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Biomagnification, also known as bioamplification or biological magnification, is any concentration of a toxin, such as pesticides, in the tissues of tolerant organisms at successively higher levels in a food chain. This increase can occur as a result of: * Persistence – where the substance cannot be broken down by environmental processes * Food chain energetics – where the substance's concentration increases progressively as it moves up a food chain * Low or non-existent rate of internal degradation or excretion of the substance – mainly due to water-insolubility Biological magnification often refers to the process whereby certain substances such as pesticides or heavy metals work their way into lakes, rivers and the ocean, and then move up the food chain in progressively greater concentrations as they are incorporated into the diet of aquatic organisms such as
zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...
, which in turn are eaten perhaps by fish, which then may be eaten by bigger fish, large birds, animals, or humans. The substances become increasingly 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.


Processes

Although sometimes used interchangeably with "
bioaccumulation Bioaccumulation is the gradual accumulation of substances, such as pesticides or other chemicals, in an organism. Bioaccumulation occurs when an organism absorbs a substance at a rate faster than that at which the substance is lost or eliminated ...
", an important distinction is drawn between the two, and with bioconcentration. * Bioaccumulation occurs ''within'' a
trophic level The trophic level of an organism is the position it occupies in a food web. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the number of steps it ...
, and is the increase in the concentration of a substance in certain tissues of organisms' bodies due to absorption from food and the environment. *
Bioconcentration Bioconcentration 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 ...
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.
Biodilution Biodilution, sometimes referred to as bloom dilution, is the decrease in concentration of an element or pollutant with an increase in trophic level. This effect is primarily observed during algal blooms whereby an increase in algal biomass reduces ...
is also a process that occurs to all trophic levels in an aquatic environment; it is the opposite of biomagnification, thus when a pollutant gets smaller in concentration as it progresses up a food web. Many chemicals that bioaccumulate are highly soluble in fats ( lipophilic) and insoluble in water (
hydrophobic In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, ...
). Lipophilic substances cannot be diluted, broken down, or excreted in
urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra. Cellul ...
, a water-based medium, and so accumulate in fatty tissues of an organism, if the organism lacks
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
s 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. For example, though mercury is only present in small amounts in
seawater Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has appro ...
, it is absorbed by algae (generally as
methylmercury Methylmercury (sometimes methyl mercury) is an organometallic cation with the formula . It is the simplest organomercury compound. Methylmercury is extremely toxic, and its derivatives are the major source of organic mercury for humans. It i ...
). Methylmercury is one of the most harmful mercury molecules. It is efficiently absorbed, but only very slowly excreted by organisms. Bioaccumulation and bioconcentration result in buildup in the adipose tissue of successive trophic levels:
zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...
, small nekton, larger fish, etc. Anything which eats these fish also consumes the higher level of mercury the fish have accumulated. This process explains why predatory fish such as
swordfish Swordfish (''Xiphias gladius''), also known as broadbills in some countries, are large, highly migratory predatory fish characterized by a long, flat, pointed bill. They are a popular sport fish of the billfish category, though elusive. Swordf ...
and
shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...
s or birds like
osprey The osprey (''Pandion haliaetus''), , also called sea hawk, river hawk, and fish hawk, is a diurnal, fish-eating bird of prey with a cosmopolitan range. It is a large raptor reaching more than in length and across the wings. It is brown o ...
and
eagle Eagle is the common name for many large birds of prey of the family Accipitridae. Eagles belong to several groups of genera, some of which are closely related. Most of the 68 species of eagle are from Eurasia and Africa. Outside this area, j ...
s 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. DDT is a pesticide known to biomagnify, which is one of the most significant reasons it was deemed harmful to the environment by the
EPA The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
and other organizations. DDT is one of the least soluble chemicals known and accumulates progressively in adipose tissue, and as the fat is consumed by predators, the amounts of DDT biomagnify. A well known example of the harmful effects of DDT biomagnification is the significant decline in North American populations of predatory birds such as bald eagles and peregrine falcons due to DDT caused eggshell thinning in the 1950s. DDT is now a banned substance in many parts of the world.


Current status

In a review, a large number of studies, Suedel et al. concluded that although biomagnification is probably more limited in occurrence than previously thought, there is good evidence that DDT, DDE, PCBs, toxaphene, and the organic forms of mercury and
arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, b ...
do biomagnify in nature. For other contaminants, bioconcentration and bioaccumulation account for their high concentrations in organism tissues. More recently, Gray reached a similar substances remaining in the organisms and not being diluted to non-threatening concentrations. The success of top predatory-bird recovery (
bald eagle The bald eagle (''Haliaeetus leucocephalus'') is a bird of prey found in North America. A sea eagle, it has two known subspecies and forms a species pair with the white-tailed eagle (''Haliaeetus albicilla''), which occupies the same niche as ...
s,
peregrine falcon The peregrine falcon (''Falco peregrinus''), also known as the peregrine, and historically as the duck hawk in North America, is a cosmopolitan bird of prey (raptor) in the family Falconidae. A large, crow-sized falcon, it has a blue-grey bac ...
s) in North America following the ban on DDT use in agriculture is testament to the importance of recognizing and responding to biomagnification.


Substances that biomagnify

Two common groups that are known to biomagnify are chlorinated hydrocarbons, also known as organochlorines, and inorganic compounds like methylmercury or heavy metals. Both are lipophilic and not easily degraded. Novel organic substances like organochlorines are not easily degraded because organisms lack previous exposure and have thus not
evolved Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variati ...
specific detoxification and excretion mechanisms, as there has been no selection pressure from them. These substances are consequently known as "
persistent organic pollutant Persistent organic pollutants (POPs), sometimes known as "forever chemicals", are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. They are toxic chemicals that adversel ...
s" or POPs. Metals are not degradable because they are
chemical elements A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler su ...
. 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. Persistent
heavy metals upright=1.2, Crystals of osmium, a heavy metal nearly twice as dense as lead">lead.html" ;"title="osmium, a heavy metal nearly twice as dense as lead">osmium, a heavy metal nearly twice as dense as lead Heavy metals are generally defined as ...
, such as
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, ...
,
cadmium Cadmium is a chemical element with the Symbol (chemistry), symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12 element, group 12, zinc and mercury (element), mercury. Li ...
, mercury, and arsenic, can have a wide variety of adverse health effects across species.


Novel organic substances

* DDT (dichlorodiphenyltrichloroethane) *
Hexachlorobenzene Hexachlorobenzene, or perchlorobenzene, is an organochloride with the molecular formula C6Cl6. It is a fungicide formerly used as a seed treatment, especially on wheat to control the fungal disease bunt. It has been banned globally under the Sto ...
(HCB) * PCBs (polychlorinated biphenyls) * Toxaphene * Monomethylmercury.


See also

* Mercury in fish *
Methylmercury Methylmercury (sometimes methyl mercury) is an organometallic cation with the formula . It is the simplest organomercury compound. Methylmercury is extremely toxic, and its derivatives are the major source of organic mercury for humans. It i ...
* Dichlorodiphenyldichloroethylene * Toxaphene


References


External links

* Fisk AT, Hoekstra PF, Borga K,and DCG Muir, 2003. Biomagnification. Mar. Pollut. Bull. 46 (4): 522-524 {{Toxicology Ecotoxicology Pollution