REPRODUCTION IN FATHEAD MINNOWS (PIMEPHALES PROMELAS) FOLLOWING WATER OR SEDIMENT EXPOSURE TO A COMPLEX URANIUM MILLING EFFLUENT ELEVATED IN SELENIUM
Northern Saskatchewan, Canada is home to a uranium milling operation that discharges a complex effluent containing elevated concentrations of nutrients, compounds and many metals including the metalloid selenium (Se). Selenium has the potential to bioaccumulate in aquatic systems even when water concentrations are low, which has resulted in the identification of Se as a constituent of concern in affected aquatic ecosystems. This research evaluated the effects of treated uranium milling effluent and contaminated sediment in isolation and in combination to determine the contribution and importance of each source to fathead minnow (Pimephales promelas) reproduction and survival. Identification of pathways of exposure is critical to the mitigation of any observed effects. Trios of fathead minnows were allocated to one of four treatments for 21-days where the following were evaluated: survival (adult and 5 day larval), larval deformities, reproductive effects (egg production, spawning events) and metal tissue burdens (muscle, ovary, eggs and larvae). In addition, Se speciation analysis was conducted on selected fish tissues. Effects were overwhelmingly effluent-mediated with little contribution observed due to the presence of contaminated sediments. The contaminated sediments tested were taken from the actual receiving environment and represented the sediment composition found in greatest abundance in areas characteristic of fathead minnow habitats. Results showed egg production significantly increased in the effluent treatments compared to the reference water treatments (p ≤ 0.05). Although egg production increased following effluent exposure, there was reduced hatching success by 23% (p = 0.001), and larval survival by 31% (p = 0.001) and a significant increase in skeletal deformities (i.e. scoliosis, lordosis) in 5 day old larvae by approximately 6-fold (p = 0.001) relative to control. Despite these effects on the offspring, when examined in an integrated manner relative to increased egg production, the mean number of normal larvae did not differ among treatments (p > 0.05) when compared to reference water treatments. Many metals including total Se and Rb significantly increased (p ≤ 0.05) in the effluent exposed algae/biofilm collected from the streams, eggs, larvae and female muscle and gonads. A shift in the speciation of Se was evident with exposure, where for the larvae selenocystine-like compounds were found to be around 80% and selenite at 5-11% of the total Se in reference water exposed larvae. However, in effluent exposed larvae selenocystine-like compounds dropped to 53-68% and selenomethionine-like compounds increased to about 28%. The algae/biofilm present in the mesocosms was identified as key in the transfer of available Se into the food chain from the water and was a source of direct dietary exposure to fish and possibly invertebrates. Additional analysis of the data was carried out using correlation and Principal Component Analysis (PCA) techniques. The results there showed a strong correlation between Se in water and algae, as well as among Se in the ovary and eggs and larvae. Correlation work was also done with Rb and strong correlations were noted between Rb in and eggs/female/day. Principal Component Analysis results showed the loading of other metals, such as Zn, Cd, and As loaded more strongly in the first component compared to Se in the third component. A summary of all the results indicate that exposure to an environmentally relevant concentration (25%) of uranium milling effluent leads to increased egg production, yet the resulting eggs and larvae experienced reduced hatching success, survival and increased incidence of deformities. While much of the focus of the initial work was on Se in the environment and fish tissues the later correlation and PCA work suggest that Se is contributor to the system but not the sole causal factor of all observed results.
selenium, fathead minnow, complex effluent, reproduction, uranium mining, larval deformities
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