Biomagnification is the process in which chemical substances become more concentrated at each trophic level

• In contrast, bioaccumulation refers to the build up of a chemical substance in the tissues of a single organism
  

Biomagnification occurs because organisms at higher trophic levels must consume more biomass to meet requirements

• Energy transformations are only ~10% efficient, so higher order consumers must eat more to meet energy demands
  

• If the chemical is persistent, higher order consumers will experience increased contamination from the substance
  

DDT (dichloro-diphenyl-trichloroethane)

• DDT is a chemical pesticide that is sprayed on crops and subsequently washed into waterways at low concentrations
  

• As it is fat soluble, it is retained within the tissues of aquatic algae instead of being excreted
  

• At each subsequent trophic level the concentration of DDT stored in the body increases due to increased food intake
  

• Very high levels of DDT were discovered in birds that preyed on fish, and was found to interfere with eggshell formation
  

• Birds exposed to high levels of DDT were found to produce thinner shells, which decreased survival rates of fledglings
  

• The use of DDT is now largely restricted in most countries (except in circumstances when dealing with mosquito larvae that transmit malaria)
  

Mercury

• Mercury is a heavy metal that can be released into the environment through activities such as coal-fired power generation and gold mining
  

• The mercury is then converted by microorganisms into highly toxic methyl-mercury, which accumulates in the bodies of consumers (such as fish)
  

• At each subsequent trophic level, the concentrations of methyl-mercury within the tissues increases due to increased food intake
  

• This can lead to mercury poisoning in humans who eat the larger predatory fish (like tuna or swordfish)
  

Biomagnification