Biomagnification is one aspect of bioaccumulation . It describes the accumulation of pollutants from the environment in living things through food. The accumulation of pollutants via the body surfaces of organisms (lungs, gills, skin) is the second aspect of bioaccumulation and is referred to as bioconcentration ; This absorption path is particularly important for many aquatic organisms that absorb substances via their gills and the skin.
Requirements for biomagnification
Biomagnification is particularly concerned with substances that have a long biological half-life , i.e. H. are only slowly broken down by living things and, due to their chemical properties (see octanol-water partition coefficient ), can be found in adipose tissue or z. B. accumulate in the bone substance. As a result, these substances accumulate and can occur in increasingly higher concentrations due to the continuous flow of substances through the food chain .
This process is essentially due to the fact that the substance of an end link in the food chain (e.g. osprey ) is built up from much more biomass from the next lower link in the food chain (e.g. fish) and the fat-soluble ( lipophilic ) substances are essentially in the eating organism remain and are enriched (accumulated). If, for example, an osprey has eaten twice as much polluted fish mass as its body weight, then the additional concentration of the pollutant per kilogram of body weight can be twice as high as in the fish. Some pollutants are partially excreted or broken down biochemically, so that exposure can be limited in time. However, interactions between various pollutants and their breakdown products can occur. Biomagnification is particularly important for very lipophilic substances as well as for some heavy metals and radioactive substances that are hardly broken down or excreted by the body. As the length of the food chain increases, the bioaccumulation factor increases under such conditions.
In addition, the enrichment in the structural and supporting tissue plays an important role. In vertebrates, these are the bones and cartilage.
For a long time, the insecticide DDT , which is used to combat malaria vectors, was considered a prime example of biomagnification . It is highly fat-soluble and is only very slowly metabolized into water-soluble compounds in the body. According to a classic study that is partly speculative with regard to the interpretation of the data, the DDT concentration from zooplankton in the ocean (0.04 ppm ) to the end consumer of the suspected food chain, the osprey (25 ppm), has increased by 625 times. According to this model, the highest concentration and therefore the greatest risk is to be expected in the case of fat-soluble persistent compounds for the end links of the food chain. Another example is Minamata disease , which is caused in humans by eating fish when they are enriched with organic mercury compounds via the food chain .
However, later studies and experiments have shown in many cases that in purely aquatic food chains (from water to plankton to fish) the process of bioconcentration , i.e. the direct absorption of pollutants through the skin or gills of the organisms, is usually more important in quantitative terms than has biomagnification. However, a certain equilibrium is established over these surfaces and when the concentration in the water drops, the fat-soluble substance is washed out of the fish (sometimes only moderately). If fish-eating birds have a significantly higher concentration than fish or invertebrates, this is also due to the fact that the connection between them cannot be in an exchange equilibrium with the surrounding medium in the same sense, but can only be partially reduced through excretion. Biomagnification plays an important role for the accumulation of pollutants in food chains on the mainland.
As a result of biomagnification, the effects of poisons, pollutants and their breakdown products can have devastating effects on the end links of the food chain (including humans), which is why many of these compounds are no longer allowed to be applied today (at least in Europe).
The term biomagnification is not only applied to consciously used poisons (e.g. chemical pesticides), but also e.g. B. also on toxic substances such as mercury , which passively or through disposal in water bodies or as contaminated sites (war ammunition, waste dumps) are present in the soil. For example, mercury accumulates in the form of lipophilic methylmercury in fish tissue and also in humans when fish is subsequently consumed.
In the metabolism it can be observed that some substances are replaced by chemically similar, but actually undesirable substances. Radioactive cesium is highly enriched in plants because its chemical behavior is similar to that of potassium . Cadmium is absorbed as a substitute in the case of calcium deficiency.
- George M. Woodwell, Charles F. Wurster Jr., Peter A. Isaacson: DDT residues in an East coast estuary: A case of biological concentration of a persistent insecticide. Science 156: 821-824 (1967).
- Bruno Streit: Bioaccumulation Processes in Ecosystems. Review. Experientia 48, pp. 955-970 (1992).
- Bruno Streit: Uptake, accumulation and release of organic pesticides by benthic invertebrates. 3. Distribution of 14 C-atrazine and 14 C-lindane in an experimental 3-step food chain microcosm. Arch. Hydrobiol./ Suppl. 55: 374-400 (1979).
- Stephan Winter, Bruno Streit: Organochlorine compounds in a three-step terrestrial food chain. Chemosphere 24: 1765-1774 (1992).
- Research into environmental radioactivity http://www.uni-protocol.de/nachrichten/id/77717/ .
- Umwelt-Survey Volume IV a, on behalf of the Federal Environment Agency, Berlin 1993.
- Bernd Beek: Bioaccumulation. New Aspects and Developments . The Handbook of Environmental Chemistry Vol. 2. Springer, Berlin 2000
- Karl Fent: Ecotoxicology . 3rd edition, Georg Thieme Verlag, Stuttgart 2007, ISBN 3131099933
- Bruno Streit : Lexicon of Ecotoxicology. 2nd edition, VCH-Wiley, Weinheim 1994