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NotesESS HLTopic 4.4Impacts of water pollution
Back to ESS HL Topics
4.4.43 min read

Impacts of water pollution

IB Environmental Systems and Societies ā€¢ Unit 4

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Contents

  • Impacts of water pollution
  • Seasonal dead zones

Impacts of water pollution

Big idea: Water pollution affects ecosystems through bioaccumulation (toxins build up in organisms) and biomagnification (toxins concentrate up food chains). Top predators ā€” including humans ā€” receive the highest doses.

Bioaccumulation vs biomagnification

Bioaccumulation

  • Toxins build up in ONE organism over time
  • Organism absorbs toxins faster than it excretes them
  • Example: mercury accumulating in a single fish
  • Influenced by fat solubility, persistence, and exposure time

Biomagnification

  • Toxin concentration increases at higher trophic levels
  • Each level contains a higher concentration than the one below
  • Example: plankton ā†’ fish ā†’ seals ā†’ top predators
  • Top predators have the highest concentrations

Substances that biomagnify

  • Heavy metals ā€” mercury, lead, cadmium
  • Persistent organic pollutants (POPs) ā€” DDT, PCBs, dioxins
  • Microplastics ā€” absorb other toxins and enter food chains
  • These substances are fat-soluble, persistent, and not easily excreted
Be able to clearly distinguish between bioaccumulation and biomagnification, and explain why toxin concentrations are highest in top predators using simple food-chain examples.
{ "blocks": [ { "type": "heading", "level": 2, "text": "Seasonal dead zones (hypoxia)" }, { "type": "callout", "variant": "key-idea", "title": "Key idea", "text": "A seasonal dead zone is an area of water where dissolved oxygen becomes very low during certain months (often summer), so many fish and bottom-dwelling animals die or move away." }, { "type": "divider" }, { "type": "heading", "level": 3, "text": "What does the term mean?" }, { "type": "styled-list", "color": "blue", "iconSet": "default", "items": [ "Dead zone means very few animals can survive there because oxygen is too low.", "Seasonal means it forms during particular times of year and may improve later.", "It is strongly linked to eutrophication (too many nutrients such as nitrogen and phosphorus)." ] }, { "type": "heading", "level": 3, "text": "Why do dead zones happen?" }, { "type": "paragraph", "text": "Excess nutrients from agriculture and wastewater increase algae growth. When algae die, decomposers break them down and use up dissolved oxygen. Warm summer water also holds less oxygen, making hypoxia more likely." }, { "type": "styled-list", "color": "green", "iconSet": "checkmark", "items": [ "More nutrients enter rivers and seas (fertilizer runoff, sewage).", "Algal blooms increase (eutrophication).", "Dead algae sink and are decomposed by bacteria.", "Decomposition consumes dissolved oxygen.", "Oxygen falls to hypoxic levels and animals die or migrate." ] }, { "type": "callout", "variant": "exam-tip", "title": "Exam tip", "text": "In data questions, look for the lowest dissolved oxygen month (often July or August). Link it to eutrophication: nutrient input ā†’ algal bloom ā†’ decomposition ā†’ oxygen drops ā†’ dead zone." }, { "type": "heading", "level": 3, "text": "Key numbers students should know" }, { "type": "styled-list", "color": "amber", "iconSet": "warning", "items": [ "Hypoxia is commonly defined as dissolved oxygen below about 2 mg/L (2 mg Lāˆ’1).", "Fish and many invertebrates avoid hypoxic water or die if they cannot escape.", "Some organisms (for example some jellyfish) tolerate low oxygen better and may increase." ] }, { "type": "heading", "level": 3, "text": "Mini self-check (fast)" }, { "type": "styled-list", "color": "purple", "iconSet": "default", "items": [ "Define seasonal dead zone in one sentence.", "State two causes of seasonal hypoxia.", "Explain one effect on a marine food web." ] } ]

Related ESS HL Topics

Continue learning with these related topics from the same unit:

4.1.1The hydrological cycle
4.1.2Water stores and flows
4.1.3Drainage basins
4.1.4Water and climate regulation
View all ESS HL topics

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IB Exam Questions on Impacts of water pollution

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How Impacts of water pollution Appears in IB Exams

Examiners use specific command terms when asking about this topic. Here's what to expect:

Define

Give the precise meaning of key terms related to Impacts of water pollution.

AO1
Describe

Give a detailed account of processes or features in Impacts of water pollution.

AO2
Explain

Give reasons WHY ā€” cause and effect within Impacts of water pollution.

AO3
Evaluate

Weigh strengths AND limitations of approaches in Impacts of water pollution.

AO3
Discuss

Present arguments FOR and AGAINST with a balanced conclusion.

AO3

See the full IB Command Terms guide ā†’

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4.4.3Ocean acidification
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Water pollution management4.4.5

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