Table of Contents
- What is Biomagnification?
- Biomagnification process
- Biomagnification factor (BMF)
- Examples of biomagnification
- Food web accumulation
- Biological magnification as a result of soil pollution
- Biomagnification of chlorinated hydrocarbons
- DDT Biological magnification
- Inorganic compounds biomagnifying in organisms
- The Biomagnification of pesticides in the food chain
- Pollution in water bodies resulting in biological magnification
- Biomagnification diagram
- Causes of biomagnification
- Biomagnification effects
- Biomagnification and Bioaccumulation
- How to Prevent Biological magnification
What is Biomagnification?
Biomagnification is the progressive concentration of a contaminant in the tissues of organisms at higher trophic levels. It is used to describe the trophic enhancement of toxins within food webs. Another name for biomagnification is biological magnification or bioamplification. Biological magnification is, however, the concentration of a specific substance (such as contaminants, pollutants, or toxins) being magnified within an organism at each increasing trophic level in a food chain. It is basically the buildup of toxins or contaminants in the food chain.
In the environment, organisms are exposed to several chemicals. Even though some of these chemicals exist in the environment at low concentrations, they may be selectively accumulated by organisms to much higher concentrations. This can cause toxicity. Hence, this accumulation up the trophic levels is referred to as biomagnification and the accumulation within the organism is bioaccumulation.
Some of these chemicals that can be biomagnified are substances such as selenium, mercury, nickel, organic compounds, and chlorinated hydrocarbons (or organochlorines). These substances are extremely insoluble in water but are very soluble in organic solvents as well as animal fats and plant oils (known as lipids). However, in high enough concentrations, these substances can cause serious health issues for marine fauna and terrestrial animals as well as humans.
Several of the chlorinated hydrocarbons are very persistent in the environment. This is because the metabolism of organisms cannot easily break them down into simpler compounds. Also, they cannot be easily broken down by ultraviolet radiation or other inorganic processes. Typical examples of bioaccumulating chlorinated hydrocarbons are a class of industrial chemicals known as PCBs as well as the insecticides DDT and dieldrin.
As the trophic level increases across a food chain, the number of contaminant accumulation increases. These contaminants or toxins build up in the fat and tissue of the organisms. In the process of biomagnification, predators accumulate more toxins than their prey. However, biological magnification is a process that involves certain contaminants such as heavy metals or pesticides finding their way into water bodies and then move up the food chain in progressively greater concentrations.
In the aquatic ecosystem, for instance, these substances are incorporated into the diet of aquatic organisms like zooplankton, which are in turn eaten probably by fish, which can be preyed on by bigger fish, large birds, animals, or humans. Due to the interconnectivity of the food chain, these contaminants become increasingly concentrated in the tissues or internal organs of organisms as they move up the food chain. As organisms take in contaminated air, water, or food, these substances that increase in concentration as they are slowly metabolized or excreted are called bioaccumulants.
Biological magnification can occur due to the persistence of these substances, food chain energetics, or a low rate of degradation of the substance. A contaminant happens to be persistent when it cannot be broken down by environmental processes. Food chain energetics involves the increase in the concentration of the contaminant as it progressively moves up a food chain. Also, due to the contaminant being insoluble in water, there can be a low or non-existent rate of internal degradation or excretion of the contaminant.
The process of biomagnification is sometimes interchangeably used with bioaccumulation. These two processes are however related but there is a distinct difference between them and bioconcentration as well. The process of bioaccumulation specifically occurs within a particular trophic level. It is the concentration increase of the contaminant or substance in certain tissues of the organisms.
Bioaccumulation is a result of the absorption of the substance from food or the environment. Moreso, bioconcentration also called biological concentration is the bioaccumulation process whereby the concentration of a substance in an organism becomes higher than the concentration of the substance in the environment around the organism.
Therefore, bioaccumulation and bioconcentration is a phenomenon that occurs within the organism, while biomagnification happens across trophic levels (food chain). However, the opposite of biological magnification occurs to all trophic levels in an ecosystem. This process is called biodilution and occurs when a pollutant gets smaller in concentration as it progressively moves up a food web.
How does biomagnification work?
Biomagnification is said to occur when the concentration of a contaminant or pollutant increases from one link in the food chain to another. This works by a polluted organism contaminating the next consumer that contaminates the next and it continues in that sequence as each trophic level consumes another. Hence, resulting in the apex predator containing the highest level of concentration of the pollutant. Therefore, for biomagnification to occur in the ecosystem, a contaminant must be mobile, long-lived, fat-soluble, and biologically active.
However, biomagnification in an aquatic food chain usually leads to biomagnification in terrestrial food chains, especially in the case of bird and wildlife populations that consume fish. Consider this example that illustrates the results of biomagnification. The concentrations of a certain insecticide in various trophic levels are determined as follows:
Water, 0.1 ng/L —> Phytoplankton ,100 ng/g lipid —> Zooplankton , 200 ng/g lipid —> Fish, 600 ng/g lipid —> Terns, 800 ng/g lipid.
As seen above, the substance was magnified and multiplied in the zooplankton by a factor of 2, the fish by a greater factor, and the terns as well. The insecticides, however, end up being biomagnified at a higher concentration in the terns such as skimmers and gulls which are the top predators.
Biological magnification can occur in both aquatic and terrestrial ecosystems. Though, it is generally used in aquatic situations. Usually, bio-amplification occurs in the higher trophic levels of the food chain or food web. However, exposure to chemicals or toxins usually happens at these trophic levels through food consumption rather than water uptake.
Examples of compounds that biomagnify
- Organic compounds
- DDT (Dichlorodiphenyltrichloroethane, or Dichloro Diphenyl Trichloroethane)
- β-Methylamino-L-alanine (BMAA)
- HCB (Hexachlorobenzene)
- Heavy metals (such as mercury, lead, chromium)
- PCBs (Polychlorinated Biphenyls)
- Monomethyl Mercury
- Chlorine waste products (such as furans and dioxins)
The 2 main groups of substances that biomagnify are organic substances and metals. These two are soluble in fats (lipophilic) and do not easily degrade. There are novel organic chemicals that are not easily degraded. Such chemicals are Hexachlorobenzene (HCB), Toxaphene, DDT (dichlorodiphenyltrichloroethane), PCBs (polychlorinated biphenyls), and Monomethylmercury. This is because organisms were not exposed previously to such substances and have not evolved specific detoxification and excretion mechanisms for them. These substances are consequently called persistent organic pollutants or POPs.
Metals, on the other hand, are not degradable too. This is because they are elements. However, those organisms that are subject to naturally high levels of exposure to metals, have the mechanisms to take and excrete them. The main issue arises when the organisms are exposed to higher concentrations of these metals than usual. In higher concentrations, these metals cannot be excreted rapidly enough to avert damage. Moreso, some persistent heavy metals are toxic and harmful to the reproductive system of organisms.
POPs and metals have high lipid affinities. Hence, instead of them concentrating in an aqueous environment like the cytosol, they will rather concentrate in tissues with high lipid content.
The process of biomagnification is sometimes interchangeably used with bioaccumulation. These two processes are, however, related but there is a distinct difference between them and bioconcentration as well.
The process of bioaccumulation specifically occurs within a particular trophic level. It is the concentration increase of the contaminant or substance in certain tissues of the organisms. Bioaccumulation is a result of the absorption of the substance from food or the environment. Bioconcentration occurs also and is the bioaccumulation process whereby the concentration of a substance in an organism becomes higher than the concentration of the substance in the environment around the organism.
Therefore, bioaccumulation and bioconcentration is a phenomenon that occurs within the organism, while biomagnification happens across trophic levels (food chain). The process of biomagnification starts with fat-soluble substances. These lipophilic substances cannot be broken down, diluted, or excreted by the organism.
Hence, if the organism lacks enzymes to degrade these substances, they bioaccumulate in the fatty tissues of the organism. Once, another organism feeds on this organism, fats are absorbed in the gut together with the substances. These substances then accumulate in the fats of this predator as well. At each trophic level, a predator has to feed on many preys as well as all of the prey’s lipophilic substances.
Let’s take mercury for instance. Mercury is absorbed by algae as methylmercury even though it is only present in small amounts in seawater. Methylmercury happens to be one of the most toxic mercury variants. This substance is absorbed efficiently but is only slowly excreted by organisms. As a result of bioaccumulation and bioconcentration, there is a buildup of methylmercury in the adipose tissue of organisms at successive trophic levels.
Zooplankton —> Small nekton —> Larger fish
However, organisms that consume these fishes also consume the higher level of mercury that has been built up in the fish. Thus, this process of biomagnification is the reason why predatory fishes and birds have higher concentrations of mercury in their tissue. Examples of such predatory fishes are swordfish and sharks and birds like osprey and eagles Herring, for instance, contains mercury at about 0.01 parts per million (ppm) and shark contains mercury at a value greater than 1 ppm.
A chemical compound, Dichlorodiphenyltrichloroethane (DDT) is said to biomagnify in organisms. Thus, biomagnification is one of the most significant reasons EPA (Environmental Protection Agency) and other organizations considered DDT harmful to the environment. This chemical compound DDT is bioaccumulated and stored in the fat of animals. The compound takes many years to break down. Thereby the amount of DDT biomagnifies as the fat is consumed by predators. As a result, DDT is now a banned substance in several parts of the world.
The process of biomagnification involves the following:
- Bioavailability of the substance
Bioavailability of the substance
The bioavailability of a substance is its availability at a given time to cross the cellular membrane of an organism from the organism’s habitat. Take acid and alkaline mine waters for example. They usually contain dissolved metals and metal-oxide particulates at very high concentrations.
Also, wetlands acidification can increase the concentrations of metals. Due to such situations, the potential bioavailability of metals in freshwater biota and aquatic plants is increased. Thereby influencing the uptake of metals in both rooted and submerged plants.
The uptake of a substance or contaminant is its entrance into an organism. A pollutant or contaminant can be taken up by the organism through inhaling, swallowing, or absorbing it through the skin. For the process of biomagnification to occur, there is an uptake of the substance by an organism. These chemicals or substances are taken by the organism without regard to their subsequent storage, metabolism, and excretion.
The biological concentration of a pollutant or contaminant is the accumulation process by which the concentration of the pollutant in an organism becomes higher than its concentration in the surrounding environment of the organism. Usually, the term bioconcentration refers to substances that are foreign to the organism.
In the field of aquatic toxicology, bioconcentration is defined as the process by which a chemical concentration in an aquatic organism as a result of exposure to waterborne chemicals exceeds that in water.
The bioconcentration for fish and other aquatic animals after uptake of a chemical either through the gills or the skin is mostly the most significant process of bioaccumulation that may later lead to a biomagnification process.
Furthermore, there are several parameters used to assess and measure bioaccumulation and bioconcentration. They are:
- Octanol-water partition coefficients (KOW)
- Biological concentration factors (BCF)
- Bioaccumulation factors (BAF)
- Biota-sediment accumulation factor (BSAF)
Bioconcentration factor (BCF)
The bioconcentration factor (BCF) is expressed and calculated as the ratio of the concentration of a substance within an organism to the concentration of the substance in the organism’s environment. BCF is simply a compute of the extent of chemical sharing between an organism and the surrounding environment it inhabits.
However, in surface water, the bioconcentration factor is the ratio of the chemical concentration in the organism to the chemical concentration in water. Hence, the bioconcentration factor is usually calculated in units of a liter per kilogram (the ratio of mg of chemical per kg of the organism to mg of chemical per liter of water).
The biological concentration factor (BCF) can be a prediction of a partitioning model that is based on the idea that chemical equilibrium exists between the aquatic environment in which the organism inhabits and the organism itself. A BCF greater than 1 will indicate that a chemical is hydrophobic or lipophilic. Hence, it serves as an indicator for the likelihood of a chemical to bioaccumulate and biomagnify.
This is the gradual accumulation of substances or chemicals in an organism over a period of time. Bioaccumulation happens when the organism egests substances or contaminants at a faster rate than the rate at which they can eliminate the substance. Substances like heavy metals enter the food chain and accumulate in the tissues of aquatic organisms. They are taken up from sources like food, water, and particles of suspended sediment.
Bioaccumulation occurs because these substances cannot be broken down for the organism to use. Even substances that are harmful to health can accumulate in the living tissues of organisms. As these substances bioaccumulate in organisms and the organisms are eaten at another trophic level and the sequence continues, biomagnification occurs.
Bioaccumulation Factor (BAF)
The Bioaccumulation factor (BAF) is the propensity of a chemical to be at a higher concentration in the organism than in the surrounding environment of the organism. Bioaccumulation factor (BAF) is expressed by dividing the chemical concentration in the organism by the chemical concentration in the habitat of the organism be it soil, water, or sediment.
However, BCF and bioaccumulation factors are similar. Both show that the organism with the chemical in its environment is at a steady state. Thus, the bioaccumulation of a chemical is often represented by BAF when assessing bioaccumulation. The bioaccumulation factor BAFs involves uptake of the substance from all exposure routes. Whereas, bioconcentration factor (BCF) expresses only the exposure from the abiotic environment. However, substances with a BAF or BCF that is higher than 5000 (wet weight basis) are said to be bioaccumulative.
Furthermore, for biomagnifying chemicals, the bioaccumulation factor is usually higher than the bioconcentration factor. The reason being that dietary exposure and uptake are included in BAF. Moreso, biomagnification factors (BMF) can express dietary enrichment as it expresses the difference in the concentration of substances between a predator and its diet.
Biomagnification factor (BMF)
The biomagnification factor (BMF) is expressed as the ratio of the chemical concentrations in the organism (CB) and the concentration of the chemical in the organism’s diet (CD).
BMF = CB/CD
It is expressed as the ratio of the observed lipid-normalized bioconcentration factor (BCF) to the Partition coefficient (Kow) which is the theoretical lipid-normalized BCF. If the BMF is equal to or less than one, then the substance or compound has not been biomagnified. But if the ratio is greater than one, then the substance is biomagnified by that factor.
For example, once a contaminant was in equilibrium in the lipids of the organism, and the contaminant’s partition coefficient (Kow) was 150,000, then its lipid normalized BCF should be 150,000. Thus, if the fish tissue concentration (normalized to lipids) were 750,000, then it would be said that the contaminant has biomagnified by a factor of five.
However, the mechanism of biological magnification is not clearly understood. Having a chemical concentration greater than its equilibrium value shows that the elimination rate is slower than chemicals that reach equilibrium. Thus, several factors regulate the uptake and elimination of a chemical from the consumption of contaminated food. These factors are specific to the organisms as well as to the chemical.
The factors specific to the chemical involves chemical properties such as:
- Solubility of the chemical
- Partition coefficient (Kow)
- Molecular weight and volume of the chemical
- The diffusion rates of the chemical between the gut, blood, and lipid pools of the organism
The factors specific to the organisms include:
- Feeding rate of the organism
- Diet preferences
- Assimilation rate into the gut,
- Rate of the chemical’s metabolism
- The rate of egestion
- Rate of organism growth
It is said that the properties of the chemical control whether biomagnification will occur. Thus, it is the transfer rate from lipid to blood that permits the chemical to attain a lipid concentration that is greater than its equilibrium value. This is why the chemicals that biomagnify have similar properties:
- It is typical of them to be organic and have molecular weights that range between 200 and 600 daltons
- They have a partition coefficient (KoWs) that is between 10,000 and 10 million
- Resistance to the organism’s metabolism
- They are non-ionic neutral compounds
- Their molecular volumes ranges within 260 and 760 cubic angstroms
- They have a cross-sectional width of fewer than 9.5 angstroms with a molecular surface area between 200 and 460 square angstroms. The molecular surface area allows these chemicals to easily pass through lipid bilayers into cells but doesn’t allow them to leave the cell easily as a result of their high lipophilicity.
However, because this disequilibrium would occur at each trophic level, it results in more and more biomagnification at each higher trophic level. Thus, as a result of exposure to chemicals that biomagnify, humans, in particular, and apex predators are vulnerable to adverse health effects. This is because they occupy a very high trophic level.
Examples of biomagnification
- Food web accumulation
- Biological magnification as a result of soil pollution
- Inorganic compounds biomagnifying in organisms
- Biological magnification of pesticides in the food chain
- DDT biological magnification
- Pollution in water bodies resulting in biomagnification
- Biomagnification of chlorinated hydrocarbons
Food web accumulation
The food-web accumulation is a typical case of biomagnification, in which substances or pollutants occur in their largest ecological concentration in predators that top the food web. An ecological food web is a complex interaction of species that are linked through their feeding relationships.
In terms of energy flow, food webs are supported by inputs of solar energy that are fixed through photosynthesis by green plants. Some of this energy is utilized by the plants and the rest are passed along to animals as plant biomass. These animals are incapable of metabolizing any other type of energy.
In the food chain, the herbivorous animals that eat plants are eaten by first-level carnivores. These first-level carnivores in turn may be eaten by higher-level carnivores with top predators at the summit of the food web. Thus, within food webs, biomagnifying substances have their highest concentrations in top predators and cause the greatest damage. The bioaccumulation of substances in the food web is an example of biological magnification.
Biological magnification as a result of soil pollution
As a result of soil contamination, the process of biomagnification may occur. An example of biomagnification occurs on some sites in semiarid regions. The soil in these regions is contaminated by selenium. In such cases, there may be hyperaccumulation of this selenium compound by specialized plant species. These plants are, however, poisonous to livestock and other large animals that graze on them. Thus, they cause a toxic reaction called blind staggers.
Milk vetches in the genus Astragalus are the most significant selenium-accumulating plants in North America. These plants are in the legume family. There are about 500 species of Astragalus in North America and 25 of these species are accumulators of selenium. These plant’s foliage can contain thousands of ppm of selenium. They contain a maximum of about 15,000 ppm which is way higher than the selenium concentration in soil.
Another such example is the serpentine soil and the vegetation that grows in it. Serpentine minerals actually contain large concentrations of iron, cobalt, nickel, and chromium. Thus, soils that are derived from this mineral can be harmful to plants. However, some plants are physiologically tolerant to these metals and grow on serpentine soils. They can bioaccumulate these metals to very large concentrations.
For instance, the normal concentration of nickel in plants is about 1–5 ppm but on sites with serpentine soils, the nickel concentration in plants is much larger. There are higher concentrations of nickel that occur in the foliage and tissues of the plants.
Plants that grow on serpentine soils have nickel concentrations of thousands of parts per million, which is actually larger than the concentration in soil. Examples of such plants are plants in the mustard family, Streptanthus polygaloides, and Sebertia acuminata.
Biomagnification of chlorinated hydrocarbons
Another biological magnification example is the biomagnification of chlorinated hydrocarbons. These chlorinated hydrocarbons are:
- The insecticides DDT, DDD, dieldrin, and methoxychlor
- Dielectric fluids (PCBs)
- Chlorinated dioxin
These chemicals have a very sparse solubility in water. Thus, they cannot be diluted into the aqueous solution that is so abundant on the earth’s surface as well as in organisms. Thus, even areas thought to be highly contaminated by chlorinated hydrocarbons have trace concentrations of these chemicals in the water.
However, chlorinated hydrocarbons have an attraction for organisms. This is because these substances are soluble in lipids and most lipids occur in biological tissues. These chemicals tend to biomagnify as chlorinated hydrocarbons are persistent in the environment. As organisms grow older, these chemicals accumulate progressively and accumulate into large concentrations especially in top predators.
From research, the top-predator animals that are older have been seen to have thousands of ppm of PCBs and DDT in their adipose tissues. Animals like the raptorial birds and fish-eating marine mammals. An organism’s biomagnification of chlorinated hydrocarbons is a well-recognized environmental problem.
DDT Biological magnification
The DDT biological magnification is a real-life example of biomagnification. DDT is moderately toxic. It has severe implications on animal and human health. A low-to-moderate exposure to DDT can cause nausea, irritation of the eyes, nose, or throat, and diarrhea. Whereas, a higher exposure can result in convulsion and tremors.
As a result of DDT being non-biodegradable, it can remain in water or soil for several years leading to the process of biomagnification. Biomagnification occurs when DDT is consumed indirectly by organisms through food. When an organism in the higher trophic level feeds on the lower organism containing DDT, the chemicals can get accumulated in the higher organism. This means the DDT travels through the food chain harming every single stratum as the concentration of DDT increases through the trophic levels of the food chain.
The biomagnification and food-web accumulation features of DDT are well known. This chemical has extremely small concentrations in water and air, with a lesser degree in soil. However, the concentrations of DDT are much higher in organisms at or close to the top of their food webs like humans and predatory birds.
A real-life example is the food-web biomagnification of DDT in the Lake Kariba of Zimbabwe. Even though DDT has been banned since the early 1970s in most industrialized countries, it is still used in many tropical countries for agriculture purposes and as insecticides. In 1982, the use of DDT for agriculture was banned in Zimbabwe. However, DDT continues to be used to control mosquitoes and tsetse flies.
The concentration of DDT in the water of Lake Kariba was not up to 0.002 ppb. In the sediment, the DDT was 0.4 ppm. It is higher in sediments than the overlying water because sediment contains a relatively large concentration of organic matter. Then the progressive biomagnification process began:
Planktonic algae contained 2.5 ppm —> A filter-feeding mussel had 10 ppm —> Two species of plant-eating fish contained 2 ppm —> A bottom-feeding fish contained 6 ppm —> The great cormorant (predatory fish and a fish-eating bird) contained 5-10 ppm —> The Nile crocodile had 34 ppm.
The Nile crocodile is the apex predator in Lake Kariba other than humans. This data for Lake Kariba shows substantial biomagnification of DDT from water to a marked food-web accumulation in herbivores to top carnivores.
Furthermore, the biomagnification of DDT caused ecotoxicological effects to birds and mammals of many species. Even organisms in habitats remote from sprayed sites were not left out. Beginning in the early 1950s, the effect on predatory birds was serious enough to cause large declines in their population.
The bald eagle, osprey, brown pelican, peregrine falcon, golden eagle, and double-crested cormorant are all examples of North American birds that suffered a decline in their population as a result of their exposure to chlorinated hydrocarbon. However, in early 1970, the use of DDT was banned and since then these birds have increased in their population.
Inorganic compounds biomagnifying in organisms
There are naturally occurring elements in the environment that occur in trace concentration. Approximately 25 of these elements are needed by plants and animals. Organisms also need micronutrients such as copper, iron, molybdenum, zinc, and rarely, nickel, aluminum, and selenium. These micronutrients can biomagnify to very high concentrations under certain ecological conditions. However, this can cause toxicity to organisms.
The Biomagnification of pesticides in the food chain
A pesticide is a toxic chemical and can find its way into the food chain. This happens when it is consumed by an animal from one trophic level to another. When a plant is treated with a pesticide and is eaten by an herbivore, the concentration of the pesticide progressively increases across trophic levels. This herbivore is eaten by a carnivore, which in turn is eaten by an animal in the higher trophic level.
The pesticide tends to become concentrated in the tissues or organs of organisms over time. Thereby when consumed, they tend to magnify across trophic levels. Hence, exhibiting biological magnification. Pesticides and certain substances tend to magnify their concentration because they are persistent substances. These substances are hardly broken down by natural environmental means. Also, they are slowly metabolized or excreted out within organisms.
The process of biomagnification occurs as the pesticide builds up in a food chain. In this process, the number of toxic chemicals increases as the trophic level increases. Hence, predators tend to have a higher concentration of the chemical than their prey.
Pollution in water bodies resulting in biological magnification
Mercury biomagnifying from trace concentrations in the environment is another example of biomagnification. Mercury biomagnification has been seen in many freshwater ecosystems. Fishes from lakes and rivers in many parts of Canada and the United States have measured mercury concentrations that exceeded 0.5 ppm.
The trace concentrations of mercury in water can lead to large contaminations of fish and other predators. However, there are fish species that are known to bioaccumulate mercury in offshore waters of North America. They are the Atlantic swordfish, halibut, Pacific blue marlin, and tunas.
These fishes can accumulate mercury from trace concentrations in seawater to higher concentrations in flesh. The concentration of mercury in water is less than 0.1 ppm. These fishes can accumulate mercury to a concentration that usually exceeds 0.5 ppm fresh weight which is the maximum acceptable concentration in fish for human consumption.
However, the contamination of fishes in the ocean by mercury is perhaps natural and is not just a recent phenomenon. Based on studies carried out, there has been no difference in the mercury contaminations of museum specimens collected before 1909 and the modern tuna.
A large fraction of 1,500 lakes that were monitored in Ontario had some fish that exceeded 0.5 ppm fresh weight (f.w) in flesh. In northern Manitoba, one remote lake had a mercury concentration that averaged 2 ppm f.w. One individual had 5 ppm in the northern pike. In the process of mercury biomagnification, larger and older fishes tend to have relatively large concentrations.
For instance, in a study of Atlantic swordfish, the average mercury concentration of animals smaller than 23 kg was 0.55 ppm. This was compared with animals weighing 23–45 kg that had 0.86 ppm and 1.1 ppm for those weighing more than 45 kg. There are also large concentrations of mercury in fish-eating marine birds and mammals that are apex predators or are close to the top of the marine food web. Also, some wildlife that consumes fish, such as mink and loons may be affected by mercury in their food.
Thus, fresh-water fish that are top predators have the largest concentrations of mercury. Moreso, the older and larger fishes are the most contaminated. However, some governments have developed fish-consumption advisories and restrictions due to the common occurrence of large mercury concentrations in fish in certain regions. For instance, about 250 lakes in Sweden have been blacklisted in terms of fish consumption. Also, about 9,400 other lakes are candidates for the same blacklisting status. About 1,200 lakes in Ontario have restrictions on fish consumption.
This is a diagram illustrating biological magnification. As seen there is a degree of chemical concentration in each trophic level of the Lakes aquatic food chain. The organic chemical happens to be persistent and the highest levels of its concentration are seen in the eggs of fish-eating birds of the herring gulls.
Causes of biomagnification
- Industrial activities
- Mining activities
- Organic contaminants
Human industrial activities contribute to the biomagnification of substances in the ecosystem. During production or industrial activities, toxic substances are released by factories and industries in the environment. These substances are discharged into the soil and water bodies. The gases emitted pollute the environment and finds their way into the food chain. Thus, leading to biomagnification.
Agricultural operations are another factor that causes biomagnification. The pesticides, fungicides, insecticides, and fertilizers used during farming operations are very toxic. They are watered down and released into the soil, lakes, rivers, and seas. These chemicals, however, contain small amounts of heavy metals like mercury, copper, arsenic, lead, and cadmium. These substances when biomagnified can cause health challenges in aquatic organisms as well as humans.
The mining activities in the Ocean have a role to play in biomagnification. Mining activities are done in the deep sea and involve extracting metals like zinc, aluminum, cobalt, gold, and silver. The process of mining, however, generates a large amount of sulfide and selenium which deposits in water and causes harm to the life in the oceans and coastal regions. These toxic substances are usually absorbed by the aquatic organisms higher in the food chain and the toxicity level is increased.
Another cause of biological magnification is organic contaminants. Biosolids and manures are processed industrially containing contaminants. Likewise pharmaceuticals and personal care products. These substances have a negative impact on the health of animals, humans, and wildlife when biomagnified across trophic levels.
- Adverse effect on human health
- Affects the reproduction and development of animals
- Extinction and population decline
- Disrupt the food chain and ecosystem
Adverse effect on human health
Biomagnification has an adverse effect on humans. It makes humans more prone to diseases such as birth defects, heart disease, cancer, kidney problems, liver failure, and respiratory disorders. In recent years, for example, a large number of humans that consume seafood regularly have been diagnosed with cancer. Mercury biomagnification happens to be the reason behind this.
Affects the reproduction and development of animals
There is an effect on the reproduction and development of aquatic organisms due to biomagnification. These aquatic creatures are affected as toxic chemicals accumulate in the important organs of the organisms. Thus, affecting their process of reproduction and development.
For instance, as a result of biomagnification of toxic substances, the eggshells of the sea-birds are very thin that they might get crushed by the birds themselves during incubation. Thus, the toxic chemicals, mercury, and selenium destroy the reproductive organs of aquatic organisms such as fishes and corals.
Extinction and population decline
Biomagnification can lead to a population decline in organisms and if not controlled can result in the extinction of species. The toxicity associated with the biomagnification of toxic substances in animals causes reproductive defects and diseases. As a result of this, organisms become unable to reproduce and either die as a result of the diseases caused by biomagnification.
This causes a reduction in their population and it can lead to the extinction of the animals in the locality. Moreso, some of the top predators affected by biomagnification are endangered species that need to be conserved. Due to biomagnification, these animals may be lost for life.
Disrupt the food chain and ecosystem
Biological magnification disrupts the food chain. The chemicals and toxic substances that are released into the water bodies disrupt the food chain. As the small organisms absorb the chemicals, they are in turn eaten up by larger animals. Thus, these substances get accumulated in the higher trophic level of organisms.
Biomagnification and Bioaccumulation
The process of biological magnification is sometimes interchangeably used with bioaccumulation. These two processes are however related but there is a distinct difference between them and bioconcentration as well. The process of bioaccumulation specifically occurs within a particular trophic level. It is the concentration increase of the contaminant or substance in certain tissues of the organisms. Bioaccumulation is a result of the absorption of the substance from food or the environment.
Moreso, bioconcentration is the process of bioaccumulation in which the concentration of a substance in an organism is higher than the concentration of the substance in the environment around the organism. Therefore, bioaccumulation and bioconcentration is a phenomenon that occurs within the organism, while biomagnification happens across trophic levels (food chain).
Biomagnification vs bioaccumulation
Biomagnification and bioaccumulation are terminologies that are usually used for metal toxicity. Bioaccumulation refers to how chemicals or toxins find their way into a food chain and accumulates in the biological tissues of the organisms (mostly aquatic organisms). This phenomenon occurs when the organism absorbs toxins or chemicals at a rate that is faster than the rate at which the toxin or chemical is eliminated or lost by catabolism and excretion.
Bioaccumulation can also be referred to as an increased concentration of a substance or chemical in an organism over a period of time. Bioaccumulation occurs once there is an uptake of substances such as metals by living organisms which are stored faster than they are excreted or metabolized.
Biological magnification, on the other hand, refers to the concentration increase of substances or pollutants as they move from one trophic level to the next. This process occurs when a toxin or pollutant increasingly builds up as it moves up through a food chain. However, biomagnification is the concentration of a chemical or toxin in the tissues of organisms at successively higher trophic levels in a food chain. This increase of the toxic substance at higher trophic levels could result from the substance being persistent in the environment, food chain energetics, and a low or non-existent rate of excretion of the substance.
How to Prevent Biological magnification
- There are legislation and restrictions that ban the disposal of certain compounds in water in order to help reduce the level of toxic compounds that biomagnify.
- Some microbes are being genetically modified to use for the bioremediation and cleanup of toxic substances from the environment.
- Also, some federal governments and states have issued advisories against eating too much of certain fish types.
- The use of pesticides should be reduced and proper industrial waste disposal and treatment should be utilized.
- Almost all products made industrially contain some kinds of heavy metals. The usage of some heavy metals should be prevented to reduce biomagnification.
- The use of some harmful products should be restricted. Some home products like PVC, lead paints, plumbing materials, CCA, and ACZA treated wood, and some others contain heavy metals like mercury and arsenic.
Biomagnification is an ever-growing threat. In the environment, organisms are exposed to several chemicals. Even though some of these chemicals exist in the environment at low concentrations, they may be selectively accumulated by organisms to much higher concentrations. This can result in biomagnification and cause toxicity.
In conclusion, the accumulation of substance up the trophic levels is the biomagnification of the substance. It involves the progressive concentration of a contaminant in the tissues of organisms at higher trophic levels. It is used to describe the trophic enhancement of toxins within food webs. The process of biomagnification involves the bioavailability of the substance, its uptake, bioconcentration, and bioaccumulation in organisms.
Organic substances and metals are the two main groups of substances that biomagnify. These two substances are lipophilic and do not easily degrade. However, biomagnification in an aquatic food chain will lead to biomagnification in the terrestrial food chains. Industrial activities, agriculture, mining activities, and organic contaminants are all causes of biomagnification.
Biomagnification has adverse effects and should be controlled and prevented. Some effects of biomagnification are: it causes several diseases in humans, affects the reproduction and development of animals as well as disrupts the food chain and ecosystem. Biological magnification is of serious concern because humans are at the top of the food chain. However, understanding the process of biomagnification is very crucial to protect humans and animals from the adverse effects of toxins and metal exposure.