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Major Categories of Tests for Ecological Assessment

There are 4 major categories of tests scientists use to study the effects of pollution on ecosystems:

  1. Chemical and Physical Tests provide information on the total concentration of specific chemical compounds in the ecosystem and information on pH, temperature, moisture, and other measures. Samples of soil, sediment, or water are collected and usually taken to a laboratory for testing using several standard laboratory methods.

  2. Toxicity Tests measure the number and severity of biological effects of contamination on the survival, growth, and reproduction of plants and animals. Most toxicity tests are conducted in the laboratory using laboratory-raised species or organisms collected in the field (from the ecosystem). Examples include:
    • Acute test (number of animal deaths) using field-collected specimens or test species such as earthworms or fathead minnows

    • Chronic growth, tumor, and functional tests of selected species (usually the most sensitive species)

    • Multigenerational reproduction and developmental tests of specific species

    • Gene and chromosome tests

    • Plant mutation tests such as stamen hair

    • Photosynthesis rates (usually tested in field)

    • Seed germination

    • Root elongation

  3. Biomarkers of Exposure are sensitive indicators of a physiological, anatomical, or biochemical response to pollution exposure such as abnormal blood changes. They can be used as sensitive monitoring tools for detecting exposure. Individual organisms usually are obtained from the ecosystem and their blood and body tissues are examined. (Biomarkers are not considered adequate measures of biological effects at the population, community, and total ecosystem levels of organization.) Examples include:

    • Bioaccumulation tests indicate the level of chemical pollution that has gathered in an individual animal or plant and the availability of those pollutants to vulnerable tissues inside the body.

    • Blood enzyme levels are used to assess exposure to certain pesticides.

    • Histopathologic tests using light microscopy, electron microscopy, and chemistry involve examinations of specific tissues and organs like the liver and kidney to detect chemical damage. (Histologic exams often are used in long-term and chronic toxicity tests to confirm findings.)

  4. Field Surveys involve observations in the ecosystem and tests on field-collected samples. Field surveys require many sampling excursions to avoid over- or underestimating. Examples include:

  • Abundances of native species and numbers of individuals within those species

  • Relative abundances of major taxa to determine community-level effects

  • Number of individuals with offspring

  • Estimates of total biomass (mass of tissue present in an individual, population, or community at a given time) or biomass of certain communities such as phytoplankton

  • Guild structure (functional feeding groups such as collector-gatherers or predators based on how organisms obtain their food) may change as a result of exposure to contamination. This can alter levels of competition for common resources.

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