Radioactivity of long lived gamma emitters in canned seafood consumed in Kuwait

Peer review under responsibility of University of Bahrain.

Abstract

A study of long-lived gamma emitting radionuclides in canned seafood consumed in Kuwait was performed. The canned seafood samples originated from four different countries. The study targeted the natural radionuclides ²³²Th, ²²⁶Ra, and ⁴⁰K. The annual effective dose from canned seafood consumption was estimated to be 5 μSv. This value was found to be several orders of magnitude less than the 0.29 mSv year⁻¹ world average of the ingestion exposure from natural sources. Hence, canned seafood consumption in Kuwait is radiologically safe for the presence of the investigated radionuclides.

Keywords:

• NORM
• Seafood
• Foodstuff
• Kuwait
• Gamma spectrometry

1 Introduction

Radioactivity in the environment originates mainly from natural sources. Natural radionuclides include isotopes of potassium (⁴⁰K), uranium (²³⁸U and its decay series), and thorium (²³²Th and its decay series). In addition to being long-lived (in the order of 10¹⁰ years), these naturally occurring radioactive materials (NORM) are normally present in environmental samples with varying quantities. Consequently, NORM are typically found in terrestrial and aquatic food chains, with subsequent transfer to humans through ingestion of food. In other words, internal radioactive exposure to the general public is directly related to the amount and type of food consumed. This firm relation raised global interest and concern toward radioactivity exposure from food intake (Al-Masri et al., 2004; Chau and Michalec, 2009; FSA, 2004; Gharbi et al., 2010; IAEA, 1989; Venturini and Sordi, 1999; WHO, 2006").

Figure 1 Gamma spectrum for a canned seafood sample, where R, T, and K indicate ²²⁶R, ²³²Th, and ⁴⁰K, respectively.

Figure 2 Activity concentration of ²²⁶Ra.

A thorough literature search reveals a relatively small number of studies on the radionuclide content of food consumed in Kuwait (Al-Azmi et al., 1999; Alrefae, 2012"). Such scarcity was the main motive to conduct the current study, in order to meet the important national requirement of establishing a baseline of radioactivity exposure to the general public from food consumption. For a systematic approach, this study focused on one type of food that is widely consumed by various age groups, namely canned seafood. Hence, the aim of this study was to quantify the content of ²³²Th, ²²⁶Ra, and ⁴⁰K in canned seafood consumed in Kuwait, and to estimate annual effective doses to the general public of various age groups due to this consumption.

2 Materials and methods

Canned fish samples were collected from the Kuwaiti local market. The collection took place between January and June of 2010. To ensure a wide-spread representation, 15 different brands were selected, that covered five different types, crab, salmon, sardine, squid, and tuna (Table 1).

Table 1 Brand names of types of samples investigated in this study.

Sample no.	Country of origin	Brand name	Type	Wet sample weight (g)	Dried sample weight (g)
1	Japan	Geisha crab meat	Crab	510	100
2	Thailand	Chef’s salmon spread	Salmon	370	100
3	Japan	Geisha sardines in tomato sauce	Sardine	645	85
4	Philippines	Ligo sardines in tomato sauce	Sardine	750	100
5	Philippines	Liyo sardines in chilli sauce	Sardine	750	74
6	Thailand	Liyo squids in natural ink	Squid	455	100
7	Thailand	Alwazzan white meat tuna	Tuna	620	100
8	Thailand	Americana white meat tuna	Tuna	370	95
9	Thailand	California garden white tuna	Tuna	370	100
10	Philippines	Century light tuna flakes hot n spicy	Tuna	720	100
11	Thailand	Dandy white meat tuna	Tuna	660	100
12	Thailand	Daniah white meat tuna in veg oil	Tuna	510	100
13	Japan	Geisha Tuna	Tuna	425	85
14	Italy	Rio Mare Light meat tuna in oil	Tuna	640	100
15	Thailand	Melek white meat tuna	Tuna	570	100

Prior to measurement, each sample was prepared in accordance to standard procedures (IAEA, 1989). The preparation included a freeze-drying process that removed the moisture, while preserving essential contents. Such process lasted 4–5 days for each sample. Then, the freeze-dried samples were powdered and placed in cylindrical containers. Dimensions of the containers were 30 mm in radius and 60 mm in height. After being sealed, the sample-filled containers were left for a period of at least 4 weeks to reach a secular equilibrium between parent radionuclides and their daughters. Measurements were performed using a high purity germanium (HPGe) p-type detector. The low background Ortec system, had an energy resolution of 1.75 keV FWHM at the 1.33 MeV ⁶⁰Co photopeak. This counting system of 80% relative efficiency was connected to a multi-channel analyzer. The detector had a cylindrical geometry with a radius of 37 mm and a height of 88 mm. Energy calibration for the detector was performed using a set of point sources. Efficiency calibration was done using a reference material (IAEA-414) with a cylindrical geometry with the same dimensions as the samples’ containers. Because this reference material is made from fish, it has the same density as the investigated samples. Hence, efficiency values (ε) were calculated using the formula (Knoll, 2000).(1) where N is the net counts of the corresponding photopeak after subtracting the background counts. P_γ is the emission probability per disintegration at this specific gamma line. A is the activity concentration of the targeted radionuclide obtained from the reference sheet that came with the reference material. t is the counting time in seconds, and m is the mass of the sample in kg.

To reduce statistical counting error, the samples were counted for a period of 86,400 s (one full day). An empty container was also counted under the same conditions to determine the background counts. For spectrum analysis, Gamma Vision software was used, where the photopeaks considered were 609 keV (²²⁶Ra), 911 keV (²³²Th), and 1460 keV (⁴⁰K). The activity concentration A (Bq kg⁻¹) of each radionuclide in each sample was calculated from the formula (IAEA, 1989).(2)

The minimum detectable activity (MDA) was calculated using the formula (Currie, 1968)(3) where S_b is the standard error in the net background count for the photo-peak. The MDA values for the counting system were calculated to be 0.32, 0.29, and 3.67 Bq kg⁻¹ for ²²⁶Ra, ²³²Th, and ⁴⁰K, respectively.

3 Results

Figs 1 and 2 present the activity concentrations for ²²⁶Ra and ⁴⁰K, respectively, in the canned seafood samples. ²²⁶Ra was detected above the MDA in 14 samples with a maximum value of 2.12 ± 0.17 Bq kg⁻¹ (sardine sample) and a minimum value of 0.36 ± 0.07 Bq kg⁻¹ (tuna sample). The average activity concentration was (±SD) 0.97 ± 0.1 Bq kg⁻¹.

As for ⁴⁰K, it was detected in all samples. The maximum value was 41.56 ± 0.57 Bq kg⁻¹ (tuna sample) and the minimum value was 4.69 ± 0.19 Bq kg⁻¹ (crab sample). The average activity concentration was (±SD) 26.47 ± 0.46 Bq kg⁻¹.

²³²Th activity concentrations were below the MDA in all samples. Hence, these values were not reported (see Fig 3).

Figure 3 Activity concentration of ⁴⁰K.

4 Discussion

The presence of the natural radionuclides in canned seafood samples was expected. Specifically, detection of ⁴⁰K in all samples was anticipated due to its natural abundance. As for ²²⁶Ra and ²³²Th, their undetection in samples does not necessarily imply their absence. It is well understood that background levels and system MDA could conceal minor photopeaks (Knoll, 2000). In fact, the infrequency of ²²⁶Ra and ²³²Th detection in food samples was reported by various authors (Ababneh et al., 2009; Hosseini et al., 2006; Jibiri and Okusanya, 2008; Yu and Mao, 1999").

The results from this study were compared with those reported in the literature. Table 2 shows the values of the present study agreeing with those reported in the literature. Such agreement is evident by the overlap of the activity concentration values of ⁴⁰K, as well as the below detection limit values of ²³²Th.

Table 2 Activity concentrations (Bq kg⁻¹) of ²³²Th, ²²⁶Ra, and ⁴⁰K in seafood samples in this study, compared with those reported in the literature.

Origin	^232Th	^226Ra	^40K	Reference
Hong Kong	BDL		40–110	Yu et al. (1997)
Italy	BDL	1	21	(Present study)
Japan	BDL	0.6–1	5–35	(Present study)
Philippines	BDL	0.6–2	20–33	(Present study)
Thailand	BDL	0.4–1	17–42	(Present study)

BDL = below detection limit.

Table 3 shows the activity concentration of the three targeted radionuclides in different food items that are reported in the literature. ²³²Th is typically unreported due to its relatively low activity in food. This behavior is seen in the present study. Similarly, ²²⁶Ra has relatively low activity in food. Again, this behavior is seen in the presented study. As for ⁴⁰K, it is clearly present in food items with various concentrations. Such variation in ⁴⁰K could be related to regional and food-type dependences.

Table 3 Activity concentrations (Bq kg⁻¹) of ²³²Th, ²²⁶Ra, and ⁴⁰K in various foodstuffs reported in the literature.

Origin	Foodstuff	^232Th	^226Ra	^40K	Reference
Brazil	Beef			80	Venturini and Sordi (1999)
	Chicken			54	Venturini and Sordi (1999)
	Beans		1	434	Venturini and Sordi (1999)
Hong Kong	Beef			91	Yu et al. (1997)
	Chicken			76	Yu et al. (1997)
Syria	Cereals			300	Al-Masri et al. (2004)

The annual effective dose from consumption of canned seafood was calculated using the following formula (UNSCEAR, 2000).(4) where D is the annual effective dose (Sv yr⁻¹), A is the activity concentration for the radionuclide (Bq kg⁻¹), E is the dose conversion factor for the radionuclide (Sv Bq⁻¹), and I is the annual intake of canned seafood (kg). Values for E were selected based on the International Commission on Radiological Protection (ICRP) classifications (ICRP, 1996) 6.4 and 280 nSv Bq⁻¹ for ⁴⁰K and ²²⁶Ra, respectively. The value of I is taken to be 10.3 kg yr⁻¹ (IAEA, 1999). It is noteworthy that this intake value covered all types of seafood, of which canned is one type. Thus, the actual intake value for canned type specifically is less. This study, however, took the conservative approach of using the relatively high intake values. The results of the annual effective dose D showed 3 μSv and 2 μSv from the ingestion of ²²⁶Ra and ⁴⁰K, respectively. Thus the total annual effective dose from ingestion of long lived gamma emitters in canned seafood is 5 μSv, which is of several orders of magnitudes less than 0.29 mSv yr⁻¹ world average of the ingestion exposure from natural sources reported in the literature (UNSCEAR, 2000). Therefore, canned seafood consumption in Kuwait is radiologically safe for the presence of the investigated radionulcides. It is important to note, however, that the activity concentration A used in dose calculations was the average for each radionuclide. Hence, the calculated doses are the average annual effective doses. Interestingly, this value of 5 μSv yr⁻¹ is close to its counterpart of 6 μSv yr⁻¹ reported in the literature (Yu et al., 1997).

5 Conclusion

Long-lived gamma emitters in canned seafood consumed in Kuwait were investigated. The samples, which were collected from the local market, originated from four different countries. The study targeted three radionuclides, namely ²³²Th, ²²⁶Ra, and ⁴⁰K. While ⁴⁰K was detected in all samples, ²²⁶Ra was detected in almost all samples, and ²³²Th was detected in none. In addition, the annual effective dose from the consumption of canned seafood was calculated for the three age groups.

The present study is the first at the national level to investigate the radioactivity of canned seafood. The findings of this study will help in establishing a baseline of radioactivity exposure to the general public from ingestion of foodstuff. However, canned seafood is only one dietary component and the focus of the present study was gamma emitters. To establish a more robust baseline, there is a need to investigate more types of foodstuffs, as well as targeting alpha and beta emitting radionuclides.

Notes

Peer review under responsibility of University of Bahrain.