Biomagnification

 Biomagnification is the process by which a compound (such as a pollutant or pesticide) increases its concentration in the tissues of organisms as it travels up the food chain. It is also known as bioamplification or biological magnification. The contaminants might be heavy metals such as mercury, arsenic, and pesticides such as polychlorinated biphenyls and DDT.

These substances are taken up by the organisms through the food they consume. When the organisms in the higher food chain feed on the organisms in the lower food chain containing these toxins, these toxins get accumulated in the higher organisms.

Thus, Biomagnification occurs when substances such as pesticides or heavy metals move up the food chain by working their way into the environment. Biomagnification can occur in almost all types of ecosystems. e. g terrestrial, aquatic.

 Pollutants in rivers or lakes are taken up by microorganisms like plankton and are eaten by aquatic organisms such as fish, which in turn are eaten by large birds, animals and humans. The substances become concentrated in tissues or internal organs as they move up the chain. As a result, organisms at the top of the food chain generally suffer greater harm from a persistent toxin or pollutant than those at lower levels.

 

The increase in concentration of a pollutant occurs in a food chain as a result of: 

1. Persistence (not broken down by environmental processes)

2. Bioenergetics in the food chain (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 and fats which carries the pollutant, which then accumulates in the fats of the predator)

3. Low rate of internal degradation/excretion of the substance often due to water-insolubility 

In order for biomagnification to occur, the pollutant must be persistent:

1.long-lived

2.mobile

3.soluble in fats

4.biologically active

 Persistent pollutants 

• If a pollutant is short-lived, it will be broken down before it can become dangerous.

• If it is not mobile, it will stay in one place and is unlikely to be taken up by organisms.

• If the pollutant is soluble in water it will be excreted by the organism.

• Pollutants that dissolve in fats (Persistent pollutants) are retained for a long time- Lipid or fat soluble substances cannot be diluted, broken down, or excreted in urine.

• They accumulate in fatty tissues of an organism if the organism lacks enzymes to degrade them.

 Eg., DDT :dichloro diphenyl trichloroethane.- chlorinated hydrocarbon, used as pesticide

•DDT has a half-life: 15 years, which means if you use 100 kg of DDT, it will break down as follows:

Year	Amount Remaining
0	100 kg
15	50 kg
30	25 kg
45	12.5 kg
60	6.25 kg
75	3.13 kg
90	1.56 kg
105	0.78 kg
120	0.39g

 

 

Causes of Biomagnification

The major causes of biomagnification:

1.     Agriculture

The agricultural pesticides, insecticides, fertilizers and fungicides are very toxic and are released into the soil, rivers, lakes, and seas. These substances contain small amounts of heavy metals such as mercury, arsenic, copper, lead and cadmium. These cause health issues in aquatic organisms and humans.

2.     Organic Contaminants

Manures and industrial products like  pharmaceuticals and personal care products contain contaminants. These substances have an adverse impact on the health of humans, animals, and wildlife.

3.     Industrial Activities

The industries and factories release toxic substances that are released into the soil, lakes, oceans, and rivers. The gaseous emissions pollute the environment which enters into the food chain leading to biomagnification.

4.     Mining Activities in the Ocean

Mining activities are carried out in the deep sea to extract metal like zinc, aluminium, cobalt, silver and gold. The mining process generates a large amount of selenium and sulphide, which deposits in water and destroys the oceans and coastal regions. These toxic substances are absorbed by the aquatic organisms and they move higher in the food chain to other organisms.

Effects of Biomagnification

Ø  Impact on Human Health- Biomagnification makes humans more prone to cancer, kidney problems, liver failure, birth defects, respiratory disorders, and heart diseases.

Ø  Effects on Reproduction and Development of Marine Creatures- The toxic chemicals accumulate in the important organs of aquatic organisms that affect their reproduction and development processes.

Ø  For eg., the shells of the eggs of the sea-birds are very thin that might get crushed by the birds themselves during incubation. The toxic chemicals, mercury and selenium destroy the reproductive organs of aquatic creatures.

Ø  Destruction of Coral Reefs- Cyanide that is used in leaching gold and fishing is the main cause of the destruction of coral reefs. Coral reefs are the dwelling and feeding grounds for many sea creatures. Their destruction affects the lives of many aquatic animals.

Ø  Disruption of Food Chain- The chemicals and toxins which are released into the water bodies disrupt the food chain. The small organisms absorb the toxins which are eaten up by larger animals. These toxins, thus, get accumulated in the higher level of organisms.