Abstract:

During March and April 2018, we performed a series of hydrocarbon incubations in Conway, SC using Macondo oil recovered during the Deepwater Horizon blowout to assess the degree of radium isotope release as a function of various degradation processes. We incubated 1 g of oil 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 one set left unamended to allow both photodegradation and microbial degradation, and another set serving as a kill control (with 10 mM ZnCl2) to only allow photodegradation. The submerged plume simulations were stored in a dark refrigerator (2 deg. C), with one set left unamended (to allow microbial degradation) and one treatment serving as a kill control (with 10 mM ZnCl2) to act as a control. Each of the treatments underwent destructive analysis at various time points (t=0 day, 1 day, 3 days, 7 days, 11 days, 14 days, and 21 days) to determine the radium isotope (Ra-224, Ra-226, and Ra-228) activities in both the aqueous phase and on the oil phase through time. These incubations were replicated during July 2018 using 2 mM CdCl2 as the kill control agent and terminated at time points of t=0 day, 1 day, 2 days, 4 days, 7 days, 11 days, 14 days, and 21 days. During the July incubations, we placed 10-L blanks for radium-free seawater (no oil) alongside the surface (i.e., outside) incubations. Any radium detected in these blanks would be due to atmospheric contamination and should be subtracted from the measured activity for the surface incubations.

Suggested Citation:

Peterson, Richard. 2019. Radium isotopes released into the aqueous phase during oil degradation: Deepwater Horizon oil incubations. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/n7-f3tw-xv54

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; this parameter reflects the storage condition of the incubation as either outside in the sunlight ('Surface') or in a dark, refrigerator at 2 deg. C ('Deep')); Treatment (no units; this parameter reflects whether the incubation had live, native microbial communities ('Live') or was poisoned ('Kill Control'); ZnCl2 concentration (mM; March and April Incubations only) or CdCl2 Concentration (mM; July Incubations only); Treatment Time (days; i.e., how long the incubation occurred for before termination); Excess Ra-224 Activity (dpm; this parameter reflects the difference between the initial (total) and 3-week (supported) measurements of Ra-224); Excess Ra-224 Activity Uncertainty (dpm; this parameter reflects the 1-sigma analytical uncertainty related to the square root of the total counts); Ra-228 Activity (dpm; this parameter is the measured Ra-228 activity); Ra-228 Activity Uncertainty (dpm; this parameter is the 1-sigma analytical uncertainty related to the square root of the total counts); Ra-226 Activity (dpm; this parameter is the measured Ra-226 activity); Ra-226 Activity Uncertainty (dpm; this parameter is the 1-sigma analytical uncertainty related to the square root of the total counts); Notes (no units). "ND" = no data (i.e., sample was not measured for this isotope) "BD" = below detection (i.e., no resolvable activity)

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. 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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