Evaluation of fluoride exposure in aluminium smelters: state of the art.

Measurements for assessment of exposure to fluoride in aluminium smelters were generally introduced about 15 years ago. A good correlation between fluoride levels in the urine and the concentration in the ambient air was found. The results of biological monitoring can be used to avoid the risk of the chronic effects of bone fluorosis. Mean values of numerous individual measurements give only the general situation in the plant concerned. For the identification of individuals with high exposure, the individual values must be considered. The urinary fluoride concentration is highly dependent on the urine rate. To obtain a measurement either from a long-term body burden or a short-term exposure the daily eliminations before work (pre-shift value) or immediately after a shift (post-shift value) must be known. Since the collection of 24-hour urine samples not feasible, it is necessary to correlate the fluoride elimination to the daily creatinine excretion, which amounts on the average to 1.8 g. The role of the HF regarding acute irritation of the respiratory tract is not yet fully clear. More information must be obtained by measuring peak values of short periods of time which are expected to be much higher and also more effective than the average values measured over a whole shift period. The suitable instruments for determination of peak values of HF are not yet available.