12. Aluminum, Al

Aluminum is the third most abundant element in nature, after oxygen and silicon. Its content in the Earth’s crust has been estimated at a level of 8%. In spite of this, the element has never been engaging in the metabolic processes of the evolving living organisms. Aluminum reaches the body of an animal mostly ingested with food. Crossing the intestinal barrier, the metal gets to the bloodstream and so is transported to various tissues using the iron-transport routes. Of the total aluminum uptake, the majority is deposited in the bone (60%) and lungs (25%), whereas much lower amounts accumulate in the muscles (10%) and the liver (3%). Cerebral accumulation of the total uptake is about 1%. Besides blood, the metal is also found in all the other body fluids of a homeothermic organism, e.g., cerebrospinal fluid, lymph, semen, sweat, or urine. Studies on aluminum toxicity involving various taxonomic groups enable concluding that the mechanisms are similar across the taxa and consist mainly in evoking oxidative stress in cells. At the cellular level, aluminum reacts with cell membranes, cytoskeletal structures, and nucleic acids. In terrestrial vertebrates, aluminum impact results in altered enzymatic activity in the central nervous system and other organs and systems of the body. The metal affects the bone tissue metabolism, impairs the function of the excretory system and liver, and also has a negative effect on erythropoiesis. Human activity observed over the last centuries has led to a rapid growth in the production of aluminum obtained from the natural sources and, as a result, to its inclusion into the trophic chains of various ecosystems. In consequence, since 1970, aluminum has been treated as a xenobiotic accumulating in living organisms, whose bioavailability is continuously increasing.