Radionuclide concentration in commercial fish species of Kuwait has been determined primarily with the intention of creating the baseline for 210Po, 137Cs, 40K, 226Ra, 224Ra, 228Ra, and 90Sr. This baseline information can be useful for issuing food advisories and determining annual intakes and radiation doses due to fish consumption. The highest fresh weight concentration of 210Po and 90Sr was in Battan and the lowest in Sobaity. Highest fresh weight 40K concentration was observed in Meid and the lowest in Battan. The 224Ra, 226Ra and 228Ra concentrations were highest in Meid, whereas the lowest was in Nuwaibi. In all the collected fish samples, 137Cs was below the detection limit.
Kuwait lies at the northwest of the Arabian Gulf (AG). The AG is a shallow waterbody located in a subtropical, hyper arid region (Sheppard et al., 2010). The Gulf borders wealthy oil producing states that are undergoing rapid technological growth owing to the recent economic impetus from a fast growing and lucrative oil-gas industry. Rapid development increases the energy needs of the region. Hence, many of the Gulf States, as well as Iran, are looking forward to the nuclear energy option.
Currently there is only a single nuclear plant in the region at Bushehr, Iran; the entire northern, western and southern coastline is without any nuclear infrastructure. The decision of the United Arab Emirates to have a nuclear plant by 2020, and other countries like Saudi Arabia and Kuwait (Huber, 2007) having nuclear aspirations is likely to influence the radionuclide levels in Gulf water and biota, which are extremely important for sustenance in the region. Elevated levels of depleted uranium have been reported from Kuwait terrestrial sediments (Cabianca, 2003).
Due to limited research and monitoring in the past, the levels of radionuclides are fairly unknown in the Arabian Gulf. Monitoring of the impact of radionuclides (from any source) in the environment requires the establishment of baseline levels in the environmental compartments, with particular attention to pathways to humans. A large fraction of radiation exposure experienced by individuals comes from food chain transfer. Naturally occurring radionuclides, specifically 40K, are the largest contributors to an internal radiation dose. They are homeostatically controlled. Radionuclides like 210Po, 226Ra, and 90Sr accumulate in certain body tissues and bones and relate primarily to dietary uptake and inhalation.
Seafood intake in Kuwait is high (Al-Yakoob et al., 1995;Bu-Olayana and Al-Yakoobb, 1998). Studies have been conducted worldwide on radionuclide concentration in food items, in order to evaluate the food safety and radiation dose from the marine pathway by consumption of marine food. A similar study had been carried out to determine radionuclide level in food (Husain et al., 2003), but apart from this no published data are available on dietary radionuclide concentrations in this marine environment. Therefore, this study aims at the establishment of a baseline of radionuclides in commercial fish species in Kuwait Marine area for 210Po, 137Cs, 40K, 226Ra, 224Ra, 228Ra, and 90Sr, respectively. This baseline information could be useful for issuing food advisories and for determining annual intakes and radiation doses due to fish consumption.
Material and Methods
Six commercial fish species that dominate the food basket in Kuwait have been considered for radionuclide determination. These species are available in territorial waters of Kuwait. Radioisotopes that were considered included 210Po, 137Cs, 40K, 226Ra, 224Ra, 228Ra, and 90Sr.
Fishes were collected from Kuwait Territorial waters by trawling during June–July, 2010 and were immediately transported to laboratory on ice. In this study, whole fish were analyzed. Standard protocols for sample collection, preparation and determination have been adopted (IAEA, 1989). All the analyzed samples were composites, prepared using 3–5 fish of similar variety and size, collected from the same location which were homogenized. The samples were dried at 115°C, pulverized and prepared for analysis in a radio-clean and metal-clean laboratory at the Kuwait Institute for Scientific Research. The dry factor for each fish was determined (Table 1).
210Pb was determined via its granddaughter nuclide 210Po using the standard silver disc technique (Flynn, 1968). Each sample was digested using concentrated nitric acid for at least 24 h and hydrogen peroxide was added to help in oxidizing the organic compounds. The resulting clear solution was evaporated to near dryness and the obtained residue was dissolved in 100 ml of 0.5 mol l−1 HCl. The solution was then heated on a magnetic stirrer to 80°C and 210Po was spontaneously plated on to a rotating silver disc after reduction of iron with ascorbic acid (Al-Masri et al., 2004). The 6 month time period was given so 210Po and 210Pb were in secular equilibrium. The discs were replated to account for any inefficiency during the first plating. A Canberra alpha spectrometer with a passive ion-implanted silicon detector (active area 300 mm2 and background count of 2.3 counts per day and minimum depletion thickness = 90 μm) was used for 210Po determination. The lower limit of detection of this method was 0.04 Bq kg−1 dry weight.
40K, 224Ra, 226Ra,228Ra and 137Cs were determined using a high resolution gamma-spectrometer. The 224Ra, 226Ra, and 228Ra activity were determined from the equilibrium activities of their progeny: 212Pb, 214Pb (214Bi), and 228Ac; and the gamma-lines used in the analysis were 238, 351.9 (609.2), and 911.2 keV, respectively. The dried samples, 100 g each, were put in pre-calibrated plastic containers and the containers were sealed and stored for a month prior to counting. The gamma spectrometer has high relative efficiency of 80% equipped with HPGe detectors. 90Sr samples were prepared adopting the Standard Operating Procedure (Lawrence, 1997) and determination was made after 21 days to allow in-growth of 90Y on Quantulus 1220 Liquid scintillation system.
Results and Discussion
Six commercial fish species which are available in territorial waters and are dominant in the food basket of Kuwait, were analyzed for their 210Po and 90Sr concentrations (Table 2). Sobaity had the lowest concentration and Battan had the highest concentration of 210Po. The 90Sr concentration was highest in Battan and lowest in Meid. Though the concentrations were not alarming, they need special consideration when looking at food chain transfers. The other radio-isotopes determined in the fish samples included 40K, 226Ra, 224Ra, 228Ra and 137Cs. Both dry weight and fresh weight were determined. Tables 3 and 4 present concentration in fishes (dry and fresh weights, respectively).
Samples were analyzed for six commercial fishes available in the food basket of Kuwait. The massic activity of 210Po varied between 0.69–3.30 Bq kg−1. The lowest concentration was measured in Sobaity and highest in Battan. Massic activity of 90Sr in fish samples varied between 1.17–4.13 Bq kg−1. The lowest massic activity was measured in Sobaity and highest in Battan. The massic activity of 40K varied between 67–132 Bq kg−1. The lowest activity was measured in Battan and highest in Meid. 224Ra, 226Ra, and 228Ra massic activity range was 0.12–2.61, 0.17–2.88, and 0.30–6.20 Bq kg−1, respectively. Lowest Ra massic activity was in Nuwaibi and the highest in Meid. Although these may be absolute activity, still more samples need to be analyzed in order to establish a species wise trend and relate it to the morphology and physiology of these fishes and also their habitat. The IAEA 414 CRM was analyzed; the massic activity of 210Pb (210Po) varied between 1.27–2.17 Bq kg−1.
Based on the baseline concentrations established in commercial fishes in Kuwait, it can be concluded that no explicit evidence exists for the risk from fish dietary sources, since there are no guidelines available for reference. Studies from the Department of Energy, Argonne National Laboratory (ANL, 2005a; ANL, 2006; ANL, 2005b) are used as reference for estimation of risk assessment. With the baseline levels seen, it can be safely concluded that the lifetime risk of encountering cancer varies between 1 in 10,000 and 1 in a billion. A follow-up study that would include establishment of baseline concentrations in other food items, human blood, milk, and urine could give a better insight into the risk assessment.
Among the six commercial fish species in the food basket of Kuwait, Battan has the highest activity of 210Po and 90Sr, while Sobaity has the lowest activity. Based on the massic activity in the fishes of Kuwait, it can be concluded that they are comparable to concentrations found in other regions of the world, with no apparent concerns and risks.
Authors are thankful to Kuwait Foundation for Advancement of Sciences for funding the study EM042C. Thanks are due to International Atomic Energy Agency for supporting the national project KUW2004. Authors are thankful to Dr. Hartmut Nies and Dr. Mats Eriksson for their technical guidance in execution of the study. Thanks are also due to Kuwait Institute for Scientific Research for supporting this research.