This blog will be discussing about the importance of bioaccumulation, biomagnification and bioconcentration.
Ahh, mercury and its chemistry.
Bioaccumulation: How does it happen?
In our body, some substances will accumulate while others pass through. So even if you consume some mercury or other types of chemical it will most likely pass through your body system. However, it’s important to drink a lot of fluids in a day to flush out harmful substances in your system.
This is a very important issue in regards to wastes, so how does bioaccumulation happen?
Bioaccumulation is the term for materials that will build up in an organism to much higher levels than are found in the backgrounds. The first thing that occurs is that the material must enter the organism. This can occur through a number of different routes, such as breathing, eating (ingesting), drinking (usually water), or through skin contact (like PCB’s!).
The material must then deposit or accumulate somewhere inside of the body.
The most common situation is that the material is lipid (fat) soluable, lipophilic and/or hydrophobic. This means the material can dissolve in fat and will dissolve into the fatty tissues of the body. When the substance is more hydrophobic (fear from water, or moves away from water), this will increase the ease with which this happens. Since waste from the body is transported by water and filtered out by the kidneys, materials that won’t dissolve in water CANNOT be excreted.
Many chemicals dissolve in water. Those that dissolve best contain atoms, molecules, or other particles that bind strongly to water molecules, more strongly than they bind to themselves. When you add a water-soluble chemical to water, water molecules surround its particles and carry them around individually. The chemical becomes separate particles and dissolves in the water. DDT, PCB’s, methyl mercury and many other organic substances fall into this category.
Storage in fat is not the only location in which this bioaccumulation can occur. Take Strontium-90 as an example, strontium-90 is known to manipulate the same properties as calcium which is used for treatment for bone cancer, because it mimics calcium in the bones and therefore can be deposited in the bones of the body! It is also possible to poison yourself with vitamin A, this way it accumulates in the liver. Eating the livers of certain high level predators (like seals or polar bears) can give you vitamin A poisoning.
Lead is another popular example for bioaccumulation. Lead can accumulate in the bones. It is eliminated only very slowly once ingested and can mimic calcium (it can also mimic iron and zinc, as well) and be deposited in bone structures.
Certain species of animal even use this as a natural defense. They can consume toxic material once it is there and the materials either rendered the animals too toxic to be consumed.
The key thing in these materials accumulating is that the body has no way of removing the material once it is there and the materials either do not breakdown or do so only slowly.
Bioconcentration
This is a type of bioaccumulation but only occurs when the material is absorbed from water, and the intake is less than the output.
Biomagnification
Biomagnification occurs when a higher level predator eats a lower level organism and ingests the substance with it. Even though the level at the lower levels of the food chain (often referred as trophic levels) may have very low concentrations, as you move up the food chain the concentrations become higher and higher.
Mercury–Inorganic or Organic Substance?
The material that will bioaccumulate and biomagnify are generally not water soluble. So if you were to consume some small amounts of mercury into your body system, it won’t be absorbed and it will only be flushed out. This generally means that the two types of molecule–those with organic structures and those that are metal. Mercury actually comes in both of these forms. In it’s inorganic form, it is actually less harmful. These forms include either the metallic form (sometimes called a quicksilver), or inorganic compounds where the Hg has bonded to another inorganic compound.
Elemental mercury or “quicksilver” does not actually absorb much through either the skin or gastrointestinal tract. The main danger here is inhalation. Inorganic compounds may be absorbed better through skin or gastrointestinal tract, but still does not penetrate the blood-brain barrier. So you would need a high or very long term exposure to cause any form of significant damage.
However, mercury is actually more problematic in its organic form.
Dimethyl Mercury is so toxic, that it can absorb through the skin and be quickly lethal (it is also considered as one of the most strongest known neurotoxins). The type of mercury bioaccumulates in our fish food chain is the monomethyl mercury (often just abbreviated as methyl mercury). Methyl mercury is a cation (positively charged ion) that is made up of 1 mercury atom attacked to a methyl group. This form is actually produced when inorganic mercury (from sources such as coal burning) is released into the atmosphere and then metabolized by an anaerobic bacteria in aquatic environments that attaches itself onto the methyl group. This is why it affects fish and organisms that consume other fish. The water is the location that the methyl mercury is actually being produced. Furthermore, the organic mercury compounds can also cross the blood brain barrier and placental barrier and cause neurological effects. Since they have the capabilities to mimic and attach to amino acids. This form is also absorbed much more readily through the gastrointestinal tract, so eating contaminated foods can result in significant amount entering the system.
Industrial release of elemental or inorganic compounds of mercury generally into bodies of water where it is transformed to methyl mercury where the large scale of incidents of mercury poisoning have occurred.
One of the most infamous case was the Minamata Incident in Japan. In this case, an industrial location dumped 27 tons of mercury compounds into the local bay between 1932 and 1968. The residents, who relief heavily on fishing, began to exhibit symptoms in the mid 1950s, which progressively worsened. As a result, over 2000 victims have been identified as the poisoning continued over the many years (even after the source was identified).
In 1955 in the Minamata Bay area of Kyushu, Japan, there was a large influx of cases of severe neurological disorders in newborn children. There were cases of cerebral palsy, some children were diplegic and others were tetraplegic. They were all mentally handicapped. Some villages had 6-12% of their newborns affected. Together, these disorders are now known as Congenital Minamata Syndrome. In 1959, it was found that methylmercury was being dumped into the bay by a plant of the Chisso Corporation.
It wasn’t until 1962 that conclusive evidence was published linking the dumping of methylmercury to these neurological birth defects. It was thought, to this point, that poisons couldn’t cross the placenta. Therefore, it took some time to confirm that an environmental pollutant could induce birth defects in humans. The link between these birth defects and methylmercury have been confirmed multiple times in animal studies.
Children with Congential Minamata Syndrome seem to be normal at birth and begin to present symptoms at approximately six months of age. They have instability of the neck, convulsions, reduced IQ, microcephaly, malformed limbs, restricted growth and an altered cerebellum. In utero exposure to methylmercury induces general brain atrophy and hypoplasia.
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