Formaldehyde is a naturally occurring organic compound, and an important industrial precursor to many other materials and organic compounds. Formaldehyde solution (formalin) is used as a disinfectant. Formaldehyde vapors are toxic, upon entry formaldehyde reacts readily with macromolecules, including DNA to form DNA-protein and DNA-DNA cross-links.

The halogen bromine (Br2) is oxidant gas, and exposure to it presents a significant threat to public health. Br2 is widely used in the manufacture of medicinal compounds, agricultural chemicals, gasoline additives, dyes, photographic chemicals, etc. Br2 causes severe pulmonary and systemic injuries; however, the mechanisms of its toxicity is largely unknown. Br2 exposure has no specific antidote, and current treatments for patients exposed to Br2 are mainly supportive, including administration of supplemental oxygen, bronchodilators, and antibiotics in cases of infection. Assisted or supported ventilation with intubation and positive-pressure ventilation may also be necessary.

Ferric nitrate is a violet crystalline solid. Noncombustible but it will accelerate the burning of combustible materials. If large quantities are involved in the fire or the combustible material is finely divided an explosion may result. Prolonged exposure of the material to fire or heat may result in an explosion. Toxic oxides of nitrogen are produced in fires involving this material. It is used for dyeing and tanning, in chemical analysis, and in medicine. Ferric nitrate is a strong oxidizing agent. Ferric nitrate can be used in in vitro model of "iron-loaded" cells. Ferric nitrate is commonly used as a positive indicator test of the phenol group.

Propionic acid (PA), also known as propanoic acid, with chemical formula C3H6O2, is an organic acid used as a food additive and found naturally on the skin and in the gastrointestinal tract. It is a byproduct of fermentation reactions and is also produced industrially from ethylene or ethanol and carbon monoxide. Propionic acid is a fungicide and bactericide, registered to controlfungi and bacteria in stored grains, hay, grain storage areas, poultry litter,and drinking water for livestock and poultry. As a food preservative, propionic acid prevents mold in bread and baked goods, and it is used as a flavoring agent in cheese and other packaged goods. The U.S. Environmental Protection Agency considers it safe and therefore, has no limitation on its use. It has been demonstrated that PA lowers fatty acids content in liver and plasma, reduces food intake, exerts immunosuppressive actions and probably improves tissue insulin sensitivity. Thus increased production of PA by the microbiota might be considered beneficial in the context of prevention of obesity and diabetes type 2. The molecular mechanisms by which PA may exert this plethora of physiological effects are slowly being elucidated and include intestinal cyclooxygenase enzyme, the G-protein coupled receptors 41 and 43 and activation of the peroxisome proliferator-activated receptor γ, in turn inhibiting the sentinel transcription factor NF-κB and thus increasing the threshold for inflammatory responses in general. Taken together, PA emerges as a major mediator in the link between nutrition, gut microbiota and physiology. The sodium salt of propionic acid was previously approved in Canada as an active ingredient in Amino-Cerv (used to treat inflammation or injury of the cervix).

Ethyl nitrite is an alkyl nitrite and the main ingredient in a traditional ethanol-based South African remedy for colds and flu known as Witdulsies and sold in pharmacies. It is known as a traditional Afrikaans remedy and may have Dutch roots, as the same remedy is apparently made by the Germano-Dutch Amish people in the USA. However FDA has blocked over-the-counter sales of this same remedy, known in the USA as sweet nitrite or sweet spirit of nitre since 1980. Ethyl nitrite use has been associated with fatal methemoglobinemia and severe anoxic metabolic acidosis in infant

Cobalamin (vitamin B12) is a cobalt-containing, B complex vitamin. B12 group (cobalamins) consist of cyanocobalamin, hydroxocobalamin, methylcobalamin and cobalamid. Neither plants nor animals are independently capable of constructing vitamin B12. Only bacteria and archaea have the enzymes required for its biosynthesis. Therefore, humans must absorb it from food. Excellent sources of B12 are foods of ruminant origin, so dairy and meat products play an important role in efforts to meet the official daily B12 intake. Vitamin B12 deficiency can potentially cause severe and irreversible damage, especially to the brain and nervous system. Vitamin B12 is used to treat vitamin B12 deficiency, including pernicious anemia.

Mercury, with the chemical symbol Hg (from Greek "Hydrargyros"), is the only metal adopting liquid form in room temperature. Mercury appears in seven natural isotopic forms. The metal is extracted from the mineral cinnabar, mercuric sulfide, in former times used also for paint. Mercury has fascinated people for millennia, as a heavy liquid metal. However, because of its toxicity, many uses of mercury are being phased out or are under review. It is now mainly used in the chemical industry as catalysts. It is also used in some electrical switches and rectifiers. Previously its major use was in the manufacture of sodium hydroxide and chlorine by electrolysis of brine. These plants will all be phased out by 2020. Elemental mercury is used in thermometers, blood pressure devices, and thermostats because its ability to expand and contract uniformly makes it useful for measuring changes in temperature and pressure. Mercury is also used in dental fillings, paints, soaps, batteries, and fluorescent lighting. Mercury will dissolve numerous metals to form amalgams and is used to extract gold dust from rocks by dissolving the gold and then boiling off the mercury. The amalgam used in dental fillings contains tin and silver alloyed with mercury. Because it works as a biocide, mercury has been used as a fungicide in paint, though this kind of paint is no longer sold. Mercury and its compounds used in dental practice may be responsible for release of mercury into the oral cavity. Compounds of mercury tend to be much more toxic than the element itself, and organic compounds of mercury (e.g., dimethyl-mercury) are often extremely toxic and may be responsible in causing brain and liver damage. Human exposure to mercury has increased through anthropogenic mercury emissions from fuel combustion, municipal incinerators, and chemical industries. Mercury is considered a major environmental toxicant throughout the world. Mercury is harmless in insoluble form, but vapor or soluble forms such as inorganic mercury or methylmercury can be extremely toxic to humans. Most human mercury exposure occurs through inhalation of elemental mercury vapor released from dental amalgam and through the consumption of fish contaminated with methylmercury.