After World War II, when DDT and other organochlorine pesticides became popular in agriculture, they were considered a safe and effective way to get rid of pests. But over the years, more and more problems associated with the use of pesticides have shown up. Major problems include:
- Harmful side effects on non-target organisms (people, animals, soil, water, etc.)
- Resurgence of pest populations (because natural control is disrupted)
- The development of resistance
- The cost
Toxicity for non-target organisms
The use of pesticides (both synthetic and organic) always involves certain risks because of their poisonous character. Who is at risk?
- The users of the pesticides.
Farmers and their family members run the highest risks. They can easily come in contact with the pesticides, for example when mixing the chemicals or when applying them to the crop.
- The consumers of farm products.
The pesticides that were sprayed on the crop can leave behind residues that will be eaten by the consumers.
- The environment.
Pesticides will not only reach the target organisms but will also kill other organisms (e.g. beneficial insects, birds, earthworms, fish) in or around the crop fields, causing loss of biodiversity, deaths of wild life, and death of farm animals. Soil, air and water bodies can easily be contaminated with these poisonous chemicals. The unavoidable destruction of beneficial insects and spiders interferes with natural pest control.
The mentioned risks are most obvious when pesticides cause acute toxicity to man, domestic animals and non-target organisms such as fish, bees, birds and soil organisms. The more subtle long-term chronic effects (disruption of endocrine system, cancer, sterility and mutagenic effects) often go unnoticed and are not yet fully understood.
Also in the environment, some pesticides have not only acute effects but also long-term effects. Especially the “persistent organic pollutants” (POPs) will continue to poison non-target organisms in the environment and will also appear as crop residues long after their use has ceased.
No pesticide, synthetic or organic, is considered “safe”. However, some are less dangerous to use than others, depending on their effect on living organisms. Before using a pesticide, it is essential to be well informed about the various effects it may have. Farmers have to know how to reduce the risks.
Pesticides kill not only the pests but also the natural enemies of these pests. That means that natural control mechanisms are disrupted and it allows the pest populations to rapidly build up again to levels that can cause serious crop damage.
The disruption of natural control can even create new pest problems. Minor pests that are usually kept at low numbers by their natural enemies will multiply rapidly in the absence of their enemies and cause outbreaks. So the control directed against one pests may result in the outbreak of another pest.
The resurgence of pest populations after removing natural enemies creates a dependence on pesticides, which obviously is not sustainable. A key element of Integrated Pest Management is therefore to avoid resurgence. Conservation of natural enemies is required so that natural control will not be disrupted.
Development of resistance
One of the first discovered problems of pesticides was that pests can become resistant to the chemicals. Unaware of how to deal with this issue, farmers then decide to spray more frequently and to apply higher doses. This just causes more problems.
Within a pest population there is genetic variation in their resistance to pesticides. If pests have not been previously exposed to a new pesticide, most individuals in the population are susceptible, but some individuals are resistant. Pesticides that are used to control the pest will kill most of the susceptible individuals, but the few resistant individuals survive. In this way the proportion of resistant individuals in the population increases. Repeated selection of resistant individuals will make that every succeeding generation of the pest will have a higher proportion of resistant individuals than the original population. Eventually, after repeated and more intensive use of the same pesticide to the same pest population, the pesticide becomes ineffective. Unfortunately, even under ideal IPM conditions pests can become resistant to pesticides. However, IPM can help in delaying the development of resistance.
The economic problems
There are two sides to the economics of pesticide use.
- Direct costs
This refer to buying the products, which requires investment by the farmers.
- While many will argue that pesticides are cheap, they form a major part of the farm inputs.
- Many farmers have become trapped in a dependence on pesticides. By using pesticides they have disrupted natural control, which results in more pests and which leads to more pesticide use.
- Indirect costs
This refers to all kind of expenses related to pesticide use, most of which are paid by the government spending tax payers’ money.
- A hidden cost is all the medical costs related to health problems and accidental deaths as a result of pesticide use.
- Governments spend millions on laboratories for residue testing, laboratories for testing the quality of pesticides, field testing of pesticides, testing of side effects, etc.
- Other costs born by the government include: costs for staff involved in registration, labeling, inspectors for implementing legislation, disposal of obsolete pesticides, cleaning of contaminated sites, etc.
- The import of pesticides requires large amount of foreign currencies.
- The pesticide residue issue is becoming more and more important in world trade. This is a development which is likely to have an adverse effect on the export market for countries that rely heavily on agriculture as a major part of their economy.
To better understand the various problems related to pesticides, read these books:
Silent Spring (1962)
by Rachel L.Carson (ISBN 0-395-68329-7)
Our Stolen Future (1997)
by Theo Colborn, Dianne Dumanoski and John Peterson Myers (ISBN 0-452-27414-1)
The Environmental Justice Foundation has produced a number of excellent reports with information on problems caused by pesticides. They can be downloaded (PDF format) at: http://ejfoundation.org/reports
What’s your poison?: Health threats posed by pesticides in developing countries
Death in small doses: A report documenting Cambodia’s pesticide problems and solutions
End of the road for Endosulfan: A call for action against a dangerous pesticide
Links to relevant websites:
See also: Did you take your poison today?
See also: Posters warning about pesticides (Thai)