The presence of contaminants in human environment has attracted serious attention in research community over the years. This is as a result of environmental and human health consequences associated with its exposure, especially at levels above the prescribed safety limits. Natural radioactivity has always been present and broadly distributed in the earth’s crust and the atmosphere, either as primordial radionuclide of uranium (238U) and thorium (232Th) decay series and radioactive potassium (40K), or as cosmic radiations that are produced constantly in the atmosphere. Primordial radionuclide of 238U and 232Th decay series and 40K which has extremely long half-lives are of great concern in terms of radiation exposure due to their gamma ray emitting potentials. This radionuclide in their decay chains are assumed to be in radiological equilibrium in any naturally undisturbed environmental medium. Human activities and industrial processes such as mining disturb their secular equilibrium thereby altering their natural state. These alterations result in the enrichment or depletion of the radionuclide in the end products and wastes which can lead to an incremental increase in the radiation risk to the population [1]. Humans are exposed to natural radiation from external sources, which include natural radionuclide in the earth (series of uranium-238, uranium-235, and thorium-232) and cosmic radiation, and by internal radiation from natural radionuclide incorporated into the body [2]. The main routes of radionuclide intake are ingestion through food, water, and inhalation. A particular category of exposure to internal radiation, in which the bronchial epithelium is irradiated by alpha particles from the short-lived progeny of radon, constitutes a major fraction of the exposure from natural sources [3]. The worldwide average indoor effective dose due to gamma rays from building materials is estimated to be about 0.4 mSvy^-1. Globally, building materials that contain radioactive nuclides have been used for many decades. As individuals spend more than 80% of their time indoors, the internal and external radiation exposures from building materials create prolonged exposure situations. The use of such materials which contain naturally occurring radionuclide for house construction may enhance the natural radiation background to which some population groups are exposed [4]. This exposure occurs on a daily basis and the ability of the radionuclide to move rapidly in air allows them to be easily transmitted into the environment in which humans come in contact with [5].

In building construction, the existence of this radionuclide in the raw material such as cement, brick, and tiles may lead to undesirable radiation exposure to the public. The major exposure problem is associated with structure that naturally acts as radionuclide-bearing material. This indoor radiation exposure is due to the presence of these radioactive elements in the building materials. Constructions materials are derived from both natural sources (e.g., rock and soil) and waste products (e.g., phosphor-gypsum, alum shale, coal, fly ash, oil shale ash, some are minerals and certain slugs) as well as from industry products (e.g., power plants, phosphate fertilizer, and the oil industry. Although building materials act as sources of radiation to the inhabitants in dwellings, they also shield against outdoor radiation [5]. In Nigeria, the commercial building materials such as cement, bricks, and tiles have been widely used. Most of them are imported from all over the world such as India, China, Italy, UAE, and Spain. However, some others are from the local supplier around Nigeria. As there is a lack of report in risk exposure for all of these building materials, in this article, focus is given to the assessment of radioactivity concentration and radiological risk indices in commercial building materials [5].  Measurement of concentration of radionuclide in building materials is important in the assessment of population exposures, as most individuals spend 80% of their time indoors. The population-weighted average of indoor absorbed dose rate in air from terrestrial sources of radioactivity is estimated to be 84 nGyh^-1. Radiation exposure due to building materials can be divided into external and internal exposure. The external exposure is caused by direct gamma radiation. An inhabitant living in an apartment block made of concrete with average activity concentrations (40 Bq kg-1, 30 Bq kg-1 and 400 Bq kg-1 for radium, thorium and potassium, respectively) receives an annual effective dose of about 0.25 mSv (excess to the dose received outdoors). Enhanced or elevated levels of natural radionuclide in building materials may cause doses in the order of several mSv [6]. The internal exposure is caused by the inhalation of radon (²²²Rn), thoron (²²⁰Rn) and their short lived decay products. Radon is part of the radioactive decay series of uranium, which is present in building materials. Because radon is an inert gas, it can move rather freely through porous media such as building materials, although usually only a fraction of that produced in the material reaches the surface and enters the indoor air [6].

The food we eat typically contains about 10Bq/kg of 40K, our body incorporates them into tissues and bone irradiating the body continually and hence our body is naturally radioactive, which refers to NORM internal to human body. The activity in the body of a reference man of 70kg is about 4,000Bq, mainly due to presence of 40K and 14C (Alison, 1968). This delivers a dose of 7µSv per year to the skeleton. Therefore, in line with routine measurements of background radiation, a substantial amount of research effort is continually invested in determining how much radioactivity is contained within certain foodstuffs that are also part of the human diet. A radioactive element in food is absorbed in bodies of plants and animals by different mechanisms that are typically dependent on its chemical properties rather than its radioactive characteristics [7]. Soil radionuclide activity concentration is one of the main determinants of the natural background radiation. Volcanic geographic structures as well as rocks that are rich in phosphate, granite and salt contain natural radionuclide like uranium-238 (238U), thorium-232 (232Th) and potassium-40 (40K). When rocks are disintegrated through natural processes, radionuclides are carried to soil by rain and flows [1]. The knowledge of natural radionuclide distribution and natural radioactivity levels in soil, water, building materials and food in the environment is important for assessing the radiation exposure to the population and is useful to set the standards and national guidelines in the light of international recommendations [1]. Humans are continuously exposed to ionizing radiation from naturally occurring radioactive materials (NORM). Although the origin of these materials is the Earth’s crust, they find their way into building materials, air, water, food, and the human body itself. Measuring the activity concentrations of radionuclide in building materials is important for the assessment of population exposures, as most individuals spend 80% of their time indoors. Knowledge of the natural radioactivity in humans and the human environment is important because naturally occurring radionuclides are the major source of radiation exposure to humans. It is an established fact that all of the construction materials contain trace amounts of natural radioactivity [8].

No doubts that radionuclide (²²⁶Ra, ²²⁸Ra, ²²⁸Th, ²³²Th, ²³⁸U and ⁴⁰K) in the soil, water, foodstuffs and building materials poses serious contamination hazards. Therefore, assessment of its level in samples media provides useful information on potential unwanted radiation exposure to humans. The analyses were carried out on data extracted in order to assess the effects of natural radionuclides in the environment using different radiation detection techniques. This article reviews some of such studies with a view of gathering vital information on the recently used techniques, discusses current situations and gives highlights of recent findings [9].

Strategic Search Terms

The research studies that investigating the radioactivity and radiological hazard of radionuclide in water, soils, building materials and foodstuffs were searched on the internet and retrieved from different databases such as Goggle Scholar, Academia, Science Direct and PudMed etc. The search terms include: Radioactivity and radiological hazard of soil & Building materials; Radioactivity and Radiological hazards of water; Activity concentrations and Radiological hazard of foodstuffs. The Data were searched and retrieved throughout 2021-2022.

Inclusion and Exclusion Criteria

Inclusion Criteria

The research papers retrieved from different databases were thoroughly checked for its eligibility by applying the criteria below: research studies that investigate activity concentrations of soil, water, building materials and foodstuffs; research studies that assess the health hazards of radionuclide in soil, water, building materials and foodstuffs and research studies investigating effective dose & cancer risk in soil, water, building materials and foodstuffs.

Exclusion Criteria

Any research studies that did not investigate, examine, determine or assessing radioactivity concentrations of soils, water, foodstuffs & building materials and their health hazard/risks were excluded in this study.

Extraction of Data

The research papers used in this work were evaluated critically and data regarding Location of the studies, Sample types, methods and activity concentrations of ²²⁶Ra, ²²⁸Ra, ²²⁸Th, ²³²Th, ²³⁸U, ⁴⁰K was extracted. Analysis of activity concentrations was performed in order to assess the radiological hazard indices and Cancer risk of radionuclide.

Selection of Study

About ninety nine (99) articles were downloaded from various databases. Repeated articles were eliminated and titles and abstract of the articles were fully and thoroughly investigated. Forty three (46) full –text articles passed the screening process and was used in this work.

Analysis

Different types of samples were collected by different Nigerian researchers such as building materials (brick, clay, soil, sand, cement and tiles), Water, Rocks and food e.t.c. The material samples were studied in their natural form. Each sample was properly catalogued, marked and coded according to its origin and the location of the sampling site. After crushing, powdering, coning and quartering, the representative samples with a maximum grain size of 1 mm were dried in an oven at a certain range of temperature until the sample weight became constant. These samples were sealed in radon impermeable plastic containers. The samples were then stored for some days to bring 222Rn and its short-lived daughter products into equilibrium with ²²⁶Ra. The Samples were analyzed using the Gamma Spectrometer with NaI (Tl) scintillation detector and HpGe detector type-p coupled with multichannel analyzer. The detector is enclosed in a thick lead shield, which reduced the background by a factor of approximately 95%. IAEA –375 reference soil standard was used for energy and efficiency calibration. The counting time for each of the samples ranged from seconds to several hours. The photopeaks observed were considered to correspond to the activities concentrations of radionuclide (such as ²²⁶Ra, ²³⁸U, ²³²Th) series in addition to the non-series ⁴⁰K [10].

Absorbed dose rate (D nGyh-1)

This refers to the amount of radiation energy absorbed or deposited per unit mass of substance. The absorbed gamma dose rates due to gamma radiations in air at 1 m above the ground surface for the uniform distribution of the naturally occurring radionuclides (238U, 232Th and40K) were calculated based on the guidelines provided by UNSCEAR, 2000. To convert activity concentration to dose the following factors was used such as 0.462, 0.604 and 0.0417 for uranium (or Ra), thorium and potassium respectively [11].  For rocks/soil the absorbed dose is given as

Absorbed dose.......... (1)

Where Cu, C_Ra, C_Th and Ck are the activity concentrations of 40K, 238U and 232Th in Bqkg^-1 respectively, same equations was used in the estimation of D for water, and foodstuffs, for building materials is given as

Absorbed dose.......... (2)

Annual Effective Dose (AED)

IAED (mSvy-1) = D (nGyh-1) × 8760 h × 0.7 Sv/Gy × 0.2x10^-6 for indoor Annual effective dose 

                          = D (nGyh-1) × 0.00123 .......... (3)

OAED (mSvy-1) = D (nGyh-1) × 8760 h × 0.8 Sv/Gy × 0.7x10^-6 for outdoor Annual effective dose

                            = D (nGyh-1) × 0.0049056 .......... (4)

Equation 3&4 was used for evaluation of Radiological hazard of building materials; similarly equation 3 was used in estimation of hazard indices of water, rocks and soils. But for foodstuffs the equation below was used in this work to evaluate Annual Ingestion Dose (AID)

    AID (mSv/y) = Ai × C × FDC .......... (5)

Where Ai is the activity of ingested radionuclides, C is the consumption rate of radionuclide, which is 3.3 kg/y for adult person consumed Grains, 170 kg/y for adults consumed cassava, and 45kg/y for adult consumed tomato FDC is the ingestion dose coefficient of radionuclide such as ²²⁶Ra (0.28µSv/Bq), ²³²Th (0.23 µSv/Bq), and ⁴⁰K (0.0062 µSv/Bq).

Hazard indices for external and internal exposure

For the assessment of excess gamma radiation from the building materials to ensure of the safety of the building materials, two indices were used in this paper. Beretka and Mathew introduced a hazard index for the external gamma radiation dose from building materials as given below [8]

The external hazard index (Hex) and internal hazard index (Hin) can then be defined as

Hex = .......... (6)

Hin = .......... (7)

Where C_k, C_U (C_Ra) and C_Th are the activity concentrations of 40K, 238U and 232Th in Bq/Kg respectively. The external hazard index (Hex) is widely used to reflect external exposure. It provides a solitary index that expresses the gamma yield from various combinations of 226Ra, 232Th and 40K in the sample. The indices were calculated by the use of activity concentrations of radionuclide available in the literatures. Equation 6 &7 was applied to every sample in this work.

Gamma Index (Iγ) and Alpha Index (Iα)

Estimation of the level of gamma radioactivity associated with different concentrations of some specific radionuclides is known as the gamma index [7], which is given as

Iγ = .......... (8)

Where C_k C_U and C_Th are the activity concentrations of ⁴⁰K, ²³⁸U and ²³²Th in Bq/kg respectively Values of Iγ ≤ 1 corresponds to an annual effective dose of less or equal to 1mSv. If Iγ in the locations exceed unity the area is radiologically Unsafe. The radionuclides ‘activity concentration in the literature was used to calculated gamma index shown in tables below for each samples in the literatures.

Iα =.......... (9)

Excess lifetime cancer risk (ELCR)

The term "excess lifetime cancer risk" connotes the risk of death of cancer in excess of the "natural" background risk, resulting from a lifetime exposure to carcinogens. In practice, exposure is not for a lifetime, competing causes are prominent, the exposure usually comprises more than one carcinogen, and the risk of cancer death may be substantially reduced by therapy [11]. The expression below used to calculate the ELCR

                                                                                                                                         .......... (10)

Where AEDR, DL, and RF are the annual effective dose equivalent, Duration of life (70 y) and risk factor (0.05 Sv^-1) respectively, the risk factor is the fatal cancer risk per Sievert. For stochastic effect, the International Commission on the Radiological Protection (ICRP 60) uses a value of 0.05 for the general public as in the case of rocks/soil, water and building materials, but in the case of foodstuffs RF is given as 5.0 x10^-5 

                                                                                                                                        .......... (11)

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