Date of Award


Document Type


Degree Name

Master of Science (MS)

Legacy Department

Environmental Toxicology

Committee Chair/Advisor

Klaine, Stephen J

Committee Member

Lee , Cindy M

Committee Member

Hoang , Tham C


The assumption of the individual effective dose is the basis for the probit method used for analyzing dose or concentration – response data. According to this assumption, each individual has a uniquely innate tolerance expressed as the individual effective dose (IED) or the smallest dose that is sufficient to kill it. An alternative to IED, stochasticity suggests that individuals do not have uniquely innate tolerance; deaths result from random processes occurring among similar individuals. While the probit method has been used extensively in toxicology the underlying assumption has not been tested rigorously. The goal of this study was to test which assumption, IED or stochasticity, best explained the response of Daphnia magna exposed to multiple pulses of copper sulfate (CuSO4) over 24 – d. Daphnia magna were exposed to subsequent age – dependent 24 – h LC50 Cu concentrations. Age – dependent 24 – h LC50 values were determined prior to the 24 – d bioassay. These LC50 values were inversely related to organism age. A Cu depuration test was conducted to determine time between Cu exposures. Results indicated that five days was sufficient for D. magna to depurate accumulated Cu and recover from previous exposure. Hence, recovery time between Cu exposures during the 24 – d test was five days. The Cu depuration of D. magna did not depend on age or Cu concentration. Daphnia magna were exposed to four 24 – h Cu exposures each separated by five days during the 24 – d bioassay. Surviving organisms were transferred after each exposure to Cu-free culture media for recovery time before the next exposure. Stochasticity best explained the survival and reproduction response of D.magna exposed to Cu.



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