Exposure of ionic hyper-regulated artemia to chlorine – 36 in a marine system Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3x816p52v

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  • Chlorine – 36 (36Cl) is produced naturally, through neutron activation of stable chlorine during nuclear weapons detonation, or from neutron capture on residual chlorine in graphite piles. It has a half-life of 301,000 years and decays by the means of beta decay with an average energy of 236.33 keV. Due to 36Cl’s long half-life and mobility in the environment, it is of potential concern in the long-term management of certain nuclear waste facilities or when decommissioning plutonium-production reactors. The existing body of research data on 36Cl is limited and often contradictory—showing extremely high uptake factors into biologic media. This study is part of a larger effort to understand both the environmental and biological mobility of 36Cl, in this case using the common Brine shrimp (Artemia Salina). These species are of interest because of their use of osmoregulation, which allows them to hyperregulate and survive in an environment with variable salinity. Brine shrimp were exposed in two simulated marine ecosystems: Tank #1 at a low water concentration 36Cl of 1.64 +/- 1.28 Bq/ml and tank #2 at a ten times higher concentration of 16.40 +/- 4.04 Bq/ml. Uptake was evaluated for mature Artemia over a period of 20 days. The uptake in both the low and high 36Cl concentration tanks followed similar cycles of uptake and efflux of 36Cl. The Brine shrimp exposed to the low activity concentration of 36Cl had an uptake rate of 35.77 +/- 6.77 (Bq/g)/day with an efflux rate of 35.79 +/- 7.26 (Bq/g)/day. The Brine shrimp exposed to ten times the concentration of 36Cl had an uptake rate of 70.02 +/- 11.81 (Bq/g)/day and an efflux rate of 62.98 +/- 11.81 (Bq/g)/day. Two conceptual models were developed using the isee software STELLA. The first model followed the hypothesis of a buildup and plateau. The low 36Cl concentration system conceptual model predicted a maximum concentration of 7.14x10¹ Bq/g. For the high 36Cl concentration system, a maximum concentration of 1.115x10¹ Bq/g was predicted. A second conceptual model was developed taking into account a cycling effect that closely mimicked the research data for both the high-concentration and low-concentration systems. The low 36Cl concentration conceptual model predicted a maximum concentration of 7.33x10¹ Bq/g and minimum concentration of 1.58x10¹ Bq/g. The high 36Cl concentration conceptual model yielded a maximum concentration of 1.22x10² Bq/g and minimum concentration of 1.79 Bq/g.
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