Dose-Response for Kaolin: The Effect of Kaolin on Workers' Health

The China Clay Industry has carried out a number of epidemiological studies of its work force to determine the effect of china clay (kaolin) on the health of its employees. The latest radiological study was carried out during 1990 and involved all four companies in the industry. This permitted the analyses to be carried out on 4112 employees. After exclusions, it was made up from of 70% of the current work force and 17% of current pensioners. During the actual survey considerable efforts were made to achieve a high level of consistency in the film colour and quality. Films were developed within 2 min of being taken, and compared to a set of standards previously agreed upon by the panel of epidemiological readers. If there was any deviation from the agreed standard then the radiographer adjusted either the X-ray machine or the processor or both to bring the films back to standard. Ninety-eight per cent of the films were recorded as film quality 2 or better, this resulted in a very high degree of agreement amongst the panel of readers as to the classification of the films. The three readings of each film were combined together using the method of Oldham to give a score, which could be used in the subsequent analyses. Full occupational histories were obtained during the 1985 Survey and have been subsequently maintained. Actual dust measurements from 1978, and levels prior to 1978, estimated using knowledge and experience in the industry, were used to derive a dust level for every job/location/time period. Dust levels and occupational histories were combined to calculate a total occupational dust dose for each employee. The relationship of X-ray score and lung function were examined together with dust dose, age, duration employed in the different occupational groups, and smoking class. In general the findings are similar to previous studies, in that most employees should not reach X-ray category 1 in a normal working life at current exposure levels.