Pesticides

Pesticides are chemicals used to kill or control populations of undesirable organisms.  Some common types of pesticides include insecticides, herbicides, fungicides, and rodenticides.

Insecticides kill insects by clogging airways, disrupting nerves and muscles, or preventing reproduction.

Herbicides kill weeds by disrupting their metabolism and growth.

Fungicides kill fungus.

Rodenticides kill rats and mice.

First Generation Pesticides

First Generation Pesticides were made from chemicals that were extracted from plants.  For millions of years plants have produced chemicals that ward off, deceive, or poision herbivores that feed on them.  Natural selection allowed herbivores to survive even though plants had defense.  The plant defenses are also favored by natural selection.  In the 1600s farmers extracted nicotine sulfate from tobacco leaves and used it as an insecticide.  In the mid 1800s farmers used two more natural pesticides named rotenone and pyrethrum.  Rotenone is extracted from the roots from tropical legumes and pyrethrum is obtained from the heads of chrysanthemums.

 

 

 

 

 

 

 

 

 

 

 

 

 

Second Generation Pesticides

Second Generation Pesticides are made by making small modifications in the molecules of other chemicals.  The creation of second generation pesticides occured after Paul Müller discovered that DDT (dichlorodiphenyltrichloroethane) was a potent insecticide in 1939.  DDT was the first second generation pesticide which was made in a laboratory.  It became the most used pesticide.  Since 1950, pesticide use has increased mor than 50-fold.  A majority of today's pesticides are 10-100 times more toxic than those used in 1950. 1/4 of pesticide use is used to rid pests in homes, gardens, lawns, golf courses, swimming pools, and playing fields.

Broad spectrum agents are pesticides that are toxic to many species.  Selective/ narrow spectrum agents are effective against a narrowly defined group of organisms.

There is also a varying persistance in pesticides.  Some can remain in the environment for years while others might only be active for weeks or days.

 

There are advantages to using pesticides.

 Pesticides have probably prevented the premature deaths of 7 million people by killing pests including mosquitos, fleas, and body lice that transmitted diseases like malaria, the bubonic plague, and typhus.   

Pesticides increase food supplies.  If there were more crop losses than what thre is currenty, food prices would go up.

 Pesticides increase profits for farmers since more crops will survive.

 Pesticides work fast and control pests quickly.  When genetic resistance occurs, farmers can use a stronger dose or use a different pesticide.

 

There are also disadvantages to using pesticides.

 Pesticides speed up the development of genetic resistance to pesticide by pest organisms.  Insects reproduce quickly and after 5-10 years they can develop immunity to pesticides through natural selection and can become stronger than before.  Many insects and weeds have developed genetic resistance to one or more pesticide.

 Farmers will have to pay more to use more pesticides and over time the pesticides become less and less effective.

 Insecticides might kill natural predators that control pest populations.  This could cause there to be more pests and a lower crop yield.

 Pesticides pollute the environment.  Only 0.1-2% of aerial spraying or ground spraying insecticides reach the target pests.  Only 5% of herbicidespplied to crops reach the target weeds.   Pesticides end up in our air, water, food, and wildlife.

 Some pesticides can harm wildlife.  Every year in the U.S. pesticides applied to cropland wipe out 20% U.S. honeybees and damages another 15%.   Pesticides also kill 6-14 million fish and over 67 million birds.

 Some pesticides can threaten human health.  Pesticides seriously poision 3.5-5 million people in developing countries each year and at least 300,000 each year in the United States.  Pesticides also cause 20,000-40,000 deaths each year.  Pesticide residue on food causes 4,000-20,000 cases of cancer each year.

 

FIFRA (Federal Insecticide, Fungicide,and Rodenticide Act) was first passed in 1947 and was ammended in 1972.  Under this act the EPA was supposed to assess the health risks of the active ingredients in pesticides that were already in use.  30 years later only 10% of the active ingredients in pesticide products have been evaluated using tests for chronic health effects.  The EPA says that they don't have funds to continue this lengthy and complex evaluation.

Congress passed the Food Quality Protection Act in 1996.  This act required the EPA to reduce the allowed levels of pesticide residue on foods by a factor of 10 when there isn't enough information on the potential harmful effects on children.