The risks to fish of exposure to polycyclic aromatic hydrocarbons from chemical dispersion of crude oil

In this thesis, I examined the risks to fish from exposure to PAH from chemically dispersed crude oil. Exposure was measured by the induction of CYP1A enzyme in hepatic tissue of exposed rainbow trout (Oncorhynchus mykiss). Median effects concentration (EC 50) values for both water accommodated fractions (WAF) and chemically enhanced WAF (CEWAF) treatments were determined to enable a comparison of magnitude in exposure. To correlate exposure to hydrocarbon concentrations, PAH concentrations at the EC 50 concentration were determined. Results showed an increase in exposure (6 to 1100 times) with chemical dispersion.; Next, I investigated the differences in exposure between WAF and CEWAF i.e. exposure to dissolved compounds (WAF) versus compounds present in droplets (CEWAF). Fluorescence microscopy revealed oil droplets adhering to gill surfaces in fish exposed to CEWAF treatments suggesting direct uptake of PAHs from droplets. It also showed diffuse fluorescence in gills of fish exposed to WAF and benzo(a) pyrene in solution, indicating uptake from solution. Gill and liver tissue analysis showed the dispersant was most effective on the low molecular weight PAHs.; Test animals tolerant of marine conditions were used to test for salinity effects on exposure and toxicity. Changes in dispersant effectiveness, PAH solubility and osmoregulatory adjustments in test fish in exposure bioassays at three salinities (0, 15, and 30) ‰ were observed to infer if any one of the factors was predominant or if they acted in combination. The findings showed a reduction in PAH solubility at higher salinity conditions, called "salting out effects".; My last set of experiments measured toxicity of chemically dispersed crude oil toxicity to fish embryos. I compared effects between, medaka ( Oryzias latipes) and mummichog (Fundulus heteroclitus), at two salinities (0 and 15‰, ppt). The results showed an increase in toxicity with CEWAF exposures compared to WAF but there was no significant difference due to species or salinity. EC50 values were also determined for medaka embryos exposed for 48 h to CEWAF at different stages of development. The values showed the latter stages to be more sensitive to hydrocarbon exposure. There was no significant difference between EC50 values derived from 48 h bioassays and the usual 12-day bioassays.; The study reinforced the notion of "knowing your oil" in risk assessments as composition of oil was seen to influence exposure and toxicity. Chemical dispersion increased risk by increasing exposure to PAHs from the crude oil. The presence of oil droplets in chemical dispersion was a significant contributer to exposure and toxicity.