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Bioaccumulation

Bioaccumulation


Bioaccumulation is the accumulation of contaminants by species in concentrations that are orders of magnitude higher than in the surrounding environment.

Bioaccumulation is the sum of two processes: bioconcentration and biomagnification. Bioconcentration is the direct uptake of a substance by a living organism from the medium (e.g., water) via skin, gills, or lungs, whereas biomagnification results from dietary uptake. Many synthetic contaminants are more soluble in fat than in water. Polychlorinated biphenyls (PCBs), for example, which can be present in lake or river water, tend to either adsorb to particles or to diffuse into cells of organisms. Thus, PCBs bioconcentrate in low trophic levels, for example, in phytoplankton by a factor of around 250. Fish that actively filter large amounts of water through their gills are subject to a much higher bioconcentration. Additionally, biomagnification takes place in predatory organisms. The PCB burden of the prey is transferred to the predator. Fish like smelt that consume large quantities of mysids and zooplankton magnify the PCB concentration. This leads to bioaccumulation factors as high as 2.8 million in predatory fish species such as lake trout and striped bass. Mammalsincluding humans that eat the fish, reptiles, and birdsfurther accumulate PCBs.

Finally, in the leading predators among marine lifethe seal and polar bearPCBs and other persistent organic pollutants (POPs) reach concentrations that cause obvious impairments of the immune and reproductive system. A significant proportion of these accumulated contaminants is transferred to the offspring by the mother's milk, resulting in, for example, abnormal sexual development, behavioral dysfunctions, and cancer. Prerequisites for a substance's strong bioaccumulation are its affinity for fat and low biodegradability, or persistence in the environment. Bioaccumulating contaminants thus far identified are the first-generation organochlorine pesticides (e.g., DDT, chlordane, and toxaphene), PCBs, dioxins, brominated flame retardants, but also some organo-metal compounds, for example, methyl mercury and tributyltin (TBT). Because of their strong bioaccumulation and toxicity, some of these substances were banned in North America and Western Europe after 1970. The bioconcentration factor (BCF) often serves as a trigger for the hazard classification of chemicals. In the European Union a BCF greater than one hundred leads to a substance's classification as "dangerous to the environment." The U.S. Environmental Protection Agency (EPA) uses a BCF of greater than 1,000 for environmentally harmful substances. In Canada chemicals with a BCF greater than 5,000 are recommended for "virtual elimination."

see also DDT (Dichlorodiphenyl trichloroethane); Mercury; PCBs (Polychlorinated Biphenyls); Persistent Bioaccumulative and Toxic (PBT) Chemicals; Persistent Organic Pollutants (POPs); Pesticides.

Bibliography

Beek, Bernd. (2000). "Bioaccumulation: New Aspects and Developments." In Handbook of Environmental Chemistry, Vol. 2: Reactions and Processes, Part J, edited by Otto Hutzinger. New York: Springer-Verlag.

Colborn, Theo; Dumanoski, Dianne; and Myers, John Peterson. (1996). Our Stolen Future. New York: Dutton.

Connell, Des W. (1990). Bioaccumulation of Xenobiotic Compounds. Boca Raton, FL: CRC Press.


Internet Resource

"Bioaccumulation and Biomagnification." Available from http://www.marietta.edu/~biol.

Stefan Weigel

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bioaccumulation

bioaccumulation An increase in the concentration of chemicals, such as pesticides, in organisms that live in environments contaminated by a wide variety of organic compounds. These compounds are not usually decomposed in the environment (i.e. they are not biodegradable) or metabolized by the organisms, so that their rate of absorption and storage is greater than their rate of excretion. The chemicals are normally stored in fatty tissues. DDT is known as a persistent pesticide, as it is not easily broken down and bioaccumulates along food chains, so that increasing concentrations occur in individual organisms at each trophic level.

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Bioaccumulation

Bioaccumulation

Resources

Bioaccumulation is the gradual build up over time of a chemical in a living organism. This occurs either because the chemical is taken up faster than it can be used, or because the chemical cannot be broken down for use by the organism (that is, the chemical cannot be metabolized).

Bioaccumulation need not be a concern if the accumulated compound is not harmful. Compounds that are harmful to health, such as mercury, however, can accumulate in living tissues.

Chemical pollutants that are bioaccumulated come from many sources. Pesticides are an example of a contaminant that bioaccumulates in organisms. Rain can wash freshly sprayed pesticides into creeks, where they will eventually make their way to rivers, estuaries, and the ocean. Anther major source of toxic contaminants is the presence of compounds from industrial smokestacks and automobile emissions that return to the ground in rainfall. Deliberate discharge of compounds into water is another source of chemical pollutants.

Once a toxic pollutant is in the water or soil, it can easily enter the food chain. For example, in the water, pollutants adsorb or stick to small particles, including a tiny living organism called phytoplankton. Because there is so little pollutant stuck to each phytoplankton, the pollutant does not cause much damage at this level of the food web. However, a small animal such as a zooplankton might then consume the particle. One zooplankton that has eaten ten phytoplanktons would have ten times the pollutant level as the phytoplankton. As the zooplankton may be slow to metabolize or excrete the pollutant, the pollutant may build up or bioaccumulate within the organism. A small fish might then eat ten zooplankton. The fish would have 100 times the level of toxic pollutant as the phytoplankton. This multiplication would continue throughout the food web until high levels of contaminants have biomagnified in the top predator. While the amount of pollutant might have been small enough not to cause any damage in the lowest levels of the food web, the biomagnified amount might cause serious damage to organisms higher in the food web. This phenomenon is known as biomagnification.

Mercury contamination is a good example of the bioaccumulation process. Typically, mercury (or a chemical version called methylmercury) is taken up by bacteria and phytoplankton. Small fish eat the bacteria and phytoplankton and accumulate the mercury. The small fish are in turn eaten by larger fish, which can become food for humans and animals. The result can be the build up (biomagnification) of large concentrations of mercury in human and animal tissue.

One of the classic examples of bioaccumulation that resulted in biomagnification occurred with an insecticide called dichlorodiphenyltrichloroethane (DDT). DDT is an insecticide that was sprayed in the United States prior to 1972 to help control mosquitoes and other insects. Rain washed the DDT into creeks, where it eventually found its way into lakes and the ocean. The toxic pollutant bioaccumulated within each organism and then biomagnified through the food web to very high levels in predatory birds such as bald eagles, osprey, peregrine falcons and brown pelicans that ate the fish. Levels of DDT were high enough that the birds eggshells became abnormally thin. As a result, the adult birds broke the shells of their unhatched offspring and the baby birds died. The population of these birds plummeted. DDT was finally banned in the United States in 1972, and since that time there have been dramatic increases in the populations of many predatory birds.

The bioaccumulation and biomagnification of toxic contaminants also can put human health at risk. When humans eat organisms that are relatively high in the food web, we can get high doses of some harmful chemicals. For example, marine fish such as swordfish, shark, and tuna often have bioaccumulated levels of mercury, and bluefish and striped bass sometimes have high concentrations of polychlorinated biphenyls (PCBs). Humans can also bioaccumulate poisons through the consumption of contaminated filter-feeding marine life such as mussels, oysters, and coral fish. The federal government and some states have issued advisories against eating too much of certain types of fish because of bioaccumulated and biomagnified levels of toxic pollutants.

Bioaccumulation can also occur in humans who are exposed for a long time to noxious chemicals in their home or workplace. Over time, even accumulation of a toxin at a low rate can produce a deterimental level of the compound in the body, particularly if the compound accumulates in fatty tissues. One example of a poison that bioaccumulates in fat is lead. While lead-based paints have been banned from sale, older homes may still contain lead painted surfaces.

Advances are being made in efforts to lessen the bioaccumulation of toxic compounds. Legislation banning the disposal of certain compounds in water helps to reduce the level of toxic compounds in the environment that are capable of being accumulated in the food chain. As well, microorganisms are being genetically engineered so as to be capable of using a toxic material such as mercury as a food source. Such bacteria can directly remove the compound from the environment.

Resources

BOOKS

Beek, B.O. Bioaccumulation New Aspects and Developments. New York: Springer Verlag, 1999.

Neff, J.M. Bioaccumulation in Marine Organisms: Effect of Contaminants from Oil Well Produced Water. Amsterdam: Elsevier Science Publishers, 2002.

PERIODICALS

Bae, W., R.K. Mehra, A. Mulchandani, et al., Genetic Engineering of Escherichia coli for Enhanced Uptake and Bioaccumulation of Mercury. Applied and Environmental Microbiology 67 (November 2001): 53355338.

Fleming, Lora E. Overview of aerosolized Florida red tide toxins: exposures and effects. Environmental Health Perspectives. 113 (2005): 618621.

Washam, Cynthia. A whiff of danger: synthetic musks may encourage toxic bioaccumulation. Environmental Health Perspectives. 113 (2005): A50A51.

Brian Hoyle

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Bioaccumulation

Bioaccumulation

The general term for describing the accumulation of chemicals in the tissue of organisms. The chemicals that bioaccumulate are most often organic chemicals that are very soluble in fat and lipids and are slow to degrade. Usually used in reference to aquatic organisms, bioaccumulation occurs from exposure to contaminated water (e.g., gill uptake by fish) or by consuming food that has accumulated the chemical (e.g., food chain/web transfer). Bioaccumulation of chemicals in fish has resulted in public health consumption advisories in some areas, and has affected the health of certain fish-eating wildlife including eagles, cormorants, terns, and mink.

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Bioaccumulation

Bioaccumulation

Bioaccumulation is the gradual build up over time of a chemical in a living organism . This occurs either because the chemical is taken up faster than it can be used, or because the chemical cannot be broken down for use by the organism (that is, the chemical cannot be metabolized).

Bioaccumulation need not be a concern if the accumulated compound is not harmful. Compounds that are harmful to health, such as mercury, however, can accumulate in living tissues.

Chemical pollutants that are bioaccumulated come from many sources. Pesticides are an example of a contaminant that bioaccumulates in organisms. Rain can wash freshly sprayed pesticides into creeks, where they will eventually make their way to rivers , estuaries, and the ocean . Anther major source of toxic contaminants is the presence of compounds from industrial smokestacks and automobile emissions that return to the ground in rainfall. Deliberate discharge of compounds into water is another source of chemical pollutants.

Once a toxic pollutant is in the water or soil , it can easily enter the food chain. For example, in the water, pollutants adsorb or stick to small particles, including a tiny living organism called phytoplankton . Because there is so little pollutant stuck to each phytoplankton, the pollutant does not cause much damage at this level of the food web. However, a small animal such as a zooplankton might then consume the particle. One zooplankton that has eaten ten phytoplanktons would have ten times the pollutant level as the phytoplankton. As the zooplankton may be slow to metabolize or excrete the pollutant, the pollutant may build up or bioaccumulate within the organism. A small fish might then eat ten zooplankton. The fish would have 100 times the level of toxic pollutant as the phytoplankton. This multiplication would continue throughout the food web until high levels of contaminants have biomagnified in the top predator . While the amount of pollutant might have been small enough not to cause any damage in the lowest levels of the food web, the biomagnified amount might cause serious damage to organisms higher in the food web. This phenomenon is known as biomagnification .

Mercury contamination is a good example of the bioaccumulation process. Typically, mercury (or a chemical version called methylmercury) is taken up by bacteria and phytoplankton. Small fish eat the bacteria and phytoplankton and accumulate the mercury. The small fish are in turn eaten by larger fish, which can become food for humans and animals. The result can be the build up (biomagnification) of large concentrations of mercury in human and animal tissue .

One of the classic examples of bioaccumulation that resulted in biomagnification occurred with an insecticide called dichlorodiphenyltrichloroethane (DDT). DDT is an insecticide that was sprayed in the United States prior to 1972 to help control mosquitoes and other insects . Rain washed the DDT into creeks, where it eventually found its way into lakes and the ocean. The toxic pollutant bioaccumulated within each organism and then biomagnified through the food web to very high levels in predatory birds such as bald eagles , osprey, peregrine falcons and brown pelicans that ate the fish. Levels of DDT were high enough that the birds' eggshells became abnormally thin. As a result, the adult birds broke the shells of their unhatched offspring and the baby birds died. The population of these birds plummeted. DDT was finally banned in the United States in 1972, and since that time there have been dramatic increases in the populations of many predatory birds.

The bioaccumulation and biomagnification of toxic contaminants also can put human health at risk. When humans eat organisms that are relatively high in the food web, we can get high doses of some harmful chemicals. For example, marine fish such as swordfish , shark, and tuna often have bioaccumulated levels of mercury, and bluefish and striped bass sometimes have high concentrations of polychlorinated biphenyls (PCBs) . The federal government and some states have issued advisories against eating too much of certain types of fish because of bioaccumulated and biomagnified levels of toxic pollutants.

Advances are being made in efforts to lessen the bioaccumulation of toxic compounds. Legislation banning the disposal of certain compounds in water helps to reduce the level of toxic compounds in the environment that are capable of being accumulated in the food chain. As well, microorganisms are being genetically engineered so as to be capable of using a toxic material such as mercury as a food source. Such bacteria can directly remove the compound from the environment.

See also Bivalves; Ecosystem.


Resources

books

Beek, B.O. Bioaccumulation New Aspects and Developments. New York: Springer Verlag, 1999.

Neff, J.M. Bioaccumulation in Marine Organisms: Effect ofContaminants from Oil Well Produced Water. Amsterdam: Elsevier Science Publishers, 2002.


periodicals

Bae, W., R.K. Mehra, A. Mulchandani, et al., "Genetic Engineering of Escherichia coli for Enhanced Uptake and Bioaccumulation of Mercury." Applied and Environmental Microbiology 67 (November 2001): 5335–5338.


Brian Hoyle

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