Study of K-40 , Ra-226 , Ra-228 and Ra-224 activity concentrations in some seasoning and nuts obtained in Rio de Janeiro city , Brazil

Rio de Janeiro city is the second most populous city in Brazil with almost 7 million inhabitants, the local market offers a great diversity of foods, nuts and seasonings, national and imported. Seasonings are used worldwide, some have a common use as salt and sugar, besides others used locally as cheiro verde, a mixture of chives (Allium schoenoprasum) and parsley (Petroselinum crispum) used in Rio de Janeiro, Brazil.


Introduction
Rio de Janeiro city is the second most populous city in Brazil with almost 7 million inhabitants, the local market offers a great diversity of foods, nuts and seasonings, national and imported.Seasonings are used worldwide, some have a common use as salt and sugar, besides others used locally as cheiro verde, a mixture of chives (Allium schoenoprasum) and parsley (Petroselinum crispum) used in Rio de Janeiro, Brazil.
According to the Onternational Food Safety Authorities Network (2011), plants used as food commonly have K-40, Th-232 and U-238 and their progenies.On a variety of concentrations, naturally occurring radionuclides are present in every part of the earth and in the tissue of all living beings.Natural radionuclides can be found almost everywhere; in soil, water and atmosphere, subjecting human beings to a daily exposure.The K-40 is responsible for about 60% of the total annual effective dose due to ingestion (United Nations Scientific Committee on the Effects of Atomic Radiation, 2008).Therefore, it is a radionuclide of relevance both in the environmental point of view and radiological protection (Zhu, 2001).
Gamma-ray spectrometry using high-purity germanium detectors (HPGe) is a procedure widely used for determining the concentrations of natural and artificial radionuclides in environmental samples.As a nondestructive technique, this method possesses advantages in multi-element analysis, simplified sample preparation (i.e., does not require any chemical separation process), and applicability for precise quantitative determination of the radioactive content in a sample.The most accurate method to determine the activity concentration of radionuclides is to use an adequate standard source with similar geometrical dimensions, density, and chemical compositions to the sample under study (Díaz & Vargas, 2008).
This study aims to determine activities concentrations for the radionuclides  in nuts and seasoning samples obtained in Rio de Janeiro City, Brazil, using a hyper pure germanium detector (HPGe) and the LabSDCS software for the calculation of self-absorption correction.

Sample analyses
The nuts and seasoning samples analyzed were acquired in informal street commerce of Rio de Janeiro city, Brazil.The samples analyzed are listed in Table 1, along with their botanical names and the physical characteristic in which they were analyzed.121/126 121 The samples were sealed in 200 mL polystyrene pots, to reach the secular radioactive equilibrium condition (at least 45 days).The non-homogeneous samples were processed and sieved in a 16 mesh screen for the appropriate use of the LabSDCS software to correct the efficiency curve due to the process of self-absorption of the photons in the sample.The Malagueta pepper was processed jointly to the oil in which it was preserved.
Were also analyzed Syrian seasoning also called bahar (powder), curry (powder), chilli (dry), chimichurri (dry) and cheiro verde (dry).Chimuchurri is a seasoning from South American origin, traditional of Argentina and Uruguay, is used for meats, curry is from Ondian origin, Syrian seasoning (bahar) is from Syrian origin, cheiro verde is from Brazilian origin and chilli is a mixture of peppers.On Table 1, all samples are Brazilian origin.

Gamma spectrometer
Radiation spectra were acquired with a HPGe detector from Canberra, model GC3020, with minimum relative efficiency of 30%, and a shield of the same brand, model 747E.The counting time used for sample spectrum acquisition was 28800 seconds.Energy calibration was performed using three radioactive sources totaling five experimental points corresponding to the peaks of 137 Cs (0.6617 MeV), 60 Co (1.17 and 1.33 MeV) and 155 Eu (0.1218 and 0.3443 MeV).
The multichannel system used was a DSA 1000 (Digital Spectrum Analyzer), with 8192 channels, with energy range from 50 keV to 2 MeV, installed at the Laboratory of Environmental Analysis and Computational Simulation, from Nuclear Engineering Department of Rio de Janeiro Federal University (LAASC/PEN/CDPPE/UFRJ).
To ensure the quality of the analysis a certified reference material of soil (089/ERA) tracked by National Onstitute of Standards and Technology (NOST) was used to generate the detection efficiency curve of the measurement system.The self-absorption correction of the photons in the samples due to different density values of the samples was performed by the LabSDCS software.
The activity concentration (AC) and respective uncertainties were determined according to the statistical uncertainties of the peak areas provided by the Genie2000 software.To measure the AC and minimum detectable activity (MDA), the latter based on Currie's derivation, were used Equations 1 and 2, respectively.
( ) ( ) where: AC is the activity concentration (Bq.kg -1 ); σ is the standard deviation of the count in the background spectrum; N L is the net area under the photo peak; m is the mass of the sample (kg); ε is counting efficiency for a specific energy (γ); P γ is the probability of emission of the measured gamma-ray (γ); t is counting time (s).
The Ra-224 AC was determined using the 238.6 keV energy of Pb-212 gamma radiation.The Ra-228 AC was measured using the 911.1 keV energy of Ac-228.The Ra-226 AC was determined using the 1120.3keV energy of Bi-214.The K-40 AC was determined using its emission line 1460.8keV.

Self-attenuation correction
The LabSDCS software makes mathematical calibrations in detection efficiency, this software includes a characterized detector and computational algorithms to make the self-absorption correction of the photons in the sample, using Monte Carlo code (Bronson, 2003).On the efficiency curve generation using the LabSDCS, the materials was simulated using the Geometry Composer from Canberra's Genie™ 2000 software package, the material of the pot was simulated for polystyrene with a density of 1.06 g/cc, chemical composition of H (7.74%) and C (92.26%).The reference material (soil, density of 1.41 g/cc) was simulated with a chemical composition based on the twelve most common chemical elements in the earth's crust, adapted by Schulze (1989): D (47%), Al (8.13%), Si (27.96%),K (2.59%), Fe (5%), Ca (3.63%), Na (2.83), Mg (2.09%), Ti (0.44%), H (0.14%), P (0.1%) and Mn (0.09%).The simulated geometry was a volume of 200 mL and the reference material was weighed to know exactly how much material was in the pot, then the efficiency curve was generated with the self-attenuation correction.
Then the gamma radiation spectra of the reference material were generated by the gamma spectrometry system installed in the LAASC.This procedure was also done in LGO (Laboratory of Gamma Spectrometry/ORD/CNEN) with the aim to verify the existence of differences between the certificate and the reference material, and also to validate the detection system.The LGO is tracked by LNMRO (Brazilian Laboratory of Metrology of Oonizing Radiations/ORD/CNEN), that is tracked by Bureau A mean correction factor was set for each energy used for this specific geometry.The LabSDCS software makes the self-absorption corrections when it simulates each sample density, and the correction factors validate the software.

Dose assessment
The committed effective dose over one year was calculated using the relation shown in the Equation 3: where: D ef is the annual effective dose (Sv.y -1 ); U is the amount of food consumed in a year (kg.y -1 ); C d is the radionuclide specific concentration in the food (Bq.kg -1 ); D f is the dose coefficient according to OCRP 119.
There is no Brazilian statistical data for the amount of seasoning and nuts consumed in one year, maybe due to small consumption when it is compared to other categories of food, such as cereals, meats, beverages, etc. (Lopes et al., 2018).Dn the other hand, the seasonings consumption has regional and seasonal characteristics.So, the average consumption could be in disagreement the committed effective dose value for a local reality.Therefore, it was estimated the annual consumption in 1 kg for all seasonings and nuts evaluated in this work.This unit value allows a simple conversion to committed effective dose, when the local consumption is different from that proposed in the present work.
Dnly the average values of the AC measured in this study were used to calculate the committed effective dose.Table 3 shows the effective dose coefficients for annual committed effective dose due to the intake of K-40, Ra-226, Ra-228 and Ra-224 radionuclides.

Results and discussions
Nuts and seasoning samples were analyzed by gamma spectroscopy and the result is shown in Table 4.All samples presented values of AC above the minimum detectable activity (MDA) for K-40, because potassium is an essential element for the development of plants.Dne sample presented value above the MDA for Ra-226 and eight samples presented values above the MDA for Ra-228 and Ra-224, that is according to the results found in soils and plants in Brazil, which indicate a higher concentration of Th-232 than U-238 (Ribeiro, 2016).
The malagueta pepper was processed along with the oil in which it was preserved.The most consumed oil in Brazil is soybean oil which was also analyzed in the LAASC/UFRJ and the specific concentration for K-40 was below the minimum detectable activity (<MDA).
Cheiro verde (mix of parsley and chives) and parsley presented the highest specific activities of K-40.As the ratio of the mixture of parsley and chive in cheiro verde is not known, there is no way to estimate the AC of K-40 for the chive.
The presence of radium isotopes in Brazil nuts is known for a long time from pioneering works.Even some observations were made on the possibilities of people who consume a considerable  -Franca et al., 1968;Parekh et al., 2008;Martins et al., 2012;Armelin, 2016).
On a study conducted by Desideri et al. (2010) on medicinal plants, the mean of AC found for K-40 in cinnamon plants (Cinnamomum zeylanicus) was 240 Bq/kg, a similar value to that found in present study.For pepper (Capsicum frutescens) was found 793 Bq/kg, a value greater than that found in present work for malagueta pepper (Capsicum frutescens) and for the paprika pepper (Capsicum annuum), plants of the same genus, but different species.For the Ra-226 the value found was 16.6 Bq/kg for cinnamon and 3.2 Bq/kg for pepper.
The Syrian seasoning (bahar) presented AC of ( 6.1 1.1 ± ) Bq/kg for the artificial radionuclide Cs-137.This radionuclide is a long-lived fission product, which may be readily metabolized by the human body.Currently, the Cs-137 contamination in food is due mainly to worldwide fallout from atmosphere, after nuclear testing and releases caused by the accidents from nuclear power plants.Yet, there is a possibility that the Syrian seasoning may have some ingredient from an Asian region that suffered major environmental impacts after Chernobyl accident in 1986.Grain trade is one of the local economies.Table 5 shows Cs-137 AC in some spices and teas analyzed.When the literature is used as parameter, Cs-137 AC measured in this work has value above the expected.Dnly Di Gregorio et al. (2004) found values of Cs-137 AC for five samples of tea above the value measured in this work.
For a behavior analysis, the samples were divided into three groups depending on the vegetal part used, namely: pericarp/seeds, leaves, stems/roots.Figure 1 shows how the behavior of each  radionuclide analyzed in the samples.The ordinates axes correspond to the mean values of AC and the respective standard deviation of the mean, which configures the mean value confidence is within the range Because Ra-226 has been measurable in only one sample, this analysis does not count on the mentioned radionuclide.
Figure 1a shows that mean of K-40 AC appears slightly larger in the leaves.The potassium element is fundamental to photosynthesis, so it is acceptable to have a higher concentration of potassium in the leaves (Terry & Ulrich, 1973;Peoples & Koch, 1979;Longstreth & Nobel, 1980), and consequently, a higher concentration of K-40.
Figure 1b shows that Ra-228 AC in the pericarp/seeds and in the stems/roots is within the range of Ra-224 AC, a fact no observed in the leaves.The mean values of AC seem to suggest that, if there is a predominant vegetal structure for Ra-224, it would be in the pericarp/seed of the plants used as seasonings.Stems/roots seasoning samples had the lowest means of AC for both radios.
From Figure 1c, stems/roots showed means of AC for Ra-228 lower than other parts of the plant.Ot was not the same for Ra-224, whose mean values of AC for stems/roots are notoriously different than pericarp/seeds.Average ratio measured for Ra-224/Ra-228 was 1.1 for stems/roots, 0.36 for leaves and 0.79 for pericarp/seeds.Ot is known that the half-life of Ra-224 is 3.7 days, so the ratio of Ra-224 / Ra-228 in plants will depend directly of both mobility and decay in situ of Ra-228 (Bull et al., 2006).
Based on the specific activity conversion factors to annual effective dose due to ingestion to members of the public (adults) tabulated in Publication 119 of Onternational Commission on Radiological Protection (2012), the effective doses of the nuts and seasonings were calculated considering the consumption of 1 kg and the results are shown in Table 6.
Cheiro verde sample (mix of parsley and chives) and parsley sample presented the highest AC of K-40 but not the highest effective dose, because the contribution of radium to the effective dose is greater than that of potassium.Table 7 shows the percentage of committed effective dose for each radionuclide studied.The radionuclide K-40 appears as the element that most contributes to the dose due to ingestion, followed by Ra-228.Although the latter appears in only 31% of the analyzed samples, its contribution is close to K-40, present in 100% of the samples.This is due to conversion factor of Ra-228, more than 111 times greater than the K-40 conversion factor, reflecting the radiobiological importance of this radionuclide.The dose due to ingestion of Ra-226 is discreet in this work because only the Brazil nut presented measurable AC for this radionuclide.Finally, Ra-224, although measurable in almost 35% of the samples, has a small conversion factor when compared to Ra-226 and Ra-228, mainly due to its low half-life, about 3.7 days.
According to United Nations Scientific Committee on the Effects of Atomic Radiation ( 2008) the global annual effective dose due to natural radiation sources is 2.4 mSv, of this total 0.29 mSv is due to ingestion.The sample resulting in highest effective dose analyzed in this study was Brazil nut, whose intake of 11 kg is enough to reach the annual effective dose due to ingestion.Still according to United Nations Scientific Committee on the Effects of Atomic Radiation ( 2008), the effective dose due to atmospheric nuclear testing and to Chernobyl accident is 7µSv/y and the effective dose due to Cs-137 found in Syrian seasoning is 0.08 µSv/y.The concentrations of naturally occurring radionuclides in foods vary widely because of differences in the background levels in soil, the climate and the agricultural conditions that prevail.There are also differences in the types of local food, such as vegetables, fruits and fish.Ot is therefore difficult to select reference values from the wide ranges of concentrations reported (United Nations Scientific Committee on the Effects of Atomic Radiation, 2008).Therefore, it is important to analyze the effective dose levels in the foods consumed, to create a local database and to use this data to discuss the biological effects at low dose rates, to characterize a region by the effective dose level, since this varies from region to region, and to measure the increase in dose levels due to human action, from nuclear testing to the application of fertilizers in agriculture.

Conclusions
K-40 AC was measured in all samples, Ra-226 AC was measured in one sample only, namely Brazil nuts.Ra-226, Ra-228, Ra-224 AC was calculated assuming the secular equilibrium between this samples.Cs-137 AC was observed only in Syrian seasoning (bahar).
The sample with the lowest derived limit was Brazil nut, with consumption of 11 kg/y.The radionuclide that most contributes to committed effective dose is K-40, with almost 49% of the total.But the potassium is uniformly distributed in the body, and its concentration is mostly under homeostatic control, and do not represent a risk to human health.Different from radium isotopes studied here, that has a long half-live, and their behavior is similar to calcium element.When ingested, radio is allocated in the individual's bone structure, increasing the internal exposure, and consequently the committed effective dose.
This study contributes to establish baseline information, because it makes available data on both specific concentration of a variety of seasoning and effective dose.

FoodstuffsFigure 1 .
Figure 1.(a) K-40 behavior in the three categories of seasoning botanical (or vegetal) origin, plus the total mean; (b) Behavioral differences of Ra-224 and Ra-228 in each category; and (c) concentration difference of Ra-224 and Ra-228 in each category studied.

Table 1 .
Samples, their physical characteristic and their botanical names.International desPoids et Mesures (BOPM), and has reached a good performance in intercomparision exercises with the MAPEP (Radiological and Environmental Science Laboratory Mixed Analyze Performance Evaluation Program) conducted by the USDDE (United States Department of Energy).Based on the AC values found in the LAASC, by the LGO and presented in the certificate of the reference material, the correction factors were created.The results are shown in the Table 2.

Table 2 .
Comparison of specific activities measured by LAASC and the LGO, and correction factors for use of LabSDCS software.

Table 4 .
Activity concentration of seasonings and nuts in Bq/kg.

Table 5 .
Cs-137 AC in some spices and teas.

Table 6 .
Effective dose for ingestion of seasoning and nuts for members of the public in µSv/y.