Explain bioaccumulation and biomagnification

WHAT are we talking about?

WHY does it happen? (the two conditions)

A substance biomagnifies only if it is:

1. Persistent — not broken down chemically/biologically (e.g. DDT, PCBs, methylmercury). If it degrades fast, it never accumulates.
2. Poorly excreted / strongly retained in tissue — the body stores it instead of flushing it out. This retention can happen two ways:
   • Fat-soluble (lipophilic) substances (e.g. DDT, PCBs) dissolve in fatty tissue rather than water, so they aren't lost in urine.
   • Protein-binding substances (e.g. methylmercury) latch tightly onto proteins in muscle/tissue, so they too resist excretion — without being lipid-soluble.

HOW does the concentration multiply? (derive it from scratch)

Let's build the maths, not memorise it.

Step 1 — Define transfer efficiency of energy/biomass between consumers. Between one consumer trophic level and the next, only about 10% of biomass transfers (the rest is lost as heat/respiration). So to build 1 kg of predator, roughly $10$ kg of prey is eaten. Why this step? Because the predator must eat many times its own mass — that's the engine of concentration. (Note: this 10% rule governs consumer→consumer steps; the first uptake from water into producers is a separate assimilation process — see the mistake below.)

Step 2 — Track the toxin, which does NOT get lost. Say prey has toxin concentration $C_{prey}$ (mass of toxin per kg of tissue). Eating mass $m_{eaten}$ of prey delivers toxin: $T = C_{prey}\times m_{eaten}$ Why this step? Total toxin swallowed = concentration × amount eaten.

Step 3 — The predator keeps (nearly) all the toxin but only 10% of the mass. Predator mass built: $m_{pred} = f\, m_{eaten}$ where $f\approx0.1$ (transfer efficiency). If a fraction $r$ of toxin is retained (assume $r\approx1$ for persistent poisons): $C_{pred}=\frac{T\cdot r}{m_{pred}}=\frac{C_{prey}\,m_{eaten}\,r}{f\,m_{eaten}}=\frac{r}{f}\,C_{prey}$

Step 4 — Simplify. The $m_{eaten}$ cancels! We get the magnification factor: $\boxed{\;C_{pred}=\frac{r}{f}\,C_{prey}\;}$ With $r=1,\ f=0.1$: $C_{pred}=10\,C_{prey}$

This is a derivation, not a dump: the ×10 comes directly from "10% biomass passes but 100% toxin passes."

Worked Examples

Common Mistakes

Flashcards

Connections

• Food Chains and Trophic Levels — the 10% energy rule powers the ×10 factor
• Persistent Organic Pollutants (POPs) — DDT, PCBs, dioxins (fat-soluble)
• Mercury and Methylmercury Cycle — protein-binding metal biomagnification
• Bioconcentration Factor (BCF) — the water→producer uptake step
• Pesticides and Silent Spring — Rachel Carson, DDT & raptors
• Ecological Pyramids — pyramid of biomass vs pyramid of toxin (inverted)
• Human Health & Fish Consumption Guidelines
• Conservation & Human Impact — parent chapter

Concept Map

Hinglish (regional understanding)