THESIS APPROVAL
THESIS APPROVAL
THESIS APPROVAL
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(LC50). However, death is not easily determined for some invertebrates, the median<br />
effective concentration (EC50) is estimated rather than the LC50. The effect used for<br />
estimating the EC50 is immobilization defined as lack of movement, loss of<br />
equilibrium defined as inability to maintain normal posture (Parrish, 1985).<br />
2. Sublethal Effects Tests<br />
These tests are designed to determine the toxic effects of a chemical to<br />
selected aquatic organisms exposed to low concentrations of the test material. In<br />
general, organisms are not usually exposed to high toxic concentration of chemicals in<br />
the aquatic environment unless they are restricted to the vicinity of a chemical release<br />
site. Thereby, a greater biomass is exposed to sublethal concentrations of chemicals<br />
than to acutely toxic lethal concentrations (Rand and Petrocelli, 1985). Sublethal<br />
effects may be studied in the laboratory by a variety of procedures. The most<br />
common effect criteria are behavioral changes, physiological changes, biochemical<br />
changes, and histological changes. Some sublethal effects may indirectly result in<br />
lethality, but they may have a profound effect on the future survival of the organisms.<br />
Behavioral effects that have received considerable attention in aquatic organisms are<br />
locomotion and swimming, attraction-avoidance, prey-predator relationship,<br />
aggression and territoriality, and learning (Rand, 1985). Physiological and<br />
biochemical tests include studies of enzyme inhibition, clinical chemistry,<br />
hematology, and respiration (Mehrle and Mayer, 1985). Finally, histological studies<br />
are also useful to determine changes in histological structure which may often<br />
significantly modify the function of tissues and organs (Meyers and Hendricks, 1985).<br />
3. Chronic Toxicity Tests<br />
Sometimes a chemical does not have adverse effects on aquatic organisms in<br />
acute toxicity tests. Chronic toxicity tests permit evaluation of the possible adverse<br />
effects of the chemical under conditions of long-term exposure at sublethal<br />
concentrations. In a chronic test, the test organism is exposed for an entire<br />
reproductive life cycle. The exposure is generally initiated with an egg and continues<br />
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