Monocrotophos is an organophosphorus (OP) insecticide, developed by
Ciba-Geigy (now Novartis) and first registered in 1965. It is a hazardous
chemical especially for conditions of use in developing countries.
What is monocrotophos?
This non-specific systemic insecticide and acaricide, used
to control common mites, ticks and spiders with contact and stomach action,
quickly penetrates plant tissue(1).
In common with other OPs, its toxic action is achieved by inhibiting
acetylcholinesterase, an enzyme essential for normal nerve impulse transmission.
It is widely used, mainly for foliar application to cotton. Monocrotophos is
corrosive(2), and stable when stored
in glass or polyethylene containers(3).
The pesticide is now out of patent, and is produced by at least 15
manufacturers, although Novartis still produces an estimated 40% of total annual
production(4). Monocrotophos is also
manufactured and exported by companies in India, China, Brazil and Argentina. In
India, for example, DowElanco makes monocrotophos in a joint venture with the
Indian company NOCIL(5).
Uses and usage
The total sales of this widely-used pesticide is roughly 3% of all insecticide
products.(6) It is registered in
approximately 60 countries. Eight of these, accounting for 60% of sales, require
detailed data on performance, chemistry, safety and environmental aspects(7).
The remaining 40% are in countries which require only assessments, summaries, or
very limited data. The product was withdrawn from use in the US, and in the
European Union is registered in Austria, France, Spain, Italy and Greece(8).
While mainly applied against cotton
pests, it is used on citrus, olives, rice, maize, sorghum, sugar cane, sugar
beet, peanuts, potatoes, soya beans, vegetables, ornamentals and tobacco.
Monocrotophos is classified WHO Ib, highly hazardous, and has been responsible
for deaths resulting from accidental or intentional exposure. It is highly toxic
orally, as well by inhalation or absorption through the skin. Early symptoms of
poisoning may include excessive sweating, headache, weakness, giddiness, nausea,
vomiting, hypersalivation, abdominal cramps, diarrhoea, blurred vision and
slurred speech. Inhalation or skin contact may increase the susceptibility to
the pesticide without showing immediate symptoms(9).
The acute oral toxicity for rats (LD50)
is 23mg/kg (males) and 18 mg/kg (females). The acute dermal toxicity for a rats
is 354 mg/kg(10). Tests on rabbits
indicate it is slightly irritating to eyes and causes reversible corneal
opacity: reports on human health indicate eye contact will cause pain, bleeding,
tears, pupil constriction and blurred vision.
Severe poisoning will affect the
central nervous system, producing inco-ordination, slurred speech, loss of
reflexes, weakness, fatigue, involuntary muscle contractions, twitching, tremors
of the tongue or eyelids and eventually paralysis of the body extremities and
the respiratory muscles. In severe cases there may also be involuntary
defecation or urination, psychosis, irregular heart beat, unconsciousness,
convulsions and coma. Ingestion of 120 mg monocrotophos can be fatal(11).
Like other OPs, monocrotophos is a
potent cholinesterase inhibitor. The no effect level (NOEL) is 0.03 ppm in rats.
It is slightly irritating to the skin and mildly irritating to the eyes(12,13).
Monocrotophos has also been shown to cause delayed neuropathy (see page 6 for
more details)(14). A study in Egypt
of farmers using OPs, including monocrotophos, found that 50% of the workers
showed signs of neurological effects such as superficial or deep sensory loss
and decrease or lost reflexes in their ankle or ankle and knee(15).
(See Pesticides Trust [now PAN UK] OP fact sheet for more data on neurological effects(16).)
Monocrotophos is not carcinogenic in rats at 0.45 mg/kg/day, the highest dose
tested(17). No significant
carcinogenic lesions were observed when rats were exposed to monocrotophos
aerosol at concentrations from 97-308 mg/m3
for one hour(18).
Researchers have generated a rat reproductive (and offspring) NOEL of 2.7 ppm,
evidenced by decreased fertility, pup viability and weight, partly attributed to
depressed maternal lactation(19).
Teratogenicity (birth defects)
Rats which received doses of 2 mg/kg per day of monocrotophos produced foetuses
with lower than average length and weight and maternal toxicity in the form of
reduced body weight gain in pregnancy at 1.0 mg/kg. No teratogenic effects were
found at 2 mg /kg/day in rats, the highest dose tested(20).
Key health issues
Concerns about the safety of monocrotophos has led to its inclusion in the Prior
Informed Consent (PIC) procedure (see page 16 for more on PIC). Governments are
informed that formulations which exceed 600 g/litre of active ingredient may not
be safe because of their impact on human health under conditions of use in
developing countries. Governments which wish to prohibit these formulations can
notify the PIC secretariat. Their decisions will be circulated to exporting
Many incidents in developing countries
have been linked to monocrotophos. It is often difficult to trace an incident to
a particular active ingredient: frequently a 'block' of pesticides commonly used
in a region may be linked to a survey indicating occupational and other health
impacts in the area. Monocrotophos has been pointed to as a cause, in the
- Brazil, Parana State Monocrotophos
caused 107 of 412 reported incidents analysed in 1990, and the toxicology
centre and health clinics also noted 1,650 incidents involving monocrotophos
between 1982 and 1991(22).
- Paraguay In a region where monocrotophos is
one of the most commonly used active ingredients there have been numerous
cases of pesticide poisoning; monocrotophos was identified as the cause of
paralysis in children in cotton-growing areas by the Ministry of Public
Health and Welfare which found that 2-3 weeks of frequent exposure caused
paralysis in children and acute poisoning in adults(23).
- Egypt In a cotton growing region of Egypt the
health of 14 farmers who spray was compared with a control group from the
same region. Monocrotophos is widely used and 61% of those surveyed showed
symptoms of chronic pesticide poisoning(24).
- Philippines, Cordillera region Monocrotophos
was one of the pesticides widely used by farmers in a survey that found all
farmers suffered some adverse health effects(25).
- Indonesia In observations of 906 spray
operations of 214 farmers commonly using monocrotophos and other OPs, over a
three-month period, researcher found a significant increase-from two to
fifty-fold-in the symptoms of pesticide toxicity during the spraying period.
Of these spray operations, 21% brought on three or more neurobehavioural and
intestinal signs of poisoning(26).
Fate in the environment
The EU has classified monocrotophos as dangerous for the environment(27).
Monocrotophos has a half life of 14-21 days at pH9 and 25oC,
with the rate decreasing at lower pH's and increasing at higher temperatures.
Degradation on soil exposed to natural sunlight is rapid (half life less than 7
days) and on dark control samples is slower (half-life approximately 30 days).
Monocrotophos is mobile in soil, and although it degrades rapidly it may possess
potential for groundwater contamination.(28)
Monocrotophos is one of the most toxic pesticides to birds and is extremely
toxic other wildlife, highly toxic to bees. It is toxic to shrimps and crabs,
moderately toxic for fish and non-toxic for microorganisms. The acute LD50
for birds ranges from 0.9-6.7 mg/kg body weight, and for honey bees 33-84 ug/bee(29).
There are numerous reports of avian
mortality attributed to monocrotophos. The most recent occurred in Argentina,
where an estimated 20,000 hawks died over an area of approximately 200km by 250
km in 1996. More than 700 dead hawks were found in one roost. Ornithologists
suggested that monocrotophos used against grasshopper pests in the region was
responsible, with hawks affected by direct exposure to the spray or secondary
poisoning through eating contaminated grasshoppers. Scientists from Canada and
the US had observed that smaller numbers of hawks were returning after migrating
to South America. Miniature satellite transmitters attached to hawks led to the
discovery. The major manufacturer, Novartis, joined meetings which agreed not to
use monocrotophos in the region and encouraged other local distributors to stop
selling the pesticide. A campaign to inform farmers was also supported by
OPs do not have long persistence and are generally found at low levels in food.
Monocrotophos is not used in the UK, and testing imported food in 1996 found low
levels (0.03 mg/kg) in one sample of dried currants (of eight tested) imported
from Greece. Testing by UK food industry sources found monocrotophos residues in
dwarf beans (0.07 mg/kg)(31).
Maximum residue limits have been set in some products in the range of 0.02-1
mg/kg, and the acceptable daily take is 0.0006 mg/kg body weight(32).
Monocrotophos and some of its
metabolites have been identified in the milk, muscle, and liver of cows and in
the milk of goats following ingestion of this chemical(33).
Pre-harvest intervals have been set in
several countries and are generally in the order of 7-15 days for vegetables and
potatoes, maize and citrus and 28-30 days for other crops(34).
White fly resistance has caused plague-like outbreaks on
cotton crops(35). Records over time
show that resistance to monocrotophos of the Colorado potato beetle on Long
Island, US, appeared more quickly than to almost any other pesticide, within one
year of introduction(36).
Ways to reduce exposure
Full protective clothing should be worn, including a
respirator when mixing and spraying tall crops. Use of flaggers should be
avoided. All equipment and protective clothing should be washed thoroughly after
use and clothing should be laundered separately from family clothing.
Unprotected workers should be kept out of treated areas for 48 hours37.
Manufacture, formulation, agricultural use and disposal of monocrotophos should
be carefully managed to minimize contamination of the environment.
In view of the high toxicity of monocrotophos, it should not
be considered in hand-applied ULV spraying practices38.
Monocrotophos is a widely used, and extremely dangerous insecticide. It has now
been included in the PIC procedure, in recognition of the health problems caused
by formulations with a high percentage of the active ingredient. Its low cost
and many applications will present a challenge to users looking for safer
alternatives, or measures which will protect health.
Germany May not be handled by adolescents
and pregnant and nursing women.
Indonesia Monocrotophos was banned for use in rice in 1986 because
of insect resistance and certain formulations phased out in 1994.
Kuwait Severely restricted: to use on plants up to the flowering
Malaysia Registration for use only on coconut and oil palm by
Philippines In 1990 the Fertilizer and Pesticide Authority issued
Circular No. 01, which included a severe restriction on monocrotophos for use
only in bean fly control. A six month phase out period took effect from 29
Sri Lanka Severely restricted. Import prohibited since July 1995.
US Voluntarily withdrawn by the registrant in 1989. Before
withdrawal it could be used only by certified applicators. No remaining uses are
allowed. Main concern is toxicity to non-target species, especially birds.
1. Tomlin, C. (ed), The Pesticide Manual, Tenth Edition, Crop Protection
Publications. British Crop Protection Council and Royal Society of
2. IPCS, Monocrotophos Health and Safety guide, No. 80, IPCS International
Programme on Chemical Safety, UNEP and ILO, WHO, Geneva, 1993.
3. EPA Pesticide Fact Sheet No. 72, US Environment Protection Agency, 1985
4. Ciba, Monocrotophos: Information for participants
at the fifth FAO/UNEP joint meeting on PIC, Rome, October 1992.
5. Dinham, B., The Pesticide Trail: The impact of
trade controls on reducing pesticide hazards in developing countries, The
Pesticides Trust [now PAN UK], London, January 1995.
6. Op. cit. 4.
7. Op. cit. 4.
8. Active Substances Authorized by Plant Protection
Products, DOC.3010/VI/91-Rev.12, September 1995.
9. Watterson , A., Pesticide Users' Health and Safety
Handbook: An international guide, Gower Technical, Aldershot, UK, 1988.
10. Op. cit. 3.
11. FAO/UNEP, PIC Decision Guidance Document,
Monocrotophos, June 1997.
12. Op. cit. 3.
13. Op. cit. 2.
14. Hill v Tomkins, Judgement of HH Smith, J (QBD)
delivered on 17 October 1997.
15. Amr, M. et. al. 'Neurological effects of
pesticides', study by the Industrial Medicine and Occupational Diseases
Faculty of Medicine, Cairo University, reported in Pesticides News 30,
16. Pesticides News, 'Fact sheet-Organophosphate
insecticides' No. 34, December 1996, p. 20.
17. Op. cit. 3.
18. EXTOXNET Pesticide Information Notebook, Cornell
University, Ithaca, USA, 1995.
19. Op. cit. 3.
20. Op. cit. 3.
21. Op. cit 11.
22. Dinham, B., The Pesticide Hazard: A global health
and environmental audit, Zed Books, London and New Jersey, 1993, pp 87-88.
23. Ibid. pp120-121.
24. Op. cit. 15.
25. Cheng, Dr. Charles L., Medical Director, Baguio
Philipino-Chinese General Hospital, Baguio city, Philippines 'Pesticides and
Hazardous Effects on the Benguet Vegetable Farmers, 1993, (In Dinham, 1995
pp 76-7. Op. cit. 22.)
26. Hirschhorn, Norbert, 'Study of the Occupational
Health of Indonesian Farmers who Spray Pesticides, the Indonesian National
IPM Program', FAO (UTF/INS/067/INS), Jakarta, August 1993 (In Dinham, 1995,
pp 59-60). Op. cit 5.)
27. Op. cit. 11
28. Op. cit. 3.
29. Op. cit. 2.
30. 'Action to halt hawk deaths', Pesticides News 35,
March 1997, p. 6.
31. MAFF/HSE, Annual Report of the Working Party on
Pesticide Residues: 1996, MAFF, London 1997.
32. FAO/WHO, Pesticide Residues in Food, 1993
Evaluations, Joint Meeting on Pesticide Residues (JMPR), FAO, Rome, Plant
Production Paper Monocrotophos.
33. Op. cit. 3.
34. Op. cit. 11.
35. Denholm, I, and Devonshire, AL (Eds), Resistance
'91, Elsevier, London and New York, 1991.
36. Metcalf, RL, Insect Resistance to Insecticides,
Pesticide Science, Vol 26, 1989, pp 333-358.
37. Guidelines for personal protection when working
with pesticides in tropical countries, FAO, 1990.
38. Op. cit. 2.
39. Control actions in Germany, Kuwait, Malaysia, Sri
Lanka and the US see PIC DGD (op. cit. 11), and control actions in
Philippines and Indonesia see The Pesticide Trail (op. cit. 5.), pp 79 and
[This article first
appeared in Pesticides News No.38, December 1997, p20-21]