Bioaccumulation

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Lesson notes

Definition of Bioaccumulation

**Bioaccumulation** is the process by which **toxic substances** build up in the tissues of organisms over time.
Toxic substances include **pesticides**, **heavy metals** (e.g., mercury, lead), and other pollutants.
These toxins enter the environment through **air**, **water**, or **soil**.
Once in an ecosystem, toxins move through the **food chain** and become more concentrated in animals higher up.

Example: Mercury

**Mercury** is a heavy metal released from industrial processes like **coal burning**.
In aquatic ecosystems, mercury is absorbed by **plankton**.
Small fish eat plankton and **accumulate** mercury in their bodies.
Larger fish (e.g., tuna, trout) eat smaller fish, increasing mercury concentration.
Top predators (including humans) can have **dangerously high** mercury levels, leading to **neurological disorders**.

Example: DDT

**DDT** was a pesticide used extensively in agriculture.
It accumulated in the environment, especially in **aquatic ecosystems**.
Small organisms absorbed DDT; it became highly concentrated in **birds of prey** (e.g., eagles, ospreys).
High DDT levels caused birds to lay eggs with **very thin shells**, which often broke before hatching.
This led to a significant **decline in bird populations**, and DDT was banned in many countries.

Preventing Bioaccumulation

Reduce the release of harmful chemicals and pollutants into the environment.
Use **less toxic alternatives** to pesticides.
Enforce **stricter regulations** on industrial waste.
Ensure **proper disposal** of toxic materials.

Key Points

Bioaccumulation leads to **higher toxin concentrations** in organisms at higher trophic levels.
Human activities (e.g., industry, agriculture) contribute to the release of toxins.
Health risks include **neurological disorders** (mercury) and **reproductive failure** (DDT).
NHS advises limiting tuna consumption to **2 steaks per week** due to mercury bioaccumulation.

Energy pyramid showing bioaccumulation: toxin concentration increases at higher trophic levels.

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Practice questions

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1.What is bioaccumulation?
Easy
- AThe increase in concentration of a toxic substance in the tissues of organisms over time
- BThe breakdown of toxic substances in the environment
- CThe movement of organisms from one habitat to another
- DThe process by which organisms produce toxins
2.Which of the following is an example of a toxic substance that can bioaccumulate?
Easy
- AOxygen
- BWater
- CMercury
- DCarbon dioxide
3.Bioaccumulation occurs when toxic substances build up in which part of an organism?
Easy
- AThe digestive system only
- BThe tissues
- CThe fur or feathers
- DThe external environment
4.A small fish in a polluted river absorbs 2 units of a toxin. If a larger fish eats 10 of these small fish, how many units of toxin does the larger fish accumulate?
Medium
- A2 units
- B10 units
- C20 units
- D12 units
5.A top predator in a food chain eats 15 animals, each with 10 units of toxin. How many units of the toxin does the predator accumulate from eating these animals?
Medium
- A10 units
- B15 units
- C150 units
- D25 units
6.Why is it advised that adults eat no more than 2 tuna steaks per week?
Medium
- ATuna is low in protein
- BTuna may contain high levels of mercury due to bioaccumulation
- CTuna is difficult to digest
- DTuna is an endangered species
7.Why was the pesticide DDT banned in many countries?
Medium
- AIt was ineffective against insects
- BIt caused birds to lay eggs with thin shells that broke easily
- CIt increased crop yields too much
- DIt was too expensive to produce
8.Which of the following best explains why top predators are most affected by bioaccumulation?
Hard
- AThey eat only plants
- BThey are at the highest trophic level and accumulate toxins from all lower levels
- CThey have larger bodies that produce more toxins
- DThey are exposed to toxins directly from the environment

Revision notes

## Bioaccumulation **Bioaccumulation** is the process by which toxic substances build up in the tissues of organisms over time. These toxins include chemicals like pesticides, heavy metals (e.g., mercury, lead), and other pollutants that enter the environment via air, water, or soil. Once in an ecosystem, toxins move through the food chain and become more concentrated in animals higher up the chain. ### Examples - **Mercury**: Released from industrial processes (e.g., coal burning). In aquatic ecosystems, plankton absorb mercury; small fish eat plankton and accumulate mercury; larger fish (e.g., tuna) eat smaller fish, concentrating mercury further. Top predators (including humans) can suffer health risks like neurological disorders. - **DDT**: A pesticide that accumulated in the environment, especially in water. It became concentrated in birds of prey (e.g., eagles), causing thin eggshells that broke before hatching, leading to population declines. DDT is now banned in many countries. ### Prevention - Reduce release of harmful chemicals. - Use less toxic alternatives to pesticides. - Enforce stricter regulations on industrial waste. - Proper disposal of toxic materials. ### Key Points - Toxins become more concentrated at each trophic level. - Bioaccumulation can cause serious health and environmental problems. - Human activities (e.g., industry, agriculture) contribute to bioaccumulation.

Bioaccumulation: The process by which toxic substances build up in the tissues of organisms over time.
Toxin: A poisonous substance that can cause harm to organisms.
Food chain: A sequence of organisms where each is eaten by the next, showing the flow of energy and materials.
Mercury: A heavy metal that can bioaccumulate, released from industrial processes like coal burning.
DDT: A pesticide that bioaccumulates, causing thin eggshells in birds of prey; now banned in many countries.
Top predator: An animal at the top of a food chain, with no natural predators, which often has the highest concentration of toxins.

Flashcards

What is bioaccumulation?

Bioaccumulation is the process by which toxic substances build up in the tissues of organisms over time.

Name three types of toxic substances that can bioaccumulate.

Pesticides, heavy metals (e.g., mercury, lead), and other pollutants.

How do toxins enter the environment?

Through air, water, or soil.

What happens to toxin concentration as you move up a food chain?

Toxins become more concentrated in the bodies of animals higher up the food chain.

Give an example of a heavy metal that bioaccumulates and its source.

Mercury, released from industrial processes like coal burning.

Describe the bioaccumulation of mercury in an aquatic food chain.

Mercury is absorbed by plankton, then small fish eat plankton and accumulate mercury, larger fish eat small fish and accumulate more mercury, and top predators (including humans) get dangerously high levels.

What health risks are associated with high mercury levels in humans?

Neurological disorders.

Why is there NHS advice to eat no more than 2 tuna steaks per week?

Because tuna are large predatory fish that can have high mercury levels due to bioaccumulation, which can be harmful to health.

What is DDT and why was it used?

DDT is a pesticide used extensively in agriculture to control insects.

How did DDT affect birds of prey like eagles and ospreys?

DDT caused them to lay eggs with very thin shells that often broke before hatching, leading to population decline.

Why was DDT banned in many countries?

Because it accumulated in the environment and caused severe harm to wildlife, especially birds of prey.

What are two ways to prevent bioaccumulation?

Reducing release of harmful chemicals and using less toxic alternatives to pesticides.

How can stricter regulations help reduce bioaccumulation?

By enforcing stricter regulations on industrial waste and ensuring proper disposal of toxic materials.

A small fish has 2 units of toxin. If a larger fish eats 10 such small fish, how many units does the larger fish have?

20 units (assuming all toxin is retained).

A top predator eats 15 animals each with 10 units of toxin. How many units does the predator accumulate?

150 units.

Name two human activities that contribute to bioaccumulation.

Industrial processes (e.g., coal burning) and use of pesticides in agriculture.

What is an example of a pollutant that bioaccumulates in aquatic ecosystems?

Mercury or DDT.

How does bioaccumulation occur in an ecosystem?

Toxins enter the environment and are absorbed by small organisms; as larger organisms eat smaller ones, the toxins accumulate and become more concentrated in higher trophic levels.

What is the difference between bioaccumulation and biomagnification?

Bioaccumulation is the buildup of toxins in an individual organism over time; biomagnification is the increase in concentration as toxins move up the food chain. (Note: Source uses bioaccumulation broadly.)

Why are top predators most affected by bioaccumulation?

Because they consume many prey animals, each with accumulated toxins, leading to the highest concentrations in their bodies.

What effect did DDT have on bird eggshells?

It caused eggshells to become very thin and fragile, often breaking before chicks could hatch.

How can using less toxic alternatives to pesticides help?

It reduces the amount of harmful chemicals entering ecosystems, thus decreasing bioaccumulation.

What is a heavy metal that can bioaccumulate and cause health issues?

Mercury or lead.

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