Substances in Water from Natural Sources
Section: 10. Chemistry of the Environment | Syllabus: Cambridge AS Level Physics 9702
Substances in Water from Natural Sources Overview Water from natural sources (rivers, lakes, seas) contains various dissolved and suspended substances. Some are beneficial while others are harmful pollutants.
Substance Effect Beneficial or Harmful Dissolved oxygen Essential for aquatic life (fish, plants) ✓ Beneficial Metal compounds (e.g., lead, mercury) Toxic to humans and aquatic organisms ✗ Harmful Plastics Pollutes water, harms wildlife, does not decompose ✗ Harmful Sewage Contains harmful bacteria and uses up dissolved oxygen ✗ Harmful Harmful microbes Cause diseases in humans and animals ✗ Harmful Nitrates (from fertilisers) Cause excessive algae growth (eutrophication) ✗ Harmful Phosphates (from fertilisers & detergents) Cause excessive algae growth (eutrophication) ✗ Harmful Eutrophication The process where excessive nutrients (nitrates and phosphates) in water cause rapid algae growth.
When algae die and decompose, bacteria use up dissolved oxygen, killing fish and other aquatic life. Key Pollutants Heavy metals: Accumulate in organisms, causing poisoning Plastic waste: Non-biodegradable, persists in environment Sewage: Contains pathogens and organic matter that depletes oxygen Agricultural runoff: Nitrates and phosphates from fertilisers
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