1. Soil Microorganisms and environmental quality (I)
Topic 8
Ms Sherina Kamal

2. Outline Soil microorganisms Xenobiotics Properties of xenobiootics
Groups of xenobiotics
Source of xenobiotics
Fate of xenobiotics
Impact of xenobiotics
Biodegradation of xenobiotic compounds

3. Soil microorganisms and their function
Bacteria
Fungi
Protozoa
Nematodes
Arthropods
Earthworms

4. Xenobiotics A combination of two different roots Xeno
The Greek, means strange, unnatural or different
Biotic
…………………………………

5. Xenobiotics
Man made chemicals present in the nature at high concentrations
May not be recognized by biochemical processes in plants and microorganisms
Resistant to degradation in the environment
Rate of degradation very slow
Has adverse effects on human and on ecological health
Can include many compounds in agricultural activities

6. Properties of xenobiotic compounds
Non recognizable as substrate by microbes to act upon and degrade it
It does not contain permease which is needed for transport into microbial cell
Large molecular nature makes it difficult to enter microbial cell
They are highly stable and insolubility to water adds to this property
………………………………

7. Groups depending on their chemical composition
Halocarbons
consist of halogen group in their structure
Mainly used in solvents, pesticides, propellants
highly volatile and escape into nature leading to destruction of ozone layer of atmosphere
The compounds present in insecticides, pesticides, leach into soil where they accumulate and result in biomagnification
Polychlorinated biphenyls (PCBs)
…………………………………………………………………………………….
mainly used in plasticisers, insulator coolants in transformers
chemically and biologically inert adding on to its recalcitrant nature

8. Groups depending on their chemical composition
Synthetic polymers
mainly used to form plastics like polyester, polyvinyl chloride
insoluble in water and of high molecular weight explaining the recalcitrant property
Alkylbenzyl Sulphonates
consist of a sulphonate group which resists break down by microbes
They are mostly found in detergents
Oil mixtures
oil spills occur covering a huge area the break down by action of microbes becomes non effective
They become recalcitrant as they are insoluble in water and some components of certain oils are toxic in higher concentrations

9. Source of xenobiotic compounds
Petrochemical industry
Oil/gas industry, refineries
Chloride
………………
Plastic industry
The use of chemicals in the production process
Complex organic compounds
Plasticizers
Cross-linking agents
Anti-oxidants

10. Source of xenobiotic compounds
Pesticide industry
Benzene
…………………………..
Paint industry
Solvents
……………………..
Methyl isobutyl ketone
…………………………….

11. Factors effect the xenobiotic biodegradation
Substrate specificity
Type of aromatic compound
Electron acceptors
Oxygen, sulphate, nitrate
Other nutrients
C, N, P or micronutrients
…………………………
Substrate availability

12. Fates of Xenobiotics Fates of xenobiotics …………………………………
Stabilization of parent compounds or some ……………………. of the compound, in soil

14. Possible environmental fate of a xenobiotic compound

15. Hazards posed by xenobiotic compounds
hazards posed by xenobiotics are ………………
highly toxic in nature and can affect survival of lower as well as higher eukaryotes
It also poses health hazards to humans
…………………………………
reproductively and even known as a trigger for causing cancer
……………… and remain in the environment for many years leading to ………………… or ………………………
They also find a way into the food chains and the concentrations of such compounds was found to be high even in organisms that do not come in contact with xenobiotics directly

16. Xenobiotics and Environment
Xenobiotics pose threat to the environment
They pollute the environment
…………………
Synthetic polymers such as plastics and nylon are insoluble in water
Oil is also a pollutant
many of its compounds are biodegradable
degraded at different rates
Oil is recalcitrant mainly
its insolubility in water
…………….. of some of its compounds

17. Impact of xenobiotic compound to soil and plants

18. How Do Oil Spills Affect Plants?
One of the ways that oil spills affect plants is oil blocks sunlight from reaching the plants and organisms below the water's surface
Sunlight and its different rays including ultraviolet rays are important for cells ………………. and ………………….
The oil itself is damaging to the plants but it also damages the water and reduces the nutritive value the water gives the plant
An oil spill has short-term effects on plant photosynthesis and also long-term effects as the plants struggle to recover only to encounter hidden pockets of oil

19. How Do Oil Spills Affect Plants?
The impact of oil spills on plants lies with its ……………………..
In order to produce food and energy, a plant must be able to carry out gas exchange with the environment
The coating of oil on the leaves of plants prevents the ……………. or pores from receiving carbon dioxide from the air
The result is slow growth and …………………… of plants

20. Biodegradation of xenobiotic compounds

21. Biodegradation of xenobiotic compounds

22. END OF LECTURE