DP Chemistry: Biochemistry & the environment
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Biochemistry & the environment

B.6 Biochemistry & the environment (2 hours)

Pause for thought

Photograph taken in the Vietnam War museum in Ho Chi Minh City

It is generally well known that dioxins, which were made infamous by the spraying of Agent Orange during the Vietnam War, are highly toxic. They can be formed when persistent organic pollutants (POPs) are combusted at insufficiently high temperatures and the rules surrounding industrial waste incinerators are now very stringent.

Perhaps less well-known, but equally toxic, are the rather similar PCBs. There are 209 possible configurations for polychlorinated biphenyls with the general formula C12H(10-x)Clx, of which about 130 have been used commercially. Although they are now banned they were used extensively as a coolant fluid in transformers and capacitors. This is because they reduced the chances of electrical fires occurring due to their high thermal stability and their high electrical resistance. However, although they are no longer used, they persist in the environment and are fat-soluble so also undergo biomagnification. This is a particular problem with fish farming. Farmed salmon contain up to five times as much PCBs as wild salmon. This is thought to be due to the fact that they are fed on ground-up fish, which are already high in PCBs. Because of these high levels of PCBs the Environmental Protection Agency in the USA recommends that people should not eat more than one helping of farmed salmon per month.

Nature of science

Scientists have the responsibility to consider ways in which the products of their research and findings have a negative impact on the environment, and to find ways to counter this. For example, the use of enzymes in biological detergents and to break up oil spills, and green chemistry in general.

Learning outcomes

After studying this topic students should be able to:

Understand:

  • Chemicals found in an organism that are not normally present there are known as xenobiotics.
  • Bacteria or other living organisms can consume or break down biodegradable or compostable plastics.
  • Host–guest chemistry involves the creation of synthetic host molecules that selectively bind to specific guest species, such as toxic materials in the environment, and so mimic some of the actions performed by enzymes in cells.
  • Enzymes have been developed to help in the breakdown of oil spills and other industrial wastes.
  • Enzymes found in biological detergents can improve the energy efficiency by enabling effective cleaning at lower temperatures.
  • The increase in concentration of a substance in a food chain is known as biomagnification.
  • Green chemistry, also called sustainable chemistry, is an approach to chemical research and engineering that seeks to minimize the production and release to the environment of hazardous substances.

Apply their knowledge to:

  • Discuss the increasing problem of xenobiotics such as antibiotics in sewage treatment plants.
  • Describe the role of starch in biodegradable plastics.
  • Apply host–guest chemistry to the removal of a specific pollutant in the environment.
  • Describe an example of biomagnification, including the chemical source of the substance. Examples could include heavy metals or pesticides.
  • Discuss the challenges and criteria in assessing the “greenness” of a substance used in biochemical research, including the atom economy.

Clarification notes

Students are not expected to know the specific names of “green chemicals” such as solvents.

When explaining host–guest chemistry the emphasis should be on non-covalent bonding within the supramolecule.

International-mindedness

The term 'green chemistry', which was first coined in 1991, and the acceptance of its philosophy has led to developments in education and legislation in many different countries.

Most countries have banned the use of the pesticide DDT due to its toxic effects and biomagnification. It does, however, continue to be used in countries where malaria remains a major public health challenge.

Teaching tips

This is an important topic but one that is difficult to teach, as ultimately it tends to be rather factual and requires the students to learn the information rather than deduce much of it. The only calculations they might be asked to perform are on the atom economy of a reaction or possibly interpreting a graph that shows biomagnification. Other examination questions on this sub-topic are more likely to be of the ‘describe’ or ‘explain’ variety.

There are really several different sub-headings to cover and it may be good to get students to choose one to research, either individually or in small groups, and report their finding to the rest of the class. These sub-headings are xenobiotics, biodegradability (including biodegradable plastics and the use of enzymes in detergents), host-guest chemistry, biomagnification and green chemistry. Many of the classic examples are worth covering. For xenobiotics include DDT, PCBs, PCCDs, heavy metals and antibiotics. Use incidents and examples to illustrate the effects on the environment. These might include the Deepwater Horizon disaster (to illustrate the use of enzymes in cleaning up oil spillage) and the effect that the biomagnification of DDT had on birds of prey.

Study Guide

Page 132

Questions

For ten 'quiz' questions (for quick testing of knowledge and understanding with the answers explained) see MC test: Biochemistry & the environment.

For short-answer questions see Biochemistry & the environment questions together with the worked answers on a separate page Biochemistry & the environment answers.

Vocabulary list

xenobiotic
biodegradable
biomagnification
dioxin
PCB (polychlorinated biphenyl)
PCDD (polychlorinated dibenzodioxin)
DDT (dichlorophenyltrichlorethane)

Teaching slides

Teachers may wish to share these slides with students for learning or for reviewing key concepts.

  

Other resources

1. Rachel Carson first brought biomagnification into the spotlight in her book 'Silent Spring', first published in 1960 - particularly the problems with using the pesticide, DDT. This is an interesting historic account of her work.

  Pesticides, DDT and Silent Spring

2. A rather fast-talking video on how oil spills can be cleaned up.

  Cleaning up oils spills

3. How biodegradable is biodegradable plastic?

  Biodegradable plastic

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