APES 8.8 Bioaccumulation and Biomagnification

Bioaccumulation

  • Definition: The buildup of persistent organic pollutants (POPs) or fat-soluble contaminants in organisms over time, rather than being excreted as waste.

  • Key Examples of POPs:

    • Methylmercury: A prominent example that does not dissolve easily in water, thus persisting and accumulating in organisms.

  • Process:

    • Due to fat-solubility, POPs build up in tissues rather than entering the bloodstream or exiting as waste.

    • Individual organisms refer to this process as bioaccumulation.

Biomagnification

  • Definition: Refers to the increasing concentration of fat-soluble pollutants within higher trophic levels in a food web.

  • Process Overview:

    1. Entry into Ecosystems: PoPs enter sediments or soil (e.g., marine or terrestrial ecosystems).

    2. Ingestion by Producers: Plants (phytoplankton or grass) absorb these contaminants.

    3. Consumption by Primary Consumers: Primary consumers (e.g., zooplankton or small fish) ingest contaminated plants, leading to bioaccumulation.

    4. Trophic Level Transfer: As secondary and tertiary consumers eat primary consumers, they accumulate even higher levels of contaminants due to the 10% energy transfer rule.

    • Key Concept: Energy transfer leads to increased consumption of biomass and therefore higher POPs accumulation in higher trophic levels.

Biomagnification of DDT

  • DDT Overview: A broad-spectrum insecticide that is carcinogenic and persists in the environment, accumulating in ecosystems.

  • Mechanism of Toxicity:

    • DDT remains in sediments, enters bottom feeders, which bioaccumulate it.

    • Example Numbers:

      • Zooplankton: 0.04 parts per million (ppm) of DDT.

      • Small Fish: 0.5 ppm after consuming zooplankton.

      • Large Fish: 2 ppm.

      • Osprey (quaternary consumer): 25 ppm.

    • Effect of Biomagnification: Leads to significant health impacts, including thinning of eggshells in birds like bald eagles, causing population declines.

Biomagnification of Methylmercury

  • Sources: Released into the atmosphere primarily through coal combustion; also by volcanic activity.

  • Conversion to Methylmercury: Elemental mercury converted by bacteria in aquatic ecosystems.

  • Process Overview:

    • Methylmercury taken up by phytoplankton:

    • Bioaccumulated by zooplankton, which are then consumed by larger fish, leading to increasing concentrations.

    • Example of Food Chain Levels:

      • High-level consumers (e.g., sharks) accumulate very high levels due to consuming large amounts of contaminated biomass.

  • Human Exposure: Consumption of large predatory fish can lead to high levels of methylmercury in humans, causing neurotoxicity.