Bioaccumulation in a Food Chain
Please note that numbers and ratios used in this activity are not accurate. In reality,
there is generally a 10% buildup of bioaccumulating toxins as they move up the trophic
pyramid. See next page for background information on bioaccumulation.
Materials: 16 ping-pong balls (or marbles); 16 small cups with green mark for algae; 8 slightly larger cups with
“Insect” written on them or stickers of insects that eat algae; 4 larger cups with “Crayfish” written on them, or
crayfish stickers; 2 larger cups with “Bass” written on them, or a bass sticker; 1 larger container with “Loon”
written on it, or a loon sticker; a toy stuffed loon or large picture of a Common Loon. Mark ping-pong balls with a
red mark for poison. Note: clear containers are best to use so that students can easily see how many balls are in a
container.
Activity:
1. Set out 16 small cups with green ‘Algae’ mark; add one ball to each.
2. Set out 8 small ‘Insect’ cups, 4 ‘Crayfish’ cups, 2 ‘Bass’ cups, and 1 ‘Loon’ cup, all empty, and the loons.
3. Explain that each of the ‘Algae’ cups have been contaminated by pesticide runoff from lawns and farms.
Each ball represents one unit of pesticide that the algae cannot utilize or excrete, and thus has built up or
‘bioaccumulated.’
4. Show the ‘Insect’ cups and explain that each insect requires 2 of the ‘Algae’ cups to meet its energy needs.
(You may need to remind students that as one moves up the trophic pyramid, only 10% of energy is
transferred, so the larger the consumer or the higher up the pyramid levels, the greater the number of
organisms required from lower on the pyramid.) Pour the balls from 2 ‘Algae’ cups into one ‘Insect’ cup;
repeat for all 8 ‘Insects.’ Have students note the number of units of toxin in each insect. (2 in each)
5. Each of the 4 ‘Crayfish’ require consumption of 2 insects to meet their energy needs, so pour the contents
of 2 ‘Insect’ cups into each of the 4 ‘Crayfish’ cups. Have students note the number of units of toxin now
in each crayfish. (4)
6. The ‘Bass’ need 2 ‘Crayfish’ to provide enough energy, so pour 2 of the ‘Crayfish’ cups into each of the
‘Bass’ cups. Ask students how many units of toxin are now in the ‘Bass.’ (8)
7. The loon is the apex predator in this scenario. (Adult loons are sometimes taken by eagles but generally
have no other predators.) The loon will require 2 ‘Bass’ to provide its energy, so pour the balls from the 2
‘Bass’ cups into the ‘Loon’ cup. Have students note the number of units of toxin in the apex predator. (16)
8. Discuss with students what will happen next. If the loon’s threshold for toxicity, i.e. the amount of toxin
needed to make it ill, is 20 units, the loon will not have problems at this time. If the threshold is 10,
however, the loon may show signs of poisoning. If a fatal amount is 15 units, the loon would die.
9. Conclude with a discussion of how it is important to keep toxic substances out of our air, water, and soil,
even if we have not yet seen a problem. (It may be building up unnoticed.) What can students do to help
reduce toxins?
- Dispose of hazardous waste properly
- Buy ‘green’ products that are not made with hazardous chemicals and have no hazardous byproducts.
- Buy ‘less stuff’ so there is less manufacturing which may generate harmful waste.
- Decrease use of fossil fuels.
- Use fewer pesticides, herbicides, and cleaning chemicals around the home.
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Bioaccumulation in a Food Chain
Definitions and Background Information:
Bioaccumulation is an increased concentration of a substance, especially hazardous substances, in the
tissues of an individual organism due to uptake from food, water, and/or sediments.
Biomagnification (also called bioamplification or biological magnification) is an increased concentration
of a substance, especially hazardous substances, occurring within a food chain, as individuals consume
organisms up the trophic levels.
Bioaccumulation occurs when more of a substance is taken in (through ingestion, inhalation, or
absorption) than is lost through excretion or degradation of a toxic substance. Many substances that
bioaccumulate are lipid-soluble, thus accumulate and are stored in fatty tissue. When fat is metabolized
for energy, the toxic substances are released and cause acute poisoning. Mercury (both natural and that
from industrial pollution) and DDT are two examples of lipid-soluble toxic substances. Other toxic
substances may be chemically similar to compounds the body uses, and may be integrated, such as
Strontium-90 (from atomic fallout). Strontium-90 is very similar to calcium chemically and thus becomes
absorbed into bone, where it causes long-term damage and is not easily removed.
Apex predators such as swordfish, sharks, osprey, and eagles have much higher concentrations of mercury
in their tissues than they would have from direct exposure alone, because of bioaccumulation. As an
example, EPA studies (1997) indicate that herring (lower on the trophic pyramid) contains mercury at
approximately 0.01 ppm; shark, an apex predator, contains mercury at greater than 1 ppm, or 100 times as
much. This is why young children and pregnant & nursing women have
been advised to avoid eating apex predator fish: shark, swordfish, king
mackerel, and tilefish; albacore (white) tuna has less mercury than these
fish but should be limited to once per week for these persons. Other fish
that are lower in the trophic pyramid have less mercury and are safer to eat,
per the EPA.
Bioaccumulation may be used as a defense against predators- some animals consume toxic plants or
animals, and then accumulate enough of the toxin to harm a larger predator, which will then avoid it.
Some caterpillars do this, as does the tobacco hornworm, which consumes tobacco plants. Nicotine from
the tobacco plants accumulates within its body to toxic levels, causing potential predators to avoid the
hornworm.
Other naturally-produced toxins can bioaccumulate, such as the ‘red tide’ marine algal blooms that are
absorbed by filter-feeders such as clams. The clams then become toxic and cannot be eaten by humans.
Compounds not normally considered toxic can bioaccumulate to toxic levels. The classic example is
shown by the advice to arctic explorers: “Don’t eat polar bear liver.” The native people had known this
for centuries. Polar bears are pure carnivores that only eat other carnivores. The Arctic’s cold water fish
are rich in Vitamin A (hence ‘cod liver oil’ as a remedy), and are eaten in great quantities by seals. The
Vitamin A concentrates in the tissues of the seals, and the food chain continues with polar bears eating
numerous seals, thus consuming even larger amounts of Vitamin A; this then concentrates in the livers of
the polar bears. Early arctic explorers who ate polar bear liver became very ill from ‘hypervitaminosis A,’
or excessive Vitamin A intake, and some died from its toxicity. Seal and husky dog liver have caused the
same illness and death. Most other animals, however, have much lower amounts of Vitamin A in their
livers and can be eaten without fear of excessive vitamin A intake.
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