Future section


 235th Meeting – June 2003:

Annual Variations in the Use of, and Exposure to Pesticides among Hmong Farmers in Northern Thailand

A talk by Dr. Peter Kunstadter

Present: Sean Ashley, Hans-Dieter Bechstedt, Parinya Bhanuwase, John Cadet, Jim Campion, Ken Dyer, Roy Hudson, Jack Kelly, Marc, Sophie and David Lallemant, Patcharin Nawichai, John C. Quicker, Lamar and Chongchit Robert, Carina zur Strassen, Caroline Subkaen, Jessica Wilson. An audience of 18.

This  summary of Peter’s talk was compiled by your convenor from the handout that Peter had prepared for the talk. 

Since the 1970s, Hmong farmers have changed from ‘organic’ subsistence shifting cultivation to fixed-field cash crop farming using chemical pesticides.

This paper considers some of the behavioural and biomedical consequences of the shift from land-extensive, labour-intensive ‘organic’ subsistence production for home use, to land- chemical- and machine-intensive fixed-field farming of cash crops for lowland and international markets. The Hmong community selected for study is about 30 km from Chiang Mai. Villagers concentrate on the production of lichee fruit, most of which is sold to lowland merchants and canneries, which entails the seasonal use of many different chemicals including pesticides.    

We report results of behavioral surveys in April 2002, and blood tests in April 2002 (peak of pesticide use), October 2002 (end of pesticide use), and January 2003 (3+ months without pesticide use) to track seasonal changes in use of, and exposure to pesticides in a random sample of 26 Hmong households (232 individuals from 1 year old to as old as they get), and discuss culturally appropriate options to reduce expose.

The question to be asked before we go any further is, ‘Why are the Hmong farmers using pesticides?’ The answer to that is to be found in recent history.

Tradition and Change

Hmong farmers were traditionally using a land-extensive, labour-intensive long cultivation-long fallow system of shifting cultivation – slash and burn.

Their major subsistence crops were upland (dry) rice and maize, and their major cash crop was opium.      

Starting in the mid-1960s, the Royal Thai Government, with international (UN) and bilateral (US and other Western countries) assistance, introduced ‘crop substitution’ of non-narcotic cash crops to reduce opium cultivation as one initial step in the total eradication of the sale and use of narcotics.  

In the mid-1980s, after the construction of an extensive highland road network, the Royal Thai Government changed its highland development policies and began serious efforts to destroy opium crops and arrest opium producers, stop shifting cultivation and prevent access to highland areas defined to belong to the Royal Forest, and restrict movement out of and between existing villages. Stopping shifting cultivation and preventing access to highland areas effectively reduced the area of land available for cultivation by up to 90% for some farmers. The success of this new policy quickly destroyed the traditional Hmong economic system.

Responses to Change

In response to these changes, the Hmong highlanders were forced to change. In response to their perception of land shortages they rapidly reduced desired family size and cut birth rates by using modern family planning methods. They increased enrollment of their children in school, which has resulted in an increase in perceived costs and a decline in the perceived economic value of their children. They have adopted a large variety of cash crops that require the intensive application of chemicals (Hmong respondents in our sample reported using 70 different kinds of chemical in the 12 months before April 2002. These chemicals included fertilizers, herbicides, insecticides, fungicides, hormones, and adherents.) plus the use of farm machinery (small ploughs, sprinkler irrigation, chemical spray pumps), none of which had been used traditionally.    

Materials and Methodology

We interviewed all household members over 15 years of age to regarding – demographic and socioeconomic characteristics, their use of and potential exposure to pesticides, their use of measures to prevent or reduce exposure, and the prevalence of symptoms associated with exposure to pesticides.

We screened for cholinesterase inhibition using rapid (treated paper) test of finger-stick blood from all participating household members over one year old.

We examined venous blood for chromosomal aberrations from 2 adults in each household.

A summary of the results

In the screened population of sample households there were 102 males / 105 females.

Education is strongly associated with age and gender. Most children of both sexes are currently enrolled in school. Adults aged 20-39 have more education than older adults. Males over 20 years old have more education than females.

Thai language ability is associated with age and gender, and the distribution is similar to that of education.  

The religion of this community is about one-third animist, one-third animist + Buddhist, and one-third Christian.

Occupation – Most adults are farmers. The highest percentage is in the 20-39 age group, with a ratio by gender of 87% male to 96% female.

Beliefs about pesticides

Benefits – The major benefits perceived from the use of pesticides are the improvement of crops and the killing of insects, weeds, pests and diseases.

Negative effects – The major negative effects perceived by our sample are physical illness and harm to the environment.

When asked in more detail about the perceived effects of pesticides on their health, 31% of male and 24% of female respondents reported experience of specific symptoms – headaches, dizziness, blurred vision, tingling limbs, numb hands and feet, vomiting, itchiness, skin sores and allergies. They are also concerned that pesticides can cause not only illness but also disability and death.

The major effects on children’s health perceived by our respondents are illness and death. Children’s illnesses specified by respondents are – Will not grow or develop normally, unconsciousness, itching, crippled, blind, dizzy, brain damage, decreased immunity, difficult breathing, vomiting, fever, headaches, weak, blurred vision, and yellow and pale skin.

Methods of Application of Pesticides

The usual method of application of chemicals is by machine spray, with fertilizers broadcast by hand. Respondents reported that all chemicals are applied, that is actually holding the spray gun, much more often by men than by women, ignoring the fact, however, that women usually carry the hose from the machine-powered pump while men are doing the spraying.

Screening for Cholinesterase Inhibition

None of the villagers of all ages and both sexes who were screened had ‘normal’ levels of cholinesterase inhibition and a large proportion had ‘risky’ or ‘dangerous’ levels.

Male/female differences (higher proportion of males with ‘risky’ or ‘dangerous’ levels) are significant for ages 10-19 (p = 0.04) and 20-39 (p = 0.02).

Symptoms associated with Pesticide Exposure

A substantial proportion of respondents reported symptoms ‘sometimes’, ‘often’ and ‘every time’ after pesticide applications. Reported symptoms included – headache, dizziness, blurred vision, numb or tingling hands and feet, itching, nausea, and vomiting.

Behaviour and Exposure to Pesticides

Protective measures to reduce exposure to pesticides include – wearing a mask, gloves, boots and waterproof or heavy clothing, and staying out of a field after application. A large proportion of individuals, especially children, do not use protective clothing or any other methods to prevent exposure to pesticides.

The results of screening showed that adults who use masks only ‘sometimes’ or ‘never’ are twice as likely to have ‘dangerous’ levels of cholinesterase inhibition as those who use masks ‘always’ or ‘most of the time’. Also that a much higher proportion of men and women who have ‘dangerous’ vs. ‘safe’ levels of cholinesterase inhibition do not wear gloves regularly.

In reality, as a result of the land-use policies imposed upon them by the Thai Government, 100% of the villagers are exposed to pesticides. Their homes are now cheek by jowl with the orchards and farmland, and even when their land is at a distance away from the village, families live in field huts during the spraying months. The powerful machine pumps they use to apply the chemicals atomize the pesticides into a chemical-laden mist that shrouds the whole area, until the wind carries it on to the next village, or town, or city.     

In summary

The widespread use of pesticides and other farm chemicals is associated with perceived benefits to improve crop yield and price and kill insects, and to speed work and decrease labour.

Most villagers are aware of risks associated with the use of pesticides. These risks include health risks, both to themselves and their children, and risks to the environment.

Screening for exposure to organophosphate pesticides by testing for cholinesterase inhibition at the season of maximum use of pesticides shows high levels of exposure both among those people who apply pesticides and those who do not, and that the highest proportion of the population at ‘dangerous’ levels are among young children and males and females of reproductive age.

Screening during seasons of low use and no use showed a decline in levels of cholinesterase inhibition.

Adults in the study population show a larger number of chromosomal anomalies than in a control population. The meaning of these results is, however, not yet clear.

Villagers are aware of the risks and do use various methods to reduce exposure. These methods include the safe storage of pesticides and wearing protective clothing.

The use of protective clothing is more common and more consistent for men than women.

Adults who report wearing masks and/or gloves ‘sometimes’ or ‘never’ while applying pesticides are more likely to have ‘dangerous’ levels than those who wear them ‘always’ or ‘most of the time’.

There is no relationship between the level of cholinesterase inhibition and other protective measures – wearing boots, heavy protective clothing and staying out of fields after application of pesticides.

Into the future

We are discussing possible interventions with villagers to reduce their exposure. Methods to reduce exposure and constraints of the use of pesticides being suggested to villagers are:

Always wear a full set of protective clothing when applying pesticides. Villager’s response to this is that protective clothing is hot, extremely uncomfortable and makes it hard to move up and down hills and handle equipment.

Reduce or stop using pesticides altogether. Their response to this is that pesticides are necessary to insure quality, yield and a high price for the product.

Keep all children out of fields at all times. This is not practical because of the need for breast-feeding mothers and older children to labour in the fields.

Restrict pesticide application to one area in one day. Two reasons why this is not practical. Firstly because some households have orchards in different areas and its not practical to spray on different days. Secondly because some farmers sell their crop to brokers when trees are in bloom in January. Brokers have their own spray teams and schedules, over which farmers have no control.


Our sample population is heavily exposed to pesticides.

The use of pesticides is driven largely by economics.

We are continuing in discussions with villagers to find a method of decreasing exposure that is effective, economically and environmentally feasible and locally acceptable.

Market forces, including increased production and falling prices of lichees, are already making villagers consider other crops.

Selection of the appropriate combination of crops and cultivation methods is complicated by annual variations in crop yields and prices and the rapid responses of farmers throughout Thailand to market conditions.

The Hmong farmers have been forced, by external agents, between a rock and a hard place. There are very few, if any, alternatives open to them which do not include the inevitable extinction of their culture.     

In answers to questions from the audience, Peter explained that pesticides are nerve agents, exactly the same as nerve gases, which kill insects by disrupting the chemical transmitters in their nervous system. The same chemical transmitters are found in the nervous systems of all creatures, including homo sapiens.

Pesticides are used worldwide. They are dangerous and, in Western countries, their use is subject to strict regulations. The dangers are exacerbated in Thailand firstly because there is no effective system of regulation in force to educate and monitor farmers. Unfortunately most farmers here work on the principle that if some is good then more is better. And secondly because Western chemical companies dump chemicals in third world countries that they are prohibited from selling in the West.

Should the ‘outside world’ be concerned about the plight of Hmong farmers? Yes, there is one good, selfish, reason why they must be. The instructions on the side of the pesticide container say stop spraying at least two weeks before harvesting. Traders, who buy a crop while it is still on the tree, will continue spraying up to the day of harvesting. Unless the residue is completely removed it will stay on the fruit and into the can. On a sample of canned lichees that we bought locally, the labels were written in Thai, English, Japanese and Chinese.

 After the question and answer session, the meeting adjourned to the Alliance Cafeteria where members of the audience engaged Peter in more informal discuss over drinks and snacks.