All about oxygen - characteristics, role, applications

Written by Sarah Gehrke, MSN, RN

Oxygen makes up about 65% of the mass of the adult body—most of this is in the form of water.

Elements of the human body. (Wikimedia Commons/CC BY-SA 3.0)

Oxygen also makes up approximately 50% of the mass of the Earth’s crust and 21% of the atmosphere (air)—the rest of the atmosphere is mostly nitrogen (78%). Earth is the only planet in the solar system with an oxygen-rich atmosphere.

Oxygen characteristics

Oxygen is critical for chemical reactions that keep the body alive, including the reactions that produce adenosine triphosphate (ATP)—a compound that cells use to store and transfer energy. Brain cells are sensitive to a lack of oxygen because they require a high and steady production of ATP.

Brain damage is likely within five minutes without oxygen (cerebral hypoxia), and death is likely within ten minutes. A steady supply of oxygen is essential for cardiac function and viability.

According to the National Library of Medicine’s PubChem database:

An adult human, at rest, inhales 1.8 to 2.4 grams of oxygen per minute. This amounts to more than 6 billion tonnes of oxygen inhaled by humanity each year.

At rest, the heart consumes approximately 8–15 mL O₂/min/100 g of tissue. This is significantly more than the brain consumes (approximately 3 mL O₂/min/100 g of tissue) and can increase to more than 70 mL O₂/min/100 g of myocardial tissue during vigorous exercise.

The molecular formula for oxygen is O₂, which represents the chemical bonding of two oxygen atoms.

Dioxygen is the physical form, or allotrope, of oxygen that surrounds us. Our atmosphere also contains trioxygen, known as ozone (O₃)—this allotrope is highly reactive and damages lung tissue.

Water (H₂O) is the most prominent and well-known oxygen compound. Oxygen is electronegative, which means that it can bond with almost every other element. Some of these bond-forming reactions can only occur at elevated temperatures.

Cold water can hold more dissolved oxygen than warm water, and freshwater can contain more dissolved oxygen than saltwater. Consequently, the warmer and saltier the water, the less dissolved oxygen it can hold.

Oxygen is an odorless, colorless gas at standard pressure and temperature. Oxygen condenses at –297.4°F (–183.0°C) to a pale blue liquid (liquid oxygen), and upon further cooling it freezes at –361.9°F (–218.8°C).

Naturally occurring oxygen has three stable isotopes: 16O, 17O, and 18O. The most abundant isotope is 16O and is mostly synthesized in massive stars after the hydrogen fusion process. After hydrogen and helium, oxygen is the third most abundant element in the universe.

Biological role of oxygen

The biogeochemical cycle of oxygen occurs within three main reservoirs: the atmosphere, the biosphere (all life on this planet), and the Earth’s crust.

The oxygen cycle

Plants are the primary creators of atmospheric oxygen through the process of photosynthesis. In the diagram of the oxygen cycle below, you can see how oxygen is used and cycled by plants.

Photosynthesis in plants. (Illustration by Ahmed Raza.)

The cycling of carbon and oxygen is interconnected. Plants use carbon dioxide (CO₂), water, and sunlight to produce sugars and release oxygen. Humans and animals breathe in oxygen and then breathe out carbon dioxide, which plants can use during photosynthesis.

Processes that use oxygen

Breathing—During respiration, air passes through the bronchial tubes, or airways, into the lungs. In the alveoli, O₂ diffuses into the blood while CO₂ diffuses from the blood into the lungs to be exhaled.

Decomposing—During aerobic decomposition, microorganisms use O₂ as they break down dead plants and animals and release CO₂.

Rusting—This is also known as oxidation. When iron rusts, it reacts with O₂.

Combustion—Three things are necessary for fire: oxygen, fuel, and heat. Burning carbon-based fuels consumes O₂ and typically releases CO₂. Oxygen is not explosive, but oxygen accelerates combustion.

Processes that produce oxygen

Plants—Produce O₂ through photosynthesis.

Sunlight—Some production of O₂ occurs when sunlight reacts with water vapor in the atmosphere.

Processes that produce carbon dioxide

Since the start of the Industrial Revolution, humans have increased the CO₂ concentration in the atmosphere through activities including deforestation, intensive land use, and burning fossil fuels.

NASA attributes the warming observed since the mid-20th century primarily to human activities that have increased atmospheric greenhouse gases. Carbon dioxide can remain in the atmosphere for thousands of years.

Decreasing carbon dioxide production

Each person has a “carbon footprint,” meaning the amount of greenhouse gases directly and indirectly emitted because of their activities.

Household carbon footprint calculator—Estimate your household’s carbon footprint.

Go carbon neutral—Carbon neutrality means balancing greenhouse gas emissions with an equivalent amount removed from the atmosphere or offset.

Go carbon negative—Becoming carbon negative means removing more CO₂ from the atmosphere than an individual or organization emits. Reducing emissions is the first step; carefully evaluated carbon-removal projects can address remaining emissions.

Why did Pacific Medical Training become carbon negative?

The impact of human behavior on the delicate balance of the ecosystem cannot be overstated. We have acted with such reckless abandon for so long now that we have actually had a serious negative effect on Earth’s natural systems. Humans have a responsibility to understand their own personal contribution to this balance, particularly those involved in industry and big business.

History of oxygen

The first description of the substance we now call oxygen was made in the 1600s by the Polish alchemist Michał Sędziwój. This discovery was not widely known, and oxygen was independently rediscovered by Carl Wilhelm Scheele and then Joseph Priestley in the 1770s.

Later, the French chemist Lavoisier renamed the compound oxygen because of its ability to form acids. The term oxygen comes from the Greek word “oxygenes” meaning “acid producer.”

In the nineteenth century, scientists realized that they could liquefy oxygen by compression and cooling. By 1891, scientists could produce enough liquid oxygen for research. Four years later, the first process to generate liquid oxygen was commercially viable.

Industrial use of oxygen

The basic oxygen process uses high-purity oxygen to convert molten iron and scrap metal into steel.

Other industrial applications of oxygen include making or processing plastics, paper, glass, ceramics, pharmaceuticals, and petroleum products.

Liquid oxygen is combined with liquid hydrogen to make rocket fuel.

Medicinal use of oxygen

Oxygen has various uses in health care—treatment is flexible enough for use in inpatient, outpatient, and emergency settings. It can help treat ailments such as heart disorders, pneumonia, and chronic obstructive pulmonary disease (COPD).

The pulmonary circulation brings blood to the lungs, where oxygen diffuses into the blood before entering the systemic circulatory system. Supplemental oxygen increases the oxygen content of the blood in patients with hypoxemia and should be administered when clinically indicated.

When providing life support, airway care and rescue breaths improve a person’s chance for survival. Other life support use includes oxygen supplementation for astronauts and scuba divers.

Hyperbaric oxygen therapy (HBOT) delivers 100% oxygen at pressures greater than atmospheric pressure. It is an accepted treatment for decompression sickness and is also used for several other specific indications, including selected chronic wounds, delayed radiation injuries, and carbon monoxide poisoning. HBOT is not approved to treat or cure cancer, autism, or diabetes itself.

Ozone can inactivate microorganisms and is used in some water-treatment processes. Although medical O₃ is promoted for numerous diseases, evidence for these uses is limited, and inhaled ozone can damage the lungs.

The Food and Drug Administration states:

Ozone is a toxic gas with no known useful medical application in specific, adjunctive, or preventive therapy. In order for ozone to be effective as a germicide, it must be present in a concentration far greater than that which can be safely tolerated by man and animals.

Oxygen has also found its way into recreational use. Oxygen bars offer oxygen exposure that is higher than normal, for a fee. It is touted to produce mildly euphoric experiences; however, research doesn’t back this claim.

Safety and precautions

At elevated partial pressures for prolonged periods of time, oxygen can be very toxic; it can cause convulsions and many other health problems. Contact with liquid oxygen can cause skin and eye irritation as well as burns and frostbite. In the early to mid-1900s, it was a common therapy to place premature babies in incubators with a high percentage of oxygen; this ceased when a correlation was found between this practice and a blindness called retinopathy of prematurity (ROP).

Symptoms of oxygen toxicity. (©

Wikimedia Commons/CC BY-SA 3.0)

Supplemental oxygen can correct hypoxemia; however, unnecessarily high oxygen exposure can cause hyperoxemia and place patients at risk of oxygen toxicity.

Hyperventilation is rapid and deep breathing that creates a low level of CO₂ in the blood. An individual may hyperventilate in an emotional state, such as anxiety, or from a medical condition such as infection or bleeding. Furthermore, a hyperventilation response can occur in someone when adjusting from a low to a high altitude—the individual’s rate and depth of ventilation increase to compensate for the reduction in the partial pressure of oxygen.

Home care for hyperventilation

Respiratory depression, or hypoventilation, causes an increase in the concentration of CO₂ in the blood. Hypoventilation is not the same as respiratory arrest, in which breathing stops entirely.

What is obesity hypoventilation syndrome?

Oxygen is like any other prescription drug; its beneficial effects must be balanced against its adverse effects. No drug or supplement is completely without risks.