Biomagnification

Introduction

Biomagnification is the accumulation of toxic substances in living organisms at higher levels compared to non-living environments..

These toxic substances are usually heavy metals like mercury and arsenic and pesticides like DDT.

The biomagnification process affects the entire food chain. The process begins when organisms ingest non-essential or toxic substances from their environment. Every time a lower-level organism carrying such substances is eaten by a higher-level organism, the unwanted substances are transferred along the food chain. At the highest level, we see the highest accumulation of these substances. 

Some minerals are essential for the growth of living organisms. However, the overaccumulation of non-toxic and non-essential substances in living organisms affects the entire food cycle.

Meaning of Biomagnification

Biomagnification, bioamplification, or biological magnification, is the accumulation of toxic substances by organisms at different levels of the food chain.

This occurs when agricultural waste, domestic waste, and industrial waste are dumped in the natural environment, including water sources such as rivers, lakes, oceans, sewers, and streams.

The bottom feeders in the food chain, such as zooplankton and algae, consume the toxic substances in the ocean. These substances are gradually carried to the top of the food chain (trophic level organisms).

The accumulation of these contaminants increases from level to level.

As humans are high up on the food chain, the accumulation of these contaminants is high.

Examples of Biomagnification

In many areas, especially ones with stagnant pools of water, pesticides like DDT are sprayed to curb the growth of mosquitoes. However, the pesticide does not just affect the mosquitoes. Trace quantities of the pesticide remain in the environment and mix with the water body.

Low-level organisms, especially aquatic organisms, end up ingesting the DDT from their environment. The DDT gets deposited in the fatty tissues of the organisms, where it takes many years to digest. As these low-level organisms are consumed by higher-level organisms, the concentration of DDT increases as it moves up the food chain.

Another example of biomagnification is the presence of mercury in fish. Larger fish such as tuna, shark, orange, and mackerel contain a higher percentage of mercury than small fishes. This mercury stays in the fish as it does not get digested or takes many years to get digested. Birds like eagles consume mercury-contaminated fish. Thus, we would find a trace amount of mercury in the eagle. If the mercury concentration in fish is 0.002 ppm, then an organism like the eagle would have 2 ppm of mercury.

Causes of Biomagnification

There are many causes of the accumulation of toxic substances in living organisms. Some causes are the products used in agriculture, industrial activities, organic contaminants, and deep-sea mining.

Products Used in Agriculture

Fertilizers and pesticides have a high amount of toxic substances and contribute significantly to biomagnification. Farmers use many inorganic fertilizers, herbicides, pesticides to boost the growth of their crops. 

When it rains, these fertilizers and pesticides are carried with the runoff from the fields, which flows into rivers and oceans.

As a result, the organisms in the rivers and the ocean consume these toxic materials,  affecting the entire food chain.

Industrial Activities

Many industries release their waste into the ocean, leading to biomagnification. For instance,  petroleum refineries release their waste containing many harmful materials such as arsenic, cobalt, nickel, mercury, etc.

Organic contaminants

When an excess of organic substances like carbon, nitrogen, and phosphorus are present in the ecosystem due to industrial use or proliferation of some kinds of plants, it can result in biomagnification.

Some materials used in paramedical and personal care products, such as manures and biosolids, also contribute to biomagnification.

Mining in the ocean

When mining the ocean for coal, oil, or metals like zinc, gold, silver, aluminum, other substances like selenium and sulfide are also released into the environment. These materials are then deposited in coastal regions, which impacts marine ecosystems.

Effects of Biomagnification

Biomagnification has far-reaching impacts on the entire food chain.

Impact on human health

Biomagnification can cause numerous health complications and diseases in human beings, such as cancer, heart disease, brain damage, congenital disabilities, respiratory ailments and so on. 

Effects on reproductive systems of marine and coastal organisms

The toxic materials accumulated in the organs of coastal and marine animals affect their reproduction. For example, the eggs produced by seabirds with toxins in their system are weak and break easily, unable to survive even the incubation period.

Destruction of coral reefs

Coral reefs form the base of some of the richest marine ecosystems, supporting many aquatic species. However, in the process of gold mining, cyanide  is used for leaching. It is one of the reasons for the destruction of coral reefs. The life cycle of aquatic life gets affected.

Disruption of the food chain

The release of toxic chemicals into water bodies affects small organisms, which is the primary cause of disturbance of the food chain.

Smaller organisms are contaminated by toxic substances. On consumption of these fishes, higher trophic level organisms also get affected.

Bioaccumulation and Biomagnification

Bioaccumulation and biomagnification are two different processes caused by toxic substances. 

In the bioaccumulation process, the toxic substance enters the organisms by direct accumulation in the tissues. The toxic substance builds up in the organisms in this process.

The bioaccumulation process occurs in two ways.

In the first method, more chemicals, pesticides, and toxic materials enter the body than the time required for the breakdown. That is, consumption is more than excretion.

In the second method, the chemical cannot be excreted and accumulates until the organisms die.

Biomagnification is the process of accumulation of contaminated toxic substances in living organisms at higher levels compared to the accumulation of a substance in non-living organisms—the toxic materials in the biomagnification process transfer from one trophic level to another.

Biomagnification represents the percentage of toxic materials from one organism level to another level, but bioaccumulation represents the accumulation of toxic substances in one single organism.

For example, the DDT percentage in one single fish represents bioaccumulation. 

The increase in the percentage of DDT from one level to another level indicates biomagnification.

Another example is the consumption of mercury by living organisms. Small fish, zooplankton, and algae consume some traces of mercury, which is called bioaccumulation. The transfer of mercury from one tropic level to another is biomagnification.

Difference between Biomagnification and Bioaccumulation