GEOCHEMICAL RISK-FACTORS FOR MENTAL FUNCTIONING, BASED ON THE ONTARIOLONGITUDINAL-STUDY OF AGING (LSA) .6. THE EFFECTS OF IRON ON THE ASSOCIATIONS OF ALUMINUM AND FLUORIDE WATER CONCENTRATIONS AND OF PH WITH MENTAL FUNCTIONING, BASED ON RESULTS OBTAINED FROM THE LSA AND FROM DEATH CERTIFICATES MENTIONING DEMENTIA

Previous papers in this series noted a positive association between al uminum water concentrations and a measure of mental impairment, and a negative association between fluoride concentrations and the same meas ure of mental impairment. The results obtained were qualitatively simi lar to the corresponding associations obtained from death certificate data that list Alzheimer's disease as the underlying cause of death. I n addition, the results were also qualitatively similar to the results obtained in a number of other studies carried out at different times, in different areas and using different outcome measures for the measu re of mental impairment. The present study concerns the role of iron c oncentrations and specifically, whether when taking iron concentration s into account, the previously noted associations involving aluminum a re maintained. The results show that this seems to be the case and als o suggest that iron can compete with aluminum, and can both increase o r decrease the likelihood of showing signs of mental impairment. The r esults do not indicate consistently that by modifying the methods of w ater purification, using iron instead of aluminum, the treated water w ill be less biotoxic, although there could be instances, particularly when the aluminum concentrations are relatively high, when the use of iron compounds is beneficial.