Pesticides are toxic chemicals designed to be deliberately released into the environment. Although each pesticide is meant to kill a certain pest, a very large percentage of pesticides reach a destination other than their target. Instead, they enter the air, water, sediments, and even end up in our food. Pesticides easily contaminate the air, ground and water when they run off from fields, escape storage tanks, are not discarded properly and especially when they are sprayed aerially.
Pesticides are a contributing factor to air pollution. This pollution can occur when a pesticide is released into the air and the particles are carried by the wind. The chemicals then end up in areas for which they are not intended. Because pesticides are used to kill ‘pests’, they can be potentially dangerous to other wildlife as well. Pesticides in the air can also contribute to global warming and the depletion of the ozone layer.
Pesticides can also be found in rain, ground water, streams, rivers, lakes and oceans. There are 4 major ways that pesticides can reach the water: it can drift outside of the area of where was sprayed, it may leach through the soil, it could be carried as runoff, or it may be spilled accidentally. Studies by the UK government show that pesticide concentrations exceed those allowable for drinking water in some samples of river water and groundwater.
The use of pesticides decreases the general biodiversity in the soil. If there is no chemicals in the soil there is a higher soil quality, and this allows for higher water retention, necessary for plants to grow.
Nitrogen fixation, which is necessary for the growth of many large plants, is hindered by pesticides that can be found in soil. This can lead to a large decline of crop yields. Application of pesticides to crops that are in bloom can kill honeybees, which act as pollinators. This creates a decrease in crop pollination and reproduction.
Animals may be poisoned by pesticide residues that remain on food after spraying. An application of pesticides in an area can eliminate food sources that certain types of animals need, causing the animals to relocate, change their diet, or starve. Poisoning from pesticides can even make its way up the food chain; for example, birds can be harmed when they eat insects and worms that have consumed pesticides.
There is evidence that birds are being harmed by pesticide use. Rachel Carson's book Silent Spring discusses the loss of several bird species due to accumulation of pesticides in their tissues. Types of fungicides used in farming are only slightly toxic to birds and mammals, but may kill off earthworms, which can in turn reduce populations of the birds and mammals that feed on them. Another way they are affects is that some pesticides come in granular form, and birds and other wildlife may eat the granules, mistaking them for grains of food. A few granules of a pesticide are enough to kill a small bird. Herbicides may also endanger bird populations by reducing their habitat.
Fish and other aquatic biota may be harmed by pesticide-contaminated water. Application of herbicides to bodies of water can cause plants to die, diminishing the water's oxygen and suffocating the fish. Repeated exposure of some pesticides can cause physiological and behavioral changes in fish that reduce populations, such as abandonment of nests, decreased immunity to disease, and increased failure to avoid predators.