Nearly 60 years ago, chromium, as the trivalent ion, was proposed to be an essential element, but the results of new studies indicate that chromium currently can only be considered pharmacologically active and not an essential element. Chromium is a mineral that humans need in very small quantities. Good sources include broccoli, liver, and brewers' yeast. Taking chromium by mouth is effective for preventing chromium deficiency. It is also taken by mouth for depression, Turner's syndrome, polycystic ovary syndrome (PCOS), lowering "bad" cholesterol, raising "good" cholesterol in people taking heart medications called beta blockers, obesity, metabolic syndrome, heart attack, schizophrenia, bipolar disorder, binge eating disorder, and a disease called reactive hypoglycemia. Chromium has been marketed as an agent to reduce body mass and develop muscle; however, such marketing claims are no longer allowed in the United States because they are not supported by experiments. Trivalent chromium has also been proposed as a therapeutic agent to increase insulin sensitivity and affect lipid metabolism. Although effective in certain rodent models, beneficial effects in humans have not been unequivocally established.

Silicon is a trace element that resembles carbon and can form silicon-carbon as well as silicon-oxygen, silicon-hydrogen and silicon-nitrogen bonds. It may have a role in a number of areas of human physiology and metabolism, especially bone and connective tissue formation, but possibly also gene expression and cardiovascular health. The exact biological role(s) of silicon in bone health is still not clear, although a number of possible mechanisms have been suggested, including the synthesis of collagen and/or its stabilization, and matrix mineralization. Silicone-based products are widely used in the management of hypertrophic scarring and keloids. The mechanism of action of silicone therapy has not been completely determined but is likely to involve occlusion and hydration of the stratum corneum with subsequent cytokine-mediated signaling from keratinocytes to dermal fibroblasts.

Barium hydroxide, Ba(OH)2, is also known as baryta. Barium hydroxide crystallizes as the octahydrate, which can be converted to the monohydrate by heating in air. The anhydrous hydroxide has only a secondary industrial importance; the monohydrate and octahydrate are used in industry on a far larger scale. Barium hydroxide, especially the monohydrate, is used to produce organic barium compounds such as additives for oil and stabilizers for plastics. In addition, barium hydroxide is used for dehydration and deacidification, especially for removing sulfuric acid from fats, oils, waxes, and glycerol.

Gallium (Ga) is an element. It is a soft, slivery blue metal that becomes liquid (and silvery white) above room temperature. Gallium has been investigated for its anticancer properties since it was discovered that 67Ga(III) citrate injected in tumor-bearing animals localizes to tumor sites. Gallium has been investigated for treatment in multiple types of cancer (bladder cancer, lymphoma, multiple myeloma, paget's disease, and prostate cancer). Different generations of gallium salt are being evaluated for their antitumor efficacy and are in preclinical or clinical development. Gallium might also display antimicrobial activity, and is thought to disrupt iron homeostasis in certain bacteria and fungi.

Rhodium is a hard, shiny, silvery metal. The major use of rhodium is in catalytic converters for cars (80%). It reduces nitrogen oxides in exhaust gases. Rhodium is also used as catalysts in the chemical industry, for making nitric acid, acetic acid and hydrogenation reactions. It is used to coat optic fibres and optical mirrors, and for crucibles, thermocouple elements and headlight reflectors. It is used as an electrical contact material as it has a low electrical resistance and is highly resistant to corrosion. Rhodium is a rare element with no known natural biological function. Rhodium complexes show diverse biological activities against various targets, including enzymes and protein-protein interactions. Dimeric mu-Acetato dimers of rhodium(II) as well as monomeric square planar rhodium(I) and octahedral rhodium(III) complexes have shown interesting antitumor properties. On the other hand, rhodium is a suspected carcinogen.

Indium sulfate (In2(SO4)3) is a grayish-white powder. It is hydroscopic and has a monoclinic crystal structure. Indium sulfate is being marketed as the newest miracle dietary supplement and is falsely advertised as a dietary aid as an enhancer of food and mineral absorption, an anti-aging supplement, a blood pressure lowering supplement. There is no scientific support for claims that indium has beneficial effects. Indium sulfate can cause the accumulation of indium in the kidney, oxidative damage, pathological changes and dysfunction in the kidney of rats.

Thallium is a soft, silvery-white metal that tarnishes easily. Most thallium is used by the electronics industry in photoelectric cells. Thallium oxide is used to produce special glass with a high index of refraction, and also low melting glass that becomes fluid at about 125K. An alloy of mercury containing 8% thallium has a melting point 20°C lower than mercury alone. This can be used in low temperature thermometers and switches. Thallium is more toxic to humans than mercury, cadmium, lead, copper or zinc and has been responsible for many accidental, occupational, deliberate, and therapeutic poisonings since its discovery in 1861. Its chemical behavior resembles the heavy metals (lead, gold and silver) on the one hand and the alkali metals (K, Rb, Cs) on the other. It occurs almost exclusively in natural waters as monovalent thallous cation. The solubility of thallous compounds is relatively high so that monovalent thallium is readily transported through aqueous routes into the environment. Thallium can be transferred from soils to crops readily and accrues in food crops. The fascinating chemistry and high toxicity potential make thallium and its compounds of particular scientific interest and environmental concern. Radioactive isotope thallium-201 is a radiopharmaceutical used in myocardial perfusion imaging (MPI) using either planar or single photon emission computed tomography (SPECT) techniques for the diagnosis and localization of myocardial infarction. Thallium-201 may also have prognostic value regarding survival, when used in the clinically stable patient following the onset of symptoms of an acute myocardial infarction, to assess the site and size of the perfusion defect. Additionally, Thallium-201 may be used in conjunction with exercise stress testing as an adjunct in the diagnosis of ischemic heart disease (atherosclerotic coronary artery disease) and is also indicated for the localization of sites of parathyroid hyperactivity in patients with elevated serum calcium and parathyroid hormone levels.

Rubidium Rb-82 is a radioactive drug is indicated for Positron Emission Tomography (PET) imaging of the myocardium under rest or pharmacologic stress conditions to evaluate regional myocardial perfusion in adult patients with suspected or existing coronary artery disease. Rb-82 is analogous to potassium ion (K+) in its biochemical behavior and is rapidly extracted by the myocardium proportional to the blood flow. Rb+ participates in the sodium-potassium (Na+/K+) ion exchange pumps that are present in cell membranes. The intracellular uptake of Rb-82 requires maintenance of ionic gradient across cell membranes. Rb-82 radioactivity is increased in viable myocardium reflecting intracellular retention, while the tracer is cleared rapidly from necrotic or infarcted tissue. Rubidium Rb-82, a nonreactor produced tracer, is believed to have superior accuracy compared to Tc-99m and Tl-201 SPECT, with 5-20 times lower radiation dose. Specific drug-drug interactions have not been studied. Unintended radiation exposure has occurred in some patients who received rubidium Rb-82 chloride injections at clinical sites where generator eluate testing appeared insufficient.

Osmium is a shiny, silver metal that resists corrosion. It is the densest of all the elements and is twice as dense as lead. Osmium has only a few uses. It is used to produce very hard alloys for fountain pen tips, instrument pivots, needles and electrical contacts. It is also used in the chemical industry as a catalyst. Osmium has no known biological role. The metal is not toxic, but its oxide is volatile and very toxic, causing lung, skin and eye damage. Osmium compounds are attracting increasing attention as potential anticancer drugs. Osmium complexes are considered interesting alternatives to ruthenium-based anticancer agents because of their relative inertness and sufficient stability under physiological conditions.