Bio-accumulating

Bioaccumulation is the accumulation of substances, such as pesticides, or other chemicals in an organism. Bioaccumulation occurs when an organism absorbs a substance at a rate faster than that at which the substance is lost by catabolism and excretion. Thus, the longer the biological half-life of a toxic substance, the greater the risk of chronic poisoning, even if environmental levels of the toxin are not very high. Bioaccumulation, for example in fish, can be predicted by models. Hypotheses for molecular size cutoff criteria for use as bioaccumulation potential indicators are not supported by data.Biotransformation can strongly modify bioaccumulation of chemicals in an organism.

Bioconcentration is a related but more specific term, referring to uptake and accumulation of a substance from water alone. By contrast, bioaccumulation refers to uptake from all sources combined (e.g. water, food, air, etc.).

An example of poisoning in the workplace can be seen from the phrase "mad as a hatter" (18th and 19th century England). The process for stiffening the felt used in making hats more than a hundred years ago involved mercury, which forms organic species such as methylmercury, which is lipid-soluble, and tends to accumulate in the brain, resulting in mercury poisoning. Other lipid-soluble (fat-soluble) poisons include tetraethyllead compounds (the lead in leaded petrol), and DDT. These compounds are stored in the body's fat, and when the fatty tissues are used for energy, the compounds are released and cause acute poisoning.

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