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D4.2.9—Biomagnification

Biomagnification raises persistent toxin concentrations at higher trophic levels because consumers ingest many contaminated organisms and cannot rapidly eliminate pollutants.

Syllabus
First assessment 2025
Objective
D4.2.9
Level
HL

Exam analysis

Chance of appearing8%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper3
Typical marks2–3

Common command terms

  • Explain
  • Define
  • State
  • Discuss
  • Identify
  • Suggest
  • Deduce
  • Outline
  • Justify

Scoring notes

Common mistake
Describing biomagnification as any pollution effect, without explaining increasing concentration at successive trophic levels.

Recent exam appearances

May 2025Paper1B ["HL"] · TZ22(a)[ 2 ]D4.2.9—Biomagnification
November 2024Paper3 ["HL"] · TZ018[ 6 ]D4.2.9—Biomagnification
May 2023Paper3 ["HL"] · TZ218(c)[ 3 ]D4.2.9—Biomagnification
May 2018Paper3 ["HL"] · TZ116(e)[ 2 ]D4.2.9—Biomagnification
May 2017Paper3 ["HL"] · TZ216(e)[ 2 ]D4.2.9—Biomagnification

Coverage 2012–2025 · Updated 16 Jul 2026

Bioaccumulation Happens within Organisms; Biomagnification Happens across Trophic Levels

Process Comparison being made
bioaccumulation toxin concentration in one organism increases over time because uptake exceeds breakdown and excretion
biomagnification toxin concentration per unit biomass increases from one trophic level to the next

Persistence prevents rapid degradation; fat solubility and poor excretion retain compounds such as DDT; predators consume contaminant loads from many prey.

A food-chain pyramid shows DDT concentration increasing from producers to primary and secondary consumers and a top predator, alongside one fish accumulating more toxin over time.

A Dilute Persistent Pollutant Can Reach a Toxic Dose in Top Predators

  1. A dilute persistent pollutant enters producers from water or soil.
  2. Primary consumers eat many contaminated producers.
  3. Predators retain pollutant faster than they eliminate it and consume many contaminated prey.
  4. Concentration per gram of tissue increases at successive trophic levels.
  5. Long-lived top predators receive the greatest dose and may suffer reproductive or neurological harm.
DDT property or effect Consequence
persistent and fat-soluble retained in animal tissues
biomagnifies birds of prey receive high tissue concentrations
disrupts calcium deposition thin eggshells crack more easily, reducing breeding success

The pollutant does not create extra mass at each trophic level. Concentration rises because predators assimilate contaminants from many prey while biomass and energy are lost between levels.

Human Use Is Sustainable Only When Ecological Recovery Remains Possible

measure stock and ecosystem condition → keep removal and pollution within recovery capacity → monitor delayed and indirect effects → reduce pressure or restore processes when indicators deteriorate

Pressure Mechanism to name
excess nutrient input bloom → dead biomass → decomposer respiration → high BOD → hypoxia
persistent toxin retention within organisms plus concentration across trophic levels
marine plastic persistence, fragmentation, entanglement, ingestion and chemical transfer
harvesting removal relative to recruitment, growth, age structure and habitat condition
degraded habitat connectivity, species interactions and succession restored through rewilding

A resource being renewable, a crop yield being high or a restoration site becoming greener is not enough. Sustainability claims require evidence that future ecological capacity is retained.

Biomagnification exam focus

[ 6 ]

Discuss the use of DDT (dichlorodiphenyltrichloroethane) in the control of the malarial parasite.

Concept essentials

  • Biomagnification requires a pollutant that persists and accumulates in organism tissues.
  • Predators at higher trophic levels receive larger pollutant loads by eating many contaminated prey.
  • DDT, DDE, mercury, PCBs, and triclosan illustrate toxic effects on top consumers and humans.