3. Bioaccumulation or biomagnification occurs when toxins (usually hydrophobic o

Question

3. Bioaccumulation or biomagnification occurs when toxins (usually hydrophobic or lipophilic) accumulate within the body tissues of the organisms that ingest containing the chemical. One famous bioaccumulating chemical is DDT which was described in the late 1960s by Rachel Carson as the explanation behind the disappearance of many species of fish-eating birds, including osprey and bald eagles. The figure below shows how DDT concentrations increase with trophic level in an aquatic ecosystem, a process known as biomagnification. DDT concentration (parts per million) osprey 25 ppm Large fish 2 ppm (8 pts!!!) Given what you know about food chains and energy transfer, explain the reason that biomagnification of DDT happens in the aquatic food chain shown at right. Small fishh o.5 ppm (4 pts.) Describe two scenarios where a food chain, when compared to the one here, could have less severe biomagnification or none at all, even though the contaminant is still present (you can choose any contaminant you want.) Zooplank 0.04 ppm Water 0.000003 ppm

Explanation / Answer

A.

Biomagnification = Biological concentration = Biological amplification

It refers to the accumulation of harmful chemicals in higher organisms through a food chain.

Examples:

Minimata disease in Japan (1952)

Mercury disposed in water ----> Phytoplankton ----> Zooplankton ----> Small fish ----> Large fish ----> Humans

DDT accumulation:

DDT disposed in water ----> Phytoplankton ----> Zooplankton ----> Small fish ----> Large fish ----> Osprey

In a food chain, only 10% of the energy is transferred from one trophic level to the other. However, most of the food chain pyramids are straight i.e, the number of organisms at lower trophic levels is less than the number of organisms at the higher trophic levels.

So, a higher order organism consumes more number of lower order organisms. For example, a fish eats thousands of planktons in its lifespan. An osprey eats hundreds of such fishes. So, if lower order organisms contain a harmful metabolite which they can not neutralize, it will be transferred to the higher order organism. Since higher order organism eats more number of such lower order organisms, it will accumulate the non-metabolizable harmful chemical as well. This refers to bioaccumulation.

B.

i. In a parasitic food chain, a large number of parasites infect a single host organism. If the host contains a non-metabolizable harmful substance, all the parasites will acquire a fraction of the chemical. Hence, the concentration decreases.

ii. Assume that a plant is growing in a saline soil. It will accumulate soil in its tissues. When birds and insects ingest the plant tissue, the concentration in each of those organisms will be diluted.

Related Questions

Navigate

• Browse (All)
• Browse 3
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.