8.8 Biomagnification

Bioaccumulation and Biomagnification

Definitions

  • Bioaccumulation: The absorption and concentration of compounds, especially fat-soluble ones, in the cells and fat tissues of organisms over time.

    • Examples of compounds that bioaccumulate include persistent organic pollutants (POPs) and methyl mercury.

  • Biomagnification: The increasing concentration of fat-soluble pollutants (POPs) at each successive trophic level up the food chain or food web.

Overview of Processes

  • Fat-soluble compounds, like POPs and methyl mercury, do not dissolve easily in water.

    • This characteristic causes them to:

    • Have difficulty entering the bloodstream.

    • Be excreted from the body efficiently.

    • Consequently, these compounds build up in fat tissues, resulting in higher concentrations in the organism over time.

Trophic Levels and Energy Transfer

  • Primary Producers: Often phytoplankton, located at the base of the trophic pyramid.

  • Primary Consumers: Organisms such as zooplankton and bottom-feeding fish that consume primary producers and accumulate POPs in their tissues.

  • Secondary Consumers: Predators that eat primary consumers, taking in the accumulated POPs as they feed.

  • Due to the lower transfer efficiency (approximately 10% rule of energy transfer), organisms at each successive trophic level must consume more biomass for sufficient energy, leading to:

    • Increasing levels of POPs and methyl mercury through their lifetimes.

Examples of Biomagnification

  • Larger predators such as salmon, dolphins, and whales often exhibit the highest levels of POPs and methyl mercury accumulation.

  • DDT (Dichloro-Diphenyl-Trichloroethane):

    • Was banned in many developed nations but persists in the sediments of numerous bodies of water.

    • It enters the ecosystem through bottom feeders and zooplankton, leading to increased concentrations in higher trophic levels.

    • Predatory birds, like eagles and ospreys, accumulate high levels of DDT, which has been linked to thinning eggshells and contributing to the decline of these bird populations.

    • This decline triggers the passage of endangered species protection legislation.

  • Methyl mercury:

    • Emitted from coal burning and volcanic activity, methyl mercury is carried by wind and deposited into water systems.

    • In water, bacteria convert mercury into toxic methylmercury, which is taken in by phytoplankton and biomagnified through the food chain.

    • Methylmercury reaches the highest levels in apex predators, including certain fish (e.g., tuna), sharks, and whales.

    • This neurotoxin adversely affects the central nervous system of animals, and human exposure typically occurs through the consumption of larger predatory fish.

    • This exposure poses significant health risks, particularly affecting developing fetuses, leading to developmental and reproductive system disruptions.

Summary and Implications

  • Understanding bioaccumulation and biomagnification is crucial, as these processes illustrate the impact of human activity on ecosystems and highlight the risks to public health, especially concerning food consumption safety for larger predatory fish from contaminated waters.

Bioaccumulation: The process by which a single organism absorbs and concentrates pollutants over time in its tissues.
Biomagnification: The increasing concentration of those pollutants as they transfer up each trophic level in the food chain.