RADIONUCLIDES IN PRODUCED WATER FROM NORWEGIAN OIL AND GAS INSTALLATIONS CONCENTRATIONS AND BIOAVAILABILITY

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1 RADIONUCLIDES IN PRODUCED WATER FROM NORWEGIAN OIL AND GAS INSTALLATIONS CONCENTRATIONS AND BIOAVAILABILITY D. Ø. ERIKSEN, R. SIDHU, E. STRÅLBERG, K. I. IDEN ** Institute for Energy Technology (IFE) K. HYLLAND, A. RUUS, O. RØYSET Norwegian Institute for Water Research (NIVA) M. H. G. BERNTSSEN National Institute for Nutrition and Seafood Research (NIFES) H. RYE The Foundation for Scientific and Industrial Research (SINTEF) Substantial amounts of produced water, containing elevated levels of radionuclides (mainly 226 Ra and 228 Ra) are discharged to the sea as a result of oil and gas production on the Norwegian Continental Shelf. So far no study has assessed the potential radiological effects on marine biota in connection with radionuclide discharges to the North Sea. The main objective of the project is to establish radiological safe discharge limits for radium, lead and polonium associated with other components in produced water from oil and gas installations on the Norwegian continental shelf. This study reports results indicating that the presence of added chemicals such as scale inhibitors in produced water has a marked influence on the formation of radium and barium sulphates when produced water is mixed with sea water. Thus, the mobility and bioavailability of radium (and barium) will be larger than anticipated. Also, the bioavailability of food-borne radium is shown to increase due to presence of such chemicals. 1 Introduction Substantial amounts of produced water (143 Mm 3 in 24) are discharged to the sea in connection with oil and gas production on the Norwegian Continental Shelf. Produced water from some installations contains elevated levels of 226 Ra and 228 Ra. In 23 a systematic survey on the levels of 226 Ra, 228 Ra and 21 Pb in produced water from all 41 Norwegian platforms discharging produced water was conducted for 5 consecutive months. The concentration of 226 Ra and 228 Ra varied between below detection limit (.5-1 Bq/L) to 16 Bq/L and 21 Bq/L, respectively. 21 Pb levels were below detection limit. On the basis of these results annual discharges of 44 GBq 226 Ra and 38 GBq 228 Ra were calculated. This corresponds to an average concentration of 3.3 and 2.8 Bq/L of 226 Ra and 228 Ra, respectively [1]. ** corresponding author: dag.eriksen@ife.no Czechoslovak Journal of Physics, Vol. 56 (26), Suppl. D D43

2 D. Ø. Eriksen et al. It is generally assumed that when produced water rich in barium and poor in sulphate is brought into contact with seawater, rich in sulphate, radium will co-precipitate with barium as sulphates. Depending on the size, the particles will either be transported with the water currents, settle immediately, or sorb onto other organic or inorganic particles. Sequentially they will reach the seafloor. Due to chemical similarities between barium and radium the speciation of radium is determined by the much higher concentrations of barium. However, data on the speciation of radium and barium and the effect of components in produced water are rather limited. In today s oil production, chemicals, e.g. scale and corrosion inhibitors, emulsion breakers and surfactants, sulphide removers, are added to ease the operation. These chemicals are usually organic compounds comprising functional groups, which may also interact with cations such as Ra 2+ and Ba 2+. Thus, radium may exist in compounds more easily accessible for uptake in biota than the inorganic aqueous or food-borne form. Two major contributors to emission to sea from installations on the Norwegian sector are Troll B and C. To avoid the formation of CaCO 3 scale at the Troll field, the scale inhibitor SI 447 (MI Production Chemicals, Norway) is used at an average concentration of about 13 mg/l produced water. This is a low molecular weight polycarboxylic acid adjusted to ph 9-1. Although designed for reaction with Ca 2+ ions, it may also interact with dissolved barium and radium. In this manner it may affect the sedimentation and mobility of barium and radium, when discharged produced water mixes with seawater. An understanding of how different compounds in produced water affect the mobility, bioavailability, and sedimentation of radium is essential in order to determine the fate and effects of radium discharges. Sediment-dwelling organisms may be an important group of marine organisms that might be exposed to the relevant radionuclides. Once taken up by sediment dwelling invertebrates, the nuclides can be transferred to higher level of the marine food chain (fish), ultimately forming a potential risk for human consumption. In addition to the food-borne route of exposure, water-borne exposure would be expected to form an alternative route by which fish can be contaminated. The relative uptake from the different exposure routes and the effect of chemicals on the bioavailability of radionuclides are of great importance when assessing possible consequences for animal welfare and food safety. For evaluation purposes the behaviour of radium in produced water must be compared to radium already present naturally in seawater. 2 Experimental Controlled tests have been performed for measuring the BaSO 4 particle size distribution when barium containing aqueous solutions, with or without SI 447, mix with seawater containing sulphates. The particles formed were filtered through standard equipment and the particle size distributions were determined by laser scattering using a Malvern Mastersizer 2. The morphologies of the particle fractions were studied using SEM, Hitachi S48. Assuming the impact on the particle size distribution of BaSO 4 from dilution is independent on the chloride concentration barium solutions using Ba(NO 3 ) 2 and pure water were used as starting points. D44 Czech. J. Phys. 56 (26)

3 Radionuclides in produced water concentrations and bioavailability Food-borne bioavailability is here defined as that fraction of an orally administered dose reaching the systemic circulation of the animal [2]. It can be quantified (in % uptake from feed) by the integral of the concentration of Ra in blood as a function of time after a single dose. This can thus be determined by comparing the calculated area under concentration vs. time curves (AUC) for Ra from food or injected directly into the blood. To enable measurement of uptake of 226 Ra in fish through food, 226 Ra with and without scale inhibitor was added to fish food. To make sure that the nuclide could be traced the concentration used was higher than that found in seawater, i.e. 1 Bq per 1 g of fish. The concentration of 226 Ra in seawater off the Norwegian coast is 1 2 Bqm 3 [3]. The fish (juvenile cod) were force fed orally by administering a dose of food directly into the stomach with a syringe. The amount of food depended on the weight of the fish so that all fishes were exposed to the same dose. Samples of blood were then taken at predetermined times [4]. Liquid scintillation counting was used for measuring 226 Ra and daughters. The samples were stored until radioactive equilibrium was obtained. Thus no decay corrections were necessary. The blood was dissolved in 1-2 ml Solvable and 2 ml UltimaGold AB was added. Both solutions were purchased from Perkin Elmer. Using Quantulus (LKB Wallac Oy) with peak shape analysis a good separation of alpha- and beta radiation was obtained. Although the quenching in some samples was considerable, the loss of alphas seems to be low. Examples of alpha spectra from blood samples are shown in Fig. 1 left and right parts, respectively. For each spectrum the background was subtracted and the peak area defined manually. Then the integral was calculated. At each sampling time an average of the four samples were used in the determination of the uptake in the blood. In Fig. 1 left, the content of Ra is followed as a function of time after exposure. In Fig. 1 right, α-spectra from blood samples taken from four fishes with the same exposure, and at the same time after exposure are shown. The figure indicates the Counts per channel Time 1.5 hours Time 3 hours Time 6 hours Time 12 hours Counts per channel All samples taken 3 hours after exposure Channel numbers Channel numbers Fig. 1. Left part: α-spectra of 226 Ra measured with Quantulus and UltimaGold AB as scintillator of blood samples taken from fish with the same exposure, but at different times after food had been administered into the stomach. Right part: α-spectra of 226 Ra measured with Quantulus and UltimaGold AB as scintillator of blood samples taken from four fishes with the same exposure, and at the same time after exposure. This figure indicates the individual variation found. Czech. J. Phys. 56 (26) D45

4 D. Ø. Eriksen et al. individual variation, i.e. a standard deviation of 3% is found. This is the major contribution to the stochastic errors in these experiments. To study the uptake of Ra directly from water and to measure any effect of added scale inhibitor an exposure test was performed. Juvenile Atlantic cod (Gadus morhua) (approximately 4 g) was purchased from a commercial breeder. Twelve aquaria holding 5 L each were arranged in a semi static system with air-supply (bubbling). The experiment was designed with four groups, each with three replicate tanks. In addition to a control group being exposed to only background levels of Ra, one group was exposed to seawater with enhanced content of Ra, one to Ra with.1 mg/l scale inhibitor (SI 447), and the last group to Ra with 13 mg/l SI 447. All the three latter groups were exposed to seawater containing 1 Bq/L 226 Ra. The water was changed every third or fourth day and fish were sampled at predetermined intervals, i.e. at days, 3, 1, and 27 the final day. From each fish samples of gills, blood, liver, skin, kidneys and carcass were taken. The fish tissues were dissolved in Solvable and treated as in the previous experiment. To measure the amount of biological accessible Ra during the exposure from seawater test MnO 2 -based disks in DGTs (Diffusive Gradients in Thin films) [5] were used. Filters coated with MnO 2 were purchased from Nucfilm, Switzerland, and DGTs prepared at NIVA s laboratory in Oslo. After exposure of the DGTs in the aquaria for a suitable time, the MnO 2 disk was rinsed with deionised water and the 226 Ra activity determined using alpha spectrometry. All experiments involving fish were performed at NIVA s Marine Research Station Solbergstrand. Fresh seawater was supplied from 6 m depth in the Oslofjord. The used, radioactive water batches were disposed of in tanks where Ra was removed by scavenging with MnO 2. The precipitate was allowed to settle and the water was filtered through an activated carbon filter prior to release to sea. 3 Results Without the inhibitor a 1.5 mm concentration of Ba in seawater gives BaSO 4 particles with an average particle size of about 8 µm, while when 1 mg/l SI 447 is added to this water the particle decreases to about 3 µm. These results suggest that the inhibitor has an effect on controlling the size of BaSO 4, and thereby also the sedimentation rate and the mobility of radium. Additional results show that both the amount of BaSO 4 particles and their sizes decrease rapidly upon dilution with seawater. BaSO 4 particles formed in the presence of SI 447 show different morphology than the particles formed without its presence. Fig. 2 shows an example of crystals formed with and without the presence of scale inhibitor. It is clear that the inhibitor acts by hindering the crystal growth. The results from force-feeding of cod indicate a much stronger increase in Ra-uptake from food when scale inhibitor is present, i.e. approx. 6% vs. approx. 12%. Fig. 3 shows the concentration curves of intravenous injection and uptake through food. The results from the exposure of cod from water indicate very low uptake directly from the water. Gill-tissue was the only tissue in which one could observe a slight increase in Ra in the exposed groups over the control group. The results are shown in Fig. 4. Although there D46 Czech. J. Phys. 56 (26)

5 Radionuclides in produced water concentrations and bioavailability Fig. 2. Morphology of BaSO 4 -particles measured by SEM. In the left hand sample the crystals have been allowed to grow freely, while in the sample on the right hand side the presence of scale inhibitor has stopped the growth. The scales are identical on both pictures.. Concnetration in whole blood (mbq ml -1 ) Intravenous injection of radium+scale inhibitor Intravenous injection of radium Concnetration in whole blood (mbq ml -1 ) Oral administratin of radium + scale inhibitor Oral administration of radium Time (hours) Time (hours) Fig. 3. Uptake of radium in juvenile cod from feed with, and without scale inhibitor, SI 447. The left hand side shows the concentration as a function of time of Ra and Ra + scale inhibitor after intravenous injection, and the right hand side shows the corresponding spectra after exposure through food. are large standard deviations it is qualitatively clear that increased concentration of radium increases the uptake and moreover, the presence of scale inhibitor, i.e. SI 447, increases the uptake even more. The DGT showed a linear uptake as a function of time with an efficiency of 6% of theoretical uptake. The measured DGT-responses are shown in Fig. 5. The response is linear with a χ 2 -fit of Conclusions The speciation of radium in produced water from oil- and gas installations has been shown not only to depend on the barium concentration and the mixing with seawater sul- Czech. J. Phys. 52 (22) A47

6 D. Ø. Eriksen et al.: Radionuclides in produced water concentrations and bioavailability Concentration of 226 Ra in gills (mbq/g) Ra + SI Linear fit to Ra+SI Ra + 1*SI Linear fit to data Ra added Fit to Ra added data Blank samples Linear fit to blank samples Exposure time (days) Fig. 4. Uptake of radium in juvenile cod from seawater containing 1 Bq/L 226 Ra with and without scale inhibitor, SI 447 added. 226 Ra-concentration (Bq m -3 ) Days of exposure Ra Ra + Scale inhibitor Ra + 1xScale inhibitor Average values Linear fit to average Fig. 5. Uptake of radium with MnO 2 -DGTs from seawater containing 1 Bq/L 226 Ra with and without scale inhibitor, SI 447 added phate, but it may be influenced by the presence of added chemicals like scale inhibitors. Moreover, the added chemicals will change the ability of fish to take up radium. The DGT showed uptake independent of the presence of scale inhibitor. This is not in accordance with the results from fish gills. The reason may be that the MnO 2 -absorbent does not absorb organically bound Ra, so that only inorganically bound Ra is measured. Nevertheless, such DGTs offer an interesting possibility for measuring the Ra present in seawater, and the development and use of them are thus investigated further. Acknowledgement: The collaboration acknowledges the financial support from the Research Council of Norway through the PROOF-programme. Also, we acknowledge the efforts of the staff at Marine Research Station Solbergstrand. References [1] Gäfvert, T. and Færevik, I.: Natural Radioactivity in Produced Water from the Norwegian Oil and Gas Industry in 23. NRPA Report 25: 2, (25). [2] McCloskey, J.T., Schultz, I.R., and Newman, M.C.: Environ. Toxicol. Chem. 17 (1998) [3] Gäfvert T. et al.: Radioactivity in the Marine Environment 22. Results from the Norwegian National Monitoring Programme (RAME), NRPA Report 24: 1 [4] Berntssen M.H.G. et al.: Radioactivity in produced water from Norwegian oil and gas installations dietary bioavailability of radium ( 226 Ra) in Atlantic cod by use of production chemicals. To be published [5] Bodrogi, E., Kovács, T., Jobbágy, V., and Somlai, J.: Radioprotection, Suppl. 1, 4 (25) S833. D48 Czech. J. Phys. 56 (26)