A Look at the Use of Herbicides in the United States

Categories: Ecology

Each year in the United States of America over 69 percent of the available water is used for agriculture and 8 percent is used for domestic uses. Sewage, industrial waste and agricultural chemicals such as herbicides, pesticides, and fertilizers are the main point of water pollution. In the year of 1995 the EPA (Environmental Protection Agency) reported that 37 percent of our country's lakes and estuaries, and 36 percent of our country's rivers are too polluted for basic uses including fishing and swimming during all or part of the year.

However taking into account that Earth's usable water resources is less than 3 percent of Earth's total water resources, this a humongous amount. Water is necessary for agricultural use such as growing crops, and giving livestock refreshment. In the seventies massive use of the pesticide DDT led to horrendous biological effects such as the destruction of entire ecosystems. As a result of the biological damage the U.S. Federal Government outlawed the use of DDT.

Since then, more pesticides and in particular herbicides have been developed. The manufactures of these herbicides claim that these herbicides have no environmental impact whatsoever. However doubts have been cast on these claims, anti-pesticide organizations claim that herbicides (2, 4-Dichlorophenoxyacetic acid in particular) cause NHL (Non-Hodgkin's lymphoma) and other types of cancer. Because the active ingredient in many herbicides is 2, 4-D, the paper will mainly focus on this chemical.

Research for Herbicides the definition of a herbicide is a substance that controls weeds in a crop without destroying that crop.

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They are sold under a variety of trade names with many active ingredients. Herbicides can be applied to plants at various stages of growth or directly to the soil, and affect plants at a cellular or tissue level. Some inhibit plant growth by targeting certain essential amino acids or growth regulators; some prevent the plants from photosynthesizing, while others kill plants by destroying cell membranes on contact. The herbicide, 2, 4-D fits in that definition, but will it and other herbicide brands (Weed-Stop, Roundup, etc.) destroy our faltering environment, eliminate vital food webs, and confuse the delicate biosphere of our planet? There is much controversy surrounding that, but the answer is still unknown.

Some background information on the chemical 2, 4-D is important before continuing. 2-4-D is one of the members of the phenoxy family. The phenoxy family is one of the first selective herbicides developed. It was introduced in 1946 and quickly became the most widely used herbicide ever. Even after over 50 years of use, the herbicide is still the third most used herbicide in the United States and Canada and the most widely used worldwide. In a recent report released by the U.S. Department of Agriculture (NAPIAP Report NO. 1-PA-96) concluded that should 2, 4-D may no longer available, the cost just to American farmers would total more than $1,683 million dollars (1.683 billion) annually. This chemical undoubtedly has been a major weapon against the fight for world hunger. 2, 4-D is used to control broadleaf weeds, grassed and other monocots, woody plants, aquatic weeds, and non-flowering plants. 2,4-D is a plant-growth stimulator similar to gibberellic acid. It stimulates nucleic acid, protein synthesis, enzyme activity, respiration, and cell division. 2,4-D is absorbed through the stems, plant leaves, and roots and travels throughout the plant. 2, 4-D also accumulates in growing tips. 2,4-D is highly toxic to non-target plants and ranges from being nontoxic to highly toxic to fish and other invertebrates. Amine salt forms of 2, 4-D are generally non-toxic to fish. The compounds most toxic to fish include the 2,4-D ester formulations: N-oleyl-1, 3-propylenediamine salt, and the N, N-dimethyl-oleyl-linoleylamine. The 2,4-D compounds that are most toxic to invertebrates are the ester and dimethyl amine formulations.

Recently suspicions have been brought up that 2, 4-D may cause cancer especially non-Hodgkin's lymphoma. However, the European Union and the United States Department of Agriculture have no evidence that 2,4-D causes non-Hodgkin's lymphoma or any other cancer. The current EPA toxicology file has 2,4-D to be non-mutagenic and non-teratogenic. A review of new 2, 4-D developmental toxicity studies published in Toxicological Sciences (60, 121-131, 2001) concludes that developing animals are not uniquely sensitive to 2, 4-D. More evidence was provided that pesticides and herbicides (such as 2, 4-D) do not cause cancer when The National Cancer Institute of Canada's Advisory Committee on Cancer Control (ACOCC) set up an expert panel to examine the cancers resulting from pesticide use. The result determined by the panel was the cancers in the general population caused by pesticides and herbicides are extremely low (Report of a Panel on the Relationship between Public Exposure to Pesticides and Cancer, Cancer, 80:2019-33. 1997). Even more surprising is that when a meta-analysis of cancer among farmers which consisted of 37 studies, showed that farmers have no increased risk of getting cancer despite working around chemicals such as 2, 4-D. The study even showed that farmers have a lower chance of getting cancer due to their healthy lifestyle. Also, the University of Nebraska conducted a study that showed the farmers applying 2, 4-D for 21 days have no higher risk (statistically insignificant). In an effort to re-register 2, 4-D under a different category, the EPA conducted 114 research studies under the re-registration program, the results are 2,4-D has moderate to low acute toxicity. The LD50 (rats) ranges from 699 mg per kg of body weight (2,4-D acid) to >1000 mg/kg for ester and amine formulations. From an LD50 standpoint, 2,4-D is less toxic than caffeine and slightly more toxic than aspirin.

At the concentrations, which may be found in the environment, 2,4-D is highly unlikely to present a threat to wildlife.

Sub chronic effects are generally limited to very high doses when compared to the exposure levels humans may face in the environment.

2,4-D has low reproductive toxicity.

2,4-D does not cause birth defects.

Chronic effects are also limited to high doses.

Based on the extensive toxicology, it is highly improbable that 2,4-D causes cancer.

2,4-D has low potential to cause neurotoxicity in short and long term exposures.

2,4-D does not cause genetic damage.

Despite the overwhelming evidence that 2,4-D does not cause death and/or cancer, anti-pesticide groups continue to advocate strongly that 2, 4-D is indeed a mutagen. They claim that 2, 4-D absorbed through the skin will cause extensive damage of the nervous system. They also claim that large doses of 2,4-D have caused digestive distress and effects on the neuromuscular system and ingestion of large quantities of 2,4-D formulations has led to death within 1 to 2 days of poisoning.

2,4-D also has no long lasting environmental effects. The half-life of 2, 4-D in soils is about 6.4 days in southern soil and 8.3 in high-organic matter soil. The half-life of 2,4-D in water is about 2-4 weeks. The chemical 2, 4-D is also biodegradable, 2, 4-D will degrade to forms of carbon and are not persistent in soil water or vegetation. 2,4-D residue assay can be easily measured accurately using spectrophotometry, and gas liquid chromatography of derivates with electron capture detection.

There have been many toxicology studies done with 2,4-D. Most of the results of the toxicology test turned out to be that 2, 4-D was not particularly toxic and is classified as a Category III or Category IV. However, in some cases such as eye irritation 2, 4-D turns out to be a Category I. The results of the acute oral toxicity tests in male and female rats with the dimethylamine salt of 2,4-D, the acute oral LD50 was 1100-4650 mg/kg (Toxicity Category III). The diethanolamine salt of 2,4-D was in the range of Toxicity Although the primary active ingredient in many herbicides is 2, 4-D, this does not stop herbicides with or without 2,4-D to be non-toxic to birds and humans. The more common effect herbicides have on birds is the alteration of their habitat. Animals such as birds and plants have evolved to be mutually reliant on each other. Just as plants depend on animals for pollination or seed dispersal, birds rely on plants for the basis of their food supply. For seed-eating birds such as sparrows and finches, the removal of seeds and plants from their habitat can greatly decrease their population size and genetic diversity. For insect-eating birds the relationship is indirect but just as important. Because the plants die, the insects that rely on the plant for food also die. This in turn affects the insect eating birds. Also, agricultural run-off can pollute a small pond or lake. This could directly affect waders, shorebirds, waterfowl, kingfishers, and fish-eating raptors. Plants are also used by birds for nesting and shelter. Not only are they used by some birds for building their nest, they also affect the microclimate of a habitat influencing precipitation, humidity, and temperature. Agriculture can affect birds and their populations drastically. The commonly used herbicide Roundup is a non-selective herbicide. In order to help farmers out, scientist have genetically engineered crop seeds so that Roundup does not affect these crops. Farmers are then free to use as much Roundup as necessary. Sometimes the amount of Roundup used by these farmers are excessive. This causes the Roundup to drift to nearby bushes, hedgerows, and shelterbelts. The result of this carelessness is the loss of habitat for many birds especially in the central and northern prairie states. Not only do herbicides have agricultural uses, but they also have uses in forestry. When land is cleared, non-selective herbicides are applied to kill undergrowth so that competition between the planted trees and the undergrowth is drastically reduced. Once this happens the natural diversity is lost to form monocultures of commercial timber. Without the diversity of habitat the diversity of birds also cannot be sustained.

Herbicides have extensive domestic uses as well as commercial uses. The most common place for herbicides to be applied domestically is, well, the backyard. Most homeowners, taking pleasure in a "clean-cut yard" will apply extensive amounts of both selective and non-selective herbicides to their backyard. Sure this will kill weeds, but it will also kill insects that depend on the weeds. When the natural diversity of the habitat is gone and all is left is Bermuda grass, then the insects depending on the weeds are also killed. What occurs from this is totally self-induced. This creates an imbalance between predator species and pest species. Then the homeowner wonders why there are so many insects in his/hers yard. So naturally they go out and buy tons of pesticides and then methodically spray it on their yard. Some pesticides and herbicides are toxic to invertebrates (see results of experiment) which directly reduce the number of prey base to birds causing their population to dwindle.

When the herbicide has done the intended job of killing the weed or whatever, it's not going to disappear from the face of the Earth. Like the saying "What goes around, comes around". The herbicide instead is absorbed into the soil. In many instances, herbicides are toxic to beneficial soil organisms, such as nitrogen-fixing bacteria and mycorrhizae. Mycorrhizae are fungi that have evolved with the root systems of plants and facilitate the uptake of essential nutrients. Herbicides have been shown to kill beneficial soil microorganisms, resulting in the overgrowth of other harmful bacteria and fungi. Herbicides also have been shown to kill nitrogen-fixing bacteria. Nitrogen-fixing bacteria are essential to the Nitrogen cycle and plants need the bacteria for amino acid synthesis and growth. When this bacteria dies, usually the habitat begins to die to. Currently there are ways to "save" the habitat but they rarely work. Applying pre-fixed nitrogen to crops via fertilizers can be accomplished, but natural habitats rarely benefit. In many instances applying pre-fixed nitrogen to aquatic habitats will result in a negative affect.

When applied, the herbicide will inevitably end up somewhere else, through means of seepage, runoff, erosion, evaporation, or fog transportation. Whatever the means of transportation, much of the herbicide will end up in our rivers, lakes, and streams. Many herbicides and their additives are directly toxic to aquatic invertebrates and fish. Herbicides kill algae and aquatic plants in waterways, which can lead to nitrification and eutrophication and destroy the food base for other aquatic organisms at the base level.

Inevitably herbicides must be used. No matter how much evidence produced that herbicides do in fact destroy the environment, the fact that they do a major part in preventing world hunger cannot be ignored. Until someone invents a "perfect" herbicide that does not harm the environment in any way, then it must be accepted that there is no way that environmental damage can be totally avoided. However, damage on the environment can be lowered by controlling the amount and position the herbicide is applied. Even by looking at the weather report on the six o'clock news can help. Seeing if a major storm will hit in the next three days can save plenty of plants. Because using herbicides is necessary, the proper way to handle these chemicals are very important. Goggles to protect the eyes (remember 2, 4-D is a Category I in that) and gloves to protect the hands and skin are also very important. But, if chemicals are accidentally splashed or spilled and came into contact with skin. Washing your hands with soap and hot water thoroughly could prevent irritation. If irritation does develop, medical attention is needed. If the chemical is accidentally swallowed drink plenty of milk, egg white, and water. If the person is conscious, induce vomiting. If a large spill occurs, please call Chemtrec at 1-800-424-9300 for advice.

Research for Planarians 

The planarian is a remarkable group of species which evolved the ability to have remarkable powers of regeneration. This will be discussed later. For now, background information on planarians is needed. Planarians belong in the genus Dugesia in the order Tricladida which is in the class Turbellaria which is in the phylum Platyhelminthes. Most species of the class Turbellaria are parasites and feed on invertebrates and dead animal matter. Almost all of the class is obligated to live in the water, although few species gained the ability to live on land, it is restricted to moist environments. Turbellarians are thought to have given rise to the parasitic flatworm classes, the tapeworms, and the flukes. They have no circulatory system (to distribute food and oxygen) and no excretory system (to remove wastes), rather, their flattened body allows for direct exchange of oxygen and wastes with their cells and aquatic environment. Also all Turbellarians are triploblastic with ectoderm, endoderm and mesoderm. These are the first animals we have considered that have a true mesoderm with mesodermal organs.

The anatomy of a Turbellarian is relatively simple. The mouth is on the underside of the body and leads to the pharynx and gut. Turbellarians are classified according to the shape of the gut: simple and saclike (Neorhabdocoela), branched (Polycladida), three-lobed (Tricladida), divided, or entirely absent. The central nervous system of planarians consist of a brain and two ventro-lateral nerve cords. Cross fibers that run between the two cords form a ladder-like pattern. Sensory structures include paired simple eyes (not true eyes because only light is sensed) which are called ocelli, paired anterior (toward the head) sensory lobes (chemosensory), and numerous touch-sensitive cells in the epidermis. There are cells in the head although there are no permanent cell. The cells in the brain are specialized for sensing chemicals, touch, and water current. There is no statocyst in the planarian, although some other Platyhelminthes do possess these structures. The body is covered with cilia, especially on the underside. The cilia are used in movement and are aided by cells called rhabdoids that secrete a mucous blanket on which the worm glides. Musculature is relatively complex with longitudinal, circular, and oblique dorsoventral muscle fibers that run throughout the mesoderm. Muscular motions also assist in movement.

Turbellarians are simultaneous hermaphrodites meaning they can produce egg and sperm at the same time. A single individual cannot self-fertilize and must rub against another individual in order to reproduce. Thus planarians can reproduce sexually. Mating can also be asexual, by splitting, which is called fission. Another form of asexual reproduction would be if the worm was cut and it grew a new body. Occasionally and rarely, a adult may reproduce by spontaneous binary fission as illustrated. The resulting small tailpiece will become a pharynx and becoming a feeding worm within two weeks. However, most freshwater planarians are sexual and are exclusively oviparous. Being oviparous means that they deposit their fertilized eggs. Environmental conditions such as light and temperature influences whether reproduction will be sexual or asexual.

Even though planarian regeneration has been studied for decades if not centuries, the answers still remain elusive. Scientists agree that planarians capable of regeneration maintain and utilize a reservoir of embryonic stem cells called neoblasts (mesenchymal cells). Depending upon the species, neoblasts comprise up to 30% of the total number of cells in an adult worm. These totipotent cells, which are scattered throughout the worm's body and which are capable to give rise to any other cell type, perform two roles. They replace cells that die in the course of normal means and they provide the cellular raw material for regeneration and wound healing. Regeneration is quite rapid; within as little as 15 minutes after amputation, epithelial cells at the edge of the wound close over the lesion. Within a day, a high number of neoblasts accumulate beneath the wound epithelium. Then, a combination of cell migration and cell division leads to an exponentially growing aggregate of regenerating cells underlying the epithelium. This structure is called the blastema. Within about 5 days, depending on temperature, newly differentiated structures become evident within the growing blastema and under optimal conditions regeneration of lost body parts is complete within about 10 days after amputation. Currently there are two theories to explain planarian regeneration. A theory called the "Gradient Diffusion Model" theorizes that substances are produced in the brain that inhibit head formation and promote tail formation, these substances are strongest near the brain and becomes gradually weaker toward the tail. When the body is cut, the concentration of these substance provide vital information on where the cut part originated from. However, you must remember, this is only one of two popular theories. The other theory is that each cell in the planarian is somehow designated a position in the planarian. When the planarian is cut the cells begin to divide and differentiate according to their positions. This theory is called the "Polar Coordinate Model". Support for the "Gradient Diffusion Theory" comes from a two-headed planarian. A two-headed planarian is called a Janus-head. The "Polar Coordinate Model" theory does not allow to have mixups like this. What is also very interesting of planarians, is that they have evolved a primitive ability to retain memory. When scientist's train a fully grown planarian on how to find water in a maze, when the fully grown planarian is cut in half the second half can find the water much more quickly than untrained ones. This indicates a beginning of a ability to retain memory.

The class Turbellaria often have very odd symbiotic relationships. Commensalism may progress into parasitism or even predation. Also the class Turbellaria contains many parasitic orders. Eighty percent of all species in the class Turbellaria are parasites. The hosts of the parasites are very far ranging aquatic organisms (from hippos to squids). Also the parasites are usually ectoparasitic (feed on gills or skin).

Decades after decades and centuries after centuries, the regeneration ability of planarians will never fully be known. No matter how detailed the ability can be examined, there will always be mysteries on the miracle of regeneration. However, will are closing in on the secret. New research shows that genetics plays a huge role in regeneration. Even the genes that control regeneration have been isolated. Who knows? Maybe in hundreds of years humans can gain the ability of regeneration.

Analyses of Experimental Data (Quantitative) 

The result of the experiment were concurrent with the hypothesis "If the liquid medium is the control (pure spring water), then the planarians will regenerate better." The herbicide tested (and all herbicides because basically they all contain the same ingredients but in different amounts) had a profound effect on planarians. In the pure group, the herbicide was too dark so that the planarians could not be observed directly. However, since the planarians in the 1:10 dilutions all died the second day, an assumption was made that the planarians also died in the pure group. The herbicide had a affect the planarians all the way to the 1:10,000 dilution and the herbicide could be felt through the 1:100,000 dilution. Also, I noticed the herbicide used also sped up decomposition and planarians that died in a higher concentration decayed faster than ones in a lower concentration. I believe that this phenomenon is the direct result of the herbicide. The chemical or group of chemicals that cause this should be isolated and tested for their safety of use.

Planarians Alive after Nine Days (Percentage) The reason their were more survived and regenerated planarians in the 1:1,000,000 than in the control group was that since the water in the control group was changed first along with the egg, the last dilution 1:1,000,000 had about half an hour time more of feeding time (picking the planarians out of the egg yolk was hard! You try it!). So, overall they were better fed.

Planarians Showing Regenerative Signs After Nine Days (Number)

In the 1:1000 dilution the reason the planarians went down on days seven, eight and nine is (Hint: Look on the first chart) that they died. Also, in this chart the nutritional differences between the control and 1:1,000,000 dilution is clearly seen. At the end of nine days, the number of planarians showing signs of regeneration in the 1:1,000,000 dilution is two more than the control. There is obviously something amiss. Also, the data here concurs with the data in the first chart.

Analyses of Experimental Data (Qualitative) 

The qualitative analyses in this experimentation consists of two graphs. The graphs are based on the chart information; number that survived, and number that showed regenerative signs.

The second graph is the number of planarians showing signs of regeneration. The second graph should concur like the second chart concurred with the first. The second graph is given in the exact same format except the scale used in the second graph was different (because the second graph is not a percentage, instead it is a number). Another difference was the some dilutions were missing in the second graph. An explanation for this is that some of the dilutions were so high that the planarians didn't even have a chance to regenerate. They died before a change in their bodies was even noticeable.

The 1:1000 dilution is clearly seen to have risen then fallen.

Conclusion 

Since the specific chemical 2, 4-D was not tested, the effects of the chemical are unknown. However, a herbicide containing 2, 4-D at relatively high concentrations had a profound effect on herbicides. The herbicide killed with deadly speed. If massive amounts of the herbicide was to be applied on a farm, the environmental aftershock could be disastrous. The last segment of the nitrogen cycle is decomposition. The bacteria decompose the dead body so that the nitrogen can be reused. This particular herbicide not only kills with speed, but the dead matter decomposes at a amazing rate.

No matter how much are how little herbicides damage the environment. They still are a chemical that alters the environment. I doubt that a "perfect" herbicide will ever be found, so until the scientists or researches find the "perfect" herbicide, we are left with the second best choice: to practice environmental conservation and ecosystem protection. The Earth has sustained itself for billions of years in perfect equilibrium. Let us not destroy the equilibrium and trash our home. Not only is this are home for today, it is also a home for the millions of years to come.

 

 

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A Look at the Use of Herbicides in the United States. (2021, Oct 31). Retrieved from http://envrexperts.com/free-essays/essay-about-look-use-herbicides-united-states

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