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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:
- 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.
- 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).
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
- 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)
reproduction and developmental tests of specific species
- Gene and chromosome
- Plant mutation tests
such as stamen hair
- Photosynthesis rates
(usually tested in field)
- Seed germination
- Root elongation
involve observations in the ecosystem and tests on field-collected
samples. Field surveys require many sampling excursions to avoid
over- or underestimating. Examples include:
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.)
- Abundances of native
species and numbers of individuals within those species
- Relative abundances
of major taxa to determine community-level effects
- Number of individuals
- 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.