BY DIVYA RAJPUT

BIOMAGNIFICATIONEXAMPLE

CAUSES OF BIOMAGNIFICATIONPROCESS OF BIOMAGNIFICATION

EXAMPLEBIOCONCENTRATION

PROCESS OF BIOCONCENTRATIONBIOACCUMULATION

SUBSTANCES THAT BIOMAGNIFYTEN PER CENT LAW

FOOD CHAIN EXAMPLE

The increase in the concentration of harmful chemical substances like pesticides in the body of the living organisms at each tropic level of a food chain is called bio magnification.Biomagnification, also knownas bioamplification or biological magnification, occurs when the concentration of a substance, such as DDT or mercury, in an organism exceeds the background concentration of the

substance in its diet.

Biological magnification often refers to the process whereby certain substances such as pesticides or heavy metals move up the food chain, work their way into rivers or lakes, and are eaten by aquatic organisms such as fish, which in turn are eaten by large birds, animals or humans. The substances become concentrated in tissues or internal organs as they move up the chain. Bioaccumulants are substances that increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolized or excreted.

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EXAMPLEThe following is an example showing how bio-

magnification takes place in nature: An anchovy eats zoo-plankton that have tiny amounts of mercury that the zoo-plankton has picked up from the water throughout the anchovies lifespan. A tuna eats many of these anchovies over its life, accumulating the mercury in each of those anchovies into its body. If the mercury stunts the growth of the anchovies, that tuna is required to eat more little fish to stay alive. Because there are more little fish being eaten, the mercury content is magnified.

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CAUSES OF BIOMAGNIFICATION¶ Persistence – where the substance can't

be broken down by environmentalprocesses

¶ Food chain energetics – where the substance concentration increases progressively as it moves up a food chain

¶ Low or non-existent rate of internal degradation or excretion of the substance – often due to water-insolubility

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PROCESS OF BIOMAGNIFICATION

‡ Bioaccumulation occurs within a trophic level, and is the increase in concentration of a substance in certain tissues of organisms' bodies due to absorption from food and the environment.

‡ Bioconcentration is defined as

occurring when uptake from the water

is greater than excretion.Thus, bioconcentration and bioaccumulation occur within an organism, and

biomagnification occurs across trophic (food chain) levels.

Although sometimes used interchangeably with "bioaccumulation", an important

distinction is drawn between the two, and with bioconcentration.

Biodilution is also a process that occurs to all trophic levels in an aquatic environment; it is the opposite of biomagnification, thus a pollutant gets smaller in concentration as it progresses up a food web.

Lipid, (lipophilic) or fat soluble substances cannot be diluted, broken down, or excreted in urine, a water-based medium, and so accumulate in fatty tissues of an organism if the organism lacks enzymes to degrade them. When eaten by another organism, fats are absorbed in the gut, carrying the substance, which then accumulates in the fats of the predator. Since at each level of the food chain there is a lot of energy loss, a predator must consume many prey, including all of their lipophilic substances.

DDT is thought to biomagnify and biomagnification is one of the most significant reasons it was deemed harmful to the environment by the EPA and other organizations. DDT is stored in the fat of animals and takes many years to break down, and as the fat is consumed by predators, the amounts of DDT biomagnify. DDT is now a banned substance in many

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EXAMPLE For example, though mercury is only present in small amounts in seawater, it

is absorbed by algae (generally asmethyl mercury). It is efficiently absorbed, but only very slowly excreted by organisms. Bioaccumulation and

bioconcentration result in build up in the adipose tissue of successive trophic levels : zooplankton, small nekton, larger fish, etc. Anything which eats

these fish also consumes the higher level

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of mercury the fish have accumulated. This process explains why

predatory fish such as swordfish and sharks or birds like osprey and eagles have higher concentrations of mercury in their tissue than could be accounted for by direct exposure alone. For example, herring contains mercury at approximately 0.01 parts per million (ppm) and shark contains mercury at greater than 1 ppm.

BIOCONCENTRATIONAccumulation of harmful chemicals such as

pesticides in the living organisms like plants,

animals and humans unknowingly, through the

food chain, is called Bioconcentration. It is the

accumulation of a chemical in or on an organism

when the source of chemical is solely water.

Bioconcentration is a term that was created for

use in the field of aquatic toxicology.

Bioconcentration can also be defined as the

process by which a chemical concentration in an

aquatic organism exceeds that in water as a result

of exposure to a waterborne chemical.INDEX

PROCESS OF BIOCONCENTRATION¡ Pesticides are poisonous chemical

substances which are sprayed over crop plants to protect them from pests (harmful small animals) and diseases.

¡ These chemicals pesticides mix up with soil and water.

¡ From soil and water, these pesticides are absorbed by the growing plants alongwith water and minerals.

¡ When herbivorous animals eat plant food, then these poisonous chemical pesticides go into their bodies through the food chain.

¡ And when the carnivorous animals eat herbivores, then the pesticides get transferred to their bodies.

¡ Man being an omnivore, eats plant food as well as herbivores.

¡ So, the pesticides present in plant food and herbivores also get transferred to the man’s body through food.

¡ Thus, pesticides enter the food chain at the producer level (plant level).

¡ And in the process of transfer of food through food chains these harmful chemicals get concentrated at each tropic level.

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BIOACCUMULATION§ An increase in the

concentration of a

pollutant in a biological

organism compared to

its concentration in

the environment.

§ Collecting of substances

in an organism or part

of it.§ It is how pollutants

enter a food chain.

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SUBSTANCES THAT BIOMAGNIFYThere are two main groups of substances that biomagnify.

Both are lipophilic and not easily degraded. Novel organic substances are not easily degraded because organisms lack previous exposure and have thus not evolved specific detoxification and excretion mechanisms, as there has been no selection pressure from them. These substances are consequently known as "persistent organic pollutants" or POPs. Metals are not degradable because they are elements.

Organisms, particularly those subject to naturally high levels of exposure to metals, have mechanisms to sequester and excrete metals. Problems arise when organisms are exposed to higher concentrations than usual, which they cannot excrete rapidly enough to prevent damage. Some persistent heavy metals are especially harmful to the organism's reproductive system.

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The Ten percent law for the transfer

of energy from one trophic level to the next was introduced by Raymond Lindeman(1942). According to this law, during the transfer of energy from organic food from one trophic level to the next, only about ten percent of the energy from organic matter is stored as flesh. The remaining is lost during transfer, broken down in respiration, or lost to incomplete digestion by higher trophic levels.

During the transfer of energy through successive tropic levels in an ecosystem, there is a loss of energy all along the path. No transfer of energy is 100 per cent. The studies of transfer of energy in different food chains in a large number of ecosystems has revealed a uniform pattern of transfer of energy, which is given by 10 per cent law. The 10 per cent law is one of the most useful generalisations about the magnitude of loss of energy in food chains. According to ten per cent law, only 10% of energy entering a particular tropic level of organisms is available for transfer to the next higher tropic level. All the energy transfers in a food chains follow the 10% law which in simple terms means that the energy available at each successive tropic level is 10% of the previous level. Thus, there is a progressive decline (gradual reduction) in the amount of energy available as we go from producer level to the higher tropic levels of organisms.

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FOOD CHAINPlants absorb 1 percent sun energy for primary production and can store only 10% of the utilized energy as net production available for the herbivores. When the plants are consumed by animal, about 10% of the energy in the food is fixed into animal flesh which is available for next trophic level (carnivores or omnivores). When a carnivore or an omnivore consumes that animal, only about 10% of energy is fixed in its flesh for the higher level.

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EXAMPLESuppose 1000 joules of light energy emitted by the sun falls on the plants. Plants convert only 1% of the light energy falling on them into chemical energy of food. So energy which will be available in plant matter as food will be only 1% of 1000 joules, which comes to 10 joules. The remaining 1000– 10 = 990 joules of light energy or solar energy which is not utilized by plants is reflected back into the enviroment. The 10% law will not apply at this stage. It will apply only in the transfer of energy in food chain.

Now, let us apply 10% law to the food chain:

Plants -> Herbivores -> Carnivores.

The plants or first tropic level has 10 joules of energy in it. Now, according to 10% of joules of energy (which is 1 joule) will be available for transfer at the next tropic level, so that the herbivore (deer) will have only 1 joule of energy stored as food at the secod tropic level. Applying the ten percent law again we find that 10% of the remaining 1 joule (which is 0.1 joule) will be transferred to third tropic level of carnivore (lion). So, the energy available in the lion as food will be only 0. 1 joule. We will now solve some problems based on ten per cent law.

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