Natural radionuclide content in horticulture plants from former tin mining land and health risk assessment: A case study on Bangka Belitung Island, Indonesia

As a tin producer in Indonesia, Bangka Belitung has abandoned tin mining land containing natural radionuclides, and its use for cultivating horticultural crops has health risks. The aim of the research was to determine the contribution of former tin mining land to natural radionuclide contamination in horticultural products and to assess the radiation hazards by determining the annual effective dose and excess lifetime cancer risk (ELCR). The methodology includes sampling vegetables, fruit, and tubers from several villages in Bangka. Measurement of natural radionuclides using a Gamma Spectrometer at their specific energy. The research results showed that the radionuclides Ra-226, Th-232, K-40 were found in vegetables, fruit, and tubers samples. The highest Ra-226 was found in bitter melon and spinach, Th-232 in cassava leaves, spinach, and bitter melon, while K-40 in bitter melon, spinach, cassava leaves, papaya leaves, mustard greens. The activity rank of Ra-226, Th-232, and K-40 is shown in tubers > vegetables > fruit. The total annual effective dose (AED) from vegetable and fruit consumption is 0.6330 mSv/year, as recommended by UNSCEAR (1 mSv/year), except consumption of tubers (galangal). The ELCR value of vegetable, fruit, and cassava (tubers) consumption is 1.08x10−3; 0.75x10−3; and 0.42x10−3, as recommended by the ICRP.


Introduction
Bangka Belitung is known as a producer of tin ore, as well as several other types of minerals, such as granite, quartz, iron ore, zircon, monazite, and kaolin.Almost a third of world tin production comes from Indonesia, moreover, most of it comes from the Bangka Belitung Islands.However, tin mining activities have left behind ex-mining land that is suspected to contain a number of natural radionuclides.The use of former tin mining land for agricultural activities related to land potential and constraints has been researched by Agustin et al [1].
The total area of former tin mining land in the seven districts is 124,838 ha, including an area of 12,147 ha of covered voids [2].Data from 2012 recorded that around 7,000 hectares of former tin mining land in Babel Province had been reclaimed and allowed to be planted with food crops.There are several problems with the use of ex-mining land in Bangka, including cases of soil fertility, issues of pollution in agricultural products, and farming skills on ex-mining land to produce maximum products.However, IOP Publishing doi:10.1088/1755-1315/1297/1/012097 2 farming communities in Bangka are very interested in utilizing former tin mining land and have started to do so with various agricultural commodities, such as rice and vegetables.The government supports in order to increase the use of this land for food crop cultivation.The government has issued Law No. 18 on food, and it is stated that food safety is a condition and effort needed to prevent food from possible biological, chemical, and other contamination that can disturb, and endanger human health [3].Chemical contaminants in food are chemical elements, such as natural radioactive elements that are accidentally and undesirably present in food originating from the environment which can disrupt, harm, and endanger human health.Foodstuffs that contain chemical contaminants and are consumed directly or indirectly can affect human health, so the government needs to regulate food safety.
A Natural Radionuclide is an element in nature that is unstable and will emit radiation continuously throughout its half-life to become stable or a nuclear species is radioactive.These elements emit radiation in the form of alpha particles, beta particles, or gamma rays.Humans are exposed to natural radiation from external sources, including radionuclides in the earth (soil) and cosmic radiation (outside the earth), as well as internal radiation from radionuclides that enter the human body.The main route of entry of these radionuclides is through the consumption of food and water, as well as inhalation of air containing natural radionuclides.Radiation emitted by natural radionuclides includes primordial radiation terrestrial radiation, and internal radiation.Generally, humans are exposed to radiation due to the presence of natural radionuclides such as K-40 and the decay of the U-238 and Th-232 series in the soil.The concentration of these radionuclides in the soil and the rate of exposure to them vary over a wide range of values and depend on environmental factors, such as local geology and climate [4].
Uranium, Th, and their decay products are dangerous because they cause radiation.By nature, uranium is radioactive, being unstable, so the element is in a constant state of decay for a more stable arrangement.High radiation exposure by intake of U-238, Th-232, and their decay in a short time can cause symptoms, such as nausea, vomiting, and even death.However, exposure to low levels of radiation from the environment does not cause direct health effects, although it does contribute to increasing cancer risk.As much as 66% of U-238 absorbed by the body can be lost through urine, the rest is distributed and stored in the kidneys, 12-25% is stored in bones, and 10-15% in soft tissues [5].The radionuclides or radioactive substances that are ingested and absorbed in the blood will accumulate in certain body tissues and damage these tissues.An ecological study in the United States reported consuming water containing Ra-226 resulted in high mortality from bone cancer.In addition, there is also an increased rate of bladder cancer in men, breast cancer in women, and lung cancer.It was reported that people in the Bangka-Belitung Islands received a higher radiation dose compared to the world average value for normal areas [6].

Sample Collection and Preparation
The sample consists of vegetables, fruits, and tubers which are commonly consumed by people in Bangka-Belitung Island Province and its surroundings, and a total of eighteen (18) samples were collected for the investigation.Samples that are old enough to be harvested are collected directly from ex-mining land on Bangka Island.Then the sample is put into a plastic bag that has been coded to be sent to the laboratory for further treatment.In the laboratory, samples of vegetables, fruits, and tubers were cleaned of dust, adhering sand, and washed under running water, and rinsed with distilled water.Samples were air-dried, cut into pieces, weighed, and dried in an oven at 105 o C to constant weight, and then pulverized [5]- [7].Furthermore, the sample was sieved to ensure uniform particle size and weighed into the Marinelli beaker, and the Marinelli beaker was sealed.Samples in Marinelli beaker were left for ± 1 month until secular equilibrium was reached [5]- [7].

Radioactivity measurements
The radioactivity measurement in the samples used a Gamma Spectrometer equipped with an ORTEC p-type coaxial high purity Germanium (HPGe) detector, with a relative efficiency of 60% and a resolution of 1.95 keV (FWHM) in measurements with Co-60 at a gamma energy of 1332 keV for 24 hours.The natural radionuclide of U-238 was measured as Th-234 at -energy 92.37 and 62.26 keV, Ra-226 as Bi-214 and Pb-214 at -energy 609.31 and 351.92 keV respectively, Th-232 as 228Ac at energy of 911.07 and 968.97 keV, Th-228 as Pb-212 and Tl-208 at -energy of 238.63 keV and 583.2 keV respectively, while K-40 is measured directly at -energy 1460.75 keV [5]- [7]- [8].Radionuclide concentration activity is calculated using Equation-1, while Minimum Detected Concentration (MDC) uses equation-1 [5]- [7]: where: A is the concentration of radionuclide in the sample (Bq/kg), Ns is the gamma count rate (s -1 ), Nb is the background of gamma count rate (s -1 ), γ is the HP Ge detector efficiency of specific -ray, pγ is the transition probability of gamma decay, W is sample weight (kg).Whereas  is the uncertainty of measurement, xi is data value -i, x ̅ is the average of data value, n is data amount.The MDC (Minimum Detectable Concentration) calculation with a 95% confidence level uses the following equation-2 [5]- [7]: where: MDC is the Minimum Detectable Concentration (Bq/kg), NBG is the background gamma count rate (s -1 ), t BG is the counting time of background (seconds), γ is the HP Ge detector efficiency of specific -ray, pγ is the emission probability of gamma decay, W is the sample weight (kg), Cf is the selfabsorption correction factor.

Annual of effective dose
In order to estimate the annual effective dose due to consumption of foods containing radionuclides, it is necessary to calculate the annual intake of radioactivity per person for each radionuclide ingested.Radionuclide intake through ingestion is well described by the ICRP Human Gastrointestinal Tract Model [9]- [10].To obtain the effective dose ingested, the radioactivity of each radionuclide ingested per year is multiplied by its dose conversion coefficient [11].Finally, the total ingested dose is obtained by summing the contributions of all radionuclides.The calculation formula to obtain an estimate of the effective dose is as follows [9]- [12]: Where: AED is the Annual Effective Dose by ingestion of radionuclide (i, Sv/y), Ai is the specific activity of radionuclide i (f, Bq/kg fresh weight), DCFi (mSv/Bq) is the dose conversion factor of radionuclide i in the ingested food for adult (ages more than 17 years), 0.28×10 -6 for Ra-226, 0.23×10 −6 for Th-232, and 6.2×10 -9 for K-40, I v is the consumption rate of the food crops (v, kg/y) [13].The rates of food consumption such as vegetables, fruits, and tubers in Bangka 2022 are shown in Table 1 [14]-[15]- [16].

Estimation of cancer risk
The impact of consuming food containing radionuclides exceeding the reference value is internal radiation exposure, and this has received great attention throughout the world.The negative impact of exposure to ionizing radiation is on the health of biological tissue.This high energy ionizing radiation will interact with biological tissue and cause ionization, and then release charged particles and free radicals and cause changes in cell structure and damage to deoxyribonucleic acid (DNA).Damage to DNA causes gene mutations, chromosomal aberrations, and cell damage or death.The health impacts of long-term radiation exposure through ingestion of radionuclides include cancer and leukemia.Cancer due to exposure to ionizing radiation is still one of the most dangerous diseases [9].Based on this, in addition to calculating the annual effective dose received, the lifetime cancer risk (ELCR) is also calculated.According to ICRP, the risk factor for fatal cancer at low doses is 0.05 (Sv -1 ), and ELCR was to estimate the potential carcinogenic effects of the long-term consumption of food (in this case vegetables, fruits, and tubers).Estimated lifetime cancer risk (ELCR) can be calculated using the following equation [4]- [17]: Where: ELCR is Excess Lifetime Cancer Risk, AED is the annual effective dose due to ingestion (Sv/y), DL is the duration of life or the lifetime expectancy of people in Bangka is 71.14 years [18], and RF is the fatal cancer risk factor per Sievert (ICRP 60 uses values of 0.05 for the public exposure) [19].

Radioactivity of Natural Radionuclides in the Sample
The activity concentration of Ra-226, Th-232, and K-40 in vegetables, fruits, and tuber in the former tin mine area of Bangka-Belitung Province is presented in Table 2.  [4] 0.0300 0.0005 -Table 2 shows that all samples analyzed contain natural radionuclides Ra-226, Th-232, and K-40, with activity concentrations exceeding the UNSCEAR reference value [4].The activity concentration of K varies greatly, ranging between 3.20-1680.52Bq/kg and its concentration is higher than Th-232 (0.09-11.97Bq/kg) and Ra (0.04-2.17Bq/kg).This is because potassium is an important element and is needed for growth, whereas plants cannot carry out isotopic differentiation [20].
The activity concentration of Ra-226 in several vegetable ranges from 0.04-2.15Bq/kg, and the highest is found in bitter melon (2.15 Bq/kg) and spinach (1.30Bq/kg).Meanwhile, in fruit samples, it was between 0.23-1.22Bq/kg, and the highest was found in key lime (1.22 Bq/kg) and guavas (0.99 Bq/kg).Radium-226 in galangal (tuber) samples was higher (2.17 Bq/kg) than in cassava (0.97 Bq/kg).Vegetables grown on land around the cement industry contain radionuclides Ra-226 and Th-232 as much as 22.37 Bq/kg and 212.84 Bq/kg respectively, compared to this study, the Ra-226 activity is higher but the K-40 is lower [21], This means that the cement industry contributes Ra-226 to horticultural products.
The activity concentration of Th-232 in vegetables ranges from 0.09-11.97Bq/kg, the highest in cassava leaves (11.97 Bq/kg), followed by spinach (4.90 Bq/kg), bitter melon (4.64 Bq/kg), mustard greens (2.97 Bq/kg), and papaya leaves (2.72 Bq/kg).Thorium-232 in fruit samples ranged from 0.23 -8.18 Bq/kg, the highest in key lime (8.18 Bq/kg) and papaya (1.42 Bq/kg).Thorium-232 in tubers was found to be higher in cassava (9.69 Bq/kg) than galangal (2.53 Bq/kg).Other researchers stated that the concentration of radionuclide activity in unwashed samples was higher than in washed samples, so washing vegetables and fruit would reduce the level of surface contamination [20].
It was reported that vegetables grown on former tin mining land in Peninsular Malaysia contained K-40 higher than Ra-226 and Th-232, with rank K-40 > Ra-226 > Th-232 [22].However, vegetables grown on former tin mining land in Bangka Belitung contained K-40 higher than Th-232 and Ra-226, with rank K-40 > Th-232 > Ra-226 [23].There is a difference between the former tin mining land in Peninsular Malaysia and Bangka Belitung, it seems that the land in Bangka Belitung contains slightly higher levels of Th-232 than in Malaysia.The radioactivity in fruits showed that concentration of K-40 > Th-232 > Ra-226, similar to radioactivity in tubers [23].These two researchers reported higher values than the present study, except for K-40.It was reported that high thorium activity is especially found in tubers and leafy vegetables.Cassava, papaya, and red spinach have the maximum values of Thorium at 17.35; 21.04, and 16.20 with correspondingly higher values for uranium [24].

The annual effective dose
The annual effective dose that consumers receive by ingestion due to consuming food that contains radionuclides depends on the number of foods consumed per year (consumption rate), and the activity concentration (level) of radioactivity in the food sample.The calculation of the annual effective dose is based on the metabolic model developed by the International Commission on Radiological Protection (ICRP) [9], and the result of the calculation is shown in Table 3.

Assessment of Cancer Risk
To estimate the potential carcinogenic effects due to long-term consumption of vegetables, fruit, and tubers containing natural radionuclides, the lifetime cancer risk (ELCR) has been calculated, and the results are shown in Table 4. Central Bureau of Statistics (2022) states that the rate of vegetable consumption in Bangka is 143.57kg/y, and fruit is 111.02 kg/y, while cassava and galangal consumption rates are 34.89 and 4295 kg/y respectively [16].UNSCEAR reports that the average vegetable intake of adults in the world is 500 kg/year, higher than the Bangka consumption rate (143.57kg/y for eleven kinds of The total annual effective dose from vegetable and fruit consumption (in the case of Bangka Belitung) is 0.30 and 0.21 mSv/y, as recommended by UNSCEAR (0.3 mSv/y).
ELCR or Excess Lifetime Cancer Risk is defined as the probability that a person will develop cancer during their lifetime due to exposure to radiation from food intake containing natural radionuclides.In most cases, people generally get cancer when they reach old age.The ELCR values of vegetable, fruit, and tuber (cassava) consumption in this study were obtained at 1.08x10 −3 , 0.75x10 -3, and 0.42x10 -3 respectively, which are higher than the world safe limit value (0.29×10 −3 ), as recommended by ICRP (3.5x10 -3 mSv/y) except for tuber consumption [11].However, it can be said that there is a radiological risk [4], which means that the probability of getting cancer throughout life due to consuming vegetables, fruits, and cassava is respectively 1080, 750, and 420 persons per one million population of Bangka Belitung.Cancer is the main cause of death throughout the world, almost 10 million deaths occurred in 2020.According to data from the Indonesian Ministry of Health in 2022, the incidence of cancer in Indonesia is 136 people per 100,000 population, or is in 8 th place in Southeast Asia [26].Potential health risks associated with long-term exposure to radionuclides Ra-226 and Th-232 include muscle weakness, paralysis, kidney disease, liver disease, cardiovascular disorders, chromosomal abnormalities, leukemia, benign, bone and pancreatic tumors, cancer, and death.

Conclusion
Based on the results, it can be said that vegetables, fruit, and tubers cultivated on former tin mining land contain a number of natural radionuclides Ra-226, Th-232, and K-40.Concentration activity of radionuclides in tubers > vegetables > fruit.There is a tendency for leafy vegetables, such as spinach, cassava leaves, papaya leaves, mustard greens, and bitter melon to contain higher levels of radionuclides Ra-226, Th-232, and K-40 than other types of vegetables.Key orange fruit contains the highest natural radionuclides compared to other types of fruit The estimated annual effective dose received by the public is very dependent on the consumption rate (consumption pattern) of horticultural products, and the type and content of radionuclides in horticultural products.Even though the concentration activity value in horticultural products is still lower than the UNSCEAR recommended reference value, long-term consumption patterns can have an impact that needs to be taken into account, especially on body health.
ELCR provides an estimate of the probability that a person will be affected by carcinogenic effects from the behavior of consuming horticultural products containing radionuclides Ra-226, Th-232, and K-40 in the long term.The highest probability of getting cancer occurs from consuming galangal > key lime > cassava > spinach > cassava leaves > bitter melon.Galangal is a type of tuber plant that has the ability to absorb more elements from the soil than other types of plants, besides that the consumption rate of galangal is high because it is widely used as a spice in everyday cooking.As a result, the consumption of galangal provides a higher annual effective dose than others and will affect the ELCR value.The ELCR value is closely related to the annual effective dose level and the duration of consumption.In this study, the ELCR value of consumption of galangal, key lime, cassava, spinach, cassava leaves, and bitter melon grown on former tin mining land will provide a higher potential risk of developing cancer compared to consumption of other types.Like galangal, the consumption rate of key lime fruits is also relatively high because it is widely used as a drink and food mixture by the people of Bangka Belitung.In the world, cancer is the main cause of death throughout the world, although the cause is sometimes not very clear, so research continues to be carried out to protect society from this incident.

Figure 1 .
Figure 1.Location of sampling