Date of Award

Winter 1992

Document Type


Degree Name

Doctor of Philosophy (PhD)


Ocean & Earth Sciences



Committee Director

David J. Burdige

Committee Member

John R. McConaugha

Committee Member

Alexander E. MacCubbin

Committee Member

Raymond W. Alden, III


The eggs of the Japanese medaka (Oryzias latipes) were employed in a number of studies to develop a routine, standardized assay which can assess the acute and sublethal impacts of individual toxicants and complex mixtures. The eggs of this Cyprinodont minnow were topically treated with each toxicant or mixture dissolved in membrane permeable dimethylsulfoxide (DMSO) solvent. Nine chemicals were initially evaluated with two, pentachlorophenol (PCP) and tributyltin chloride (TBTCl), subsequently selected for extensive evaluations of salinity tolerance and the accuracy of the topical exposure method for representing a typical immersion exposure. The amount of material actually penetrating the eggs was determined for a number of these chemicals, as were the optimum rearing conditions for the eggs. To determine the usefulness of this assay in field studies, surveys of lower Chesapeake Bay tributary water and sediment samples were performed using the MELA approach.

The results indicate that the proposed assay is very useful for the evaluation of the developmental effects of individual toxicants as well as complex mixtures. The salinity tolerance studies indicated that salinity (up to 20ppt for PCP and 35ppt for TBTCl) elicited no significant effect on the toxicity of the two test substances on developing embryos. In addition, it appears that if the bioconcentration factor (BCF) is well established for a chemical, it may be possible to extrapolate to an equivalent medium concentration for a given topical dose. The permeability data indicate that the toxicants penetrate into the eggs at levels well correlated to their octanol-water partition coefficients, suggesting that passive transport is occurring, even in the presence of a membrane permeable carrier.

Finally, the field studies demonstrate that the MELA approach is very useful for evaluating the relative toxic/teratogenic potential of numerous sites, simultaneously. The data from the MELA treatments often correlated well with other biological assays and with chemical data on a site specific basis.


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