Biomagnification is a similar but distinct concept from bioaccumulation.

Biomagnification encompasses the concept of bioaccumulation. Whereas bioaccumulation is the concentration of a substance in a single organism or trophic level, biomagnification is the compounding of concentration as one moves through the food chain or "up" through each trophic level. For example, though mercury is only present in small amounts in seawater, bioaccumulation builds it up in the fat tissue of herbivorus fish. Anything which eats these fish also consumes the higher level of mercury the fish have accumulated. This process explains why predatory fish such as swordfish and sharks have higher concentrations of mercury in their tissue.

Sources

• http://www.marietta.edu/~biol/102/2bioma95.html
  
• http://www.greenfacts.org/glossary/abc/biomagnification-biomagnify.htm from GreenFacts.
• http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ec/m3/s4/ (excellent graphic)
  
• http://toxics.usgs.gov/definitions/biomagnification.html
  

See also