Uranium mining and milling operations at Key Lake, Saskatchewan, Canada, have been releasing effluent since 1983, resulting in the accumulation of selenium in surface water, sediment, and biota in downstream lakes relative to pre-development and reference lake conditions. Elevated selenium can pose a risk to fish and bird populations in aquatic ecosystems as a result of the trophic transfer of selenium from the base of the aquatic food web. This research program was designed to address specific knowledge gaps related to the bioaccumulation of selenium at the benthic-detrital link of aquatic food webs. To fulfill this objective, laboratory and in situ field experiments were conducted using the benthic invertebrate Chironomus dilutus to identify the exposure pathway(s) and selenium species associated with the bioaccumulation of selenium by benthic invertebrates downstream from the Key Lake operation.
Laboratory bioaccumulation tests that exposed midge larvae to 4.3 µg/L as dissolved selenate for 10 d resulted in negligible accumulation of selenium. However, larvae rapidly accumulated selenium over 10 d of exposure to 3.8 and 1.8 µg/L selenite and seleno-DL-methionine (Se-met), respectively. Furthermore, once selenium was accumulated by the larvae from the selenite and Se-met treatments, the majority of it was retained after a 10 d depuration period in clean water. When additional midge larvae were exposed to selenium until emergence, selenium accumulated during the larval stage was passed onto the adults following metamorphosis, with only a small percentage of the selenium (< 5%) transferred to the exuvia. Selenium speciation analysis using X-ray absorption spectroscopy showed that increases in total selenium concentrations corresponded to increased fraction of organic selenides, modeled as selenomethionine, in C. dilutus larvae and adults.
Results from the 2008 in situ caging study confirmed that surface water is not a significant selenium exposure pathway for benthic invertebrates at Key Lake. Chironomus dilutus larvae accumulated between 20- and 90-fold more selenium from exposure to sediment compared to exposure to surface water in the high exposure lake. In response to these findings, a second in situ experiment was conducted in 2009 to investigate the importance of dietary selenium (biofilm or detritus) vs. whole-sediment as an exposure pathway. Larvae exposed to sediment detritus (top 2 â 3 mm of sediment) from the exposure site had the highest selenium concentrations after 10 d of exposure (15.6 ± 1.9 µg/g) compared to larvae exposed to whole-sediment (12.9 ± 1.7 µg/g) or biofilm (9.9 ± 1.6 µg/g). Biofilm had lower total selenium concentrations than the detritus and whole-sediment fractions, but nearly 80% of the selenium was present as organic selenides similar to selenomethionine. Biofilms appear to be an enriched source of organic selenium and are important food items for many benthic consumers. Integrating the separate lines of evidence that were generated during laboratory and in situ bioaccumulation tests helped strengthen the understanding of selenium accumulation in the benthic-detrital food web and subsequent trophic transfer of selenium to benthic invertebrates.
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-06072012-205335 |
| Date | 08 June 2012 |
| Creators | Franz, Eric Duncan |
| Contributors | Liber, Karsten, Janz, David, Pietrock, Michael, Sanderson, Hans |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-06072012-205335/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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