Types of pesticides and health problems
We have at least 500 types of pesticides, and the number of different products for sale is consequently even higher. The main groups of pesticides are categorized into the following five groups:
- Insecticides (killing insects)
- Herbicides (killing plants)
- Fungicides (killing fungus)
- Rodenticides (killing rodents, like mice and rats)
- Bactericides (killing bacteria)
There are many different types of pesticides within each of these five groups. They have different effects on human health, but the most common and typical adverse health effect of pesticides is their effect in the human nervous system. This is in particular typical for the insecticides, and here some of these are described more in detail. Many of these are called nerve gases, and they are actually used as chemical weapons in wars, in addition to the use in agriculture. This indicates the seriousness of the health effects from these substances.
|Insecticides||Main health effects|
|Chlorinated hydrocarbons. Examples: DDT, lindane, endosulfane||Neurotoxins, affects kidney and liver, affects reproduction (abortions). Some are carcinogenic (cause cancer)|
|Organophosphates. Examples: Malathion, parathion||Nerve gases (acetylcholinesterase inhibitor)|
|Carbamates. Examples: Aldicarb, carbaryl||Nerve gases (acetylcholinesterase inhibitor)|
The chemical structure of DDT. © Colourbox
One type of pesticide that affects the nervous system is DDT, or the full name 1,1,1,-trichlor-2,2,-bis (p-chlorophenyl) ethane. This compound has been used a lot, not only in agriculture, but also in the struggle against malaria and typhoid fever. This substance is a very toxic neurotoxin; meaning it affects the nervous system seriously. After high exposures DDT can cause tremor, seizures and even death. This toxin may also cause long term, chronic effects after exposure to lower levels of the substance for a longer period, and may cause ataxic gait and tremor in the affected workers.
Spraying pesticides in a wheat field using a tractor. Animals in the area might become exposed to the substances by accident. © Colourbox
DDT has been banned in many countries, as it is stored in the fat tissue of the body of both humans and animals for a long time (years) before it is excreted. When DDT is sprayed on plants, animals and humans can eat DDT in the plants afterwards. Humans can eat animals with DDT as well, and this consumption increases the DDT exposure. Due to this, DDT can cause adverse effects for many years, as it accumulates in the environment. It can be difficult to avoid this exposure, both for humans and animals, when the spraying is performed over large field areas.
Pesticides can also be sprayed on the fields using a small aero plane. The population in the area are at risk of pesticide exposure. © Colourbox
Acute and chronic health effects
Maybe you remember from week 1 of this course, that we often divide the description of health effects from a substance in two groups; the acute effects and the chronic effects. Pesticides most often can cause both of these types of health effects. They are very often what we call “highly toxic”. That means that persons can die after short time exposures to high levels of the substances.
However, many of the pesticides can also give chronic effects. Long-term exposure (weeks, months or years) to pesticides may cause chronic diseases such as cancer, and damage to the reproductive system, the liver, the brain, and other parts of the body.
Chemical structure of the insecticide lindane. © Colourbox
Some pesticides are clearly known to have serious long term effects. For instance, some pesticides, like lindane, mankozeb and pentachlorophenol are categorized as carcinogenic and may cause cancer. Several of the pesticides are categorized as harmful to reproduction, either by causing adverse side effects of the unborn baby or by causing spontaneous abortions. However, we lack knowledge about such side effects for many of the pesticides we use today, and we are uncertain about the effects on the health.
Health effects from lindane exposure:
- Skin irritation
- Nervous systems effects (headache - dizziness - serizures - death)
- Affection of hormone levels (thyroid)
Like for instance, lindane, several health effects are well known, such as effects on skin and the nervous system. Lately, the substance has been classified as a known human carcinogen. However, it has also been suggested that lindane may affect the level of thyroid hormone levels and that the substance may affect brain development. This side effect of lindane is not yet clear.
As mentioned earlier in this lecture, the number of different pesticides is huge. We have hundreds of pesticide products in the market. Most of the pesticides are toxic for the pests, and also for other types of organisms. Still, we know little about the long term health effects from many of the pesticides in use today. For many of the pesticides it is not clear whether they are harmful for the reproduction of workers or if they are carcinogenic, or have other serious side effects.
© University of Bergen/Author: B.E. Moen