Bioaccumulation
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This article was researched and written by a student at the University of Vermont participating in the Encyclopedia of Earth's (EoE) Student Science Communication Project. The project encourages students in undergraduate and graduate programs to write about timely scientific issues under close faculty guidance. All articles have been reviewed by internal EoE editors, and by independent experts on each topic.
Contents
Introduction
Bioaccumulation is a process resulting in the concentration of substances in living tissues. The term is used often in reference to such chemical contaminants that may do harm to organismsas chlorinated pesticides and heavy metals. Nonetheless,organisms do accumulate chemicals and minerals needed for their survival—thismay be referred to as bioaccumulation. Many substances enteringorganisms are eventually eliminated in wastes; whereas such othersas heavy metals and fat-soluble organic substances (for example, persistent organic pollutants or POPs) may remain in the body for long periods of time. The U.S. Environmental Protection Agency uses the term persistent, bioaccumulative and toxic pollutants (PBTs) to categorize substancesthat raise human health and environmental healthconcerns. Depending on their affinity for fatty tissue and the length of the body's exposure, PBTs may accumulate in high concentrations and may cause physiological problems. PBTs enter the organism through a variety of active and passive means, including respiration, food intake, and epidermal (or skin) contact.
Types of Bioaccumulation
- Organismal - Compounds present in an organism's environment may concentrate in the body over time. For example, fish that swim frequently in contaminated water may build up pollutants in their fatty tissues. This type of accumulation, in organismsexperiencing continuous environmental exposure, is linear.
- Trophic transfer - Here, fat-soluble compounds pass from prey to predator. The more prey that are eaten, the greater the magnification of the compound as it travels up the food chain. Such organisms at the top of the food chain as humans or polar bears, can receive the highest concentrations. This process is sometimes referred to as biomagnification, since the concentration of pollutant in the predator is a large multiple of thatmeasured inthe prey.
- Soil Bioaccumulation - PBTs that are dumped into surrounding environmentsfrom specific waste sites or that leak from specific factories are point-source pollutants. Often, the substancesbind to soil particles and persist until they are removed through erosion, water percolation, or uptake by plants, microorganisms or animals in soils or sediments. This process includes both linear accumulation through abiotic processes, and biomagnification—as pollutant-laden bacteria and fungi are consumed by earthworms and other detritivores (or detritus eaters). Often, soil bioaccumulationis the initial source of PBT exposure for terrestrial organisms. Such methodsas phytoremediation (using plants to remediate)and mycoremediation (using fungi to remediate)have proven useful in removing or even breaking down pollutants in soil, and could be increasingly important solutions in the future.
Examples
Chlorinated pesticides
DDT, a chlorinated pesticide used heavily on U.S. farms in the middle of the 20th century, was found to bioaccumulate through earthworms to organisms higher on the food chain. Various songbirds, waterbirds and birds of prey experienced drastic population decreases during the 1950s due to such severe reproductive problems as overly thin, breakable eggshells. These problems were associated with widespread spraying of DDT. Writer and biologist Rachel Carson affected U.S. policy and public perception regarding pesticides greatly by describing the devastating effects of DDT in her 1962 best-selling book, Silent Spring.
Heavy metals
A study of bioaccumulation in cyprinid fish of the Kor River in Iran found high levels of mercury in the fishes’ muscles, liver, kidneys, brain, and gonadal tissue. One species was sampled in three river stretches: the Upper, Central, and Lower Kor, and the monitored fish proved to have significantly higher mercury contamination in the middle reach of the river where two cities (Shiraz, Marvdasht) produced industrial metals.
In Japan during the 1950s, strange cases of human neurological disorders and death began to appear in Minamata City and other industrial areas. The "Minamata Disease" was traced to fish and shellfish that contained high levels of methylmercury, and that had beeneaten by local townspeople. The methylmercury was traced to the Chisso Corporation's Minamata factory, the largest Japanese producer of acetaldehyde (a chemical used in manufacturing plastics) during the 1950s. Methylmercury is formed during the production of acetaldehyde, and the factory had been discharging a large amount of methylmercury via wastewater directly into the Yatsushiro Sea. People who ate a lot of the contaminated fish over a long period of time were especially at risk for Minamata Disease.
Synthetic industrial compounds
Polychlorinated biphenyls, or PCBs, aresynthetic chemical substancesused in a large number of mechanical and electrical systems because of their high thermal and chemical resistance. They do not break down easily—remaining in the environment for long periods of time and that build up as inputs continue. Exposure to, and the consequent bioaccumulation of, PCBs has been associated with cancer in animals, as well as negative effects to the immune, reproductive, nervous and endocrine systems. When PCBs are disposed of through incineration, dioxins (Public Health Statement for Chlorinated Dibenzo-p-dioxins (CDDs)) are formed—another type of bioaccumulated compound that has shown extremely disconcerting long-term effects on the human body. The result of PCB and dioxin bioaccumulation has revealed itself in the fat of polar bears and in human breast milk of Inuit women, sometimes at toxic levels.
Related terms: bioconcentration, biomagnification, biotransformation, biomonitoring
Further reading
- Carson, Rachel. Silent Spring. New York: Houghton Mifflin Co, 1962.
- Johansen, Bruce E. 2002. The Inuit's struggle with dioxins and other organic pollutants. The American Indian Quarterly 26(3): 479-490.to http://muse.jhu.edu/journals/american_indian_quarterly/v026/26.3johansen.pdf
- Kinney, C.A., E.T. Furlong, D.W. Kolpin, M.R. Burkhardt, S.D. Zaugg, S.L. Werner, J.P. Bossio, & M.J. Benotti. 2008. Bioaccumulation of pharmaceuticals and other anthropogenic waste indicators in earthworms from agricultural soil amended with biosolid or swine manure. Environ. Sci. Technol. 42(6):1863-70.
- National Institute of Minamata Disease, Japan Ministry of the Environment To http://www.nimd.go.jp/english/
- Taherianfard, M., M. Ebrahimi & S. Soodbakhsh. 2008. Bioaccumulation of Mercury in Fishes of Kor River. Australian Journal of Basic and Applied Sciences 2(4): 904-908.To http://insipub.net/ajbas/2008/904-908.pdf
- World Health Organization, "Dioxins and their effect on human health" To http://www.who.int/mediacentre/factsheets/fs225/en/index.html
