Natural radioactivity content in various building materials of Chennai, Tamil Nadu, India

KS Lakshmi; V Meenakshisundaram; J Punniyakotti

doi:10.4103/rpe.rpe_14_22

ORIGINAL ARTICLE

Year : 2022 | Volume : 45 | Issue : 2 | Page : 88-93

Natural radioactivity content in various building materials of Chennai, Tamil Nadu, India

KS Lakshmi¹, V Meenakshisundaram¹, J Punniyakotti²
¹ Meenakshi Sundararajan Research Centre, Meenakshi College for Women (Autonomous), Chennai, Tamil Nadu, India
² Department of Physics, Meenakshi Sundararajan Engineering College, Chennai, Tamil Nadu, India

Date of Submission	19-Apr-2022
Date of Acceptance	18-Sep-2022
Date of Web Publication	20-Dec-2022

Correspondence Address:
J Punniyakotti
Department of Physics, Meenakshi Sundararajan Engineering College, Kodambakkam, Chennai - 600 024, Tamil Nadu
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/rpe.rpe_14_22

Abstract

Natural radioactivity content in different types of building materials obtained from Chennai city has been determined. In this study, the most commonly used building materials such as clay bricks, cement, sediment, tiles, marbles, and granite have been considered for quantifying natural radioactivity content using gamma-ray spectroscopy. The annual effective dose (AED) values obtained in this study, varying from 0.04 mSv to 0.57 mSv, are deduced from the natural radioactivity content; these are lower than the European Commission Report 112 recommended level of 1 mSv. Therefore, the use of all the building materials in question, collected from in and around Chennai, in the construction of dwellings is considered to be radiologically safe for the inhabitants.

Keywords: Building materials, cement, clay bricks, marbles, radioactivity, tiles

How to cite this article:
Lakshmi K S, Meenakshisundaram V, Punniyakotti J. Natural radioactivity content in various building materials of Chennai, Tamil Nadu, India. Radiat Prot Environ 2022;45:88-93

How to cite this URL:
Lakshmi K S, Meenakshisundaram V, Punniyakotti J. Natural radioactivity content in various building materials of Chennai, Tamil Nadu, India. Radiat Prot Environ [serial online] 2022 [cited 2023 Mar 28];45:88-93. Available from: https://www.rpe.org.in/text.asp?2022/45/2/88/364555

Introduction

To provide radiation protection to the members of public due to the presence of naturally occurring radioactive materials in the building materials, appropriate steps are to be initiated to minimize the natural radiation exposures on the basis of As Low As Reasonably Achievable principle. One of the initiatives must be to estimate the natural radioactivity content in the building materials and also obtain the requisite radiological parameters and if feasible to find plausible solutions in the field of public health. Environmentalists desire that all the building materials used in the construction of dwellings and workplaces including the basic major inputs such as clay bricks, cement, soil/sediment, and other flooring and wall materials such as marble and tiles shall be analyzed for their natural radioactivity content to enable one to initiate appropriate mitigating steps, if deemed necessary, in the planning stage itself to minimize the natural radiation exposures.

Since the yesteryears of Mohenjo-Daro in the Indo-Pak subcontinent, some of the most commonly used construction materials are clay bricks, cement, sediment, marbles, and tiles. Bricks of age approximately 4000 years have been found in some cities of the Middle East and other parts of Asia. Bricks form the largest component (about 80% by volume) of building materials all over the world. These bricks, both baked and unbaked ones, are made mainly of clay/soil originating from sediments deposited by the rivers. The natural radioactivity content in the bricks is widely reported in many countries.^{[1],[2],[3],[4],[5],[6],[7],[8],[9],[10]}

Cement is one of the important major construction materials used both in urban and rural areas. Due to its high production rate and being widely used in construction industry, the natural radiation component originating from it deserves special attention as this study seeks to achieve. The natural radioactivity content of cement varies considerably depending on the geological characteristics of the raw materials from which the cement is processed. Some of the raw materials used in the production of cement include limestone (CaCO₃), shale ash, and iron oxide which contain elements such as gypsum, silicates, and aluminates that have ionization tendency.^[11] Natural radioactivity levels in cement were reported by researchers from different countries all over the world.^{[11],[12],[13],[14],[15],[16]} The knowledge of natural radioactivity in building materials, cement in particular, and the associated radiation doses due to inhalation of gaseous radon isotopes are of paramount importance for the assessment of radiological parameters to human health.

Another important building material is river sediment. River sediments consist of mineral depositions, formed through weathering and erosion of either igneous or metamorphic rocks. River sediment deposition on the riverbeds consists of sand and gravel particles with different sizes, which makes them valuable as building materials. When rocks are disintegrated through natural processes, radionuclides contained in them are carried to river sediments by rain. Primordial radionuclides of 238U, 232Th and ⁴⁰K get attached to the river sediments. When these river sediments are used as building construction materials, it might result in higher radiation exposure to the members of public. Radioactivity content of ²³⁸U, ²³²Th, and ⁴⁰K in river sediment was reported in literature.^{[17],[18],[19],[20],[21],[22]}

Of late, tiles and marbles are more commonly used as lining building materials on walls and floors in dwellings. These are made up of mixture of earthly materials (Clay) that have been pressed into shape and fired at higher temperature. Granite is also an another commonly used flooring as well as decorative building material. Granite is an igneous rock, having been formed as lava or molten rock cooled and solidified over thousands or even millions of years. Igneous rocks contain high quantities of naturally occurring radionuclides of ²³⁸U and ²³²Th; small quantities of these radionuclides are also associated with sedimentary rocks. Granite's durability and decorative appearance makes it a popular building material in homes and workplaces.

Hence, in the circumstances as detailed above, the knowledge of the natural radioactivity content in commonly used building materials is of great interest since it provides useful information in the assessment of radioactivity content of ²³⁸U, ²³²Th, and ⁴⁰K and associated human possible radiation exposure to occupants, if any.

Materials and Methods

Study area and sample preparation method

Chennai, the capital of Tamil Nadu State, India, can be said as gateway to South India. The Chennai metropolitan area was home to approximately 12 million, making it the fourth most populous metropolitan area in India [Figure 1]. In this study, 43 samples comprising six types of building materials (clay bricks, cement, sediment, tiles, marbles, and granite) have been collected in Chennai. The samples of clay bricks, tiles, marbles, and granite were grinded and powdered. The samples were then uniformly mixed, sieved, air-dried, and further dried in an oven at a temperature of 100°C to 120°C for an hour to remove the moisture content. Each sample was transferred to a 250-ml plastic container having diameter of 60 mm and height of 95 mm. The container with an inner cap was sealed hermetically and externally; an adhesive tape was put making it leak-tight and kept aside for about a month to attain secular equilibrium between radium and its daughter products before being analyzed for their natural radioactivity content using a gamma-ray spectrometer. The net weight of each of the sample was determined.

Figure 1: Study area of Chennai, Tamil Nadu State

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Gamma-ray spectroscopy

A 3” ×3” NaI(Tl) scintillation detector-based gamma-ray spectrometer was used for spectral measurements. The gain of the amplifier was adjusted to cover the entire energy range of the naturally occurring radionuclides up to 2.6 MeV (energy of ²⁰⁸Tl, one of the gamma-emitting daughter products of ²³²Th). The detector is shielded by 150 mm thick lead and augmented with graded lining shield materials (Al, Cd and Cu) covering between inside the lead shield and the detector on all sides including at the top to reduce background due to cosmic ray component by almost 98% and thus increasing the signal-to-noise ratio. Standard sources of the primordial radionuclides obtained from the IAEA in the similar geometry and having similar density and grain size of the samples were used to determine the efficiency of the detector for various energies of interest. The sealed samples were placed on the top of 3” ×3” NaI (Tl) detector and count spectra were obtained for each of the sample. Each sample was counted for 10,000 s and the net radioactivity content of the three primordial nuclides, namely, ⁴⁰K, ²³²Th, and ²³⁸U, are deduced from the count spectra. The region under the peaks corresponding to 1.46 MeV (⁴⁰K), 1.764 MeV (²¹⁴Bi), and 2.614 MeV (²⁰⁸Tl) energies is considered to arrive at the radioactivity levels of ⁴⁰K, ²³⁸U, and ²³²Th, respectively. The minimum detectable activity (MDA) of each of the three primordial radionuclides with 95% confidence level (2σ) is determined from the background radiation spectrum obtained for the same counting time as was done for the samples. The estimated MDA values are 2.22 Bq/kg for ²³⁸U, 2.15 Bq/kg for ²³²Th, and 8.83 Bq/kg for ⁴⁰K.

Results and Discussion

Radioactivity content in various building materials

All the 43 samples of six different building materials collected from within the metropolitan areas of Chennai were individually subjected to gamma spectral analysis, and the radioactivity content in Bq/kg of the three primordial radionuclides was estimated and the results are given in [Table 1]. The same is graphically represented in [Figure 2].

Table 1: Average activity levels with minimum and maximum levels of ²³⁸U, ²³²Th, and ⁴⁰K in six different building materials

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Figure 2: Radioactivity content of ²³⁸U, ²³²Th, and ⁴⁰K in various building materials

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From [Table 1], it is inferred that the average activity content of ²³⁸U, ²³²Th, and ⁴⁰K in clay brick samples was 28.9 ± 8.3 Bq/kg, 52.6 ± 7.3 Bq/kg, and 282.3 ± 38 Bq/kg, respectively. The results indicate that activity content of ²³⁸U and ⁴⁰K in clay brick samples of Chennai is found to be much lower than all other countries including India as may be inferred from [Table 2] along with corresponding references. The activity of ²³²Th levels is also almost lower in Chennai as compared to many countries (India included) except Algeria.

For the ten different cement samples, it is seen from [Table 1] that the average activity content of ²³⁸U and ²³²Th was 68.1 ± 8.3 Bq/kg and 22.5 ± 6.7 Bq/kg, respectively. [Table 2] shows the natural radioactivity levels in the cement samples of other countries for comparison. As compared to cement samples of Chennai, the ²³⁸U activity is much higher in the cement samples of Austria (276.7 Bq/kg), Malaysia (81.4 Bq/kg), Iraq (124 Bq/kg), and China (69.3 Bq/kg); it is lower in Australia, Brazil, Egypt, Algeria, and Yemen. In general, ²³²Th activity is higher in most of the counties (Included India) as shown in [Table 2], excepting Austria and Yemen. In Indian states of Punjab and Himachal Pradesh, the activity content of ²³⁸U is lower, whereas ²³²Th activity is higher than the Chennai. In the Indian state of Meghalaya, both ²³⁸U and ²³²Th are found to be higher than in Chennai. For Chennai, the radioactivity content of ⁴⁰K is below the detectable level (<8.83 Bq/kg) for all the cement samples. This might be correlated to absence of potassium feldspar mineral in the samples, since the presence of ⁴⁰K essentially depends on the quantity of potassium feldspar present in the samples.^[23]

Table 2: Comparison of radioactivity content in different types building materials collected at Chennai with other countries

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In river sediment samples, the results of the present study (Chennai, Palar river) indicate that the average radioactivity content of ²³⁸U, ²³²Th, and ⁴⁰K was found to be 15.3 ± 8 Bq/kg, 105.4 ± 7.7 Bq/kg, and 317.5 ± 35.9 Bq/kg, respectively [Table 1]. These are compared with the activity values reported by different countries including four other river sediments from India in [Table 2]. In the river sediment of Netravathi river situated in Karnataka state of India, the radioactivity levels of all the three primordial radionuclides are found to be much higher as compared to Chennai (Palar river). However, in the other three river sediments of India (Cauvery, Vellar, and Ponnaiyar), the activity levels of ²³²Th are much lower than the river sediment of Palar river, Chennai, whereas ²³⁸U activity is marginally lower or almost the same.

The results of gamma spectral measurements of flooring materials, namely, tiles, marbles and granite, that are most commonly used in buildings are outlined in [Table 1]. The average radioactivity content of ²³⁸U, ²³²Th, and ⁴⁰K, obtained for six different tiles samples, was 68.9 ± 8.2 Bq/kg, 76.1 ± 6.5 Bq/kg, and 260.4 ± 40.6 Bq/kg, respectively. The average radioactivity content of ²³⁸U, ²³²Th, and ⁴⁰K in the marble samples was found to be 17.4 ± 5 Bq/kg, 17 ± 3.6 Bq/kg, and 71.1 ± 22.3 Bq/kg, respectively. The average radioactivity content of ²³⁸U, ²³²Th, and ⁴⁰K in the granite samples was 29.7 ± 7.1, 78 ± 6.3, and 422 ± 35 Bq/kg, respectively. The natural radioactivity content of all the three primordial radionuclides in the marble samples is much lesser than those obtained for both the tiles and granite samples.

Radiological parameters in various building materials

Based on the literature,^{[24],[25],[26]} the absorbed dose rate (D) and (ii) annual effective dose (AED) only are estimated for the various building materials.

Absorbed dose rate

The absorbed dose rate can be calculated using the following formula proposed by the European Commission Report 112^[26] for building materials. The specific activity values of ²³⁸U, ²³²Th, and ⁴⁰K are accordingly converted into absorbed dose rates using conversion factors of 0.92, 1.1, and 0.08 nGy/h per Bq/kg, respectively.

D (nGy/h) = (0.92 × A_U) + (1.1 × A_Th) + (0.08 × A_K)(1)

Where A_U, A_Th, and A_Kare the activity content of ²³⁸U, ²³²Th, and ⁴⁰K (Bq/kg), respectively. The average estimated absorbed dose rates for the six different building materials are given in [Table 3]. The highest absorbed dose rate observed is in tiles (117.9 nGy/h), whereas the lowest is in marbles (8.8 nGy/h).

Table 3: Radiological parameters in different building materials

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Annual effective dose

If the absorbed dose rate value (D) is known, AED that would be obtained by the members of public can be arrived at using the conversion coefficient of 0.7 Sv/Gy as well as the following formula as recommended by the European Commission Report 112.^[26]

AED (mSv/year) = D (nGy/h) ×7000 h × 0.7 Sv/Gy × 10⁻⁶ (2)

Where D is the absorbed dose rate. The calculated AED values are given in [Table 3] as well as in the form of bar chart in [Figure 3] for all the six building materials. It may be seen from [Table 3] that the AED values for all the six building materials have not exceeded 1 mSv/year (maximum value obtained is 0.57 mSv/year for tiles).

Figure 3: Annual effective dose in various building materials

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Conclusions

Building materials are one of the potential natural sources of radiation exposure to members of public in indoors. In this study, the most commonly used building materials such as clay bricks, cement, sediment, tiles, marbles, and granite available at Chennai have been considered for quantifying natural radioactivity content using gamma-ray spectroscopy. The AED values (0.04 mSv/year – 0.57 mSv/year) are lower than the European Commission Report 112 recommended level of 1 mSv. Therefore, the use of these building materials collected from in and around Chennai in the construction of dwellings is considered to be radiologically safe for the inhabitants. This study would help in establishing the national baseline data and useful in framing the national guidelines for controlling exposures due to natural radiation sources arising from such all human activities by Indian Regulatory Agency viz., Atomic Energy Regulatory Board.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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