GEOCHEMICAL RISK-FACTORS FOR MENTAL FUNCTIONING, BASED ON THE ONTARIOLONGITUDINAL-STUDY OF AGING (LSA) .4. THE ROLE OF SILICON-CONTAINING COMPOUNDS

Following previous studies on the associations between aluminium (Al) water concentrations and relatively high risks of a measure of mental impairment, the role of silica (SiO2) as a possible confounding variab le is investigated. The bivariate associations show that the lowest od ds, representing an approximation of relative risks, are observed at ' 'mild'' SiO2 concentrations. Muitivariate analyses indicate that, if i nteraction terms are included, the odds comparing higher and lower SiO 2 concentrations are different than if an interaction term is not incl uded. There are also indications that at relatively high Al levels, hi gh SiO2 concentrations lower the odds, consistent with previous sugges tions by Birchall. The implication is that when investigating the role of Al in the etiology of various measures of mental impairment, it is important to consider the effects of other water constituents, and al so the different chemical forms of Al present in treated water. The de sirability of additional work is stressed, preferably using more defin itive outcomes than indications of mental impairment.