Background radiation and micronuclei in lymphocytes of residents in the vicinity of the mineral sand processing factory in Pulmoddai, Sri Lanka

Abstract

Lanka Mineral Sands Ltd (LMS), a government owned company, has been mining mineral sands at Pulmoddai since 1957. The mineral sands that are mined include monazite which contains thorium (Th). Th emits alpha particles on decay and gamma rays are emitted by the daughter products. Biological dosimetry has been established as a sensitive method to estimate exposure to ionizing radiation by using different techniques and the cytokinesis blocked micronuclear (MN) assay is popular for large scale exposure studies as it is an easier, faster and reliable method. The objective of the study was to determine the frequency of MN among the persons residing in the vicinity of LMS and to determine radiation levels in the area. A cross sectional study was conducted from November 2012 to September 2016 among persons 35-45 years of age. Eligible persons were invited to participate after administering a screening questionnaire A detailed questionnaire was used to gather sociodemographic and other details 10 ml of venous blood was drawn under aseptic conditions using disposable equipment by trained personnel after obtaining informed written consent. Background radiation measurements and soil samples for gamma spectrometry were collected from residences of participants. 53 employees of LMS factory, 25 residents within 5 kms from LMS, 25 residents 20- 25 kms from LMS and 29 residents from >50 kms away from LMS were included in the study Six soil samples from the LMS, 64 samples from the residences of participants and 23 samples along highways to Pulmoddai town making a total of 93 soil samples were analysed. Background radiation levels measured by the survey meter, 232Th, 226Ra and 210Pb , concentrations of soil samples were highest in the samples collected from the LMS; the background radiation levels and concentrations of 232Th and 226Ra concentrations were significantly higher in samples from the LMS than in samples of the other groups The median 4°K concentration was highest in the samples collected >50kms away from the LMS. The distance from the LMS was negatively correlated with background radiation measured by the survey meter and the activity concentrations of 232Th (r=-0.305, p=0.003), 226Ra (r=-0.422, p<0.001) and 210Pb (r=-0.369, p<0.001). 4°K activity concentration was significantly positively correlated with the distance from LMS (r=0.456, p<0.00 I). The highest median frequency of MN per 1000 BN cells was in the group residing within 5 krns from LMS with a median (IQ range) of 0.67 (0 17-2.17) There was no significant difference in the MN frequency between employees of LMS and the group residing within 5 krns from LMS. Being a resident of Pulmoddai and being exposed to X-rays were significant predictors of MN formation. Pulmoddai area had a higher background radiation level probably due to the mining of mineral sand at LMS. Residing within 5 kms from LMS was a risk factor for MN formation irrespective of employment status at LMS. Although radiation levels within the LMS were high as compared to the other areas, the risk of long term adverse health effects were low as the dose levels were much smaller than the recommended safe levels.