Assessment of natural radionuclide levels in some Nigerian made poultry feedstuff

This study investigated the radionuclide contents of naturally occurring radionuclides. Ten samples of some Nigerian made poultry feedstuff and supplements were collected and analysed using NaI(Tl) gamma(γ)-ray spectroscopy for an accumulated time of about 29000 s. The results revealed that activity concentration of primordial radionuclides 40 K, 226 Ra, and 232 Th for the samples ranged from 43.6 to 196.8 Bq/kg, 5.0 to 34.7 Bq/kg and 0.9 to 51.6 Bq/kg, respectively. The presence of anthropogenic radionuclides was not detected. The Nigerian poultry fodders were found to have relatively higher activities of 226 Ra and 232 Th compared to the activities reported for poultry feeds in other countries. However, the radionuclide concentrations are not alarming.


INTRODUCTION
Among Nigerians dwelling in rural areas, poultry meat and eggs are to some extent still considered luxury foods but in the urban areas, poultry is consumed more often due to the relatively higher income; availability of poultry meat either as fresh or frozen products, and the introduction of a chain of fast food outlets, whose recipes and menus are rich in chicken meat and eggs, is on the increase.
There has been a concern with radiation levels in food, because ingestion is one of the most common way radionuclides enter living organisms.These radionuclides find their way into the food chain from soil or air to plants, plant to animals/humans, or from other lower animals to humans.
Animal feeds are developed from an organic base (plants or animals) and are intended to provide the most complete nutrition possible (Filho et al., 2016).In an attempt to improve nutritional value of feedstuff, feed substances derived from the biota that contain some elevated levels of radionuclide activity may sometimes be added to poultry feeds.This may increase the radionuclide concentration in such feeds.
Many Nigerian made poultry feeds comprised soybean, maize, sodium chloride and a vitamin complex called "Premix Vitamínico Mineral" ("Vitamin Mineral Premix"), bone meal and fish meal.Thus, in these feed samples, *Corresponding author.E-mail: iverenageda@gmail.com.
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License  (Casacuberta et al., 2010), which supplies calcium for domestic animals such as poultry.
The food chain extends to the uptake of these radionuclides by animals from the feedstuff they eat which is deposited in their tissue and finally consumed by human.Thus, as humans ingest both eggs and poultry meat, it is expedient to monitor the radiation levels in poultry feedstuff since a part of the amount of radionuclides in the feed which animals ingest could possibly be transferred to humans via the radionuclide pathway in the food chain (Mc Donald et al., 1999;Breuninger et al., 2002;Hernandez et al., 2004).
Therefore, every source of radionuclide that has an end effect on humans whether directly or indirectly needs to be checked to ensure that substances meant for public consumption have radioactivity levels As Low As Reasonably Achievable (ALARA).
Around the world, researches have reported natural radioactivity levels in poultry fodders.However, there has been little or no reports on the concentration of natural radionuclides in poultry feeds made in Nigeria.Thus, this present work assessed the amount of natural radionuclides in samples of Nigerian made poultry feedstuff and compared the measured values with feedstuff produced in other parts of the world.

MATERIALS AND METHODS
Ten samples of Nigerian made chicken feedstuff and supplements used for poultry feeds were collected, prepared and analysed.Samples were collected on the basis of production and consumption in Nigeria.Sample collection was done by interaction with farmers, milling (manufacturing) companies and a few samples directly purchased from the market.Table 1 shows the sample collections.

Sample preparation
Collected samples of Nigerian made poultry feeds were pulverized to 200-300 mesh size, with a blender and ceramic mortar, and then homogenized to fine powder with a 2 mm-mesh sieve and packed to fill cylindrical plastic containers with inner dimension of 7.2 cm diameter and 6 cm height.This satisfied the selected optimal sample container height (Ibeanu, 1999).Each container accommodated approximately 300 g of sample which were carefully sealed (using vaseline, candle wax and masking tape) to prevent radon escape and then stored for a minimum of 28 days.This is to allow Radium and Thorium attain secular equilibrium with their (daughters) progenies.

Sample analysis
Gamma ray spectrometry technique was employed in the spectral collection of the prepared samples using the higher energy region of the γ-line.A 7.62 × 7.62 cm NaI(Tl) detector by Canberra Inc, housed in a 6 cm thick lead shield and lined with cadmium and copper sheets was used.A computer based Multichannel Analyzer (MCA) MAESTRO programme from ORTEC was used for data acquisition and analysis of gamma spectra.The energy calibration of the spectrometer was performed using certified reference material for radiometric measurement from the International Atomic Energy Agency (IAEA), Vienna.Gamma Standard sources includes: Caesium-137 and Cobalt-60; also, calibration energy of 661.60 keV for Cs-137 or 1173.2,1332.5 keV for Co-60 was used.The 1764 keV γ line of 214 B for U was used in the assessment of the activity concentration of 226 Ra, while 2614.5 keV γ-line of 208 Tl was used for 232 Th.The single 1460 keV γ-line of 40 K was used in its content evaluation.
The samples were mounted on the detector surface and each counted for 29,000 s in reproducible sample detector geometry.The configuration and geometry was maintained throughout the analysis.

Activity concentration estimation
All the obtained raw data were converted to conventional units using calibration factors to determine the activity concentration of (1 where A is the activity concentration in Bq/kg, (cps) net is    (Harb et al., 2010;Choi et al., 2008;Filho et al., 2016).The presence of anthropogenic radionuclides was not detected which shows that there was no contamination due to artificial radionuclides.

Conclusion
In this study, the activity concentrations of natural radionuclides, 40 K,  226 Ra and 232 Th in different samples of Nigerian poultry feed supplements and compounded feeds were estimated.The results were also compared with other poultry fodders in other parts of the world.Although, the Nigerian poultry fodders had relatively higher activities of 226 Ra and 232 Th, the radionuclide concentrations are not alarming.By implication, a transfer of such levels to chicken and finally to human in the radionuclide pathway will pose no danger when poultry products of meat and eggs fed from these feeds are consumed eventually by the public.
radioactivity concentration in the investigated samples was obtained as follows(Abel-Ghany et al., 2009).

Table 1 .
Samples identity and collection locations.

Table 3 .
Comparison of activity concentration (Bq/kg) of poultry feeds in different locations.