Environmental Engineering Reference
In-Depth Information
enough of it!) Toxic effects have been studied primarily in
laboratory experiments (bioassays), although there have been
some field studies of effects on populations of marine organ-
isms. Early studies of pollutant effects relied on tests that
measured lethality (death). The LC 50 —the concentration of a
chemical that caused 50% of the test animals to die (typically
in 96 hours)—was the benchmark. Regulations under laws
such as the US Federal Insecticide Fungicide and Rodenticide
Act (FIFRA) for developing safe levels of pesticides to protect
aquatic life require the standard LC 50 , which is of little eco-
logical relevance. Toxicity tests are required for a few spe-
cies:  rainbow trout, bluegill, and daphnids—one cold-water
fish, one warm-water fish, and one crustacean, all freshwater
species. Unfortunately, even today, over half a century later,
this approach—measuring what percentage of the animals die
in 96 hours—is still considered most useful in a regulatory
context. These tests do not consider sublethal effects that occur
over longer periods of time, or toxicity that is delayed, or dif-
ferences in life history among species. Knowing about effects
of longer-term, lower-dose exposures on physiology, behav-
ior, and development is essential for understanding overall
impacts of pollutants in nature.
What effects can pollutants have besides killing living things?
Extensive research has shown that toxic chemicals can disrupt
metabolic, regulatory, or disease defense systems, and reduce
reproduction. Behavior, development, and physiology are all
sensitive to pollutants. Learning about these sublethal effects
can help us understand the mechanisms of action of different
chemicals, and also to understand ecological effects in the real
world. We have learned that early life processes and stages—
eggs and sperm, fertilization, embryonic development, and
larvae—are very sensitive to contaminants, so setting “safe”
levels based on how much of a chemical will kill adults will
not protect these young stages. The hormonal control of
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