Biological Magnification
A process called __bioaccumulation__ occurs with some wastes in the following way:
1. individual organism is exposed to very low concentrations of the
hazardous chemical
2. chemical is absorbed by the individual's body and kept there
(usually in fat cells)
3. the concentration of the chemical builds up inside the individual's tissues,
eventually reaching dangerous levels
Biological magnification occurs when the _toxic_ chemicals are passed along the food
chain. The end result of the process is particularly noticeable in _top_ predators.
Examples of hazardous chemicals that bioaccumulate are pesticides (eg DDT), PCB’s,
dioxins, etc. DDT was once used extensively as an insecticide. DDT builds up in the
_fatty _ tissues of organisms. Organisms at lower trophic levels accumulate __low__
amounts. Organisms at the next higher level eat many of these lower-level organisms
and hence accumulate _high_ amounts. At the highest trophic levels, the increased
concentrations in tissues may become toxic.
Compounds that bioaccumulate are fat soluble, meaning they are not excreted by the
organism. How can we change these compounds so they do not bioaccumulate?
- use water soluble compounds
- animals excrete these compounds out of their bodies
Heavy metals and other substances
DDT is not the only toxin to biomagnify. All of the following have the potential to biomagnify:
Substance
Use & Problems
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insulators in transformers
plasticizer
fire retardant
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biomagnifies
impairs reproduction
widespread in aquatic systems
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component of petroleum products
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carcinogenic
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mercury from gold mining
many from metal processing
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may affect nervous system
may affect reproduction
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used in leaching gold
used in fishing
toxic
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concentrated by farming desert soils
reproductive failures
toxic
PCB's
polychlorinated biphenyls
PAH's
polynuclear aromatic hydrocarbons
Heavy metals:
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mercury
copper
cadmium
chromium
lead
nickel
zinc
tin (TBT or tributyltin)
cyanide
selenium