4
Trace Elements in Abiotic and Biotic Environments
1.6 HUMANS
Total body burden of Al in healthy individuals is 30–50 mg. Approximately, 50%
of Al is found in the skeleton and 25% is in the lungs, and increases with age.
Aluminum levels range from 5 to 10 mg/kg in the bone tissue and from 1 to 3 μg/L
in the serum of healthy individuals (ATSDR 2008). However, there are also other
estimations including adult body burden (70 kg) is 60 mg, of which (in mg/kg) in
bones is between 4 and 27; in the soft tissue 1–28; and in the blood 0.4 mg/L (Emsley
2011). In the blood, Al is approximately equally distributed between plasma and
erythrocytes.
Aluminum is a nonessential metal, to which humans are frequently exposed by
systemic absorption of Al ingested from water, foods, drugs, and air. In lungs, it
may be from environmental-derived particles, occupational exposure, and distribution from the blood. This metal, for a long time, was considered to be safe for
human health. Until the early 1970s, the possible toxicity of Al was not considered.
However, it was discovered that patients with kidney malfunction maintained by
dialysis developed a serious neurological syndrome called dialysis encephalopathy.
The finding of high concentration of Al in gray matter from the brains of patients
dying with this disease lead to suggestion that dialysis encephalopathy is caused by
Al intoxication. Dialysis encephalopathy is also associated with anemia and demineralization of the bones, leading to increased risk of fractures. Later work implicated
Al in the pathogenesis of Alzheimer’s disease, but there is no evidence that this
disease is caused by Al, and even the original observation of elevated Al has been
challenged in several laboratories (Halliwell and Gutteridge 2007).
It has been suggested that Al is implicated in the aetiology of Alzheimer’s disease
and is associated with other neurodegenerative diseases in humans. However, these
hypotheses remain controversial (EFSA 2008).
After absorption, Al distributes to all tissues of organisms, and accumulates in
some, especially in bones. The main carrier of the Al ion in plasma is the Fe-binding
protein, transferrin. Aluminum can enter the brain and reach the placenta and fetus.
It may persist for a very long time in various organs and tissues, before it is excreted
in the urine. At high levels of exposure, some Al compounds may affect DNA damage, in vitro and in vivo, through indirect mechanisms. Database on the carcinogenicity of Al compounds is limited.
It is considered that the use of Al nanoparticles as food additives could be a reason for the rising incidence of autoimmune diseases. Nano Al has the capability to
induce the production of free radicals, thereby resulting in the oxidative stress in
cells. Nanotoxicological effects of Al nanoparticles (Al 2 O 3 NPs) on some human
cells may be mediated through an increase in oxidative stress (Alshatwi et al. 2013).
Foods are generally the major dietary sources of Al in most countries (Table 1.2).
Aluminum in the food supply comes from natural sources, water used in food
preparation, food ingredients, and utensils used during food preparation: cookware,
beverages in Al cans, tap water, table salt, baking powders, processed cheese, and
bleached flour. Other sources of Al for humans are antacids, antiperspirants, vaccines, and other medications, as well as occupational exposure. Because of new
evidence that Al could have effects on reproductive system and developing nervous