Title: Lesson 11 B.6 Biochemistry and the environment Learning Objectives: – Describe what a Xenobiotic is and give examples – Describe biomagnification – Describe examples of amelioration

Main Menu Xenobiotics: strangers to life  Xenobiotics are chemical compounds that are found in a living organism, but are foreign to that organism  Term is also used to describe chemicals that are:  In higher-than-normal concentrations  Not produced naturally and are synthetic  Examples include:  Drugs e.g. antibiotics such as penicillin  Heavy metals e.g. Hg and Pb ions  Food additives  Hormones e.g. estrogens  Pollutants e.g. dioxins  Plastics e.g. PVC  Insecticides e.g. DDT

Main Menu What are the effects?  Non polar molecules can pass easily across the hydrophobic cell membranes  They enter cells where they may be modified by enzymes and detoxified  E.g. drugs are broken down this way in the body. In agriculture, pesticides may be metabolized, which can lead to resistance to the chemical effect  If the xenobiotic cannot be modified in the organism it may build up in the cells (bioaccumulation)  An example is mercury poisoning through the bioaccumulation of mercury compounds in the form of methylmercury

Main Menu What’s the problem?  An increasing area of concern is the existence of pharmaceutically active compounds such as antibiotic, painkillers, and chemotherapy drugs in the environment.  These can be discharged form industries or hospitals, or pass through the body unmodified or partially modified  Sewage works may only breakdown xenobiotics partially  Compounds may end up being released into the effluent and taken up by fish downstream  Waste water from sewage plants may also contain sex hormones such as female estrogens that have been released in human urine (due to the use of synthetic contraceptive pills)  Concerns that male fish have absorbed sufficient quantities of estrogen to be ‘feminized’ and unable to breed Hormones in our Environment Video Drinking Water and Prescription Drugs Video Turning Male Fish to Females Video

Main Menu Biomagnification  Natural toxins do not build up in the environment as they are broken down by enzymes  Synthetic chemicals produced by humans are not broken down naturally as there are not natural enzymes to achieve this  Therefore, synthetic chemicals build up in the air, water, soil and living cells  Biomagnification refers to the increase in concentration of a xenophobic substance in a food web  Occurs when a xenobiotic cannot be metabolized, so is taken up directly when one organism feeds on another  This causes greatest effect at the top of the food chain

Main Menu DDT  Dichlorodiphenyltrichloroethane (DDT)  Used during WWII to control the mosquitoes that are responsible for the spread of diseases such as malaria and typhus  DDT is readily soluble in fat, and does not undergo metabolic breakdown  Bioaccumulates in tissues and passes unchanged through food chains DDT - So safe you can eat it 1947 DDT - Let's put it everywhere 1946 Watch other video in folder ‘DDT and problems with pesticide’

Main Menu  Biomagnification can be seen at each feeding level (trophic level)  Organisms near the top of the food chain accumulate elevated concentrations of DDT  In the 1960s, birds of prey, such as ospreys and peregrine falcons suffered a serious decline in numbers  A thinning of their eggshells made the eggs break under the parent’s weight…  By the 1970s indiscriminant spraying was banned…  Other examples of bioaccumulation include molecules such as dioxins… Dioxins were used in the herbicide ‘Agent Orange’ during the Vietnam War

Main Menu Amelioration: Approaches to lessen the problems with Xenobiotics  Host-guest chemistry  As seen in B.3, enzymes and substrates form complexes as a result of molecular recognition and specific binding  Complexes held together by forces other than covalent bonding (depends on the 3D shape)  A host molecule can be synthesized to bind non-covalently with a guest molecule and form a supermolecule Forces include: Ionic bonds, hydrogen bonds, van der Waals’ forces, and hydrophobic interactions…

Main Menu Examples of host-guest chemistry: removing heavy metal ions  A molecule called calixarene can remove caesium-37 from nuclear waste and extract uranium ions from water  Calixarenes form a cup like structure into which the metal ion is ‘captured’  The cup like structure makes it size elective and ion-dipole interactions form between the caesium ions and the oxygen ions of the –OH groups Calixarene model (a)Flat structure (b)Cup like structure Associations between host and guest are non covalent Positively charged caesium ion held inside its cavities

Main Menu Biodegradable substances  Substances that cannot be broken down by natural processes (usually through microbial action) are said to be non bio- degradable  Usually contain carbon-halogen bonds or stable aromatic structures, which enzymes cannot break  E.g. plastics (such as PVC and polystyrene) and DDT will persist indefinitely  A compound that is biodegradable can undergo bacterial degradation and are not harmful to the environment Degradable and Biodegradable Plastics Video

Main Menu Development of biodegradable plastics  Two main types exist  Plant-based hydro-biodegradable plastic  Petroleum-based oxo-biodegradable plastic Plant-based hydro-biodegradable plastic  High starch content (usually obtained from corn)  Breakdown is initiated by hydrolysis and produces carbon dioxide and water  At high temp – decomposes quickly  When buried in landfill – takes longer to decompose and may produce methane Bioplastic You Can Eat? Video

Main Menu Petroleum-based oxo-biodegradable plastic  Derived from by-product of the oil industry  Additives, such as cobalt are catalysts for breakdown  Plastic degrades into microfragments and are eventually broken down by bacteria  Biodegradable plastics are sometimes known as compostable, because they can decompose in a compost pile, along with natural products

Main Menu Bioremediation – the use of enzymes  Fossil fuels, though natural, can be regarded as xenobiotic in sufficient concentrations e.g. in an oil spill at sea  Microorganisms can be used to ameliorate the impact because they can use it as a food source and break it down and oxidize it in respiration. This is an example of bioremediation  Different compounds in crude oil can be broken down by the microorganisms having evolved different enzymes for each compound  Temperature, nutrients, oxygen levels influence the efficiency of this process  This natural process may be too slow to prevent ecological damage Oil Spill Eater - Bioremediation Video Bioremediation Video Algae Bioremediation Waste Treatment Video

Main Menu Green chemistry (Sustainable chemistry)  A field of study in its own right  ‘Chemistry for the environment’  12 principles which include:  Minimizing production waste  Use of safe solvents  Energy efficient processes  Atom economy of processes  Examples:  Food and drink – supercritical carbon dioxide (CO 2 under pressure), can be used as a solvent which is cheap and non-toxic  Bioplastics – plastics derived from corn starch converted into resin by bacteria can replace traditional oil-based plastics  Cosmetics – production of esters for face creams can be done using enzymes at room temp instead of H 2 SO 4 at high temp  Clothing – Enzymes can replace detergents and improve energy efficiency by cleaning at lower temps

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