Environmental impact of some medications
D.6 Environmental impact of some medications (2 hours)
Pause for thought
Supercritical carbon dioxide
Solvents are traditionally volatile organic substances which are toxic to all living organisms. They affect the nervous and respiratory systems and many, particularly chlorinated solvents such as dichloromethane, affect the liver and kidneys. Many also contribute to photochemical smog by forming secondary pollutants and also some are greenhouse gases and/or contribute towards ozone depletion. Some may also pollute ground water. The pharmaceutical industry requires large quantities of solvents to produce drugs on an industrial scale and much of the solvents used ends up as waste.
Companies are more and more switching to using supercritical carbon dioxide in place of traditional organic solvents. Supercritical carbon dioxide is now used in the extraction of caffeine and essential oils from plant materials, and to extract the required product(s) during the multi-stage synthesis of drugs. This has many advantages. Supercritical carbon dioxide is much greener and safer to the environment than traditional solvents such as propanone or dichloromethane. The extractions can also occur at much lower temperatures than, for example, using steam distillation, which means that the desired products are less likely to be thermally decomposed or denatured during the extractions. Supercritical carbon dioxide is also very easy to remove. It is true that, when released into the atmosphere, carbon dioxide is a greenhouse gas, but it is not adding to the total amount of greenhouse gases if the source of the supercritical carbon dioxide was the atmosphere in the first place.
So what is supercritical carbon dioxide? Chemistry teachers are familiar with carbon dioxide gas and solid carbon dioxide, “dry ice”, but most will not have come across ‘liquid’ carbon dioxide. The critical point of carbon dioxide (not to be confused with the triple point, when all three phases exist in equilibrium) is at 304.25 K and 7.39 x 106 Pa. Above its critical point it behaves as a supercritical fluid, which expands to fill its container as if it were a gas but with a density as if it were a liquid.
Phase diagram for carbon dioxide (Image from Wikimedia Creative Commons)
Nature of Science
The design, production and distribution of medications involve considerable ethical implications and risks which need to be considered by the whole community as well as by the scientific community. Both the side effects of medications on the patient and the side effects of the development, production and use of medications on the environment (i.e. disposal of nuclear waste, solvents and antibiotic waste) need to be taken into account.
Learning outcomesAfter studying this topic students should be able to: Understand:
Apply their knowledge to:
| Clarification notesThe structure of oseltamivir can be found in Section 37 of the data booklet. International-mindednessPharmaceutical companies are multi-national companies. How do they determine how to spend their funds on research to develop new medications? For example, do they have a responsibility to research medications for rare diseases, even though it is unlikely to provide them with significant financial profit? |
Teaching tipsThis is an important topic but not easy to teach as much of it is factual, some of it is extremely complicated (e.g. the synthesis of shikimic acid, the precursor for Tamiflu) and whilst it can provoke much discussion it does not readily lend itself to one or two mark short-answer questions. The use of radioactive isotopes in medicine is covered in the AHL material so students will not be expected to know about specific isotopes but they should have some understanding of the importance of half-life as this is one of the factors that distinguish between low-level nuclear waste and high-level nuclear waste. I think they also need to be aware of the different types of radiation emitted and I do cover what happens to the radioactive element when it emits alpha or beta radiation even though balancing nuclear equations is not supposed to be covered until D.8. The video given as the first item in 'Other resources' below is well worth showing to cover this part of the sub-topic. Explain that waste volatile solvents can cause considerable harm to humans and other animals both as primary pollutants but also they can react to form secondary pollutants (e.g. peroxyacylnitrates, PAN) in the atmosphere. You may well have already covered the importance of not overprescribing and the use and disposal of antibiotics in animals in D.2. Green chemistry encourages the reduction and prevention of pollution at source. It does this by trying to minimise the use and formation of substances harmful to the environment. Explain the concept of atom economy and stress its importance to green chemistry. The different ways of synthesising oseltamivir (Tamiflu) are far too complex for IB students, so stress that each new way tries to provide a more sustainable route. The normal precursor is shikimic acid which can be obtained in low yield (2-7%) from a plant (the Chinese star anise plant). This is inefficient and environmentally unfriendly and cannot produce enough for industrial production. Synthesis of shikimic acid in the laboratory is a multi-step process with a very low atom economy. It can now be obtained in a much greener way through bioengineering using bacteria. | Study guide
Page 161 QuestionsFor ten 'quiz' questions (for quick testing of knowledge and understanding with the answers explained) see MC test: Environmental impact of some medications . For short-answer questions see Environmental impact of some medications questions together with the worked answers on a separate page Environmental impact of some medications answers. Vocabulary listlow-level nuclear waste, LLW |
Teaching slides
Teachers may wish to share these slides with students for learning or for reviewing key concepts.
Environmental impact of some medications:
Environmental impact of some medications:
Environmental impact of some medications:
Environmental impact of some medications:
Environmental impact of some medications:
Environmental impact of some medications:
Environmental impact of some medications:
Environmental impact of some medications:
Environmental impact of some medications:
Environmental impact of some medications:
Environmental impact of some medications:
Other resources
1. An excellent video from the International Atomic Energy Agency (IAEI), which looks at the methods of disposal of radioactive waste (both low-level and high-level) worldwide.
Dealing with radioactive waste
2. A video from World Business Review on the management of waste solvent which looks at how solvents are cleaned and recycled in industry.
3. A general introduction to green chemistry by Martyn Poliakoff as part of the Nottinghamscience series.
4. For those with a real interest, the following article summarises some of the different ways in which oseltamivir has been synthesised: Recent progress in the synthesis of Tamiflu