Introduction

External natural sources of radiation contribute by far to the largest proportion of human’s radiation exposure. These sources include both cosmic rays and ingestion or inhalation of naturally occurring primordial or anthropogenic radioactive material that might be present in the surface soil. In Kuwait, the surface soil has relatively uniform concentrations of naturally occurring radionuclides since the geological topography is consistent to a certain extent where, besides the coastal deposits, smooth sand sheets prevail (Saad and Al-Azmi 2002). Nevertheless, back in 1991, during the Gulf War, the heavy use of depleted uranium (400–800 tons) has undoubtedly played a significant role in the radioactive contamination of the surface soil in Kuwait, thus distorting the surface distribution of naturally occurring radionuclides. Furthermore, a significant number of operating oil wells were set on fire. The combustion of the oil wells for more than 250 days at an approximated rate of 3 million drums per day resulted in the emission of thick black smokes into the air. These enormous black smoke plumes comprising of toxic combustion gaseous products and radioactive materials has led to fly ash deposits on the surface sand and thus further contamination of the Kuwaiti territory (Barnaby 1991; Abdullah et al. 2008).

Long-term exposure to ionizing radiations can cause serious health illnesses, such as necrosis of the mouth, acute leucopoenia, chronic lung disease, cataracts, atrophy of the kidney, hepatic skin, sterility, and anemia and even death (Taskin et al. 2009). Despite the controversy in the medical and scientific communities it is hypothesized that there is a linear no-threshold (LNT) relationship between the radiation dose and the occurrence of cancer where it is suggested that any increase in radiation dose, no matter how small, could increase the risk of cancer (Brenner and Sachs 2006). In addition, scientific studies have shown that children born to mothers exposed to radiations during their pregnancy may suffer from mental retardation (NRC 2006).

In this study, previously published (Jallad 2013, 2015) concentrations of naturally occurring radionuclides Thorium-232 (232Th), Radium-226 (226Ra), and Potassium-40 (40K) in the sands of two different geographical locations that observed severe combat activity during the Gulf War back in 1991 were implemented to evaluate the radiation health hazard indices, the annual gonadal dose equivalent (AGDE), and the excess lifetime cancer risk (ELCR). The two different geographical locations were: the island of Failaka (39 km2), a Kuwaiti territory located 27 km to the east off the coast of Kuwait City in the northern part of the Arabian Gulf; and highway 80, called “Death’s Highway” or “Hell’s Highway” during the Gulf War, spanning from northern Kuwait City to the border between Kuwait and Iraq. The calculated indices, dose rates, and risk values due to the radionuclide concentrations in both areas were statistically compared with each other and were also compared with international approved values.

Experimental procedure

Sample collection and preparation

A total of 51 sand samples were collected from 17 selected locations on Failaka Island as shown in Fig. 1. Using a Global Positioning System, the samples geographic locations were discerned. Furthermore, a total of 48 sand samples were amassed from 16 chosen locations along highway 80 as shown in Fig. 2. At each of the collection sites, three samples, each weighing 500 g, were taken from an area of 1 m2. Using a plastic hand trowel, the sand samples, believed to be undisturbed (depth of 5–20 cm from the surface), were collected. The three collected samples were uniformly mixed. This homogenous sand mixture, at an estimated mass of 1.5 kg, represented the sampling site. The sand samples were placed in sealed plastic bags after which they were shipped via air to Pace Analytical Services based in Greensburg, PA, USA, for radioactive analysis.

Fig. 1
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Map of the study area on Failaka Island

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Fig. 2
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Map of the study area along Highway 80

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Measurement by gamma ray spectrometry

At Pace’s laboratory, the samples were sifted through a 1 mm mesh sieve, after which they were placed in an oven at 105 °C for overnight to dry. Once dry, the samples were crushed using a pestle and mortar then mixed uniformly to ensure homogeneity. A fraction of the crushed dried solid sample was prepared in sealed 8-ounce can geometry for analysis using a non-destructive gamma spectrometer equipped with a germanium (high purity) detector. The analysis was conducted by implementing a modified EPA 901.1 protocol (USEPA 1980). The samples were investigated for the following radionuclides: 232Th, 226Ra, and 40K.

Each sample, weighing around 350 g, was measured by using a germanium (high purity) detector. For each sample, the spectrum integration time was 30 min. The detector used was a P-type high purity germanium detector system with relative efficiency of 150 %. The detector resolution was 1.144 keV [full width at half-maximum (FWHM)] for the 661.02 keV γ-ray of 137Cs yielding a relative resolution of 0.17 %. The net area for the 661.02 keV γ-ray of 137Cs was 76 counts.

For every spectrum, the measured energy signals corresponding to the gamma photo peaks for each sample were correlated with an extensive library of known photo peaks. Both 226Ra and 235U emit a gamma ray near 186 keV. Thus, to avoid misidentification of 226Ra, once the samples were prepared according to the procedure outlined before, they were stored in the sealed 8 oz can for a minimum of 21 days to ensure the complete decay of 226Ra into its daughters namely; 222Rn (gas), 214Pb, 214Bi. In each sample, the amount of 226Ra was calculated by inference using the peaks corresponding to the strong non-interfering gamma rays exhibited by both 214Pb and 214Bi. Using known photo peaks as illustrated in Table 1 (Firestone et al. 1996), all other reported radionuclides were identified and quantified.

Table 1 Gamma-ray lines (Firestone et al. 1996) used for photopeak efficiency and activity concentration determination
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Energy and efficiency calibrations were used in calculating the radionuclides concentrations measured in all samples. This was conducted by implementing a National Institute of Standards and Technology (NIST) traceable calibration standard prepared in an equivalent geometry as the investigated samples. For each sample spectrum, ambient background radionuclides contributions related to the specific used detector were corrected for. In addition, sample collection time and date were utilized in performing decay corrections for all investigated radionuclides. Pace’s comprehensive default library was used primarily for sample gamma identification and analysis. The Regulatory Guide 4.16 (NRC 2010) type was used primarily in calculating the minimum detectable concentration (MDC) for all studied samples and was available as an option in the GammaVision V. 6.08 spectroscopy software program. For all radiochemistry analyses, this option is always chosen at Pace Labs. No abnormal incidents were encountered during either the samples’ preparation or the samples’ gamma spectroscopic analyses. All data quality goals and quality control compliance benchmarks were met, since all the analytical results were reported at the 2 sigma level (95 % confidence level) for all samples analyses.

Results and discussion

Activity in sand

The mean activity concentrations of 232Th, 226Ra, and 40K in the sand samples collected from Failaka Island analyzed along with the geographic locations were listed in Table 2. The radionuclide activity concentrations were computed in Bq/kg on a dry weight basis. Furthermore, the samples geographic locations along with the mean activity concentrations of the measured radionuclides in the sand samples collected from selected locations along highway 80 were listed in Table 3. The concentrations of the all radionuclides, including the ones listed above, measured in the analyzed collected sand samples are discussed in greater details in recently published articles (Jallad 2013, 2015).

Table 2 The locations of the sample sites on Failaka Island
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Table 3 The locations of the sample sites along Highway 80
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The t test data analysis (two tailed at 95 % confidence level) showed a significant statistical difference only in the case of measured 40K among the two different regions. As stated earlier, Kuwait’s geological topography is relatively consistent with predominating smooth sand sheets having relatively unvarying contents of naturally occurring radionuclides namely; 232Th, 226Ra, and 40K (Saad and Al-Azmi 2002). However, higher levels of the naturally occurring radionuclide 40K were detected along highway 80 which witnessed more intensive military activity including the heavy use of depleted uranium weaponry in comparison to Failaka Island. Furthermore, it is suggested that 40K, besides occurring naturally, can only result from a radiation induced transformation of another element undergoing a nuclear reaction caused by the use of depleted uranium weapons (Queck 2012).

γ-Ray radiation hazard indices

It is crucial to evaluate the γ-ray radiation threats of sand to humans on Failaka Island and along highway 80. The γ-ray radiation hazards due to the natural radionuclides 226Ra, 232Th, and 40K were appraised by different radiation hazard indices. The most widely used radiation hazard index, Raeq, can be calculated according to the equation (Beretka and Mathew 1985):

$${\text{Ra}}_{\text{eq}} = c_{\text{Ra}} + 10c_{\text{Th}} /7 + 10c_{\text{K}} /130$$
(1)

where c Ra, c Th, and c K are the activity concentrations of 226Ra, 232Th, and 40K in Bq/kg, respectively. The values of Raeq for the studied sand samples collected from Failaka Island and the sites along highway 80 are given in Tables 4 and 5, respectively. As illustrated in Table 4, the Raeq values on Failaka Island span from 27.0 to 80.5 Bq/kg, with a mean of 54.2 Bq/kg; while those along highway 80, as illustrated in Table 5, span from 35.6 to 142.9 Bq/kg, with a mean of 71.5 Bq/kg. All the Raeq values corresponding to the sand samples are well below the internationally accepted value of 350 Bq/kg (Beretka and Mathew 1985). Another radiation hazard index called the representative level index, Ir, used to estimate the level of γ-radiation associated also with the activity concentrations of 226Ra, 232Th, and 40K, can be defined as follows (Beretka and Mathew 1985):

$$I_{\text{r}} = c_{\text{Ra}} /150 + c_{\text{Th}} /100 + c_{\text{K}} /1500$$
(2)
Table 4 Gamma radiation hazard indices for the analyzed sand samples collected from Failaka Island
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Table 5 Gamma radiation hazard indices for the analyzed sand samples collected from sites along highway 80
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The index value must be less than unity to keep the radiation hazard insignificant. As shown in Tables 4 and 5, all the calculated values of Ir were below 1 except for sampling site 11 along highway 80 where I r was 1.05 Bq/kg. The external hazard index, H ex, (Beretka and Mathew 1985) used to assess the indoor radiation dose rate due to the external exposure to γ-radiation emitted by the natural occurring radionuclides in the habitats’ construction building materials, can be determined using the following equation:

$$H_{\text{ex}} = c_{\text{Ra}} /370 + c_{\text{Th}} /259 + c_{\text{K}} /4810$$
(3)

Furthermore, the internal exposure to 222Rn (the decay product of 226Ra) and its radioactive progeny (short lived products), which are all hazardous to the respiratory organs, is controlled by the internal hazard index, H in, which is given by (Beretka and Mathew 1985):

$$H_{\text{in}} = c_{\text{Ra}} /185 + c_{\text{Th}} /259 + c_{\text{K}} /4810$$
(4)

For both indices, H ex and H in, to be less than one (radiation hazard insignificant), the maximum values of Raeq must be less than 370 Bq/kg (Beretka and Mathew 1985) and 185 Bq/kg (Beretka and Mathew 1985), respectively. The calculated results of H ex for the studied sand samples collected from Failaka Island range from 0.07 to 0.22 Bq/kg with a mean of 0.15 Bq/kg as shown in Table 4, while those for sand samples collected from sites along highway 80, range from 0.10 to 0.39 Bq/kg with a mean of 0.19 Bq/kg as shown in Table 5. Similarly, the calculated values for H in on Failaka Island, are also lower than 1, ranging from 0.09 to 0.31 Bq/kg with an average of 0.19 Bq/kg, while those along highway 80, spread from 0.12 to 0.42 Bq/kg with an average of 0.23 Bq/kg. The one-way ANOVA data analysis (95 % confidence level) showed a significant difference (P < 0.05) for the calculated indices (I r, H ex, and H in) among the two different regions due to the different determined levels of 40K in the sand samples collected from the two different regions as stated earlier. When the radiation hazard index, Raeq, calculated values were compared using ANOVA among the two regions, no significant statistical difference was noted.

Annual gonadal dose equivalent (AGDE)

The gonads, the bone marrow activity, and the bone surface cells are considered as the organs of interest by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) since they are readily affected by radiation (UNSCEAR 1988). Elevated AGDE values can affect the functionality of the bone marrow resulting in leukemia. The AGDE (µSv year−1) due to the specific activities of 226Ra, 232Th, and 40K is calculated using the following equation (Mamont-Ciesla et al. 1982);

$${\text{AGDE}} = 3.09c_{\text{Ra}} + 4.18c_{\text{Th}} + 0.314c_{\text{K}}$$
(5)

The obtained values of AGDE for the studied sand samples obtained from Failaka Island and locations along highway 80 are listed in Tables 6 and 7, respectively. As shown in Table 6, the AGDE values varied from 96 to 272 µSv year−1 with a mean of 190 µSv year−1. While those in Table 7 ranged from 137 to 457 µSv year−1 with a mean of 247 µSv year−1. Most of the calculated AGDE values are around the world average for soil at 300 µSv year−1 (Mamont-Ciesla et al. 1982) except for two sites, namely sites 3 and 11 along highway 80. The Thorium activity was relatively high at locations, 3 and 11, along highway 80 compared to all the investigated sites in this study and this could be attributed to the fact that both sites were heavily bombed during the Gulf War (Table 3). The 232Th content in the bombed building material would have additionally contributed to the already naturally existing 232Th concentration related to the geological make-up of these two locations consisting of silt, sandstone, and clay (Saad and Al-Azmi 2002; Jallad 2013, 2015). Furthermore, because of the lack of definitive human data, estimates of potential genetic effects from radiation exposure on humans’ gonads are extrapolated largely from experiments in mice (Linacher et al. 1998). The risk of serious birth defects in the future offspring of irradiated parents is estimated to be 2 × 10−3 % to 3 × 10−3 % per 104 µSv (NRC 1990; ICRP 1977). If one assumes an annual gonadal dose equivalent of 2 × 103 µSv year−1, the cumulative gonadal exposure over a period of 20 years would be 4 × 104 µSv. It can be projected that the risk of serious birth defects would be 8 × 10−3 % to 1.2 × 10−2 % for 4 × 104 µSv and 4 × 10−4 % to 6 × 10−4 % for 2 × 103 µSv. Thus, the AGDE values calculated confirm the safety of the studied sites in this study. Finally, the ANOVA data analysis showed a significant statistical difference for the calculated AGDE values among Failaka Island and the sites along highway 80.

Table 6 The annual gonadal dose equivalent
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Table 7 The annual gonadal dose equivalent
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Dose rate in sand

To characterize the external primordial γ-radiation on Failaka Island and at different geographical locations along highway 80, the total absorbed dose rate, D (nGy h−1), in the air (outdoors) due to the activity concentrations of 226Ra, 232Th, and 40K (Bq/kg) in sand 1 m above the ground surface was estimated by using the formula (Viega et al. 2006):

$$D = 0.0417c_{\text{K}} + 0.462c_{\text{Ra}} + 0.604c_{\text{Th}}$$
(6)

Both Tables 6 and 7 give the estimated external gamma dose rate due to the natural gamma emitters as measured in the sand samples collected. By looking at Table 7, it can be inferred that on Failaka Island the absorbed dose rates ranged from 13.4 to 38.6 nGy h−1 with a mean value of 26.5 nGy h−1; while along highway 80 the absorbed dose rates ranged from 18.6 to 64.7 nGy h−1 with a mean value of 34.4 nGy h−1, All the calculated dose rates were lower than the world average of 55 nGy h−1 (UNSCEAR 2000) except for the two sites, namely sites 3 and 11 along highway 80. The ANOVA data analysis showed a statistical difference for the calculated dose rated among the two different areas in Kuwait.

In order to obtain a rough estimate for the annual effective dose outdoors, the conversion coefficient from the absorbed dose in air to the effective dose and the outdoors occupancy factor had to be taken into account. As proposed by UNSCEAR (2000), a conversion coefficient of 0.7 Sv G year−1 from the absorbed dose in air to the effective dose received by adults and an outdoor occupancy factor of 0.2 were used. The annual effective dose, E (mSv year−1) outdoors was calculated using the following formula (Yang et al. 2005):

$$E = D \times 24h \times 365d \times 0.7 \times 0.2 \times 10^{ - 6}$$
(7)

The obtained E values for all analyzed sand samples from Failaka listed in Table 6 spanned from 0.016 to 0.047 mSv year−1 with an average value of 0.033 mSv year−1. While those for collected sand samples from sites along highway 80 ranged from 0.023 to 0.079 mSv year−1 with an average value of 0.042 mSv year−1. The values are clearly lower than the world wide outdoors annual effective dose average of 0.07 mSv year−1 (UNSCEAR 2000) (except for the two sites, namely sites 3 and 11 along highway 80) and are also below the set-limit of 1.0 mSv year−1 (ICRP 1977), recommended by the International Commission on Radiological Protection (ICRP) as the maximum allowed annual dose for the public. The ANOVA data analysis showed a statistical difference for the calculated annual effective dose rates among the two different areas in Kuwait.

Excess lifetime cancer risk (ELCR)

Upon exposure to ionizing radiation, the probability of developing cancer over a lifetime can be estimated by calculating the excess lifetime cancer risk, ELCR (mSv year−1), according to the following equation (Taskin et al. 2009):

$${\text{ELCR}} = E \times {\text{LE}} \times {\text{RF}}$$
(8)

where E is the outdoors annual effective dose, LE is the life expectancy in Kuwait (77 years) (World Statistics 2015), and RF is the fatal cancer risk factor per Sievert, which is stochastically determined by the ICRP (1990) at 0.05 for the public.

The calculated ELCR values for outdoors exposure on Failaka Island and locations along highway 80 are listed in Tables 6 and 7, respectively. As shown in Table 6, the values on Failka Island spanned from 0.063 to 0.182 mSv year−1 with an average value of 0.125 mSv year−1, while the ones calculated along highway 80 ranged from 0.088 to 0.305 mSv year−1 with a mean value of 0.162 mSv year−1. All the values were lower than the world permissible standard of 0.29 mSv year−1 (Taskin et al. 2009) except for site 11 along highway 80. The lifetime risk of developing cancer refers to the chance a person has, over the course of his or her lifetime (from birth to death) of being diagnosed with cancer. These risk estimates provide a measure of how widespread cancer is in the United States (Howlader 2014). According to the United States National Cancer Institute’s Surveillance Epidemiology and End Results (SEER) Database (Howlader 2014), the risk that a man living in the United States will develop cancer during his lifetime is 43.3 %, while that for a woman is 37.8 %. Globally, the 2012 estimated incidence rate for all cancers (excluding non-melanoma skin cancer) is 0.11 % for males and 0.10 % for females (WHO 2012), while the worldwide lifetime risk for developing cancer is 33 % (Qureshi et al. 2014). Long-term exposure to ionizing radiation will result in an additional risk to be incorporated into the lifetime cancer risk known as Excess Lifetime Cancer Risk (ELCR). An estimated ELCR of 1, 10, 102, and 103 mSv year−1 will contribute to an additional of 0.004, 0.04, 0.4, and 4 %, respectively, for developing a fatal cancer (Moore 1993). As stated earlier, all the ELCR values calculated at the selected geographical sites in this study are well below 1 mSv year−1. When the calculated risks for the two regions were statistically compared using ANOVA, a significant difference was recognized. A number of studies were conducted in Asia to calculate the outdoor ELCR. In almost all published reports, the calculated values were lower than or slightly exceeding the world permissible standard of 0.29 mSv year−1 (Qureshi et al. 2014; Ramasamy et al. 2009; Aytas et al. 2012; Thabayneh and Jazzar 2012; Emelue et al. 2014) except for one conducted in Kerala, India (Rafique et al. 2014) where the calculated ELCR average in the soil samples was 1.7 mSv year−1, almost sixfold the world permissible standard.

Finally, only the outdoor annual effective dose was implemented in order to calculate the ELCR, since both Failaka Island and sites along highway 80 are uninhabited and all residential structures are bombed and abandoned. Thus, calculating the indoor ELCR would have been insignificant.

Conclusion

As published recently (Jallad 2013, 2015), the average activities of the radionuclides determined in the sand samples collected from Failaka Island and sites along highway 80 were low compared to mean levels recorded worldwide. In this study all the obtained values corresponding to; natural radioactivity (γ-radiation hazard indices), γ-absorbed rates, and excess lifetime cancer risk due to the activity concentrations of 226Ra, 232Th, and 40K of sand in the air show undoubtedly that both Failaka Island and sites along highway 80 can be regarded as areas with normal natural background radiation. Both the annual effective dose and the excess lifetime cancer risk values were below the acceptable set-limits, stressing further, the radiological safety of these two investigated regions in Kuwait.