Embryotoxicty in medaka (Oryzias latipes) following exposure to select alkaline earth metals: a screening bioassay
Abstract
Environmental exposure to radium, a radioactive alkaline earth metal, and barium,
a chemically similar but non-radioactive earth metal, are of growing concern. Radium
and barium levels in some groundwater aquifers exceed maximum contaminant levels,
and future groundwater resources may be increasingly at risk. Surface waters may
also be at risk from disposal of residual waters enriched in metals, including radium
and barium, from the increased use of chemical filtration processes such as ion exchange
or reverse-osmosis desalination to treat groundwater. Leaching of uranium mine tailings
generated during mining activities and industrial uses of barium, including use in
high-density oil and gas well drilling muds, serve as additional anthropogenic sources
of these metals to surface waters. Currently, there is a lack of information on the
effects of radium and barium on fish development. Such lack of data may complicate
ecological risk assessment, as recruitment of young of the year fishes have been demonstrated
to be major drivers of fish populations.
I employed a high throughput, screening level bioassay to experimentally characterize
toxicity in developing medaka fish embryos and eleutheroembryos (an embryonic phase
starting with hatching and ending with absorption of yolk sac) following exposure
to radium (radium-226 chloride) and barium (barium chloride). The ability to follow
individual embryos over time and view embryonic development through the transparent
chorion were key design characteristics of this experiment. Two endpoints, time to
hatch and mortality, were concurrently assessed.
Results of the bioassay failed to demonstrate evidence of embryotoxicity from exposure
to radium at levels up to 60,000 pCi/L. Exposure to high levels of barium (100 ppm)
resulted in earlier hatching time. Additionally, an increase in post-hatch mortality
was observed, suggesting that the chorion may play a protective role with regard to
alkaline earth metal exposure. Water chemistry appeared to affect the magnitude of
post-hatch mortality, although results between different exposure scenarios used in
the study were ambiguous. The lack of observed embryotoxicity from radium exposure
does not definitively demonstrate that radium is not toxic, as other endpoints not
assessed in this screening level bioassay may be more sensitive indicators of toxicity
and effects from exposure during development may manifest themselves at later life
stages. Results of the barium analysis suggest that young of the year fishes may
be particularly sensitive to acute exposure to high levels of alkaline earth metals.
This suggests that better management of radium and barium in the environment, including
the disposal of brine solutions enriched in alkaline earth metals to surface waters,
may be needed to reduce ecological risks to fish populations.
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https://hdl.handle.net/10161/537Citation
Nelson, Clay (2008). Embryotoxicty in medaka (Oryzias latipes) following exposure to select alkaline earth
metals: a screening bioassay. Master's project, Duke University. Retrieved from https://hdl.handle.net/10161/537.Collections
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