Radiation hazard assessment from NORM-added paint products in Malaysia

2.1 Sampling

The tourmaline powder and zirconium (Zr), which contain U and Th, are advertised as ingredients in ion paint products (Lee et al., 2016). In the present study, 20 different wall paint samples were purchased online. All the packaging or labels of the products contain no evidence of any radioactivity. We have designated the products as either ion or conventional paint, as follows: ten ion paint samples (code IP01 to IP10), ten normal paint samples (code NP11 to NP20).

2.2 Instrumentation and calibration

Each sample was transferred into a 500 mL Marinelli beaker before counted by an HPGe detector for a period of 20 h. A single geometrical configuration is maintained for all of the paint samples. The γ emissions were measured directly with an ORTEC GEM Series P-type coaxial HPGe spectrometer (GEM20-76-LB-C-SMPCFG-SV-LB-76; 1.8 keV FWHM at 1332 keV with 33% relative efficiency), which provides high-performance γ-spectroscopy over the energy range of 40 keV to several MeV. Besides Mobius cooling system, the system also employs high-resolution spectroscopy software (VISION version 8) for spectral analysis. The spectra were calibrated using a 500 mL standard multinuclides source, which provided a wide range of photon energy emissions from radionuclides distributed in a liquid matrix (²¹⁰Pb, ²⁴¹Am, ¹⁰⁹Cd, ⁵⁷Co, ^123mTe, ⁵¹Cr, ¹¹³Sn, ⁸⁵Sr, ¹³⁷Cs, ⁸⁸Y, and ⁶⁰Co). All of the γ emissions have energies greater than 200 keV, thus are unaffected by potential differences in densities between the normal liquid and the paint samples examined in the current study.

Under current measurement conditions, the ²³⁸U series had counting efficiencies of 0.64% for ²¹⁴Bi (609.3 keV) and 1.1% for ²¹⁴Pb (351.8 keV). For ²³²Th series, they were 1.24% for ²²⁸Ac (338.2 keV), 0.6% for ²¹²Bi (727 keV), 1.52% for ²¹²Pb (238.4 keV), 0.71% for ²⁰⁸Tl (583 keV), and 0.16% for ²⁰⁸Tl (2614 keV). Meanwhile, the counting efficiency for ⁴⁰K is 0.2% at 1460 keV (Al-Sewaidan, 2019; Alshahri, 2017). Except ⁴⁰K, all the γ lines consist of a high branching ratio (Clouvas et al., 2000).

The radionuclide activities in the paint samples were evaluated in secular equilibrium, with the emission lines of the relatively short-lived decay products adequately considered. The results for ²³²Th were calculated using an average of ²¹²Pb (238 keV), ²²⁸Ac (338 keV and 911 keV), ²¹²Bi (727 keV), and ²⁰⁸Tl (583 keV and 2614 keV) emissions, while the activities for ²³⁸U were calculated using an average of ²¹⁴Pb (295 keV and 351.8 keV) and ²¹⁴Bi (727 keV) (609 keV and 1764 keV). An example of spectrum for IP04 are shown in Fig. 1. The specific activity concentration for each radionuclide, $A$ (Bq kg⁻¹) is calculated by using Eq. (1) (Al-Sewaidan, 2019):

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Fig. 1

Example spectra obtained from an IP04 ion paint sample.

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2.3 Sample analysis

A Cartesian Geometry Energy Dispersive X-Ray Fluorescence (ED-XRF) spectrometer was applied for elemental analysis of the paint samples (model; NEX CG-CG1240). XRF provides a non-destructive method of determining actual content, including consumer products (Jurado-López et al., 2006; Ngo et al., 2018; Perring et al., 2017). All samples were prepared in liquid form. Four ion paint samples and two normal paint samples were analysed using XRF (Pabroa et al., 2011).

2.3.1

2.3.1 Monte Carlo (MC) simulation and evaluation of annual effective dose (AED)

The equivalent organ doses and AED from daily exposure to the painted walls of a hypothetical residential room have been estimated using the GMC radiation transport code (version 10.06 patch 3, Physics list: Geant4 electromagnetic (EM) physics (G4EmStandardPhysics option4)) (El Bakkali and El Bardouni, 2017). A MIRD5 mathematical male and female phantoms were also used in the study, with the male version shown in Fig. 2 (Lee et al., 2016; Olsher and Van Riper, 2005; Snyder et al., 1974). The male phantom was 178 cm and weighed 76 kg, while the female was 174 cm and 70 kg. Except for the skeleton and lungs, all organs were soft tissue material. The MIRD soft tissue density was 0.9869 g cm⁻³, the MIRD skeleton was 1.4862 g cm⁻³, and the MIRD lung material was 0.2958 g cm⁻³.

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Fig. 2

MIRD human phantoms for painted walls, as used in GMC simulation; (a) standing position 20 cm from the wall; (b) standing position 50 cm from the wall; (c) standing position in the centre of the room.

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The ion paint products were simulated for fictitious bedrooms with 24.31 kg and 13.52 kg of paint on the walls for Room 1 and Room 2, respectively. The room dimensions used in the simulation are from Malaysia's National Housing Standards Guidelines. The minimum size for a master bedroom (Room 1) is 3.5 m $\times$ 3.2 m, while a smaller room, Room 2, is 2.0 m $\times$ 3.3 m. Both rooms are standing at 2.8 m in height, as shown in Fig. 3 (CIDB, 2019). Fig. 2 depicts the simulated environment of Room 1 for the reference phantoms, which were standing at one of three distances from the walls: 20 cm, 50 cm, and in the centre of the room.

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Fig. 3

Standard recommended minimum dimension for bedrooms in Malaysia: (a) master bedroom (Room 1) and (b) Room 2. Source: CIDB (CIDB, 2019).

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2.4 Data analysis

The organ equivalent and average effective doses associated with the exposures have been assessed by first measuring the activity of ²³⁸U, ²³²Th, and ⁴⁰K in the ion paint samples. DCFs calculated by GMC simulation were also used, taking into account the various tissue weighting factors. The radiological protection quantity effective dose, $E_{\mathit{eff}}$ (Sv) is calculated using the following parameters as shown in Eq. (2)(Yoo et al., 2015):

The dose equivalent from exposure to the ion paint samples was also measured using a calibrated IdentiFinder 2, FLIR Survey Meter. The exposure dose rates (in Sv h⁻¹) were recorded three times for each product, and the average was calculated, which was quoted along with the standard deviation. Finally, the radionuclides contained in the ion paint samples were identified.

3.1 Activity concentration of ²³⁸U, ²³²Th, and ⁴⁰K in samples

Analysis of activity concentration for ²³⁸U, ²³²Th, and ⁴⁰K were conducted for 20 samples of paint and calculated using Eq. (1). Table 1 shows the data for the radioactivity in the wall paints, which shown ion paint IP04 had the highest activity, with values of 4449 ± 530, 31888 ± 2175, and 2963 ± 405 Bq kg⁻¹, from ²³⁸U, ²³²Th, and ⁴⁰K, respectively. There were significant differences in radioactivity content among the ion paints. The variation of ²³⁸U series activity was found to be between 1687 ± 264 and 4449 ± 528 Bq kg⁻¹, while the ²³²Th series activity was between 15649 ± 1064 and 31888 ± 2175 Bq kg⁻¹. The variation of ⁴⁰K was found to be between 1418 ± 223 and 2963 ± 405 Bq kg⁻¹. Surprisingly, normal paint samples showed the least amount of activity, to the point where they could be safely considered non-radioactive from a legal standpoint. Meanwhile, all of the ion paint products contain the U and Th amount that exceeds the exemption limit of 1000 Bq kg⁻¹ (IAEA, 2014a).

Four ion paint samples and two normal paint samples were analysed for elemental content using an ED-XRF spectrometer (Table 2). The six tested samples are primarily composed of Si, Ca, and Ti, and rare earth elements (REEs). Results showed that NORM (U, Th and K) were found in the four ion paint samples, while in the two normal paint samples, only K has been found. In comparison to normal paint, no P was detected in any ion paint sample. It was also discovered that the rare earth element cerium (Ce) was found in IP04 and europium (Eu) in IP06 at concentrations of 0.09% and 0.26%, respectively. For safety reasons, it appears that the white material Ti has been used in place of lead. As a result, a trace amount of lead element was discovered in all six samples tested. IP04 had the highest concentrations of U, Th, and Pb, with 0.026%, 0.81%, and 0.06%, respectively. U and Th concentrations (and activities) in IP04 were 260 ppm (3211 Bq kg⁻¹), and 8100 ppm (32886 Bq kg⁻¹), respectively. The results for IP04, as shown in Tables 1 and 2, are consistent.

3.2 Equivalent dose analysis

The measured energy distribution from the use of the MIRD5 mathematical phantom code was applied as the probability distribution in the generation of the source on the Rooms 1 and 2 wall surfaces. Fig. 4 depicts the IP04 results for 28 organs/tissue, with the organ equivalent dose calculated using Eq. (3) based on the location of the MIRD5 male and female phantoms. The male and female phantoms were used in two different room simulations (Rooms 1 and 2), each with three various standing positions. Fig. 4 (a-c) depicts phantom standing positions from Room 1, whereas (d-f) depicts the standing position in Room 2.

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Fig. 4

Organ equivalent dose (in mSv y⁻¹) for 28 organs/tissue using the MIRD5 mathematical male and female phantoms in standing position, for Room 1; (a) 20 cm from the wall; (b) 50 cm from the wall; (c) in the centre of the room. Room 2; (d) 20 cm from the wall; (e) 50 cm from the wall; (f) in the centre of the room.

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The maximum organ/tissue equivalent dose was observed in Room 1 at 20 cm from the wall, while the minimum organ equivalent dose was observed in Room 2. The superficial organs/tissues, such as the lung, breast, rib cage, thymus, leg bone, and thyroid, were among the most exposed organs compared to deep organs. For example, in case (a), the most significant organ equivalent dose for IP04 was found to be to the lung, at 1.25 and 1.31 mSv y⁻¹ for the male and female phantoms, respectively. The current GMC simulations are the only other known work on such material, apart from the previous study reported here (Yoo et al., 2015).

3.3 Annual effective dose analysis

By averaging the effective doses for the male and female phantoms using Eq. (2), the AED was calculated. It was assumed that a receptor would remain in the room for 8 h per day (UNSCEAR, 2000). In Room 1, with the phantom 20 cm from the wall, IP04 was associated with the most significant annual effective dose, at 1.51 mSv y⁻¹, whereas NP15 recorded the least yearly effective dose of 0.006 mSv y⁻¹ (Table 3). These findings implied that the former has a yearly effective dose more significant than the annual dose limit of 1 mSv y⁻¹ for public members (IAEA, 2016, 2014a). The effective dose was also discovered to be four times higher than that found in the centre of the same room.

Furthermore, standing 20 cm from the wall in Room 1 was assessed to give 25% greater exposure than standing in Room 2 at the same distance. The AED was much lower than the limit set for a public member when one of the ten normal paint samples was used. The alpha emissions were absorbed mainly by the wall paint, with adequate air exchange posing no significant health risk. γ radiation, on the other hand, was profoundly penetrating, affecting large areas of tissue and organs. Here, it is worth noting that the internal dose was not included in the current assessment.

The dose equivalent was also determined for the ten ion paint samples, yielding AED of more than 1 mSv y⁻¹. A calibrated IdentiFinder 2, FLIR survey metre was used for this, recording dose rates in Sv h⁻¹ and identifying the radionuclides contained within the paint samples (Table 4). IP04 presented the most effective dose equivalent, at 0.571 ± 0.07 µSv h⁻¹. Assuming daily exposure time of 8 h, the annual dose reached 1.67 mSv y⁻¹, which is comparable to the GMC results.

The use of radioactive materials in consumer products is typically regulated in developed countries. “Evaluation of EPA's guideline for TENORM” is an example from the United States (EPA, 2000). While Malaysia's Atomic Energy Licencing Board (AELB) has published consumer product guidelines titled “LEM/TEK/69” (AELB, 2016), there is still a need for safe control in the use of NORM-added consumer products. Unjustified exposures, as described in ICRP-103 (ICRP, 2007), can be applied to various consumer products. Suppose the benefits of using a consumer product to which NORM has been added cannot be demonstrated to outweigh the risks. In that case, a ban is required (EURATOM, 2013; Furuta, 2011), as appears to be the case for the currently investigated ion paint products. Consequently, a strong recommendation is made to prohibit the marketing and distribution of ion paint products in Malaysia.