Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

Supervisor

Chris Wood

Language

English

Abstract

The synthetic estrogen 17α-ethynylestradiol (EE2), an endocrine disruptor originating from birth control and hormone replacement therapy, is discharged in wastewater treatment plant (WWTP) effluents. The present study employed radio-labeled EE2 to examine the impact of temperature and salinity on the uptake of EE2 in male killifish (Fundulus heteroclitus), a model euryhaline teleost. Fish were exposed to a nominal concentration of 100 ng/L EE2 for 2 h. Actual concentrations were lower due to EE2 adsorption to the exposure system, but uptake rates were normalized to 100 ng/L. Oxygen consumption rates (MO2), whole body EE2 uptake rates, and tissue-specific EE2 distribution were monitored. EE2 uptake by freshly killed fish was negligible. In killifish acclimated to 18OC at 16 ppt (50 % seawater), MO2 and EE2 uptake were both much lower after 24-h exposure to 10OC and 4OC, and increased after 24-h exposure to 26OC. Transfer of killifish to fresh water for 24 h tended to lower EE2 uptake rate, and long-term acclimation to fresh water reduced it by about 70 %. Long-term acclimation to 100 % sea water (32 ppt) also reduced EE2 uptake rate by about 50 % relative to 16 ppt. However this was not seen in juvenile rainbow trout (Oncorhynchus mykiss) where uptake rates were the same in FW- and 16 ppt-acclimated trout. The tissue-specific accumulation of EE2 was found to be the highest (40-60 % of the total) in the liver plus gall bladder across all exposures, and the great majority of this was in the bile in killifish, regardless of temperature or salinity, whereas in trout accumulation was the highest in the carcass at 70 % of the total. The carcass was the next highest accumulator (30-40 %) in killifish, followed by the gut (10-20 %) with only small amounts in gills and spleen. Drinking rate, measured with radio-labeled polyethylene glycol-4000, was about 25-times greater in 16 ppt-acclimated killifish relative to freshwater-acclimated animals. However, drinking accounted for less than 30 % of gut accumulation, and therefore a negligible percentage of whole body EE2 uptake rates. In general, there were strong positive relationships between EE2 uptake rates and MO2, suggesting similar pathways for uptake across the gills of these lipophilic molecules. These data will be useful in developing a predictive model of how variations in key environmental parameters (salinity, temperature, dissolved oxygen) affect EE2 uptake in estuarine fish, so as to determine optimal timing and location of WWTP discharges.

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