Effects of Pesticides on the Environment & Human Health

Written by: Jenny Griffin • Edited by: Sarah Malburg
Published Jul 22, 2011 • Related Guides: Cancer | Food Chain | Pesticides

Pesticides are designed to control pests and disease-causing organisms, and while this offers some benefits to society, the downside is that they are by their very nature, harmful to all living organisms that are exposed to them. Let's take a look at what makes pesticides a pollutant.

Pesticide Dangers

Many pesticides contain persistent organic pollutants (POPs), which persist in the environment and accumulate in the fatty tissue of animals, including humans. The accumulation of toxins in the body can pose a serius health risk to living organisms, and have been implicated in causing cancer, disease, hormonal imbalances and problems associated with the reproductory system, including birth defects. Pesticides that are known to be persistent organic pollutants include aldrin, chlordane, dioxins and DDT, which is used extensively in third world countries to combat malaria. There are however, global efforts to ban the use of POPs to ensure a healthy environment and healthy human population.

Where are Pesticides Used?

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Pesticides are used extensively in agriculture and farming practices to eradicate insects, rodents, weeds and other forms of life considered to be pests. They are widely used on lawns, fields, golf courses, inside buildings, and even directly on our pets in some cases, to control pests. They are also used for controlling the spread of disease, for example, to eradicate malaria carrying mosquitos in the tropics. They come in all forms from powders, liquid sprays, gels, granules, pellets or lotions to name a few, and can be applied using various methods.

Indiscriminate Killers

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Pesticides can be classified according to various criteria, including their chemical composition and what organisms they target. The suffix, -cide, means to kill: herbicides kill herbs, all herbs; rodenticides kill rodents, all rodents; insecticides kill insects, all insects. While insecticides selectively target insects, they do not discriminate against which insects they kill, so pollinators who come into contact with the insecticide will also be killed. The same goes for herbicides, algaecides, fungicides, bactericides, and all other pesticides. Non-target organisms that perform useful and necessary functions in the ecosystem, are wiped out together with the target pest.

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The indiscriminate nature of pesticides does not end there. Animals higher up the food chain, such as fish, birds, and mammals, often fall victim to secondary poisoning, sometimes with fatal consequences, after consuming poisoned prey. This attracts attention when there is an environmental incident that results in mass mortality of wildlife, whether it is insects, fish, reptiles, birds or mammals. However, the consequences of non-lethal effects of pesticides on living organisms are often far more subtle and generally go unnoticed, but are equally, if not more dramatic.

Environmental Effects

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Persistent organic pollutants (POPs) enter the environment when pesticides are either carried further afield by winds or washed off crops by rain. The contaminated water enters the soil, and eventually makes its way into our river systems filtering through the soil or by direct run-off, and finally ends up in the sea. Because POPs do not readily break down, they pollute the air, soil, rivers and lakes, and ultimately marine ecosystems, affecting all living organisms that dwell in these habitats.

Effect on Soil

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When pesticides enter the soil, they kill the tiny micro organisms present in the soil that are important for keeping the soil healthy. Microscopic bacteria and fungi are essential for decomposing organic matter to make nutrients available to plants for growth. The decomposed organic matter, or humus, is not only rich in nutrients, but it also acts as a sponge and aids in water retention in the soil. As soil condition deteriorates, farmers compensate by adding chemical fertilizers to enhance crop growth. The poor soil condition results in nutritionally compromised crops of inferior quality.

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Effect on Wildlife

Pests can build up resistance to pesticides through natural selection, making it more and more difficult to control them without using heavier doses of pesticides or more lethal concoctions.

However, the most glaringly obvious environmental problem caused by pesticides is that they indiscriminately kill non-target species. Honey bees are disappearing at an alarming rate in a phenomenon now recognized as colony collapse disorder (CCD), where worker bees from a hive simply disappear.

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The hives cannot survive without the worker bees supplying them with pollen, and eventually die off. Because of the implications this has on the pollination of crops, and ultimately food production necessary to sustain human populations the world over, many governments around the world have sat up and taken this extremely seriously. Several studies have been undertaken on honey bee pollutions from around the world, and while preliminary results indicate that viral infection of honey bee colonies, rather than pesticides, are the direct cause of CCD, pesticides are still responsible for many unrelated isolated mass bee mortality incidents. Considering the seriousness of CCD, and the precarious nature of our bee populations, we simply cannot afford to lose our hardworking bees at the rate that we are. The reason pesticides are used in the first place is to enhance crop growth, but nature has a method of its own, and without the bees toiling away busily pollinating crops day in and day out, particularly fruit and corn, all the crop management in the world will not yield better crops.

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As pesticides are stored in body tissue, animals higher up the food chain are also at risk. A fish that is exposed to pesiticides in the water that it inhabits or through organisms that it consumes, may not necessarily die from exposure to pesticides, and a bird consuming that fish may not be adversely affected by consuming that one fish. However, a bird does not survive on eating one fish, and the problem arises when many contaminated fish are consumed and the contaminants become more concentrated in the higher organism's body tissue, often with fatal consequences.

Besides killing off wildlife, pesticides have another less obvious, but just as sinister effect. Exposure to pesticides is known to cause reproductive failure in living organisms. They can cause hormonal imbalances in frogs, fish, reptiles, birds, marine mammals, and other organisms resulting in infertility. Endangered animal species, such as marine turtles, who are already vulnerable, cannot afford to suffer further recruitment problems. Pesticide exposure can also cause birds to produce eggs with soft shells, which either break or offer little protection to the chick developing within, resulting in clutch failure. Excessive exposure to pesticides can effect embryonic development, and can cause birth defects in animals, including humans. Besides directly disrupting the reproductive system, insecticides can also effect breeding success by substantially reducing food availability for parents to successfully rear their young. For example, a reduced insect population can negatively affect survival and growth rates of insectivorous fish and birds.

Continue to page 2 to learn about the health risks of pesticides to humans, and what we can do to minimise the risks to both our envionment and ourselves.

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