| The target lipid model has been used to derive water quality objectives that are intended to be protective of chronic effects posed by hydrocarbons. However, experimental Early Life Stage toxicity data for fish are limited and further data are needed to confirm model predictions. Efforts are underway to develop a zebrafish embryo toxicity test guideline to reduce, refine and replace the use of vertebrates in animal testing. An adaptation of this method which includes embryo lethal and sub-lethal developmental endpoints after a 5 day exposure as well as larval survival and growth endpoints during a subsequent 25 day test period is described. To deliver well controlled exposure concentrations, a passive dosing system consisting of silicone coated vials and silicone O-rings was employed. This research consisted of three phases. During the first phase, phenanthrene was used as a reference substance to test efficacy of a passive dosing design as well as compare observed effect data with published effect data. Concentrations shown to cause adverse effects in this phase of the research were in the range of previous studies that have investigated the chronic effects of phenanthrene on fish. In the second phase, separate exposures to five aromatic hydrocarbons (AHs) including 1-methylnaphthalene, phenanthrene, 1, 2, 3, 4, 5, 6, 7, 8, octahydrophenanthrene, benzo(a)pyrene and chrysene utilizing the passive dosing system and ELS design were investigated. Subsequently, during phase two, six short-term (120 hour) exposures for naphthalene, 1-methylnaphthalene, biphenyl, phenanthrene, pyrene and 1, 2, 3, 4, 5, 6, 7, 8, - octahydrophenanthrene were also employed. Data collected from acute and chronic exposures were used to estimate the acute and chronic critical target lipid body burdens for zebrafish using the TLM framework. During the third phase a simple mixture of ten saturated, unsaturated, and aromatic hydrocarbons with a KOW range of ca. 4 - 7.5 was tested during a 30 day ELS test. Three treatment levels were selected to provide concentrations that corresponded to a toxic unit range above and below the predicted effect concentration assuming concentration addition. Observed acute and chronic effects with the mixture were consistent with the assumption of additive toxicity. |
