Abstract
This study focuses on the emission of alpha particles rates (EAPR) and heavy metals concentrations (HMC) in rice samples from Najaf markets using nuclear track detector (CR-39, UK) and a Flame Atomic Absorption Spectrophotometer-6300 AA, Shimadzu, Japan, respectively. This new study is showing the pollution in the environment obtained by AP and HM and the relationship between them. The highest EAPR found to be 0.069 mBq cm-2 in basmati rice (Southern Iraqi Company), whereas the lowest EAPR (0.029 mBq cm-2) is found in Indian basmati rice. The highest Fe found to be 2.7237 ppm in basmati rice (Southern Iraqi company), while the lowest (0.3997 ppm) is found in USA basmati rice. The highest Cd found to be 0.0468 ppm in Iraqi Alnasryah rice, while the lowest HMC (0.0034 ppm) is found in Indian basmati rice. The highest Pb found to be 0.2431 ppm in Babil Anbar Iraqi rice, while the lowest (0.0695 ppm) is found in Indian basmati rice. Pb and Cd levels were generally lower than the FAO/WHO recommendation limits (Pb: 0.50 ppm, Cd: 0.50 ppm) and the European Union acceptable dietary limits. In the combination of recent rice consumption data, the estimated weekly intakes of toxic element are calculated for Iraq population. No statistically significant correlation between EAPR and HMC in studied rice at the 0.05 level.
Keywords: Natural alpha particles, CR-39, pollution, heavy metals
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B. A. Almayahi, Department of Environment, Faculty of Science, University of Kufa, Najaf, Iraq. basimnajaf@yahoo.com
Introduction
The examined rice in this study is a major food in Iraq County. Recently, concern has raised about possible contamination of the crop by heavy metal. A large number of industrialized processes give rise to the contamination by heavy metals, such as cadmium (Cd), Iron (Fe) and lead (Pb) in soil, food, water, and air Almayahi et al., 2014a; Alduhaidahawi et al., 2015; Almayahi et al., 2016. The contaminants by heavy metals can be accumulated and transferred in rice. Fu et al. (2008) found the Pb with the mean level of 0.69 ppm in polished rice in a typical electronic waste recycling area from the southeast China. Huang et al. (2009) observed the high Pb concentration of 0.957 ppm in rice. Zhao et al. (2010) reported the Cd with a maximum value of 0.467 ppm in rice. These studies showed the possible contamination of rice by heavy metals. The Cd is toxic to the kidney and has a long biological half-life in the human body. Pb has shown to be associated with damage to central nervous systems, lead to the decrement of intelligence quotients in children. It is reasonable to hypothesize that the rice as the staple foods of the human containing heavy metals has the potential health risk to consumers. In current years, there is increasing environmental and global public health concern associated with the environmental contamination by heavy metals. Human exposure has risen dramatically result of an exponential increase of it use in industrial, agricultural, domestic, and technological applications (Bradl, 2002). Environmental pollution is famous in point source areas such as mining, foundries, smelters, and other metal-based industrial operation )Fergusson, 1990; Bradl, 2002; He et al., 2005(. Natural uranium consists of three radioisotopes: 238U, 235U, and 234U with the different half-life. The nucleus of radioactive is unstable, meaning transformed to other elements either emitting or absorbing particles. The unstable nucleus loses energy by emitting ionizing particles for reaching a stable state. It undergoes alpha decay by radiating alpha particles (”) with decay energy (4.679 MeV). 4He is representing one alpha (”) particle. This radioactive substance can enter human bodies through ingestion of contaminated food or water or inhalation.
The inhaled or ingested 235U leaves the body (biological T1/2=15 d) excepting a small part which stays accumulated in kidney or teeth, and bones undergoing decay. It is increased the risk of liver damage and cancer. The effect of ionizing alpha particles when entering or colliding with blood cells lead to the occurrence of leukemia, alpha particles reaction mechanism be direct with external electrons of the constituent atoms and if the provision of sufficient energy, they can throw external electrons away from the atoms. Then it will be produced a free electron and a positively charged ion and radiation ionized absorbed by human tissue has enough energy to remove electrons from the atoms that make up molecules of tissues (Valkovi”, 2000; Hada et al., 2011). The mechanism that causes the radiation damage to human tissue is through the ionization of atoms in the material. Studies on autopsy tissues have mainly aimed at determining the level for the principal alpha emitter present, namely 210Po, 226Ra, and 238U. Considering 210Po occurs at the end of the 222Rn decay chain, 222Rn exposure is considered another potential source of increased 210Po and 210Pb in the body.
226Ra is expected to be present in the bones tissue because this radionuclide tends to be moderately transferable in the physical environment. 226Ra is taken up by vegetation from the soil and assimilated efficiently from the gut when ingested by animals (NCRP, 1999). There are many types of researches on alpha emission in biological samples using a technique counting track by nuclear particle detector because of it a high resolution and the ability to detect very low-lying concentrations. CR-39 detectors are used in the radon detection and alpha particle spectroscopy to measure the natural alpha radioactivity in blood and tissues of human and animal (Henshaw, 1989; Henshaw et al., 1994; Almayahi et al., 2011; 2012a, b, c; Almayahi et al., 2014b). The main aims of this study were to assessed the natural alpha radioactivity and analyze heavy metals in rice and evaluate the health risk with respect to daily consumption of rice for general adults and find the relationship between heavy metals and alpha particles. Based on the obtained data, estimated weekly intake (EWI) of toxic metals are calculated and then compared with provisional tolerable weekly intake (PTWI).
Materials and Method
A total number of 12 rice samples are collected from the different location in Najaf city and from Najaf markets in Iraq. An alpha emission rate in rice is determined using ”-sensitive plastic track detector (PADC-TASTRACK CR-39, Track Analysis Systems Ltd, Bristol, UK). Nuclear track detector (CR-39) is an organic detector, the scientific name (Polyallyl diglyol carbonate) and commercial name (CR-39). It has a chemical composition (C12H18O7), a density of 1.31 g cm-1, and contains a general composition of the monomer on two groups’ allele . The CR-39 detector has a high sensitivity and analysis ability to record the tracks of protons, alpha particles, and fission fragments because it contains the bonds of weak carbon that breaks easily when exposed to radiation. Nuclear track detectors technology is one of the important techniques for determining the concentrations of radioactive substance due to the availability, accuracy, not requiring complex electrical equipment, and knows track detectors as electric materials ranging qualitative resistance 106-1020 Ohm-cm that generated narrow paths of radiation damage called tracks when alpha particles pass through (Durrani and Bull, 1987). The rice samples are collected from markets and agriculture lands. The rice samples are transferred to airtight polyethylene bags, labeled, and taken to the environmental lab for further analysis.
Samples were dried and manually ground by mortar and pestle and passed through a steel sieve of 75 ”m Fig. 1. All samples are weighted and placed on the sheets of the high-purity plastic ”-detector, with about a 2 ” 2 cm2 area. The detectors with samples were put in vacuum-sealed a high-density polyethylene bags (prevent the influx of radon gas and increasing range alpha particles) and clamped in position, as shown in Fig. 1. However, the most massive and energetic of radioactive emissions, the alpha particle is the shortest in range, because of its strong interaction with the matter. An Alpha particle, while not penetrating far, deposits their considerable energy in a short-range distance.
The detectors with samples sealed in a high-density polyethylene bag are placed together inside the freezer at -20 oC for 120 days to allow alpha particle tracks from the natural levels of activity in the rice to accumulate on the TASTRAK detectors. In this technique, the alpha particles are measured without the chemical treatments of the sample using CR-39 detector. At the end of the exposure period, the CR-39 detectors are etched under controlled condition in NaOH solution as reported elsewhere (Almayahi et al., 2011, 2012 a, b, c). Then the CR-39 detectors are washed and dried. The number of ”-tracks per unit area for the rice samples is counted using an optical microscope (A. Kruss. Optronic, Germany) with MDCE-5C camera at 10 ” magnification as shown in Fig. 2.
The CR-39 efficiency in this research was 85%, which was calculated using the following formula (Almayahi et al., 2014b):
(1)
where VB = bulk etch rate (”m h-1), and VT = track etch rate (”m h-1). The alpha emission rate E” is calculated using the formula:
(2)
where, T: Exposure time (Seconds), : Probability of Alpha transition, : Number of tracks produced by the samples (track cm-2), : Number of background tracks in the detector (track cm-2). The alpha particles quoted in this study includes the removal of a mean background track density. For the area of the rice powder surface in contact with the detector, the mean number of recorded alpha particle tracks is 360, with 219 as the lowest number and 523 as the highest.
The heavy metals in rice are determined using a Flame Atomic Absorption Spectrophotometer-6300 AA, Shimadzu, Japan. About 0.5 g of each of the sieved samples are digested at 180 oC for 3 h. Then 7 ml added of aqua regia, heated the mixture until it dried, add 5 ml of aqua regia, and 1 ml of of the HF acid (40%). Then heated the mixture again for two hours, then add 5 ml of 65% HNO3, and heated the mixture to dry. Then add 50 ml of distilled water to remnants of the beaker and filtered the solution for separation of solid waste to become a sample ready for the measurement of Cd, Pb, and Fe using atomic absorption spectrophotometer (Fig. 3).
The potential human health risk assessment is carried out by considering the following parameters according to Onsanit et al., 2010. The evaluated weekly intakes (EWI) and provisional tolerance weekly intakes (PTWI) are jointly established by FAO/WHO, 2004. The EWI is calculated using the following equation:
EWI (ppm Week-1 Person-1) = (Crice ” (wrc rice/body weight)) ” 103 (3)
where, Crice = mean heavy metals concentration in rice (mg kg-1), wrc rice = weekly rice consumption (g week-1) per capita for the Iraqi population (110 g per capita per day ” 7) and body weight = average body weight (kg) of the Iraqi population (60 kg).
Results and discussion
The alpha emission rates in the rice samples are found. The heights emission rate of alpha particles (0.069 mBq cm-2) found in basmati rice (Southern Iraqi Company), whereas the lowest rate (0.029 mBq cm-2) found in Indian basmati rice (International Company) as shown in Table 1. Figs. 4 and 5 show the tracks produced by the rice of typical samples.
These rates are normal and alpha particles are have not caused by cancer in studied rice, which is no clear increase in these measurements by comparison conducted with global research, so the rice samples are free of radioactive contamination. The heavy metals concentration (HMC) in the rice samples is found. The heights HMC for Fe found to be (2.7237 ppm) in basmati rice (Southern Iraqi company), whereas the lowest HMC (0.3997 ppm) found in American basmati rice (General Company for Grain Trade) as shown in Table 2. The heights HMC for Cd found to be (0.0468 ppm) in Nasiriyah Anbar rice, whereas the lowest HMC (0.0034 ppm) found in Indian basmati rice (International Company), these values are below the food sanitary standards of Cd (0.5 ppm) as shown in Table 2. The heights HMC for Pb found to be (0.2431 ppm) in Babylon Anbar rice, whereas the lowest HMC (0.0695 ppm) found in Indian basmati rice (International Company) as shown in Table 2. In sum, investigation of the Cd content of rice from different countries revealed a range from 0.0008 ppm to 0.13 ppm (mean= 0.03 ppm) (Watanabe et al. 1996). The lead content in the rice samples from various countries ranged from 0.0016 ppm to 0.0583 ppm (mean= 0.0157 ppm) (Zhang et al. 1996).
The FAO and WHO organizations provide guidelines on the intake of heavy elements by the human. The provisional tolerable weekly intake recommended through the Joint FAO/WHO Expert Committee of cadmium and lead are 7 ”g Cd kg-1 body weight per week and 25 ”g Pb kg-1 body weight per week respectively (FAO/WHO, 1972; IARC, 1993). The concentration of heavy metals in rice varied depending on their country of origin. The average concentration of Cd in Iranian rice was 0.41 ppm (Afshin et al. 2007). The mean concentrations of Cd and Pb in Australian grown rice were 0.0075 ppm and 0.375 ppm dry weight, respectively (Rahman et al. 2014). A large number of national and international organizations in worldwide (WHO, FAO, USEPA, FSANZ, ANZFA, and IEFS) set tolerable dietary intakes (TDI) limit for the heavy metals depending on body weight and age of the consumers. The calculated EWI of cadmium, lead, and iron are based on the average consumption of rice (110 g d-1) is shown Table 3. Table 3 is showed provisional tolerable weekly intake (PTWI) for the investigated heavy metals. According to the results shown in Table 3, the estimated weekly intake of Cd, Pb, and Fe in rice consumption is lower than the provisional tolerable weekly intake. The highest mean concentration (0.02576 ppm) of EWI for Pb is observed in some imported rice samples in Iran markets (Naseri et al. 2015). Estimated daily intake (EDI) for Cd and Pb of rice in China exceeded the FAO/WHO recommendation limit (Zhuang et al. 2009). Health risk will increase with consumption of other contaminated food that is not evaluated in this work.
However, rice E” is positively correlated with Fe, Cd, and Pb in the rice samples, as shown in Fig. 6. Rice Pb is negatively correlated with Fe and Cd, whereas rice Cd is positively correlated with Fe in the rice samples, as shown in Fig. 7. No statistically significant correlation between EAPR and HMC in examined rice at p> 0.05.
Conclusions
The variation in alpha emission rates as natural radioactivity in the rice collected from Najaf city may depend on the transfer rate of radionuclides from soil and water to rice plants. All the heavy metal concentrations are below the recommended limit. Pb, Cd, and Fe concentrations vary according to the following order: Fe > Pb > Cd. EWI for cadmium and lead in rice consumption is lower than the PTWI. These results conclude that the best rice can be used as food for humans is Indian basmati rice (International Company), because it has a small amount of heavy elements of a cadmium and lead that cause poisoning. In addition, Indian basmati rice has low alpha emission rate and the relationship between EAPR and HMC is a positive correlation. This study showed the emission of alpha particles is a regular rate of radioactivity naturally present in the rice. Overall, the results of alpha activities of rice samples are low and no cause dangerous effects on human health. This means that the samples are free of environmental pollution of the alpha particles. This study is useful in determining the exposure and intake rates of alpha particles and heavy metals.
Acknowledgment
The author acknowledges the financial support of the College of Science of the University of Kufa.