Impacts of Water Pollution (Cambridge (CIE) IGCSE Environmental Management): Revision Note

Water pollution & infectious diseases

• Water pollution harms both people and the environment

  • Pollutants can come from industry, agriculture and households

• Polluted water can lead to infectious diseases

Risk of infectious bacterial diseases: cholera

• Polluted water can contain bacteria, including Vibrio cholerae, which causes cholera

  • Cholera spreads when people drink or use untreated sewage-contaminated water

• Causes severe diarrhoea and dehydration

  • Severe diarrhoea can cause the loss of significant amounts of water and ions from the body, causing the tissues and organs to stop working properly

  • Can lead to death if not treated quickly

• Common where sewage systems are poor or after floods that mix human waste with drinking water

Bioaccumulation & biomagnification of toxic substances

Accumulation of toxic substances from industrial processes

• Factories may release heavy metals (e.g. lead, mercury) or chemicals into rivers and lakes

  • These substances do not break down easily

• Mercury is a common example of an industrial pollutant

  • Can enter water from metal processing, mining or waste disposal

  • Causes nerve damage and serious health problems in humans and wildlife

• Toxic substances can poison aquatic plants and animals

  • Fish may suffer kidney damage, deformities or death

• Toxic chemicals can enter human drinking water supplies

  • This can lead to long-term health risks

Bioaccumulation & biomagnification of toxic substances

Bioaccumulation

• Bioaccumulation is the gradual build-up of toxic substances in a single organism over time

  • This happens because organisms absorb toxins faster than they can remove them

  • For example:

    • A fish absorbs small amounts of mercury each time it feeds

    • Over months or years, mercury levels in the fish grow to dangerous amounts

Biomagnification

• Biomagnification occurs when toxin concentrations increase as they pass up the food chain

  • Predators eat many contaminated organisms, increasing toxin levels in their bodies

• Top predators (e.g. large fish or birds of prey) have the highest toxin levels

  • This can cause reproductive problems, weakened shells in birds, or poisoning in mammals

• DDT, a pesticide, is a well-known example:

  • DDT was a widely used insecticide in the mid-20th century that was found to have harmful effects on birds of prey such as eagles and falcons

  • When DDT was sprayed on crops, it would leach into waterways and eventually enter freshwater and marine ecosystems

  • DDT would then enter food chains (via plankton) and accumulate in the bodies of fish 

  • These fish would then be eaten by birds, which would accumulate higher concentrations of DDT

  • Because DDT is persistent and does not break down easily, it can continue to accumulate in the bodies of animals at higher trophic levels (such as birds of prey)

  • This lead to harmful effects such as thinning of eggshells and reduced reproductive success

Acid rain

• Acid rain forms when gases from burning fossil fuels (e.g. sulphur dioxide, nitrogen oxides) mix with rainwater

  • Produces weak acids that fall into rivers and lakes

• Acid rain lowers the pH of water

  • Many fish and aquatic insects cannot survive in acidic conditions

  • Damages fish gills and kills eggs

  • This reduces populations of these organisms and can disrupt food chains

• Acid rain can also leach toxic metals like aluminium from the soil into rivers and lakes

  • This further harms aquatic life

Leaching & nutrient enrichment

Leaching of nutrients

• Fertilisers from farms can be washed into rivers and lakes

  • Rainwater dissolves nitrates and phosphates and carries them away

  • These nutrients can cause rapid plant and algae growth in water

Eutrophication

• Excess nutrients lead to algal blooms

• Algae cover the water surface

• Algae block sunlight

• Aquatic plants below cannot photosynthesise and die

• Decomposers break down dead plants and algae

• This uses up oxygen, creating low-oxygen (hypoxic) water

• Fish and other animals suffocate

• This can leads to ecosystem collapse and loss of biodiversity in rivers and lakes

Stages of eutrophication