Environmental Effects of Pesticides Essay

Over 98% of sprayed insecticides and 95% of herbicides reach a destination other than their target species, including nontarget species, air, water, bottom sediments, and food.[1] Pesticide contaminates land and water when it escapes from production sites and storage tanks, when it runs off from fields, when it is discarded, when it is sprayed aerially, and when it is sprayed into water to kill algae.[2] The amount of pesticide that migrates from the intended application area is influenced by the particular chemical’s properties: its propensity for binding to soil, its vapor pressure, its water solubility, and its resistance to being broken down over time.[3] Factors in the soil, such as its texture, its ability to retain water, and the amount of organic matter contained in it, also affect the amount of pesticide that will leave the area.[3] Some pesticides contribute to global warming and the depletion of the ozone layer.[4] [edit] Air Pesticides can contribute to air pollution . Pesticide drift occurs when pesticides suspended in the air as particles are carried by wind to other areas, potentially contaminating them.[5] Pesticides that are applied to crops can volatilize and may be blown by winds into nearby areas, potentially posing a threat to wildlife.[6] Also, droplets of sprayed pesticides or particles from pesticides applied as dusts may travel on the wind to other areas,[7] or pesticides may adhere to particles that blow in the wind, such as dust particles.[8] Ground spraying produces less pesticide drift than aerial spraying does.[9] Farmers can employ a buffer zone around their crop, consisting of empty land or non-crop plants such as evergreen trees to serve as windbreaks and absorb the pesticides, preventing drift into other areas.[10] Such windbreaks are legally required in the Netherlands.[10] Pesticides that are sprayed on to fields and used to fumigate soil can give off chemicals called volatile organic compounds, which can react with other chemicals and form a pollutant called tropospheric ozone. Pesticide use accounts for about 6 percent of total tropospheric ozone levels.[11] [edit] Water In the United States, pesticides were found to pollute every stream and over 90% of wells sampled in a study by the US Geological Survey.[12] Pesticide residues have also been found in rain and groundwater.[3] Studies by the UK government showed that pesticide concentrations exceeded those allowable for drinking water in some samples of river water and groundwater.[13] Pesticide impacts on aquatic systems are often studied using a hydrology transport model to study movement and fate of chemicals in rivers and streams. As early as the 1970s quantitative analysis of pesticide runoff was conducted in order to predict amounts of pesticide that would reach surface waters.[14] There are four major routes through which pesticides reach the water: it may drift outside of the intended area when it is sprayed, it may percolate, or leach, through the soil, it may be carried to the water as runoff, or it may be spilled, for example accidentally or through neglect.[15] They may also be carried to water by eroding soil.[16] Factors that affect a pesticide’s ability to contaminate water include its water solubility, the distance from an application site to a body of water, weather, soil type, presence of a growing crop, and the method used to apply the chemical.[17] Maximum limits of allowable concentrations for individual pesticides in public bodies of water are set by the Environmental Protection Agency in the US.[3][17] Similarly, the government of the United Kingdom sets Environmental Quality Standards (EQS), or maximum allowable concentrations of some pesticides in bodies of water above which toxicity may occur.[18] The European Union also regulates maximum concentrations of pesticides in water.[18] [edit] Soil Many of the chemicals used in pesticides are persistent soil contaminants, whose impact may endure for decades and adversely affect soil conservation.[19] The use of pesticides decreases the general biodiversity in the soil. Not using the chemicals results in higher soil quality,[verification needed][20] with the additional effect that more organic matter in the soil allows for higher water retention.[3] This helps increase yields for farms in drought years, when organic farms have had yields 20-40% higher than their conventional counterparts.[21] A smaller content of organic matter in the soil increases the amount of pesticide that will leave the area of application, because organic matter binds to and helps break down pesticides.[3] [edit] Effects on biota [edit] Plants Nitrogen fixation, which is required for the growth of higher plants, is hindered by pesticides in soil.[22] The insecticides DDT, methyl parathion, and especially pentachlorophenol have been shown to interfere with legume-rhizobium chemical signaling.[22] Reduction of this symbiotic chemical signaling results in reduced nitrogen fixation and thus reduced crop yields.[22] Root nodule formation in these plants saves the world economy $10 billion in synthetic nitrogen fertilizer every year.[23] Pesticides can kill bees and are strongly implicated in pollinator decline, the loss of species that pollinate plants, including through the mechanism of Colony Collapse Disorder,[24][25][26][27] in which worker bees from a beehive or Western honey bee colony abruptly disappear. Application of pesticides to crops that are in bloom can kill honeybees,[5] which act as pollinators. The USDA and USFWS estimate that US farmers lose at least $200 million a year from reduced crop pollination because pesticides applied to fields eliminate about a fifth of honeybee colonies in the US and harm an additional 15%.[1] On the other side, pesticides have some direct harmful effect on plant including poor root hair development, shoot yellowing and reduced plant growth [28]. [edit] Animals Pesticides inflict extremely widespread damage to biota, and many countries have acted to discourage pesticide usage through their Biodiversity Action Plans.[citation needed] Animals may be poisoned by pesticide residues that remain on food after spraying, for example when wild animals enter sprayed fields or nearby areas shortly after spraying.[9] Widespread application of pesticides can eliminate food sources that certain types of animals need, causing the animals to relocate, change their diet, or starve.[5] Poisoning from pesticides can travel up the food chain; for example, birds can be harmed when they eat insects and worms that have consumed pesticides.[5] Some pesticides can bioaccumulate, or build up to toxic levels in the bodies of organisms that consume them over time, a phenomenon that impacts species high on the food chain especially hard.[5] [edit] Birds Bald eagles are common examples of nontarget organisms that are impacted by pesticide use. Rachel Carson’s landmark book Silent Spring dealt with the loss of bird species due to bioaccumulation of pesticides in their tissues. There is evidence that birds are continuing to be harmed by pesticide use. In the farmland of Britain, populations of ten different species of birds have declined by 10 million breeding individuals between 1979 and 1999, a phenomenon thought to have resulted from loss of plant and invertebrate species on which the birds feed.[29] Throughout Europe, 116 species of birds are now threatened.[29] Reductions in bird populations have been found to be associated with times and areas in which pesticides are used.[29] In another example, some types of fungicides used in peanut 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.[9] Some pesticides come in granular form, and birds and other wildlife may eat the granules, mistaking them for grains of food.[9] A few granules of a pesticide is enough to kill a small bird.[9] The herbicide paraquat, when sprayed onto bird eggs, causes growth abnormalities in embryos and reduces the number of chicks that hatch successfully, but most herbicides do not directly cause much harm to birds.[9] Herbicides may endanger bird populations by reducing their habitat.[9] [edit] Aquatic life Fish and other aquatic biota may be harmed by pesticide-contaminated water.[30] Pesticide surface runoff into rivers and streams can be highly lethal to aquatic life, sometimes killing all the fish in a particular stream.[31] Application of herbicides to bodies of water can cause fish kills when the dead plants rot and use up the water’s oxygen, suffocating the fish.[30] Some herbicides, such as copper sulfite, that are applied to water to kill plants are toxic to fish and other water animals at concentrations similar to those used to kill the plants.[30] Repeated exposure to sublethal doses of some pesticides can cause physiological and behavioral changes in fish that reduce populations, such as abandonment of nests and broods, decreased immunity to disease, and increased failure to avoid predators.[30] Application of herbicides to bodies of water can kill off plants on which fish depend for their habitat.[30] Pesticides can accumulate in bodies of water to levels that kill off zooplankton, the main source of food for young fish.[32] Pesticides can kill off the insects on which some fish feed, causing the fish to travel farther in search of food and exposing them to greater risk from predators.[30] The faster a given pesticide breaks down in the environment, the less threat it poses to aquatic life.[30] Insecticides are more toxic to aquatic life than herbicides and fungicides.[30] [edit] Amphibians See also: Decline in amphibian population In the past several decades, decline in amphibian populations has been occurring all over the world, for unexplained reasons which are thought to be varied but of which pesticides may be a part.[33] Mixtures of multiple pesticides appear to have a cumulative toxic effect on frogs.[34] Tadpoles from ponds with multiple pesticides present in the water take longer to metamorphose into frogs and are smaller when they do, decreasing their ability to catch prey and avoid predators.[34] A Canadian study showed that exposing tadpoles to endosulfan, an organochloride pesticide at levels that are likely to be found in habitats near fields sprayed with the chemical kills the tadpoles and causes behavioral and growth abnormalities.[35] The herbicide atrazine has been shown to turn male frogs into hermaphrodites, decreasing their ability to reproduce.[34] [edit] Humans See also: Pesticide residue Pesticides can enter the human body through inhalation of aerosols, dust and vapor that contain pesticides; through oral exposure by consuming food and water; and through dermal exposure by direct contact of pesticides with skin.[36] Pesticides are sprayed onto food, especially fruits and vegetables, they secrete into soils and groundwater which can end up in drinking water, and pesticide spray can drift and pollute the air. The effects of pesticides on human health are more harmful based on the toxicity of the chemical and the length and magnitude of exposure.[37] Farm workers and their families experience the greatest exposure to agricultural pesticides through direct contact with the chemicals. But every human contains a percentage of pesticides found in fat samples in their body. Children are most susceptible and sensitive to pesticides due to their small size and underdevelopment.[36] The chemicals can bioaccumulate in the body over time. Exposure to pesticides can range from mild skin irritation to birth defects, tumors, genetic changes, blood and nerve disorders, endocrine disruption, and even coma or death.[38] Some pesticides, including aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, hexachlorobenzene, mirex, and toxaphene, are considered POPs.[39] POPs have the ability to volatilize and travel great distances through the atmosphere to become deposited in remote regions.[39] The chemicals also have the ability to bioaccumulate and biomagnify, and can bioconcentrate (i.e. become more concentrated) up to 70,000 times their original concentrations.[39] POPs may continue to poison non-target organisms in the environment and increase risk to humans[40] by disruption in the endocrine, reproductive, and immune systems; cancer; neurobehavioral disorders,[39] infertility and mutagenic effects, although very little is currently known about these chronic effects. Some POPs have been banned, while others continue to be used. [edit] Pest resistance