Thorium Urinary Excretion by Gas Mantle Manufacture Workers

Abstract

Workers in a gas mantle manufacturing plant were monitored by urinary excretion bioassays using α spectrometry. Between 1986 and 1994, 32 workers were monitored, usually by one sample collection per year. Of these samples 50% contained occupationally related thorium of an extent up to 38 mBq.d -1 . A monitoring regimen providing quarterly sample collections was introduced in 1995. A constant chronic inhalation intake of a Class M aerosol corresponding to the ICRP 66 respiratory tract model and a default value of 5 μm AMAD is assumed. Provided these assumptions may be applied, the detection limits below 0.1 mBq.d -1 232 Th are obtainable which allows the detection of an interpretation level corresponding to 3% of an ALI a short time after the work was commenced. The ALI was derived from the dose coefficient of ICRP 68. Based on this dose coefficient and the ICRP 66 respiratory tract model, a committed effective dose up to 3 mSv was determined for 13 workers by the monitoring regimen. Assuming a Class S aerosol, an annual effective dose up to 42 mSv results from the excretion data.