Changes to Ecosystems (iv) Pollution

Pollution is the negative effect of a harmful substance on the environment

These are pollutants which are indirectly harmful.

• Manure
• Sewage

• Fertilisers
• Shampoo
• Detergents

eutrophic

• Indicator species
• BOD (Biological oxygen demand)

• The BOD test is a water quality test that measures the levels of dissolved oxygen in the water.  It is used to estimate the levels of biodegradable organic material there is.
• To measure the BOD:
• Two samples of water are taken (no air in bottles)
• Dissolved oxygen concentration is measured
• One sample is put in the dark (to prevent algae photosynthesising)
• Water is incubated at 20°C for 5 days and DO remeasured
• The mass of O₂ used per litre is calculated.  This reflects the mass of organic material available for bacterial decomposition.  The more oxygen used (the more demand) the more polluted the water

• Toxic pollutants are directly harmful to the health of the organism
• Examples include:
• Pesticides eg TBT and DDT
• Heavy metals eg mercury, cadmium, chromium and lead
• Radioactive waste

When a toxin is retained in the bdoy and therefore ends up at a higher concentration in the body than the environment

When a toxin increases in concentration further up the food chain as it accumulates at each level

When a toxin changes in the body into another toxin

• It is persistant
• It bioaccumulates
• It biomagnifies in a food chain
• It is an irreversible non competitive inhibitor of enzymes and can affect nervous tissue and foetal development
• Can biotransform into toxic methyl mercury

It can bioaccumulate which can lead to lead poisoning and can affect the mental development of young children

• It is a pesticide that interferes with nerve impulses in insects.
• It is non-specific and persistant with a long hal-life.
• It bioaccumulates in fatty tissues and therefore biomagnifies in food chains
• DDT can biotransform into DDE
• Both DDT and DDE reduce calcium deposition during egg formation.  This resulted in birds of prey such as osprey and peregines reducing in number (the eggs broke when parents were nesting on them)

• TBT is an antifouling agent used on boats to stop baracles growing on them
• TBT is therefore harmful to some marine organisms, including dog whelks.  TBT causes female dog whelks to develop male sexual characteristics such as a penis.  This causes them to become infertile or die