Abstract:

This dataset contains measurements of radium isotopes (224Ra, 228Ra and 226Ra) from field incubations (September and October 2018) detailing the release of radium from Deepwater Horizon archived oil and from freshly-discharged oil recovered from the Gulf of Mexico during a cruise aboard the R/V Point Sur PS19_05. The goal of these incubations is to assess the degree of radium isotope release as a function of various degradation processes. 1 g of oil was incubated with 10 L of radium-free seawater to replicate surface sheen ('Surface') and submerged plume ('Deep') degradation. The surface sheen incubations were stored outside in ambient sunlight, with some incubations left unamended to allow both photodegradation and microbial degradation, and others serving as a kill control using chemical poisons to only allow photodegradation. The submerged plume simulations were stored in a dark refrigerator (2 deg. C), with some incubations left unamended (to allow microbial degradation) and others poisoned to serve as a kill control. Each of the treatments underwent destructive analysis at various time points (from 0 days up to 3 weeks) to determine the radium isotope (Ra-224, Ra-226, and Ra-228) activities in the aqueous phase through time. The experimental variables were oil concentration, poison composition, and poison concentration. 10-L blanks for radium-free seawater (no oil) was used alongside the surface (i.e., outside) incubations. Any radium detected in these blanks would be due to atmospheric contamination and are subtracted from the measured activity for the surface incubations.

Suggested Citation:

Peterson, Richard. 2020. Measurements of radium isotopes (224Ra, 228Ra and 226Ra) from fall field incubations (September and October 2018 ) detailing the release of radium from Deepwater Horizon archived oil and from freshly-discharged oil recovered from the Gulf of Mexico during a cruise aboard the R/V Point Sur PS19_05. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/n7-nt0e-cx32

Purpose:

The purpose of this dataset is to plot the activity of various radium isotopes in water over time, to constrain the release and subsequent decay curves of radium in water containing hydrocarbons. We anticipate that more intensive hydrocarbon degradation processes will release a greater degree of radium isotopes in the thorium decay series (Ra-224 and Ra-228) to surrounding water and that the differential rates of decay of these isotopes (Ra-224 has a half-life of 3.54 days; Ra-228 has a half-life of 5.7 years) will lead to unique Ra-224/Ra-228 activity ratios as a function of degradation time. These data will form the basis of using radium isotopes as a geochronometer of hydrocarbon residence time in the marine environment.

Data Parameters and Units:

Simulated Depth (no units) – either ‘Surface’ (i.e., stored outside in ambient sunlight) or ‘Deep’ (i.e., stored in dark, cold refrigerators) Treatment (no units) – either ‘Seawater Blank’ (i.e., seawater only with no oil addition), ‘Initial’ (i.e., oil added then immediately terminated), ‘Live’ (i.e., no poison added), or ‘Kill Control’ (i.e., poison added to repress microbial populations). Termination Date (EST) – date that incubation was terminated, in EST Termination Time (EST) – time that incubation was terminated, in EST Oil Source Used (no units) – either ‘None’ or ‘Megaplume-1’ (i.e., oil collected from the Megaplume oil seep at GC-600 during PS19_05) Oil Mass (g) – mass of oil added to incubation, in g Poison Used (no units) – either ‘None’, ‘CdCl2’ (i.e., aqueous concentrated cadmium chloride), ‘ZnCl2’ (i.e., aqueous concentrated zinc chloride, or ‘CdCl2 and ZnCl2’ as a combination of both poisons Poison concentration (mM) – concentration (if applicable) of poison in the incubation Treatment Time (days) – amount of time elapsed between initiation of the incubation and termination Excess Ra-224 Activity (dpm/100L) -- measured activity of excess Ra-224 with units of dpm/100L Excess Ra-224 Activity Uncertainty (dpm/100L) -- analytical uncertainty of the measurement of excess Ra-224 activity with units of dpm/100L Ra-228 Activity (dpm/100L) -- measured activity of Ra-228 with units of dpm/100L Ra-228 Activity Uncertainty (dpm/100L) -- analytical uncertainty of the measurement of Ra-228 activity with units of dpm/100L Ra-226 Activity (dpm/100L) -- measured activity of Ra-226 with units of dpm/100L Ra-226 Activity Uncertainty (dpm/100L) -- analytical uncertainty of the measurement of Ra-226 activity with units of dpm/100L ND = no data BD = below detection N/A = not applicable

Methods:

During each termination, the oil/water incubation volumes were passed slowly (i.e., 0.5 L/min) through acrylic fiber prefilters (which collected the oil phase) and then through acrylic fibers impregnated with MnO2 (which quantitatively sorbed radium isotopes; Moore, 1976). Aqueous phase and oil phase fibers were analyzed separately on a Radium Delayed Coincidence Counter (RaDeCC) immediately for total Ra-224, then again after 3 weeks for supported Ra-224 (Moore and Arnold, 1996). The difference between these activity measurements is the reported excess Ra-224 activity. All samples for oil-phase radium isotopes were below the detectable activity for all isotopes, so are not reported in the dataset. The fibers were then sealed in air-tight cartridges to allow Rn-222 to grow in toward equilibrium with Ra-226 and measured on a radon emanation line for sorbed Ra-226 activities (Peterson et al., 2009). Selected fibers were then placed into stainless steel crucibles, ashed in a muffle furnace (550 deg. C for 8 hours), sealed with epoxy, then measured for Ra-228 activity on an Ortec planar germanium detector (Dulaiova and Burnett, 2004).

Instruments:

Radium Delayed Coincidence Counter (RaDeCC), produced by Scientific Computer Instruments. Instrument was calibrated with NIST-traceable Th-232 standards (with daughters in equilibrium) and checked periodically with this standard for QA/QC. Planar Germanium Detector (gamma detector), produced by Ortec. Instrument was calibrated with NIST-traceable Th-232 standards (with daughters in equilibrium) and checked periodically with this standard for QA/QC.

Error Analysis:

Analytical uncertainties are reported as 1-sigma errors based on counting statistics. Errors in count rate (i.e., counts per minute) are computed by the square root of the total counts. This error is then propagated throughout the activity calculations.

Provenance and Historical References:

Dulaiova, H., & Burnett, W. C. (2004). An efficient method for γ-spectrometric determination of radium-226,228 via manganese fibers. Limnology and Oceanography: Methods, 2(8), 256–261. doi:10.4319/lom.2004.2.256 Moore, W. S. (1976). Sampling 228Ra in the deep ocean. Deep Sea Research and Oceanographic Abstracts, 23(7), 647–651. doi:10.1016/0011-7471(76)90007-3 Moore, W. S., & Arnold, R. (1996). Measurement of 223Ra and224Ra in coastal waters using a delayed coincidence counter. Journal of Geophysical Research: Oceans, 101(C1), 1321–1329. doi:10.1029/95jc03139 Peterson, R. N., Burnett, W. C., Dimova, N., & Santos, I. R. (2009). Comparison of measurement methods for radium-226 on manganese-fiber. Limnology and Oceanography: Methods, 7(2), 196–205. doi:10.4319/lom.2009.7.196

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