A case study of the estimation of occupational internal dose using urinary excretion data obtained in a biomedical...

This paper presents a fundamental investigation of the screening of intakes and the estimation of internal doses for workers at a biomedical research facility from their urinary excretion data. Urine samples from the workers were collected immediately before and several days after handling radioactive materials, and 5-mL portions were measured directly with a sodium iodide scintillation detector or a liquid scintillation detector. Intakes of radionuclides and effective doses were estimated from the data using the Internal Dose Easy Calculation code. Blank levels of radioactivity and detection limits for this method were determined from the radioactivity contained in urine samples collected from volunteers working outside the controlled area (control samples). Most of the radioactivity in the control samples was attributed to K. Under the present experimental conditions, the detection limits for the committed effective doses were 7.5 x 10(-4) mSv for 125I and 6.9 x 10(-2) mSv for 35S in the case of samples collected 1 d after handling. Accordingly, it can be determined whether workers were exposed more than the recording level (1 mSv of committed effective dose) or not. No workers in the surveyed facility were found to suffer internal exposure beyond the recording levels, and their intakes were estimated to be below the detection limits in the 2-y investigation period. In an ordinary facility of biomedical research, the amount of unsealed radioactivity handled at one time is within 10 MBq in many cases, and the air ventilation and filtering systems work adequately. Under such circumstances, the present results suggest that individual monitoring, such as urine analysis, is omissible in many cases as a routine monitoring of internal exposure for workers.