Carbon monoxide

Carbon monoxide (CO). A poisonous colorless, odorless, tasteless gas. It combines with hemoglobin to form carboxyhemoglobin, which has no oxygen carrying capacity. The resultant oxygen deprivation causes headache, dizziness, decreased pulse and respiratory rates, unconsciousness, and death. (From Merck Index, 11th ed)

Individual exposure to carbon monoxide varies depending upon proximity to production sources. As motor vehicle exhaust is thought to be the single most important source of exposure, those who live in or frequently visit urban areas where there is a high density of motor vehicle traffic as well as those who commute long distances (e.g., to and from work) in their daily lives may be exposed to more ambient carbon monoxide. Individuals who live or work in buildings that are not well ventilated and have inefficiently burning furnaces, stoves, fireplaces or water heaters may also be at greater risk for exposure. Living near factories as well as waste treatment centers such as incineration and recycling facilities increases exposure. Proximity to tobacco smoke, including second-hand smoke, exposes individuals to carbon monoxide. Occupations with greater risk of carbon monoxide contact are varied and include fire fighters, traffic police, tollbooth and enclosed garage attendants, motor vehicle mechanics, coal miners and coke oven and smelter workers. Although carbon monoxide is a by product of metabolic reactions within the body, environmental sources expose an individual to levels much greater than the body is normally capable of regulating.

While carbon monoxide is a gas that is used in the manufacturing process of various chemicals and fuels, it is also a byproduct of combustion or burning of carbon-based materials. As such, carbon monoxide is released into the environment through a variety of different sources including, but by no means limited to: motor vehicle exhaust, charcoal burning, burning of plastic-containing materials, water heaters, gas furnaces, propane-fueled equipment including ice-surfacing machines in indoor skating rinks, and tobacco smoke. For some of the sources of carbon monoxide emissions, improper functioning of the machinery leading to incomplete combustion contributes to excess carbon monoxide production. In addition to man-made sources of carbon monoxide production, natural sources exist and include oxidation of methane gas, forest fires and production by oceanic microorganisms through metabolic processes.

Carbon monoxide from the environment enters the body through inhalation by the lungs. One of the primary ways in which carbon monoxide causes adverse effects to health is through its ability to bind with hemoglobin, the oxygen-carrying component of red blood cells, and form a compound called carboxyhemoglobin. This greatly reduces the bloods ability to transport oxygen throughout the body causing oxygen deprivation that can result in a variety of adverse physiological effects. Two of the tissues most sensitive to oxygen deprivation are the brain and the heart. Carbon monoxide exposure may cause a host of neurologic symptoms such as confusion, headaches, visual changes and affective disorders. Typical ambient carbon monoxide exposure is also of great concern for persons with coronary heart disease since the heart will have a decreased supply of oxygen, and it will have to work even harder to circulate available oxygen to the tissues. Persons who have decreased hemoglobin levels, such as those with anemia, are at an increased risk for the adverse effects of increased carboxyhemoglobin levels.

In addition to binding with hemoglobin, carbon monoxide can also react with other important compounds in the body, including myoglobin and cytochromes. For example, when carbon monoxide combines with myoglobin, the protein that transports oxygen within muscle cells, it can cause disruption of proper muscle functioning.

Pregnancy is a time of greater concern for carbon monoxide exposure since the body is already metabolically producing extra carbon monoxide. Carbon monoxide can cross the placenta, causing oxygen deprivation that may lead to impaired nervous system function in the fetus.