Respiratory health of brickworkers in Cape Town, South Africa. Appropriate dust exposure indicators and permissible exposure limits.

The predictive value for respiratory abnormalities of dust indicators was assessed for 268 brickworkers. The subjective/objective correlations were poor (r = 0.09). The subjective indicators were found to be predictive of early/mild abnormalities, while the objective indicators were better for more severe abnormalities. The respirable/total dust correlations were high (r = 0.99). Length of service was a good proxy predictor for most respiratory abnormalities, while respirable dust was a good proxy for respirable free silica. Simple screening measures with potential application in less-developed settings, like subjective questionnaire responses and total dust measurement, are suggested. The American Conference of Governmental Industrial Hygienists' threshold limit values for free silica and "nuisance" particulates appear to be too high to prevent the occurrence of abnormalities. The World Health Organization's health-based limit for respirable free silica (1 mg/m3) and hygienic standards of well below 5 mg/m3 would have prevented much of the respiratory abnormality found. Hygienic standards for dust and the concept of "nuisance" dust need to be reevaluated by further research.