Thorium lung burdens of mineral sands workers
- Dept. of Minerals and Energy, East Perth (Australia)
Thorium lung burdens have been measured in workers in the dry separation plants operated by the mineral sands industry in Western Australia. The thoron exhaled in the breath of 62 workers was measured using a double filter tube. Six of the workers also underwent in-vivo gamma counting to determine their thorium lung burden. A thoron exhalation rate of 4.7% was obtained from a comparison of the two data sets. Estimated thorium lung burdens from the thoron-in-breath measurements had a geometric mean value of 10 Bq. Workers had a geometric mean employment period in the industry of 9.2 y and a geometric mean total inhaled alpha activity of 9,000 Bq, estimated from contemporary personal air sampling data and a retrospective assessment of previous workplace conditions. This exposure corresponds to a mean daily intake of {sup 232}Th of 0.45 Bq. Predictions from the new Task Group lung model indicate that, for the 45 workers with a thorium lung burden in excess of the minimum detectable level (6 Bq), the daily intake of {sup 232}Th is a factor of 1.6 higher than expected. This suggests that previous intake of radioactive dust was higher than generally assumed for some workers. The application of the new Task Group lung models to the bioassay data results in an estimated mean annual committed effective dose for the workers of 8 mSv. Two workers (3%) were found to have been exposed for many years in excess of the 50 mSv y{sup {minus}1} annual limit for occupational exposure, while eight workers (13%) exceeded the ICRP`s proposed new occupational standard of an average of 120 mSv y{sup {minus}1}. All eight had been employed for more than 6 y and the majority of their exposure was attributed to early employment years, prior to extensive workplace improvements in dust control. 32 refs., 3 figs., 5 tabs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 166769
- Journal Information:
- Health Physics, Vol. 69, Issue 2; Other Information: PBD: Aug 1995
- Country of Publication:
- United States
- Language:
- English
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