a.

(ⅰ)Contract No.11526/ Regular Budget Fund(RBF).

(ⅱ)Title of project:Study of the health effects following exposure to thorium dusts of the miners in China.

(ⅲ)Institute where research is being carried out :Laboratory of Industrial Hygiene, Ministry of Health Beijing China.100088

(ⅳ)Chief Scientific Investigator:Dr Chen Xingan.

(ⅴ)Time Period Covered:2000/12/ 15 to 2001/ 12/15

b. Description of research

The research was carried out at the Baiyan Obo Rare-earth Coexistence Iron Mine from August 21st 2001 to September 28th 2001.

The total number of miners and staff members at this mine is 6 895.Among them 3 016 are dust exposed miners.

In this study, 126 dust -exposed miners were randomly selected from 3016 miners of seven dust -generating workshops, among them, 65 were from the high dust -generating workshop, that is Crushing workshop; Another 61 were from six low dust-generating workshops.

Physical measurements(exhaled thoron activity measurement)and medical examinations were carried out on each of the above -mentioned 126 dust exposed miners.

An epidemiological study on lung cancer mortality of all the dust -exposed miners and the dust -free miners and staffs in this mine during the period from 1977 -2001.3.was also carricd out.

c. Results.

(ⅰ)The thorium lung burden estimates among the 65 miners of the high dust -generating workshops, 12 of them having a thorium lung burden higher than one investigation level 2.22 Bq.The highest one of them is 6.29 Bq.While among the 61miners of the six low dust -gen erating workshops, no one having a thorium lung burden higher than 2.22 Bq, the highest one is 1.92 Bq.

(ⅱ)The number of pneumoconiosis:among the 65 miners of the high dust -generating workshop, 14 cases of pneumoconiosis of stage 0 were detected.While among the 61 miners of the six low dust -generating workshops only 2 cases of pneumoconiosis of stage 0⁺were detected.

(ⅲ)Lung cancer mortality among dust -exposed miners and dustfree miners.

An epidemiolgical study on lung cancer mortality of both the dust -exposed miners and dust-free miners and staffs was carried out in 2001, the main results were listed in Table 1.

Table 1.Showed that both the SMRs of the dust-exposed miners and the dust-free miners(controls)were all greater than 1.The SM R of the dust -exposed miners was much higher than that of the controls. The difference between these two SMRs was highly significant(χ² = 9.488, P < 0.005).It proved that the high SMR value of the lung cancers of dust exposed miners were due to the inhaled thorium and its short-lived thoron daughters.The total person -years of the dust - exposed miners and the controls was at a value of 62 712 and 34 672 respectively

d. Conclusions.

(ⅰ)Those having thorium lung burden estimate higher than 1 investigation level(2.22 Bq)was only appeared in the Crushing workshop (high dust generating workshop).The highest thorium lung burden estimate in one of the miners in this workshop was at value of 6.29 Bq. In other six low dust generating workshop, the highest thorium lung burden of one of the miners was at a value of 1.92 Bq.

(ⅱ)The number of pneumoconiosis of stage 0⁺was at a value of 14 in the crushing workshop, while only 2 in another six low dust -generating workshops.

(ⅲ)An epidemiological study on lung cancer mortality showed that the SMR of the dust exposed miners was much higher than the SMR of the controls(6.13 vs 1.90).The difference between these two SM Rs was highly signifficant (χ² =9.488, P < 0.005).This was the first evidence in humans for the carcinogenicity of thorium-232 and its short-lived thoron daughters after inhalation.

(ⅳ)More information of this study will be obtained in 2-3 weeks.