Transcript D6 Environmental impact of some medications

Medicinal Chemistry
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Radioactive isotopes are used for diagnose
and treatment.
Radioactive isotopes decay and emit alpha,
beta and gamma radiations
These radiation form ions by ejecting
electrons out of matter and in this way
damage DNA.
 131I,
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used to treat
thyroid cancer, has a
half-life of just 8 days.
60Co, used to treat
other forms of cancer,
has a half-life of 5.3
years.
Low Level Waste
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Low-level waste has a
low activity (not many
radioactive nuclei
decay each second to
produce ionising
radiation) and usually
contains isotopes with
short half-lives
(ionising radiation is
given off for a shorter
period of time).
High level waste
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High-level waste has a
high activity (many
radioactive nuclei
decay each second to
produce ionising
radiation) and usually
contains isotopes with
longer half-lives
(ionising radiation is
given off for a long
time
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Radioactive materials have the potential to be a
serious hazard both to people and to the
environment – therefore the disposal of medical
nuclear waste must be controlled carefully.
Governments set strict limits on the release of
radioactivity into the environment and
monitoring is essential to ensure that these
regulations are adhered to.
The main approaches to the disposal of nuclear
waste are ‘dilute and disperse’, ‘delay and decay’
or ‘confine and contain’. ‘Confine and contain’ is
always used for nuclear waste that has a high
level of activity.
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This includes items that have been
contaminated with radioactive material or
have been exposed to radioactivity.
Examples are gloves and other protective
clothing, tools, syringes and excreta from
patients treated with radioisotopes.
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Stored until it is safe to dispose as ordinary
waste
Some low level waste is diluted and
dispersed
High activity low level waste is buried
underground. e.g. some wastes are buried
in special concrete containers for a period
of 500 years
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This includes spent fuel rods and other
materials from nuclear reactors.
High-level waste will remain hazardous to
humans and other living things for thousands
of years.
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High level liquid waste is first is converted
to glass (vitrification) for making storage
easier.
High level waste is first kept underwater for
cooling from nine month to 10 years.
After cooling waste is transferred to casks
(Special storage tank made of steel and
concrete)
The dry casks are stored in bankers for
thousand years.
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Permanent storage of high-level radioactive
waste is a major problem and various
solutions have been suggested – such as
burying the waste deep underground in
stable geological areas. Over thousands of
years, however, it is difficult to predict what
processes could occur to cause release of the
radioactive material. Many people argue that
there is no suitable solution for the disposal
of high-level waste.
Antibiotics can enter the water supply by
several routes. These include:
1. incorrect disposal of unwanted medicines –
for example, by flushing old medicines
down the toilet.
2. agriculture – drugs given to animals will be
present in animal waste (urine and feces)
and can find their way into groundwater,
rivers and lakes. Treating water to produce
drinking water does remove some of these
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The release of antibiotics into the
environment is regarded as a particular
problem because not only can they cause
damage to aquatic organisms, but they can
also result in increased resistance of bacteria
to antibiotics. Antibiotics (antibacterials) are
used to treat a variety of conditions but if
bacteria develop resistance to antibiotics
such as penicillin, these diseases can become
much more difficult to cure.
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Green chemistry (or sustainable chemistry) is
an approach to chemical research and
chemical industrial processes that seeks to
minimize the production of hazardous
substances and their release into the
environment.
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use readily available and safe materials
have the minimum number of steps
convert as much of the starting materials as
possible into the required product at each
step – good atom economy and good yield
use as little solvent as possible
use as little energy as possible.
An important consideration in green
chemistry is the concept of atom economy
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Atom economy can be used as a measure of
how efficient a particular reaction is in terms
of converting as much of the starting
materials as possible into useful products.
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Oseltamivir has been discussed earlier as a
treatment for influenza.
Total synthesis (from petrochemical starting
materials) of oseltamivir involves huge
amounts of materials and can generate
thousands of kilograms of waste per mole of
oseltamivir made.
Therefore it was essential to develop greener
routes to the drug.
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The current commercial synthetic route
uses a naturally occurring material,
shikimic acid, as the starting material –
this cuts out several steps in the
synthesis and makes it greener.
Shikimic acid is a renewable material
that can either be extracted from
Chinese star anise or obtained from
glucose by fermentation using
genetically modified bacteria.
Even starting from shikimic acid, a
further ten steps are required to make
oseltamivir, so more work is required
to make this synthesis even greener!
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Although shikimic acid can be obtained from
star anise, this in itself causes a problem –
the yield is not very high and the production
of shikimic acid is linked to the availability of
star anise. The use of GM bacteria is likely to
provide a better long-term solution to
producing shikimic acid – fermentation uses
relatively low temperatures and an aqueous
medium, so it is a reasonably green process.
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As most of the medicinal products are
prepared in organic solvents.
Solvents contribute 80 to 90 % by mass of
medicinal products.
These solvents are mostly toxic and
hazardous for environment.
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First step in making process greener is to find
an environment friendly solvent.
If a greener solvent cannot be found then the
amount used should be reduced as far as
possible.
The next consideration is the possibility of a
solvent being recycled and reused.
If the solvent cannot be reused, then it must
be disposed of as safely as possible.