ARCHIVED - PSL Assessment Report for Aluminum Salts

The three aluminum salts, aluminum chloride, aluminum nitrate and aluminum sulphate, were included on the Second Priority Substances List (PSL2) under the Canadian Environmental Protection Act, 1999 (CEPA 1999) in order to assess the potential environmental and human health risks posed by exposure to aluminum derived from these three salts in Canada.

In December 2000, the PSL2 assessment of the three aluminum salts was formally suspended due to limitations in the available data for assessing health effects. At the same time, a State of the Science report (Environment Canada and Health Canada 2000) on the three aluminum salts was released, providing an in-depth review of toxicity and exposure information relating to human health and the environment. During the suspension period, additional health effects information was published in the scientific literature.  As well, a long-term study on the neurodevelopmental effects of aluminum, commissioned by an industry consortium, was initiated. The results of this study, however, will not be available until after the mandated publication deadline for this PSL assessment.

In Canada, municipal water treatment facilities are the major users of aluminum chloride and aluminum sulphate, accounting for 78% of the estimated 16.1 kilotonnes of the 2006 domestic consumption. Industrial water and wastewater treatment, and use in the pulp and paper industry, account for an additional 20 %. Aluminum sulphate and aluminum chloride are also used as ingredients in drugs and cosmetics, such as antiperspirants and topical creams.  Aluminum sulphate is permitted as a food additive in a limited number of products. Aluminum nitrate, used in far less quantities than the sulphate and chloride salts, may be used in fertilizers, and as a chemical reagent in various industries.  

Aluminum salts occur naturally in small quantities in restricted geological environments and aluminum can be released into the Canadian environment from these natural sources. However, since aluminum is present in relatively large amounts in most rocks, dominantly in aluminosilicate minerals, which weather and slowly release aluminum to the surface environment, the small amounts of aluminum in surface waters resulting from weathering of aluminum salts such as aluminum sulphate cannot be distinguished from other natural aluminum releases.

During their use in water treatment, aluminum salts react rapidly, producing dissolved and solid forms of aluminum with some release of these to Canadian surface waters. The amount of anthropogenic aluminum released nationally in Canada is small compared with estimated natural aluminum releases; however anthropogenic releases can dominate locally near strong point sources. Most direct release into surface waters of aluminum derived from the use of aluminum salts in water treatment processes originates from drinking water treatment plants (DWTPs). However, direct releases of process waters from DWTPs are regulated by many provincial and territorial authorities, and these releases typically occur in circumneutral water, where the solubility of aluminum is minimal. Disposal of sludge produced by municipal and industrial water treatment facilities on land through landfarming practices is a source of aluminum to the terrestrial environment. However, the presence of dissolved organic matter and inorganic chelating agents will lower the amount of bioavailable aluminum in both the terrestrial and aquatic environments.

While extensive recent data on total aluminum concentrations in Canadian surface waters are available, few data exist on levels in areas close to sites where releases occur. The situation for sediment and soil is similar, in that data exist for the Canadian environment in general, but not for areas where releases occur. A large number of environmental toxicity data are available for acidified environments, but relatively few exist for circumneutral environments similar to those where most releases occur.

Based on a comparison of highest measured and estimated aluminum levels present in both aquatic and terrestrial environments in Canada that receive direct inputs of aluminum from the use of the three aluminum salts, and Predicted No-Effect Concentrations (PNECs) derived from experimental data for aquatic and terrestrial biota, it is considered that, in general, it is unlikely that organisms are exposed to harmful levels of aluminum resulting from the use of aluminum salts in Canada. However, it is acknowledged that under some release conditions there is potential for local impacts to benthic organisms related to the settling of aluminum sludge from DWTPs onto the sediment surface. As such, it is proposed that the three aluminum salts (i.e., aluminum chloride, aluminum nitrate, aluminum sulphate) are not entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity.

With respect to the human health risk assessment, both epidemiological and experimental animal data were reviewed.  While positive significant associations between aluminum in drinking water and the development of Alzheimer's disease (AD) or other forms of dementia have been observed in some studies, a weight-of evidence analysis of all available data does not provide sufficient scientific support at this time for a causal relationship between aluminum in drinking water and AD.  Considering experimental animal studies, the dose at which neurotoxic, reproductive, and developmental effects have been repeatedly observed was used to establish an exposure level of concern.

The human health risk assessment, carried out on the basis of total aluminum exposure, suggests thata proportion of individuals, particularly in the younger age groups, may be exposed to levels of total aluminum that, when compared to the exposure level of concern (derived from studies in experimental animals measuring neurotoxic effects), results in margins that may not be adequate.  For most age groups, food is estimated to be the primary source of exposure to aluminum.

Aluminum chloride, aluminum nitrate, and aluminum sulphate are not significant contributors to aluminum in the diet. The use of aluminum sulphate and aluminum chloride for the treatment of drinking water contributes less than 1 % of the total aluminum intake in children, the most sensitive age group.  Thus, the three salts are not considered to be significant contributors to the overall health risk.

Food additives in Canada are regulated under the Food and Drugs Act. The Food Directorate of Health Canada is currently re-evaluating dietary exposure to aluminum and reviewing current uses of aluminum-containing food additives.

Based on the information available for human health and the environment, it is proposed that the three aluminum salts, aluminum chloride, aluminum nitrate, aluminum sulphate, are not entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity or that constitute or may constitute a danger to the environment on which life depends. It is also proposed that aluminum chloride, aluminum nitrate and aluminum sulphate, are not entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health. It is therefore proposed that aluminum chloride, aluminum nitrate and aluminum sulphate do not meet the definition of "toxic" under section 64 of the Canadian Environmental Protection Act, 1999.