Methyl parathion is an organophosphate (OP) insecticide
that has caused many health problems - particularly in developing countries -
since its introduction onto the market in the early 1950s. This fact sheet
provides information on the hazards associated with methyl parathion, focusing
also on recent restrictions on its application in the US, implemented because of
misuse of the product.
What is methyl parathion?
Methyl parathion was originally developed by the
German pesticide company Bayer. It is a non-systemic pesticide that kills pests
by acting as a stomach poison.
It is used to control chewing and
sucking insects in a wide range of crops, including cereals, fruit, vines,
vegetables, ornamentals, cotton and field crops(1).
Methyl parathion is generally applied as a spray, mainly as an emulsifiable
concentrate formulation. The recommended application rates are 15-25g of active
ingredient per 100 litres(2).
The basic manufacturers of methyl parathion are All
India Medical Co (India), Bayer India, Bayer Mexico, Cheminova (Denmark), Rallis
India and Sundat (Singapore)(3). In 1993, other production facilities existed in
Brazil, the former East Germany, China and the former USSR. Although not used in
the UK, methyl parathion is widely used throughout the world, and is registered
in at least 38 countries(4).
Information on global sales and
production data are not widely available. For the financial year 1995-96, India
produced an estimated 2,200 tonnes of technical grade methyl parathion(5).
Cheminova, a major producer, sells US$
15 million per year in the US, one of its key markets for this product(6).
Overall the company recorded a 10% rise in sales in 1996. Its forecasts for
future growth in methyl parathion have however been affected by an agreement to
withdraw certain formulations in the US (see below)(7).
The World Health Organisation classifies methyl
parathion as a class Ia 'extremely hazardous' pesticide(8). It is highly toxic
by inhalation and ingestion, and moderately toxic by dermal adsorption (it is
also readily adsorbed through the skin). The oral LD50 in rats is 2.9 mg/kg, in
mice is 33.1-119.5 mg/kg, in rabbits is 19-420 mg/kg and dogs is 50 mg/kg(9).
The dermal rat LD50 is 44-67 mg/kg.
Like other organophosphate
insecticides, methyl parathion is a cholinesterase inhibitor (see the
Organophosphates fact sheet PN34 pp20-21). When inhaled, the first adverse
effects are a bloody or runny nose, coughing, chest discomfort and difficulty
breathing. Skin contact may cause localised sweating and involuntary muscle
contractions. Following exposure by any route, other systemic effects may begin
within a few minutes, or be delayed for up to 12 hours. These may include
pallor, nausea, vomiting, diarrhoea, abdominal cramps, headache, dizziness, eye
pain, blurred vision, constriction or dilation of the pupils, tears, salivation,
sweating and confusion. In severe cases, poisoning will affect the central
nervous system, producing in-coordination, slurred speech, loss of reflexes,
weakness, fatigue, and eventual paralysis of the body extremities and
respiratory muscles. Death may be caused by respiratory failure or cardiac
Effects reported in workers repeatedly exposed to
methyl parathion include impaired memory and concentration, disorientation,
severe depressions, irritability, confusion, headache, speech difficulties,
delayed reaction times, nightmares, sleepwalking, drowsiness and insomnia(11).
There are no epidemiological studies on
effects related only to methyl parathion exposure(12).
The International Agency for Research on
Cancer evaluated methyl parathion in 1983, and concluded that the available data
do not provide evidence that methyl parathion is carcinogenic to experimental
animals. No data on humans were available(13).
Mutagenicity tests have been both positive and
negative. The results of most of the in vitro studies with both bacterial
and mammalian cells were positive(14).
The WHO recommended that more definitive
studies should be conducted on residues of methyl parathion in fresh foods(15).
Residues are regularly detected in a range of fruit and vegetables. In the UK
during 1995, researchers found residues in imported celery, dessert grapes and
oranges, all below maximum residue limits (16).
Fate in the environment
Methyl parathion has a half-life in aqueous
solution of 175 days(17), and 10 days to two months in soils(18). The rate of
degradation increases with temperature and with exposure to sunlight. When large
concentrations of methyl parathion reach the soil, as in an accidental spill,
degradation will occur only after many years(19).
The US Environmental Protection Agency
(EPA) may have detected 4-nitrophenol, a methyl parathion breakdown product, at
very low levels in drinking water wells. The EPA is uncertain and cannot
quantify the amount or frequency of 4-nitrophenol in drinking water because the
analytical technique is not reliable(20).
Methyl parathion is unlikely to
Methyl parathion is highly toxic for aquatic
invertebrates with most LC50s ranging from <1 µg/litre to about 40µg/l(21).
In 1992, a massive bird kill occurred in Costa Rica after it was applied by
plane in a cotton field(22). Methyl parathion has been implicated in the deaths
of waterfowl in Spain and the acute poisoning of fish, birds, cattle and wild
animals in the Sudan(23).
Hazards in developing countries
Conditions in developing countries make it extremely
difficult to associate a particular active ingredient with a poisoning incident.
In the early 1950s the manufacturers
introduced a powder formulation of methyl parathion which caused problems
because of the poor conditions of use in developing countries. Methyl parathion
became the mainstay of pest control in cotton, and very quickly there were
hundreds of poisonings from this single product, and reportedly dozens of
In Oarana State, Brazil, pesticide
incidents compiled by the Toxicological Information Centre and Health Clinics
noted 1,243 incidents involving methyl parathion between 1982-1991(25).
There is evidence that methyl parathion
is not used safely in Central America. Research carried out in 1996 shows that
methyl parathion caused a number of documented poisonings among agricultural
labourers involved in Nicaraguan cotton production. In some cases they have
ended up in hospital with classic OP poisoning(26).
Cheminova, the Danish manufacturers of
methyl parathion, says it only sells to developing countries if they carry out
'safe farming'. However, researchers on the ground in countries like Guatemala
and Nicaragua say methyl parathion is rarely used safely.
- The WHO has set out a number of safety remarks for methyl
- methyl parathion may only be used by trained personnel;
- A field sprayed with methyl parathion may not be entered
for 48 hours after application;
- methyl parathion may not be sprayed by hand;
- people may not be used as markers when spraying from the
There is evidence that these recommendations are broken in
Problems in the US
Recently, there have been a number of important US
prosecutions involving methyl parathion. Over 1,500 homes and businesses in
Mississippi and Ohio were sprayed with methyl parathion by unlicensed operators.
Methyl parathion is not permitted for use indoors in the US. The authorities had
to relocate over 1,100 people in temporary accommodation, and clean up costs
could reach US $50 million. In addition, local vets reported deaths of household
pets due to methyl parathion exposure(29).
These events led the US EPA to cancel
the registrations of emulsifiable concentrate formulations. These came into
effect on 30 April 1997, following a voluntary agreement with the US
registrants, led by Cheminova. Cheminova is to carry out a public education
programme on the proper use of the insecticide(300.
On 13 March 1997, Dock Eatman, Sr of Moss Point
Mississippi was convicted by a jury of illegal spraying of the insecticide
methyl parathion in homes and other buildings in the Pascagoula (Miss.) area in
1995 and 1996. Eatman did not have a licence for commercial pesticide
application. This insecticide is only approved for outdoor agricultural use.
Eatman faces a maximum of 21 years in prison and/or up to US $2.1 million in
fines. This case is being investigated by the EPA's Criminal Investigation
Division, the FBI and authorities from the state of Mississippi(31).
Lutellis Kilgore of Elyria Ohio, was also
charged on 21 March 1997 with illegal use of methyl parathion. He allegedly
applied the insecticide in a manner inconsistent with its label to more than 60
properties without an application certificate. The spraying led to a US $20
million publicly-funded clean up of the affected properties. Kilgore faces a
maximum of one year in prison and/or a fine of up to US $100,000 for the illegal
application and five years in prison and/or a fine of up to US $250,000 for
making false statements to federal investigators(32).
Methyl parathion is banned in Indonesia, Sri Lanka and
Tanzania, and is severely restricted in Colombia, Korea, China and Japan. It is
one of five pesticides identified for inclusion in the Prior Informed Consent
Procedures of the Food and Agriculture Organisation on the grounds of causing
problems under conditions of use in developing countries.
As a hazardous OP pesticide, methyl parathion is
regularly misused in developing countries. The measures taken recently in the US
should help to reduce potential problems, but they merely highlight the
difficulties of using such a product in conditions like Central America, where
protective clothing and training are often lacking or ineffective. As a result,
methyl parathion should be more severely restricted in developing countries.
1. Tomlin, C (Ed.), The Pesticide Manual, tenth
edition, BCPC/ Royal Society of Chemistry, 1994, p771.
2. Methyl Parathion Health and Safety Guide No. 75,
World Health Organisation, Geneva, 1992.
3. Methyl Parathion, Prior Informed Decision Guidance
Document, FAO/UNEP Joint Database, IRPTC, Geneva, Update, 17 September 1996.
5. Agrow No. 265, 27 September 1996, p19.
6. Methyl Parathion: EPA's challenge, C&EN, 17
7. Agrow No. 280, 16 May 1997, p4.
8. The WHO Recommended Classification of Pesticides by
Hazard, International Programme on Chemical Safety, Geneva, 1996.
9. Op. cit. 3.
10. EXTOXNET Pesticide Management Program, Cornell
University, US, 1994.
12. Op. cit. 3.
13. IARC Monographs on the Evaluation of Carcinogenic
Risks to Humans, Lyon, France, 1983, pp144-145.
14. Op. cit 10.
15. Methyl parathion, Environmental Health Criteria
No. 145, WHO, Geneva, 1993, p18.
16. Annual Report of the Working Party on Pesticide
Residues: 1995, Ministry of Agriculture Fisheries and Food/Health and Safety
17. Op. cit. 15. p22.
18. Op. cit. 10.
19. Howard, P.H., (Ed.), Handbook of Environmental
Fate and Exposure Data for Organic Chemicals, Vol. III: Pesticides, Lewis,
20. Op. cit. 10.
21. Op. cit 3.
22. Dinham, B., The Pesticides Hazard, The Pesticides
Trust [now PAN UK], London, 1993, p105.
23. Op. cit. 3.
24. Made in Denmark (Danish video on methyl
parathion), TV94, Nųrrebrogade 66 C, Copenhagen, Denmark, 1997.
25. Op. cit. 22.
26. Op. cit. 24.
27. Op. cit. 2.
28. Op. cit. 24.
29. Parathion disaster in Mississippi, PANUPS,
Pesticide Action Network North America, 21 February 1997.
30. Agrow, No. 280, 16 May 1997, p16.
31. US EPA, press release, 27 March 1997.
32. US EPA press release, 4 April 1997.
[This article first
appeared in Pesticides News No.36, June 1995, p20-21]