There have been a number of epidemiological studies to determine if aluminium in drinking water plays a role in Alzheimer’s disease. Elevated concentrations of aluminium have been found in the autopsied brains of people who had suffered Alzheimer’s disease, in regions of the brain containing large numbers of the neurofibrillary tangles which are characteristic of the disease and aluminium has been proposed as one of a number of causal agents.
Aluminium has also been associated with two severe neurodegenerative diseases: Parkinsonism dementia (PD) and amyotrophic lateral sclerosis (ALS). Both conditions have a high incidence amongst people in areas where aluminium is naturally present in food and drinking water. Both PD and ALS are characterised by loss of motor function and the presence of neurofbrillary tangles in the brain.
One hypothesis suggests that chronic nutritional deficiencies of calcium and magnesium lead to increased absorption of aluminium, resulting in its deposition in neurons of the brain.
There is considerable evidence that aluminium is neurotoxic as evident in kidney dialysis patients, in whom the gut barrier is bypassed, can accumulate aluminium in their blood resulting in an encephalopathy known as dialysis dementia. Investigations have established a correlation between the concentration of aluminium in water used to prepare dialysis ﬂuid and the incidence of dialysis dementia.
Aluminium has also been linked to other conditions associated with the use of dialysis units including osteomalacia (a softening of the bones) and anaemia. As it is important to counteract the effects aluminium in water has on the body, reverse osmosis or deionisation units are now used to treat dialysis water before use, and aluminium concentrations are kept below 0.01 mg/L.
Calcium is the most abundant metal in the human body. It is the main constituent of bones and teeth and it has key metabolic functions.
Calcium is largely responsible for water hardness, and may reduce the toxicity of other compounds. Elements such as copper and zinc are much more toxic in soft water.
Epidemiological studies have found an association between inhalation of hexavalent chromium compounds and lung cancer, especially in humans occupationally exposed during chromate production. There is no evidence that organs other than the lung are affected or that ingestion of hexavalent chromium compounds can cause cancer. There are suffcient animal data to indicate that many hexavalent chromium compounds are carcinogenic.
Hexavalent chromium compounds also cause mutations and chromosome aberrations in a variety of test systems. The mutagenic activity can be decreased or abolished by reducing agents, such as gastric juice. In animal studies, orally administered trivalent chromium compounds have not been shown to induce cancer or to induce mutations in genetic material.
The International Agency for Research on Cancer has concluded that hexavalent chromium is carcinogenic to humans (Group 1, suffcient evidence of carcinogenicity in humans); and that trivalent chromium is not classifable as to its carcinogenicity to humans (Group 3, inadequate evidence in humans and inadequate evidence in animals) (IARC 1990).
The absorption of copper by the gastrointestinal tract is in the range of 25–60%, depending on a number of factors, including copper speciation and copper dietary status (Olivares et al. 1998). Copper is stored in the liver, brain and muscle tissue. High concentrations can also be found in the kidneys, heart and hair. Copper is eliminated from the body mainly in the bile.
Many cases of copper poisoning have been reported, including cases involving the poisoning of children who had their food prepared in copper or brass pots (Tanner 1998). Copper poisoning has resulted in cirrhosis of the liver and, in extreme cases, death. Other less severe symptoms associated with the consumption of water containing 3–5 mg/L copper (but not 1 mg/L) are gastrointestinal symptoms such as nausea, abdominal pain and vomiting (Pizarro et al. 1999). Infants are thought to be most susceptible,
though in one study of 3-month-old infants given water containing 2 mg/L copper over 9 months there were no acute or chronic adverse consequences (Olivares et al. 1998). In the genetic disorders Wilson’s disease and idiopathic copper toxicosis, sufferers are particularly susceptible to copper (Lönnerdal and Uauy 1998).
Iron is one of the most abundant metals in Earth’s crust. Iron may also be present in drinking-water as a result of the use of iron coagulants or the corrosion of steel and cast iron pipes during water distribution.
Manganese is an essential nutrient needed for proper functioning of human body. Effects of very high levels of manganese occur mainly in the respiratory tract and in the brain. Symptoms include hallucinations, forgetfulness and nerve damage. Manganese can also cause Parkinsonism, lung embolism, bronchitis.
Mercury is used in the electrolytic production of chlorine, in electrical appliances, in dental amalgams (silver fillings which are banned in most countries due to the health risk) and as a raw material for various mercury compounds.
The toxic effects of inorganic mercury compounds are seen mainly in the kidney in both humans and laboratory animals following short-term and long-term exposure. In rats, effects include increased absolute and relative kidney weights, tubular necrosis, proteinuria and hypoalbuminaemia.
Molybdenum is found naturally in soil and is used in the manufacture of special steels and in the production of tungsten and pigments, and molybdenum compounds are used as lubricant additives and in agriculture.
Potassium permanganate is mainly used for the oxidation and removal of iron and manganese; it can also be used as a disinfectant, or to control tastes and odours.
Zinc is an essential trace element found in virtually all food and potable water in the form of salts or organic complexes. Concentrations in tap water can be much higher as a result of dissolution of zinc from pipes.
In humans, consumption of very high amounts of zinc can result in nausea, vomiting, diarrhoea and abdominal cramps. The major effects of long-term exposure to zinc are copper defciency, anaemia and gastric erosion.