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A general term for the accumulation of substances (chemical species) such as pesticides or other organic chemicals, in an organism or part of an organism resulting in a higher concentration of the substance in the organism than in its environment.

Some chemical species are absorbed and concentrated in specific organs. Bioaccumulation increases the dose effect and can make any substance toxic but may also be a useful biological process for the organism. Watersoluble organometals will normally be excreted and probably not bioaccumulate.

Biologically useful bioaccumulation

  • Iodide ions will concentrate in the thyroid where they are used to make thyroid hormone

Bioaccumulation with a potential of being harmful

  • Lead ions may concentrate in bone where they are harmless unless released into the bloodstream
  • Strontium ions and plutonium ions concentrate in bone where their radioactivity may cause bone marrow mutations and leukaemia
  • Fat soluble organometal compounds, like organoleads, may concentrate in fats, where they are harmless unless released to the bloodstream on fat breakdown, and the nervous system, where they cause harm.


The accumulation process involves the biological sequestering of substances that enter the organism through respiration, food intake, epidermal (skin) contact with the substance, and/or other means.

The level at which a given substance is bioaccumulated depends on

  • the rate of uptake
  • the mode of uptake
  • how quickly the substance is eliminated from the organism
  • transformation of the substance by metabolic processes
  • the lipid (fat) content of the organism
  • the hydrophobicity of the substance
  • environmental factors
  • other biological and physical factors
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