Bioaccumulation is the term bioaccumulation refers to the net accumulation over time of metals [or other persistent substances] within an
organism from both biotic other organisms and abiotic soil, air, and water sources Fig. 3.
http:www.greenfacts.orgglossaryabcbioaccumulation- bioaccumulate.htm
Source: Wisconsin Department of Natural Resources http:www.greenfacts.orgglossaryabcbioaccumulation-
bioaccumulate.htm Fig. 3. An example of the Bioaccumulation
C. Bioconcentration
Bioconcentration is the specific bioaccumulation process by which the concentration of a chemical in an organism becomes higher than its
concentration in the air or water around the organism. Although the process is the same for both natural and manmade chemicals, the term bio-concentration
usually refers to chemicals foreign to the organism. For fish and other aquatic animals, bioconcentration after uptake through the gills or sometimes the skin is
usually the most important bioaccumulation process Extension Toxicology
Network, 1993.
Bioconcentration differs from bioaccumulation because it refers only to the uptake of substances into the organism from water alone. Bioaccumulation is the
more general term because it includes all means of uptake into the organism. Though sometimes used interchangeably with bioaccumulation, an important
distinction is drawn between the two. Bioaccumulation occurs within a tropic level, and is the increase in concentration of a substance in an individuals
tissues due to uptake from food and sediments in an aquatic milieu.
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Bioconcentration is defined as occurring when uptake from the water is greater than excretion Landrum and Fisher, 1999. Thus bioconcentration and
bioaccumulation occur within an organism, and biomagnification occurs across tropic food chain levels
http:en.wikipedia.orgwikiTalk .
B. History of Biomagnification
According to the ISI Science Citation Index, the first use of the term in the title of a peer-reviewed article was in Johnson Kennedy 1973. However, the
concept traces back to Rachel Carson
s book, Silent Spring, published in 1962. In Chapter 3 of Silent Spring,
he describes the process but does not name it as
biological magnification. Interestingly, she focuses on terrestrial systems, but most research has been done in aquatic systems. Carson drew attention to the
issue, and other ecologists and toxicologists examined its occurrence in many systems. As
DDT ,
PCBs ,
mercury , and other substances were found through the
1970s to occur at strikingly high concentrations in the upper reaches of food chains, the concept of biomagnification of lipophilic substances became firmly
established. It is presented in most introductory ecology and environmental science texts.
However, by the 1990s, some researchers began to question the roles of bioaccumulation versus biomagnification. For one thing, tissue concentrations of
substances did not always increase uniformly with the tropic level Landrum and Fisher, 1999. LeBlanc 1995 proposed that what is really bioaccumulation to
different degrees is mistaken as biomagnification, because: •
Lipid contents of organisms increase with the tropic level
• Elimination efficiency of the substances decreases with tropic level because the larger organisms have relatively less surface area to
process and excrete substances, for their body size. Thus the pattern of increased tissue concentration with higher tropic levels could
be due to these differences in bioaccumulation. However, this proposal was based on rather limited data.
In 1990, Rasmussen et al. compared PCB levels in lake trout sampled from lakes with different numbers of tropic levels. Inputs to these lakes were
small and relatively constant. The shorter the food chain in the lake, the lower the concentration of PCBs in the tissue of trout, which feed at the top of the chain at
least when they are large. This pattern is what is expected if biomagnification
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occurs. Additionally, they noted that the amount of PCB in tissues increased 3.5 times per tropic level, but the amount of lipids as a proportion of tissues
increases much less, only 1.5 times per tropic level Rasmussen et al., 1990.
III. Biomagnification Occurrence
A.
Process of Biomagnification
According to Miller 2006, the chemicals that enter the biosphere of living systems as a result of industrial processes are not all beneficial or natural.
Plants for instance, need carbon and nitrogen, but there are many things that we have introduced into the world through industrial processes that are harmful to
ourselves and other living creatures. We have produced dangerous chemicals that enter living systems and accumulate through the process of
biomagnification, an increase in concentrations in living tissue as one travels up the food chain. Plants organisms that can photosynthesize, thereby gaining
energy from sunlight are consumed higher up the food chain by animals that cannot photosynthesize, and animals higher up the chain then eat these animals.
At the top of the chain is the apex predator that serves as an indicator species for the whole ecosystem: an interactive collection of numerous creatures. Food webs
are more complicated than food chains in that the relationships are not linear, but rather a collection of many interconnections of food chains. The creatures that
eat photosynthesizing bacteria may be eaten by many creatures, but these critters may also help in the digestion of larger animals which are connected in
webs of relationships rather than a linear chain upwards. Pollution enters these webs and chains at all levels and the
concentrations increase up the many chains, until it could pose a threat to the animals at the top of the chain. Human society is often at the top of the food
chain. The animals we eat can potentially pollute us. We have learned that what we have polluted the environment with can wind up on our dinner plate due to
biomagnification. These pollutants can cause problems and cancer in human beings as well as creatures in the wild. For example, DDT had a deleterious
effect on brown pelicans by interfering with the production of their eggs, which were too thin to incubate their young. When the use of DDT was diminished the
brown pelicans made a recovery. Pollution is also one of the factors that lead to the demise of wildlife
populations. Through natural cycles we have all encountered and ingested
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