Pollution: Pesticides in Natural Ecosystems


Pesticides play an important role in boosting the economy of the agricultural industry by providing effective pest control, and their continued use is essential for enhancing the productivity.14 It is estimated that food supplies would immediately fall to 30%-40% due to the ravages of pests if pesticides are not usedJ2! A United Nations report stated that population growth is a major problem facing our planet. In 1900, there were 1.6 billion people on the planet. In 1992, this has risen to 5.25 billion, and by the year 2050, it will reach 10 billion. Developing countries are more affected by this explosive increase in world population. Presently, our dependence on pesticides has increased up to the extent that if modern agriculture was operated without chemical control, the crop production will probably decline in many areas, food price will soar far higher, and food shortage will become more severe. Although pesticides have played an important role in enhancing crop yields, they have also come up with various environmental problems. When present above permissible limits, they act as pollutants, creating pesticide pollution. Many pesticides are present today in different concentrations in various components of our environment such as air, water, and soil. More than 5,00,000 people are either killed or incapacitated every year by poisoning, and most of these casualties occur in developing nations.OI

Ecologically, however, pesticides have created two major problems that were not previously anticipated. As pollutants, they contaminate numerous natural ecosystems [terrestrial: forest, grassland, desert, etc.; aquatic: fresh water (running water such as spring, stream, or rivers or standing water such as lake, pond, pools, puddles, ditch, and swamp); and marine (deep water bodies such as ocean or shallow ones such as a sea and estuary)] not intended to be targets. Second, most of them have directly/indirectly affected human health. The objective of this entry is to provide basic knowledge on pesticide exposure and to understand issues on residues in the natural ecosystem.


History of Pesticides and Pesticide Problems

The term pesticide covers a wide range of compounds including insecticides, fungicides, herbicides, rodenticides, molluscicides, nematicides, plant growth regulators, and others. In the 1940s, dichlorodiphenyltrichloethane (DDT) became the first widely available synthetic insecticide. It was highly effective, but it showed signs of becoming less effective as insects became resistant to it. It accumulated in the bodies of animals and high up the food chain by biomagnifications and bioconcentrations, causing problems with reproduction. Rachel Carson’s Silent Spring in 1962 drew the attention of environmentalists to the disaster that was gathering pace across the globe. Public awareness of problems with pesticides grew by the 1970s when DDT was banned in many countries. It is still used in some places for malaria control, and it is still present in the bodies of many animals, even hundreds of miles away from where it has not been used. The introduction of other synthetic insecticides—organophosphate (OP) insecticides in the 1960s, carbamates in the 1970s, and pyre- throids in the 1980s, as well as herbicides and fungicides in 1970s-1980s, contributed to a great extent in pest control and agricultural output. The consequences of pesticide use have resulted in serious health implications to man and his environment. There is now overwhelming evidence that some of these chemicals pose potential risk to humans and other forms of life and unwanted side effects to the environment.141 The worldwide deaths and chronic illnesses due to pesticide poisoning numbered about 1 million per year.151

The problem is more serious when pesticides that are banned are used indiscriminately. Banned pesticides are still used on crops that are not consumed directly, e.g., cotton. Few people think of cotton as food, but once the fiber is removed, two-thirds of the cotton crop winds up in the food we eat. Every year in the United States, half a million tons of cottonseed oil goes into processed salad dressings, baked goods, and snacks like Fritos and Goldfish. Another 3 million tons of cottonseed is fed to beef and dairy cattle, which also eat vast amounts of the cotton by-products known as “gin trash.”161

How Do Pesticides Sprayed on Agro-/Horti-Ecosystems Enter Natural Ecosystems?

Almost less than 1% of the total pesticides applied actually hit the target organisms.171 Most reach nontarget sectors of agro-ecosystems and/or spread to surrounding ecosystems as chemical pollutants. The pesticide somehow “leaks” into another ecosystem via movement of water from one body to another via outflow streams or seepage into the water table. Some pesticides might evaporate into the atmosphere and be carried elsewhere by winds. Regardless of how the leak occurs, the pesticide could affect accidental targets; e.g., a volatile insecticide used to control mosquitoes evaporates and kills bees; thus, a wide variety of plants do not get pollinated, thereby affecting their yield. The pesticide may also be taken in by migratory animals (birds in particular) and carried elsewhere; the toxin may affect the birds’ reproduction in some way, or those birds might be eaten up by a higher order of predators and the toxin may inflict some injury to them. Either way, this would affect the balance of predation in some land-based ecosystem. The movement of systemic insecticides’ active ingredient into floral parts may indirectly impact natural enemies that feed on plant pollen or nectar as a nutritional food source.18,91

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