Aluminum is the third most common element in the earth's crust and is present in soil, water and air. Aluminum's physical and chemical properties make it ideal for a variety of uses in food, drugs, consumer products, and water treatment processes.

In recent years, increased attention has been focused on possible adverse effects of aluminum in drinking water on human health. Several epidemiological studies have reported a slightly increased incidence of dementia in communities where drinking water is high in aluminum and these studies have raised concerns among the media and public.

At present, there is no guideline for safe levels of aluminum in drinking water in Canada. Health Canada is evaluating the literature on the adverse effects of aluminum on humans and animals. The department was to present its health-based risk assessment to the Federal-Provincial Subcommittee on Drinking Water by the spring of 1996. Using the information contained in the risk assessment, the Subcommittee will consider a drinking water guideline for aluminum, which will be published in Health Canada's Guidelines for Canadian Drinking Water Quality.

Aluminum has historically been considered to be relatively non-toxic in healthy individuals, who can tolerate oral daily doses of as much as 7.2 grams of aluminum without any apparent harmful effects. However, there is now abundant evidence that aluminum may cause adverse effects on the nervous system.

Kidney disease patients who are exposed to high levels of aluminum in dialysis fluids and medications, develop dialysis encephalopathy, a progressive form of dementia characterized by speech and behavioral changes, tremors, convulsions, and psychosis. Most experts agree that high levels of aluminum in dialysis fluids and medications are responsible for the dementia, and controlling these levels of aluminum significantly reduces the incidence of this disease.

Aluminum has also been associated with severe diseases of the nervous system, such as Parkinson's disease, amyotrophic lateral sclerosis (Lou Gehrig's disease), and Alzheimer's disease, but the association is not completely understood. An unusually high incidence of amyotrophic lateral sclerosis and Parkinson's dementia in indigenous populations of Guam and New Guinea suggest a possible correlation with local environmental conditions, which include high levels of aluminum and low levels of calcium and magnesium in soil and food.

It has been demonstrated that humans with these disorders tend to have high levels of aluminum in some areas of their brains, although it has not been demonstrated that the presence of aluminum in the brain initiates onset of the diseases.

Intake of large amounts of aluminum can also cause anaemia, osteomalacia (brittle or soft bones), glucose intolerance, and cardiac arrest in humans. We do not know the effects in humans exposed to low levels of aluminum over a long period, but earlier onset or progression of a wide range of diseases of the nervous system is a distinct possibility.

The first recognizable symptoms of Alzheimer's disease are usually memory lapses, disorientation, confusion, and depression. These symptoms mark the start of progressive mental deterioration. Alzheimer's disease is characterized by pathological changes and in many cases, accumulation of aluminum in the brain tissues. There may be many different types of Alzheimer's disease.

A number of theories on the causes of Alzheimer's disease have been proposed and are currently under investigation, including genetic factors, abnormal proteins, infectious agents, environmental agents such as aluminum, other metals or solvents, and metabolic changes. There is growing evidence that complex interactions exist between such factors as aging and genetic predisposition and the series of events that leads to the onset of Alzheimer's disease.

From what we know at present, the evidence linking aluminum and Alzheimer's disease is far from conclusive, but we also cannot be sure that there is no relationship. Many epidemiological studies have shown a positive association between exposure to aluminum in drinking water and the incidence of Alzheimer's disease. However, this does not prove that aluminum is the cause.

Also, the evidence is not entirely consistent. Evidence that aluminum does not cause Alzheimer's disease includes the inability to induce Alzheimer's disease-type changes in the brains of laboratory animals exposed to aluminum, the absence of Alzheimer's disease-type changes in brains of patients suffering from dialysis encephalopathy and the lack of aluminum accumulation in tissues in Alzheimer's disease-affected brains in some studies.

Humans are constantly being exposed to aluminum via food, air, and water. Aluminum is also used in many drugs (e.g. antacids), consumer products (e.g. cooking utensils) and water treatment processes (as coagulants). The average adult probably takes in about 9 to 14 milligrams of aluminum each day from all exposure routes, but primarily (90 percent) from food, including food processed with aluminum-containing additives, food cooked in aluminum pans and food packaged in aluminum containers. In general, exposure to aluminum from drinking water is very low (below 3 percent) compared with that from food and drugs.

Although most of our daily aluminum intake comes from food, aluminum in food appears to be bound to other food substances and thus is in a form that cannot be absorbed into the bloodstream. In fact, it seems that the body's main defence against aluminum in food is that it does not allow aluminum to pass through the intestinal wall.

In contrast, recent research has shown that aluminum from drinking water can be absorbed to some extent in both animals and humans. This is because the aluminum in water following water treatment processes seems to be in a largely "free" (i.e. unbound) form. However, the amount of aluminum absorbed from drinking water is usually very small. One reason for this is that the presence of food in the stomach reduces the absorption. Absorption then is greatest when water is drunk on an empty stomach.

The guideline that Health Canada will be recommending for aluminum will be based on the amount of "free" aluminum present in drinking water, not the "total" aluminum that is currently measured and quoted in Canada and other countries.

Waterborne micro-organisms (bacteria, viruses, protozoa) are a very serious health risk. Aluminum compounds are used in drinking water treatment to remove these harmful micro-organisms and particles that can protect them from disinfection, by coagulating them, or causing them to clump together into larger particles.

These large particles are then removed by sedimentation and filtration. Aluminum-based compounds also remove naturally occurring organic matter present in water, thus reducing the formation of disinfection by-products. These are the products of the reaction between chemicals used for disinfection and naturally occurring organic matter, some of which may cause cancer (e.g. trihalomethanes).

Alum (aluminum sulphate) and polyaluminum chloride are the most widely used coagulants, because they are effective, readily available, and relatively inexpensive. However, under some circumstances, or if not used properly, their use can result in elevated levels of residual aluminum in finished drinking water.

Several other chemical coagulants are available, such as iron compounds (ferric chloride) and organic polymers. The choice of a coagulant is based on a number of interrelated factors. Water chemistry, such as pH or acidity level, temperature, etc., is the main factor that determines which type of coagulant will perform most effectively. Each alternative has advantages and disadvantages, including potential health and environmental concerns.

The most important reason why aluminum-based coagulants are chosen, is that the alternatives do not always remove pathogens and particles as well. If a treatment plant was specifically designed to use alum with a certain type of water, it is not always possible to use an alternative without adversely affecting water quality. As well, these alternative coagulants are generally more costly, require additional facilities to transport, handle or store them, and may be more hazardous to work with.

There is no easy or inexpensive way to remove aluminum from tap water in the home. Steam distillation and a process called reverse osmosis are effective, but both processes require the purchase of expensive equipment and frequent maintenance.

Like tap water, bottled waters vary in their aluminum content. Aluminum may be found in some bottled waters because it occurs naturally at the source. Also, some bottled water manufacturers use tap water with or without additional treatment; if aluminum is in the tap water, it may also be in the bottled water.

The water provided by municipal water suppliers is safe. First, the water usually meets all provincial guidelines for purity. Guidelines are very stringent and are designed to protect human health. Second, municipal water suppliers monitor their water on a regular basis to ensure that the guidelines are met; in most municipalities, this includes an attempt to keep aluminum levels low, despite the current lack of a guideline for aluminum.

Finally, water treatment processes are carefully monitored and controlled to ensure that any process failure is immediately detected and corrected.

The major responsibility for ensuring that drinking water is safe lies with the provinces. A consistent approach to improving drinking water quality is provided by Health Canada's Guidelines for Canadian Drinking Water Quality (soon to include the aluminum guideline), which are designed to ensure that Canadians have access to wholesome and safe drinking water.

In the federal domain, Treasury Board uses these guidelines as standards for native reserves, military bases, etc. In addition, Health Canada is working on a new Drinking Water Safety Act to establish enforceable standards for drinking water quality within federal jurisdiction and to develop standards for chemicals used in water treatment, such as alum; for plumbing materials in contact with water; and for point-of-use water treatment devices.

Editor's Note:Aluminum in Drinking Water and Human Health is one of a series of Issues produced by the Health Protection Branch of Health Canada for the public, media, and special interest groups; they are available in English and French. For additional copies of Issues contact: Health Canada/Santé Canada, Publications, Ottawa, Ontario, K1A 0K9, Fax: (613) 941-5366.