Page
  1. 1
    1
  2. 2
    2
  3. 3
    3
  • Level: GCSE
  • Subject: Science
  • Document length: 1186 words

Find out how halogens are used in the manufacture of herbicides and polymers and environmental problems associated

Extracts from this document...

Introduction

Find out how halogens are used in the manufacture of herbicides and polymers and environmental problems associated. Organohalogen compounds are organic compounds that contain at least one halogen (fluorine [F], chlorine [Cl], bromine [Br], or iodine [I]) bonded to carbon. They are subdivided into alkyl, vinylic, aryl, and acyl halides. In alkyl halides all four bonds to the carbon that bears the halogen are single bonds; in vinylic halides the carbon that bears the halogen is doubly bonded to another carbon; in aryl halides the halogen-bearing carbon is part of an aromatic ring; and in acyl halides (also called acid halides) the halogen-bearing carbon is doubly bonded to oxygen. Organohalogen compounds differ widely in chemical reactivity, depending on the halogen and the class to which they belong, and they may even differ within a class. A halogen substituent is considered a functional group, and the transformations of organohalogen compounds rank among the most important in organic chemistry. Many organohalogen compounds, especially organochlorine compounds, are important industrial chemicals; they are used as solvents and pesticides and as intermediates in the preparation of dyes, drugs, and synthetic polymers.

Middle

are sometimes applied by the jar method, whereby the tops of weeds are bent over and immersed in jars of poisonous solution. The herbicide is drawn into the rest of the plant and into connecting plants, gradually killing the entire system. Wild morning glory, poison oak, and camel thorn are sometimes treated in this manner. Chlorinated benzene and certain aromatic solvents are used to control aquatic weeds by adding them directly to the watery medium. Herbicides are chemicals used to kill plants. Their potential to produce toxicity in humans is rather low. High doses of 2,4-D, however, can produce muscular and neurological symptoms (Table 1). The systemic toxicity of 2,4,5-T is lower than that of 2,4-D, but 2,4,5-T is more irritating.During the Vietnam War, Agent Orange, a mixture of 2,4-D and 2,4,5-T, was used as a defoliant. The 2,4,5-T used in the Agent Orange was contaminated with tetrachlorodibenzodioxin (TCDD), or dioxin. Although TCDD is extremely toxic to some animals, it is less so to others, but it does cause birth defects and cancer in laboratory animals.

Conclusion

High DDT levels in birds were associated with fragile eggshells and reproductive abnormalities. Potential harm to wildlife and humans, along with the fact that many insects had become resistant to DDT, prompted the United States Environmental Protection Agency (EPA) to impose an almost complete ban on its use in 1972.A second chlorine-containing aromatic compound that is widespread in the environment is 2,3,7,8-tetrachlorodibenzo-p-dioxin (known simply as dioxin).Dioxin is formed in small amounts as a by-product in the synthesis of the herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), in chlorine-based bleaching processes during paper production, and whenever organic material burns in the presence of a source of chloride ion Cl-, as in forest fires, for example. It is a very stable compound and gradually accumulates in the environment. Because dioxin is exceedingly toxic, carcinogenic, and teratogenic to test animals, regulations designed to limit further environmental contamination have been implemented.A group of aryl halides called polychlorinated biphenyls (PCBs) were formerly prepared on a large scale for use as heat-transfer mediums and insulating materials in transformers and other electrical equipment. Many of the problems associated with DDT and dioxin as environmental pollutants apply to PCBs as well, and PCB production was banned by the EPA in 1979.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our GCSE Living Things in their Environment section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Living Things in their Environment essays

  1. Early Humans?

    Although the same characteristic evolving twice is not unheard of (e.g. wings in birds and insects), Pickford and Senut seem resolved in rendering all other hominin genera obsolete. Many other paleoanthropologists believe that Orrorin should be classified as Ar. kadabba as the two species are of similar ages, were discovered in close proximity, and have a few similar dental features.

  2. Fungal Pathogens in Humans.

    In pregnant women, the likelihood of vaginal candidiasis is high since there is an increase in glycogen levels in mucosal tissues, which stimulates overgrowth of Candida. This infection may be passed as thrush to her baby following birth, before the natural flora of protective bacteria is established (Kendrick, 2000).

  1. Branded Bleach is more effective at killing E. coli than Non branded bleach - ...

    Use bacteria grown from the same starting date. There are also independent and dependent variables. The independent variable is the type of bleach used either branded or non-branded: Domestos or Somerfield thick bleach. The area of the zone of inhibition caused by the action of bleaches on the bacteria is the dependent variable.

  2. Evolution, Natural selection and Darwinism

    The best example can be seen from he Galapagos finches as their bills are specialized to eat different food of their own island. <Ref.1 - p448, p452-453 & Ref.4 - p207-208> Sympatric speciation In sympatric speciation, intrinsic factors, such as chromosomal changes (in plants)

  1. An Investigation to find the Effect of Distance from the Sea on the Number ...

    carbon dioxide and water was in excess). Increasing photosynthesis would reduce the competition for shelter, in turn causing the animal species population to increase (ignoring factors like desiccation). However, eventually there would be a limiting factor limiting the photosynthesis. Even though, when the sea level is low the plant species

  2. What Factors are responsible for the success of Insects?

    through the modification of the basic insect body plan. Modifications of insect feeding parts produced organs able to collect food from a variety of different sources, leading to a diversification of insect species. For example, it is estimated that half of all insects feed on the living tissues of higher

  1. Science Chemistry Casestudy

    Ensures that consumers have access to affordable food that is also safer and more nutritious. - Produces larger crops - Helps farmers increase crop productivity and quality - Helps remove the hardship of hand weeding - Helps safeguard public health by controlling or eliminating pests that cause disease and property damage.

  2. Grizzly Bears

    Their first meal after their winter hibernation would probably be a carcass of a moose or caribou that didn't survive the winter. Grizzlies have to eat a lot in order to survive the winter when they hibernate. Near the sea, grizzlies may find a beached whale or a dead sea lion or walrus.

  • Over 180,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work

Marked by a teacher

This essay has been marked by one of our great teachers. You can read the full teachers notes when you download the essay.

Peer reviewed

This essay has been reviewed by one of our specialist student essay reviewing squad. Read the full review on the essay page.

Peer reviewed

This essay has been reviewed by one of our specialist student essay reviewing squad. Read the full review under the essay preview on this page.