The toxicity of alkyl-chrysenes and benz[a]anthracenes to embryonic fish
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Alkylated polycyclic aromatic hydrocarbons (alkyl-PAHs) are major constituents of crude oil, and the 3-5 ringed alkyl-PAHs have been identified as the main components chronically toxic to fish. While chysene homologues have higher cytochrome P4501A (CYP1A) induction potencies than alkyl-phenanthrenes, there is little characterization of toxicity for 4-ringed alkyl PAHs. This study measured the chronic toxicity of chrysene, benz[α]anthracene, and some alkylated congeners to the embryos of Japanese medaka (Oryzias latipes) using the partition-controlled delivery method (PCD) of exposure. This exposure method relies on the partitioning of chemicals from polydimethylsiloxane (PDMS) films, loaded with various concentrations of test chemical, to embryo rearing solutions. The objectives of this thesis were: (1) to further characterize the PCD method with a series of 4-ringed PAHs; (2) to evaluate the effects of different chemical structures on the toxicity of test compounds; and (3) to extend structure toxicity relationships from alkyl-phenanthrenes. The PCD method generated a gradient of aqueous concentrations for test compounds, and these exposure concentrations were maintained constant for the 17-day period. Benz[α]anthracene showed higher toxicity than chrysene. Toxicity increased with the degree of alkylation on the ring structures, except that 2-methylbenz[α]anthracene was less toxic than the unsubstituted benz[α]anthracene. Substitutions at the middle region contributed to a higher toxicity than substitutions at the distal region. While actual mechanisms for these compounds to cause toxicity are unknown, the narcotic mode of action seems to be not involved due to the lack of mortality. Within the range of test concentrations, the chronic sublethal toxicity was limited by the low solubility of the test compounds. A structure toxicity relationship was illustrated by the regression between log EC50s and log Kow values. In addition to hydrophobicity represented by log Kow, structural dissimilarities between compounds and physical characteristics such as aqueous solubility limits should be taken into account in toxicity assessments with alkyl-PAHs. This research is the first toxicological assessment of alkyl-chrysenes and benz[α]anthracenes which is essential for a better understanding of structure toxicity relationships of alkyl-PAHs, and will contribute to more accurate ecological risk assessments of PAH contamination.