Study on thorium excretion for inhabitant of high background radiation areas of Tamil Nadu

The extent of human exposure to naturally occurring radionuclides depends on the background radioactivity in the area of residence. Internal exposure occurs from radionuclides present in the food chain and through the inhalation of the suspended dust in the air. Once in the human body, these radionuclides get partially accumulated in the vital organs and delivers radiation doses to individuals. There are regions (particularly coastal zones) in southern Tamilnadu in India, where the radiation levels are high due to presence of monazite, a Thorium (Th) rich ore mineral in the beach sand causing continuous exposure to Th by ingestion and inhalation. Internal dose to an individual can be assessed by measuring the urinary excretion of thorium. Thorium in urine can be analyzed using various analytical methods like fluorescence spectroscopy, alpha spectrometry, neutron activation analysis (NAA), and mass spectrometry. Alpha spectrometry is an efficient method for the determination of the short lived thorium isotopes namely ²²⁸Th, ²'3⁰Th in biological samples by radiochemical separation where as for ²³²Th, the mass detection levels are high due to low specific activity. The excreted thorium in urine is at ultra trace levels hence very sensitive methods like pre-concentration NAA (PCNAA) and high resolution ICPMS (HR-ICP-MS) are two competent analytical method used. HR-ICP-MS has a high sample throughput, short turnaround time and high sensitivity. The TDS and organic contents in urine are high and can get deposited on the sample introduction tubing, interface cone orifices, resulting in disturbance in sample flow rate, system signal loss and instability hence it is important to remove these interferences before analysis using HR-ICP MS. Acid digestion of urine and radiochemical separation of thorium from the bulk helps to resolve the problem. The aim of the study was to standardize and measure the urinary excretion of thorium for inhabitants of HBRA using HR-ICP-MS. These results will be useful for assessment of internal exposure and also will serve as reference data range for further investigations of this exposed populations to natural radiations and for other epidemiological studies