pesticide use in agriculture

8/10/2019 Pesticide use in Agriculture

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Alyssa Bucci

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The Effect of Pesticides on Ecosystems and Possible Sustainable Alternatives

Since their development in the 1950s, chemical pesticides have become a prominent part

of agriculture. They are sought after for their ability to kill weeds, insects, fungi, and other pests

in order to increase crop yield and decrease the incidence of vector borne diseases (Aktar, 2009).

Over 1 billion tons of pesticides are used in the United States every year, and agricultural use

accounts for 80% of this (Sustainable Table, 2013). The most popular type of pesticides used are

herbicides, which are used to kill weeds. Other types of pesticides used in agriculture include

insecticides (kill insects), fungicides (kill fungi), and nematicides (kill nematodes). (Aktar, 2009)

There are currently over 350,000 current and historical pesticide products registered in

the United States and these products can be classified based on their chemical composition.

(Sustainable Table, 2013) Three of the most common chemical insecticides in use are

organophosphates, carbamates, and pyrethroids, which all work by inhibiting the nervous

systems of target insects. (Types of Pesticides, 2012) The most common herbicides are

glyophosphates (i.e. Roundup) which inhibit amino acid production in weeds, atrazines which

inhibit photosynthesis, and 2.4-Ds, which cause uncontrolled and deformed weed growth. (Todd,

2012) Its also important to note that organochlorines, although currently banned by the EPA,

were once a highly used class of insecticides. The best known of these is DDT, which was

extremely effective at killing mosquitos. After Rachel Carsons book Silent Springexposed its

negative effects on the reproductive systems of wildlife, DDT was banned in the 1970s. (Carson)


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However, organochlorines are highly persistent in the environment, and can still be detected in

soils even though most have been phased out of use. (Environmental Effects)

Pesticides have many benefits. They increase crop yields, which decreases the price of

food and makes healthy foods like fruits and vegetables more affordable for the population.

Food grain production has increased four-fold since the introduction of pesticides in the 1950s

due largely to the introduction of chemical pesticides and fertilizers. (Aktar, 2009) Pesticides

have also been effective in eradicating vector borne diseases. (Aktar, 2009) For example DDT is

a major component in controlling the spread of malaria in areas like Africa and India. However,

they also have severe negative effects on the environment and the people exposed to them.

Although pesticide and chemical fertilizer usage in agriculture has led to great advancements in

food production, overuse of these pesticides has adverse effects on multiple aspects of the

ecosystem, including the soil, water, and non-target organisms.

Pesticides and chemical fertilizers have been shown to have detrimental effects on soil

quality over time. Pesticides are either directly applied to soil, enter the soil through treated

seeds, wash off from foliage, or enter the soil through spray drift. Their persistence in the soil

and in the environment depends on many factors including the chemical properties of the

pesticide and physical, chemical, and biological properties of the soil. (Environmental Effects)

Ideally, pesticides would all break down into less harmful compounds through biological or

chemical processes after doing their jobs. (Soil Quality, 1998) However, this is often not the

case. Hydrophobic pesticides are persistent and have a tendency to bioaccumulate and strongly

bind to soil. Examples of these are organochlorines like DDTs as well as endrins and lindanes.

Most of these are banned in the United States because they stay in the environment for a long

time (Aktar, 2009). In the Czech Republic, DDT residues were found in soils more than 20 years


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after they had been banned. In addition, pesticide residues were found in areas where they had

never been used, indicating that they were highly mobile, which is another issue of high concern.

(Shegunova, 2007) Although research has shown the significant dangers of using DDT, many

people are still using it. A study in Romania from 2010 shows that DDT was detected in high

concentrations in many soil samples, indicating that it was most likely being used in rural areas

despite the fact that it was banned in the European Union decades ago. (Ferencz, 2010) It is

important that farmers understand the consequences of using persistent pesticides prior to

applying them to their crops.

The mobility of pesticides in the soil is another important aspect to consider. Polar

pesticides like carbamates, transformation products of organophosphates, and many herbicides

are very soluble in water. Therefore, they can dissolve in groundwater in agricultural fields and

move offsite through runoff and leaching. The dissolved pesticides can in turn pollute local

waterways, affecting aquatic ecosystems and drinking water supplies. (Aktar, 2009) Increasing

organic matter in soil can potentially remedy this by increasing the sorption of the pesticide to

the soil, but this is not a perfect fix. High yield conventional agriculture has a tendency to

deplete soil organic matter, which decreases pesticide sorption and increases mobility.

(Environmental Effects)

In addition, pesticides damage soil microbial communities and can decrease soil fertility.

Overuse of pesticides can decrease the populations of beneficial soil microorganisms. These

microorganisms perform many important functions in the soil including carbon sequestration,

nitrogen fixation, recycling of nutrients, regulation of soil organic matter, and detoxification of

noxious chemicals. Microorganisms are also a source and sink of nutrients and control soil

organic matter mineralization. (Liu, 2007) The type and severity of effect on microbial


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every major river tested due to both agricultural and urban influences. (Aktar, 2009) In many

cases, more than one pesticide was found in a body of water. So even if the levels of one

pesticide are low enough to be of little concern, the combined effect of multiple pesticides can be

very harmful.

Pesticides enter groundwater by way of leaching through the soils of agricultural fields,

seepage from contaminated surface waters, or improper disposal techniques like injecting them

in wells. As was mentioned previously, contaminated groundwater is a major concern because

groundwater is a primary source of drinking water for many towns and cities. Because the

pesticides take time to travel from the soil surface to the aquifer, there is often a time lag

between the time of application and the appearance of the pesticide in groundwater. The time

lags dangerous because it can give farmers and regulators the impression that the water is not at

risk of contamination until it is too late. And once groundwater is contaminated, it is difficult

and costly to clean. The United States Geologic Survey has found at least 143 different

pesticides and 21 transformation products in US groundwater, and has detected pesticide

pollution in over 43 states. (Pesticides in Groundwater)

Pesticides can also pollute surface waters through runoff and aerial spray drift. The

degree to which a body of water is contaminated depends on multiple interconnected factors.

The solubility of the pesticide in water, mode and rate of application, texture and topography of

the soil, distance between the farm and the water body, and the amount of precipitation all

influence how much of a pesticide ends up contaminating the water. (Willis) In addition, the

degree of damage the pesticide does to the aquatic ecosystem depends on characteristics of the

pesticide like toxicity and persistence, as well as the toxicity of the degradates of that pesticide.

The affinity of the pesticide to settle in different environmental compartments (solid matter,


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liquid, gas, and biota) also determines what kind of effect it has on the ecosystem (FAO).

Because there are so many factors contributing to the effect of pesticides on water, it is difficult

to predict how a given pesticide will affect a specific environment. When water is exposed to

multiple different pesticides, the situation gets even more complicated. However, through

scientific study, some general trends have been discovered concerning this issue.

Pesticides are formulated to kill plants and insects, so it is not surprising that they can

cause significant damage to aquatic organisms and their habitats. The effects of a pesticide vary

widely, so generalization is difficult. Some of the common effects include suppression of the

immune and endocrine systems of aquatic animals, reproductive inhibition, teratogenic effects,

and in extreme cases death of the animal. (FAO) Small invertebrates are especially sensitive,

and when these organisms die, the organisms that eat them lose a food source which greatly

increases competition for resources, and requires them to travel farther to find food. For

example, diazinon (an organophosphate insecticide), chlorpyrifros (also an organophosphate

insecticide), and pyrethroids are toxic toCeriodaphnia andHyalella invertebrates. (Pesticides

and Water Quality) Fish feed on these invertebrates, so if they disappear, the entire food chain is

disrupted. Herbicides like atrazine and oxadiazone can also decrease algae populations, which

are key food sources for fish and other organisms. (Aktar, 2009) Although one farm using one

type of pesticide may not cause much of a problem, when small quantities of multiple types of

pesticides from multiple farms accumulate, they can reach toxic doses. In addition, lipid soluble

pesticides like organochlorines are stored in the tissues of fish and other aquatic animals and

bioaccumulate as they move up the food web, so animals high up on the food chain can

potentially be exposed to high levels of pesticides. (Environmental Effects)


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Two organophosphate insecticides, trichlorfon and dichlorvos, have been extensively

studied for their effect on carp immunity. Trichlorfon is used on cereals, vines, fruits, potatoes,

grass, and tobacco. Dichlorvos is a degradation product of trichlorfon in water and is used on

fruit trees and vines. These compounds are very toxic to both fish and humans. They are

cholinesterase inhibitors, so exposure to small amounts of these insecticides can cause a buildup

of acetylcholine. For example, carps bathed in trichlorfon have depressed nonspecific immune

response, namely a decrease in the phagocytic ability of neutrophils, a decrease in lysozyme

activity, and an increase in cerulopasmin activity. Because of their high toxicity, the LD50values

of trichlorfon and dichlorvos in carp and other fish are relatively low, but despite this they are

often used to control planktonic invertebrates in fish farming. (Dunier, 1993)

The important concept to understand about the interaction between pesticides and water

is that one farmer treating his crops with the standard quantity of pesticides is not going to

initiate a large fish kill. Problems arise when pesticides are overused or not used in the right

manner or when many small doses of pesticides accumulate to toxic levels. Therefore with

proper training and precautions it may be possible to use pesticides while having minimal effect

on water quality, but it would be a difficult thing to do.

Pesticides do not only affect aquatic organisms. Insecticides can kill beneficial insects

and spiders in addition to the pests they are meant to eradicate. Herbicides can also affect these

species by damaging their natural habitat and leaving them without a place to live. Bird

populations can be affected through eating pesticide treated seeds and insects. For example,

birds with repeated exposure to the herbicide trifluralin experience lower reproductive success

due to cracked eggs. (Aktar, 2009) The insecticide DDT has also been shown to cause egg shell

thinning. And just as in aquatic species, bioaccumulation of pesticides occurs as they move up


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the food chain, so higher up species can ingest very high levels of pesticides. Finally, pesticides

can reduce biodiversity in ecosystems because over time, pesticide tolerant species will have

more reproductive success than sensitive species. In extreme cases, these sensitive species could

face extinction.

It is clear that pesticides have a number of negative impacts on the environment.

However, they are important aspects of modern conventional agriculture, and people need to eat.

So what are the alternatives? Organic farming is a method that has been growing significantly

over the past years in which food is grown without the use of synthetic pesticides or fertilizers.

This practice also emphasizes maintaining high soil quality through practices like crop rotation

and growing cover crops so that farmland can remain productive without synthetic fertilizers.

The main concern with organic farming is that organic farms have lower yields than

conventional ones, and will not be able to feed the worlds growing population. In many cases

this is true, but there have been studies that have found no difference in crop yield between

organic and conventional farms. For example, a study published inRenewable Agriculture in

Food Systemsby Bajgai et. al.investigated the effect of sweet corn residue incorporation in a

corn-cabbage rotation on crop yield and other factors in both organic and conventionally

managed soils. The study found no difference in crop yield between the two systems, which the

scientists attributed to equivalent levels of macro-nutrients. (Bajgai, 2013) For organic growing

to be successful, farmers would have to be educated on proper techniques like natural

fertilization methods, soil management, and maximizing crop production. Even so, it is unlikely

that organic growing will take over conventional growing in the near future, but integrated pest

management could provide a happy medium.


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Integrated pest management uses information on the life cycle of pests and their

interaction with the environment to limit the use of synthetic pesticides. (Integrated Pest

Management) This way, smaller quantities of pesticides are used, and only when needed. If

more farmers take up this practice and also pay attention to the pesticide usage of nearby farms,

it may be possible to use pesticides with little negative effects on the surrounding environment.

In addition, these farmers should incorporate the soil management techniques of organic farming

to maintain high nutrient levels and healthy microbial populations. The largest pesticide

problems have risen from overuse and mismanagement, so even though they are not beneficial to

the environment by any means, integrated pest management combined with good soil

management practices may be a solution that is accepted by environmental activists as well as

farmers and the general population.

In conclusion, pesticides, although useful, can cause severe damage to the environment.

Much more research is needed to determine the long term and large scale effects of pesticide

usage, as well as possible alternatives. For the time being, we should more thoroughly educate

farmers who use these chemicals, as well as the people who consume the food they grow.


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Shegunova, Penka, Jana Klanova, and Ivan Holoubek. "Residues of Organochlorinated

Pesticides in Soils from the Czech Republic."Environmental Pollution146.1 (2007):

257-61.

"Soil Quality Concerns: Pesticides." Urban Programs Resource Network. USDA Natural

Resources Conservation Service, Jan. 1998. Web. Nov. 2013.

Todd, B., and G. W. Suter, II. "Herbicides Introduction Tab | CADDIS: Sources, Stressors &

Responses | US EPA."EPA. Environmental Protection Agency, 31 July 2012. Web. Nov.

2013.

"Types of Pesticides."EPA. Environmental Protection Agency, 9 May 2012. Web. Nov. 2013.

Willis, Guye H., and Leslie L. McDowell. "Review: Pesticides In Agricultural Runoff And Their

Effects On Downstream Water Quality."Environmental Toxicology and Chemistry1.4

(1982): 267-79.

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