Lithium (from the Greek word "lithos" meaning stone) is the lightest of all metals. In purified form, it possesses some unique properties. For example, it has the highest specific heat of any solid element and therefore is very useful in heat transfer applications, however it is corrosive and requires special handling. Lithium is also a leading contender as battery anode material due to its high electrochemical potential.
It does not occur "free" (purified or uncombined) in nature, but is found joined (ionized) as various salts in nearly all igneous rocks and hydrated in many mineral springs * and seawater. Traces of lithium are also found in numerous plants, plankton, and invertebrates ranging from 69 to 5,760 parts per billion. Nearly all vertebrate tissue and body fluids have also been found to contain lithium at slightly lower levels ranging from 21 to 763 parts per billion. However, it is not known whether lithium has a physiological role in any of these organisms. In natural seawater, lithium is found hydrated at substantially low levels (Actual Test Results) and usually ranges from 140 to 250 parts per billion. Only near hydrothermal vents ** under the oceans does natural seawater contain elevated levels of lithium. Here it approaches 7,000 parts per billion.
The lithium ion is exceptionally small and has, therefore, an exceptionally high charge to radius ratio . As a result, its properties are considerably different from similar ions found at much higher concentrations in seawater such as sodium and potassium. Contrarily, its hydrated radius (size of the ion in water solution) is much larger than similar ions found in seawater and therefore exhibits very different solution properties such as very low vapor pressure, freezing point, and other colligative properties. This large solvation shell around the lithium ion also causes it to have lower mobility in solution.
The aforementioned properties of the lithium ion contribute to its unique behavior and effects in a variety of environments. The chloride salt of lithium is one of the most hygroscopic materials known and is therefore used in many air conditioning and drying systems. Of greater relevance, is its ability to control crystal shape in synthetic crystals of Aragonite. This property is interestingly reminiscent of the morphology observed in the shells of many mollusks . In general, the lithium ion has been well documented to have profound biological effects of varying intensity on the gamut of lifeforms. Numerous publications have confirmed its influence on enzyme activity, metabolism, respiration, and active transport.
More specifically, the lithium ion has demonstrated significant bacteriostatic activity towards various lactic acid microorganisms. This has prompted the development of a lithium containing toothpaste to prevent dental caries, however, lack of clinical experience precludes assessment of its therapeutic value. In the late nineteenth century, Herbst discovered that the lithium ion has powerful morphogenetic effects on developing sea urchin eggs . Since then, lithium has been proven to cause morphological deviations in representatives of almost the entire animal kingdom, but seems most dramatic in primitive embryological systems. Deviations ranging from exogastrulation to cyclopia (development of one-eyed monsters) have been observed in tunicates, cyclostomes, teleosts, cephalopods, and many other organisms. These effects are believed to be a result of the lithium ions ability to interfere with metabolic processes that are responsible for the determination and differentiation of a developing embryo.
One of the most striking features of the lithium ion is its resemblance to the sodium ion with respect to transport in biological systems. Experiments on goldfish gills and amphibian skin have clearly demonstrated an active transport of the lithium ion through tissues. However, as noted earlier, the effects of the lithium ion are distinctly different from those of the sodium ion on various tissues and organisms. These effects have also been extensively studied on nerve tissue from many organisms. The results of these studies are beyond the scope of this work, but it seems prudent to mention that lithium causes a variety of changes in nerve tissue ranging from mild to severe and sometimes are permanent.
A prominent effect of lithium on the nervous system can be found in the field of medicine. Here it is used to treat severe mental disorders such as manic-depression by controlling mania and stabilizing mood swings. Although its therapeutic value has been debated, there is no doubt that a number of manic patients have benefited from lithium treatment. Its effects differ markedly from the results of treatment with tranquilizing agents. The patients do not appear to be "drugged" or drowsy, but are quiet and cooperative, often capable of normal daily activities while on a maintenance treatment. The lithium ion seems to counteract the manic symptoms in a specific way, however, little is understood about the mechanism of its therapeutic action. The literature states that lithium is relatively toxic to animals and man . Interestingly, its toxicity is not only related to the amount of lithium administered but is also dependent upon the sodium intake.
In closing, it is evident that lithium can have some profound effects
on a variety of chemical and biological systems. Although it has been
intensively studied, little is known about the details of lithium's
action including required concentrations and mechanisms by which changes
(1) A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry - A Comprehensive Text. Fourth Edition, Chapter Seven.
(2) S. Sims, J. Didymus, and S. Mann, Habit Modification in Synthetic Crystals of Aragonite and Vaterite. J. Chem. Soc., Chem. Commun., 1031-1032 (1995)
(3) E. Gralla, and H. McIlhenny, Studies in Pregnant Rats, Rabbits and Monkeys with Lithium Carbonate. Toxicol. Appl. Pharmacol. 21, 428-433 (1972)
(4) M. Schou, Biology and Pharmacology of the Lithium
Ion. Pharmacol. Rev. 9, 17-58 (1957)
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* The lithium content of mineral waters is usually about 7,000 parts per billion ( Actual Test Results ) and was believed to be responsible for its reputed effects on rheumatoid diseases including gout.
** Formed deep within the oceans where the earth's crust opens and heats nearby seawater to almost 400°C. This creates an unusual chemistry rich in minerals and hydrogen sulfide. As a result unique biological communities colonize these vent environments and contain many organisms that are not found anywhere else on earth.