watercourses. Not phytotoxic. Not persistent.
1.5 PUBLIC HEALTH PROGRAMME
1.5.1 Common formulations
0.2-0.4% dusts; 0.2-0.4% solutions in kerosene or petroleum
distillate; 0.05-0.10% solution, with additional agents, in kerosene as
flying insect sprays; synergists are included in the formulations. 0.5-
2% shampoos for human and pet usage. Repellant to mosquitos and biting
flies: used in insect repellant creams (including aerosols) and
mosquito coils.
1.5.2 Susceptible pests
Active against mosquitos, flies, cockroaches, lice, including human
body lice, and other public health insects.
1.5.3 Use pattern
Applied as thermal fogs, mists for non-residual control on a
repetitive application basis in situations such as kitchens, food
stores, factories, etc., where toxic residual insecticides cannot be
used. Thermal fogs of 0.05% pyrethrins + 0.40% piperonyl butoxide used
for fly Control. ULV sprays used against mosquitos, houseflies, and
tetse. Alcohol solutions applied to free water mains of arthropod
infestations.
1.6 HOUSEHOLD USE
1.6.1 Common formulations
0.15-0.30% dusts; 0.15-1.2 "aerosol" pressure packs; 0.05-0.10%
sprays; synergists and additional killing agents are often included.
Mosquito coils containing 0.15-0.5% (unsynergised) pyrethrins.
1.6.2 Susceptible pests
Mosquitos, houseflies, midges, cockroaches, etc.
1.6.3 Use patterns
Aerosol fly sprays use more than half the total production of
pyrethrum and mosquito coils about one third. Used in aerosols and
sprays to give rapid knockdown, killing power being increased by use of
a synergist. Flushing action useful in expelling insects from hiding
places. Mosquito coils give protection from biting for five to seven
hours, depending on mosquito density and ventilation.
PYRETHRINS
Part 2 - Toxicology and risks
Common name: pyrethrins
Date sheet No. 11
Date issued: March 1975
2.1 TOXICOLOGY - MAMMALS
2.1.1 Absorption route: Absorbed by the respiratory route and poorly
from the gastrointestinal tract. Not absorbed to a significant degree
through the skin. Allergic reactions may result from dermal exposure;
incidence is probably related to degree of refinement of extract being
lower as degree of refinement increases.
2.1.2 Mode of action: nervous system stimulation proceeding from
excitation to convulsions to tetanic paralysis and muscular
fibrillation.
2.1.3 Excretion products: oxidation and hydrolysis products are
excreted in the urine. Oxidation of the isobutenyl side chain of the
chrysanthemumic acid portion of the molecule may be a more important
route to detoxification than hydrolysis of the ester linkage. Some
pyrethrins are also excreted unchanged.
2.1.4 Toxicity, single dose
Oral: LD50 rat 500-1000 mg/kg
Dermal: LD50 rat. > 1800 mg/kg
Most susceptible species: not known
2.1.5 Toxicity, repeated doses
Oral: see dietary studies
Inhalation: no information
Cumulation of compound: does not accumulate in mammalian
tissues.
2.1.6 Dietary studies
Short-term: no information
Long-term: no significant effect on growth and survival of
rats was seen when the animals were fed a maximum dietary level
of 5000 ppm for two years. Slight though definite liver damage
was seen at 1000 and 5000 ppm but not of 200 ppm. A further
trial is being carried out.
2.1.7 Supplementary studies of toxicity
No information.
2.1.8 Modifications of toxicity
There is some doubt whether methylenedioxy synergists such as
piperonyl butoxide increase the toxicity of pyrethrins to mammals as
they do to insects.
2.2 TOXICOLOGY - MAN
2.2.1 Dangerous doses
Single: no information
Repeated: no information.
2.2.2 Observations of occupationally exposed workers
Allergic manifestations, particularly contact dermatitis have been
encountered in persons occupationally exposed to pyrethrum flowers or
crude extracts of pyrethrum.
2.2.3 Observations on exposure of the general population
The general population Will not be expected to be affected by
pyrethrins under normal conditions of use.
2.2.4 Observations of volunteers
Two hundred human subjects (177 females, 23 males) were patch tested
for skin sensitivity and irritation using pyrethrins at 1% in water
simulating formulation. This level did not produce primary irritation
and was not a sensitizer to human skin.
2.2.5 Reported mishaps
None.
2.3 TOXICOLOGY TO NON-MAMMALIAN SPECIES
The entries in these sections are intended to draw attention to
special risks and to give warnings of any needs for special
precautions.
2.3.1 Fish
Toxic to fish.
2.3.2 Birds
Not toxic to birds.
2.3.3 Other species
Not toxic to bees under the conditions of use. Toxic to cold-blooded
animals generally.
PYRETHRINS
Part 3 - For regulatory authorities
Common name: pyrethrins
Data sheet No. 11
Date issued: March 1975
RECOMMENDATIONS ON REGULATION OF COMPOUND
3.1 RECOMMENDED RESTRICTION ON AVAILABILITY
(For definition of categories, see introduction.) Liquid
formulations over 50% category 4. All other formulations,
category 5.
3.2 TRANSPORTATION AND STORAGE
Should be transported or stored in clearly labelled leak-proof
containers out of reach of children, away from food and drink.
Avoid contact with metals other than aluminium or tin.
3.3. HANDLING
All formulations
Pyrethrum flowers and crude pyrethrum extract may cause contact
dermatitis and other allergic responses in some subjects.
3.4 DISPOSAL AND/OR DECONTAMINATION OF CONTAINERS
All formulations
Containers may be decontaminated (for method see paragraph 4.3 on
part 4). Decontaminated containers should not be used for food and
drink. Containers that are not decontaminated should be burned or
should be crushed and buried below topsoil. Care must be taken to
avoid subsequent contamination of water sources.
3.5 SELECTION, TRAINING AND MEDICAL SUPERVISION OF WORKERS
Persons with a history of asthma, hay-fever or allergies should be
excluded from contact. Warning of workers to avoid contact desirable.
Pre-employment and periodic medical examination not required.
3.6 ADDITIONAL REGULATIONS RECOMMENDED IF DISTRIBUTED BY AIRCRAFT
No special regulations recommended.
3.7 LABELLING
Minimum cautionary statement
None.
3.8 RESIDUES IN FOOD
3.8.1 Maximum residue levels
The Joint FAO/WHO Meeting on Pesticide Residues (1972) has
recommended the following limits:
Raw cereals....................................... 3 ppm
Fresh fruit and vegetables, dried fruit
and vegetables, oil seeds, tree nuts.......... 1 ppm
Dried codfish..................................... 3 ppm
PYRETHRINS
Part 4 - Prevention of poisoning in man and emergency aid
Common name: pyrethrins
Data sheet No. 11
Date issued: March 1975
4.1 PRECAUTIONS IN USE
4.1.1 General
Pyrethrins comprise a slightly toxic insecticidal extract from
pyrethrum flowers. it is rapidly detoxified in the gastrointestinal
tract.
4.1.2 Manufacture and formulation
T.L.V.
ACGIH 5 mg/m3; USSR -
Pyrethrins are not "manufactured" but are obtained by extraction of
the pyrethrum flower. Because of possible allergic responses contact
with the crude extract should be avoided as far as possible.
4.1.3 Mixers and applicators
When opening the container and when mixing care should be taken to
avoid contact with the mouth and eyes. If necessary a facial visor and
gloves should be worn. Mixing, if not mechanical, should always be
carried out with a paddle of appropriate length. Splashes must be
washed from the skin and 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 pyrethrins and associated with their application
should observe the precautions described in 4.1.3 under "mixers and
applicators".
4.1.5 Other populations likely to be affected
None.
4.2 ENTRY OF PERSON INTO TREATED AREAS
Persons can enter treated areas immediately after spraying without
being exposed to hazardous amounts of pyrethrins.
4.3 DECONTAMINATION OF SPILLAGE AND CONTAINERS
Residues in containers should be emptied in a diluted form into a
deep pit taking care to avoid ground waters. The empty container may
be decontaminated by rinsing two or three times with water and
detergent and scrubbing the sides. Hands should be protected during
this work. Decontaminated containers should not be used for food and
drink.
Spillage should be removed as much as possible by washing the area
with 5% sodium hydroxide solution and then rinsing with large
quantities of water.
4.4 EMERGENCY AID
4.4.1 Early symptoms of poisoning
Contact dermatitis is by far the most common manifestation of
toxicity. This effect may be due to impurities in the extract.
Sometimes other allergic symptoms are evident such as sneezing, serous
nasal discharge and nasal "stuffiness". A few cases of extrinsic
asthma have been reported.
4.4.2 Treatment before person is seen by a physician if these symptoms
appear following exposure
If the above symptoms appear following exposure to pyrethrins the
person should stop work, remove contaminated clothing and wash the
affected skin with soap and water, if available, and flush the area
with large quantities of water. In mild cases of ingestion, no active
measures. If oil-based materials are swallowed, give a glass of milk;
do not give an emetic. In severe cases, avoid regurgitation of oil in
the lungs. Give gastric lavage. In case of respiratory symptoms, give
oxygen and atropine.
PYRETHRINS
Part 5 - For medical and laboratory personnel
Common name: pyrethrins
Data sheet No. 11
Date issued: March 1975
5.1 MEDICAL DIAGNOSIS AND TREATMENT OF CASES OF POISONING
5.1.1 General information
Pyrethrins comprise a slightly toxic extract of the pyrethrum flower
which is of high insecticidal activity. The active ingredients are
poorly absorbed from the gastrointestinal tract and also by the
respiratory route but not to a significant degree through the skin. The
compounds are excreted as oxidation and hydrolysis products in the
urine. Allergic reactions are by far the most common toxic effect in
humans.
5.1.2 Symptoms and signs
The most common symptom of pyrethrins toxicity is contact dermatitis.
This manifestation is caused by impurities in crude extract and ground
flowers. There is usually mild erythematous vescicular dermatitis with
papules in moist areas and intense pruritis. A bullous dermatitis may
also develop. Some individuals have nasal symptoms including sneezing,
nasal congestion, and serous discharge. A few cases of extrinsic
asthma have been reported; these cases appear most common in
individuals with a previous history of asthma. There have been rare
cases of severe anaphylactic shock with peripheral vascular collapse
and respiratory difficulty. Little information is available on direct
toxic effect of pyrethrins; based upon animal studies, injection of
high doses could presumably lead to central nervous system stimulation
resulting in convulsions, muscular fibrillation and finally tetanic
paralysis.
5.1.3 Laboratory
There are no practical laboratory methods for determining the degree of
absorption of pyrethrins. Presence of chrysanthemumic acid or its
derivatives in the urine would presumably be indicative of absorption
but their absence cannot be construed to imply that pyrethrins have not
been ingested.
For dermatological effects positive patch tests with pyrethrins are
helpful in diagnosis. Eosinophilia may accompany an acute allergic
reaction and mucous nasal smears should be examined for the presence of
eosinophils.
5.1.4 Treatment
If a large quantity of pyrethrins has been ingested, unless the patient
is vomiting, gastric lavage should be performed using 5% sodium
bicarbonate solution if available. if there are convulsions or muscular
fibullation, diazepam should be used. For allergic reactions,
antihistamines taken orally are of value.
5.1.5 Prognosis
Chance of complete recovery from any toxic effect of pyrethrins is
good, provided that there is no further direct contact with the
insecticide.
5.1.6 References of previously reported cases
The following reference gives methods of treatment to be used in
cases of poisoning:
Hayes, W. J., jr (1963) Clinical Handbook on Economic Poisons, U.S.
Publ. Hlth Ser. Pubi. No. 476, p. 76
5.2 SURVEILLANCE TESTS
There are no practical surveillance tests.
5.3 LABORATORY METHODS
References only are given.
5.3.1 Detection a compound
For analysis of pyrethrins in crops, etc., see McClellan (1964). Moore
(1970) discussed residues of pyrethrins in foodstuffs and referred to
suitable gas-chromatographic methods of analysis. He has described a
method suitable for eggs, animal tissues and milk and its products
(1971). A gas-chromatographic method applicable to milk and animal
tissues is also described by the US Food and Drug Administration (1971)
and quoted by Zweig & Sherma (1972). See also Head (1967).
REFERENCES
Head, S. W. (1967) The quantitative determination of pyrethrins by gas-
liquid chromatography, Part I: detection by electron capture,
Part II: detection by hydrogen flame ionisation, Pyrethrum Post,
9(1), 12
McClellan, D. B. (1964) In: Zweig, G., ed., Analytical methods for
pesticides, plant growth regulators and food additives, Vol- II,
Academic Press New York and London, p. 408
Moore, J. B. (1970) Terminal residues of pyrethrin-type insecticides
and their synergists in foodstuffs, Residue Reviews, 33, 87
Moore, J. B. (1971) Paper submitted to the International Symposium on
Recent Advances in Research on Pyrethrum, The Natural
Insecticide, Minneapolis, USA, 30-31 August, (Unpublished)
US Food and Drug Administration (1971) Pesticide analytical manual,
Vol. II, Section 120, 128
Zweig, G., ed., (1972) Analytical methods for pesticides, plant growth
regulators and food additives, Vol. VI, Academic Press, New York
and London, p. 465