How Hazardous Materials Harm the Body

Absorption and injection are two routes of entry that occur through direct skin contact with a hazardous material.

Chemicals and hazardous substances may enter the body by several routes, and the nature and onset of signs and symptoms may vary accordingly. Gases, vapors, and aerosols, when inhaled, may be absorbed through any part of the respiratory tract, from the mucosa of the nose and mouth to the alveoli of the lungs. The eye may also directly absorb them. Aerosol particles larger than 5 micrometer (μm) tend to be retained in the upper respiratory tract, while those smaller than 1 µm tend to be breathed in and out again, although some of these smaller particles may be retained. Droplets of liquid and, less commonly, solid particles may be absorbed through the surface of the skin and mucous membranes. Toxic compounds with a characteristic action on the skin can produce their effects when deposited on the skin as solid or liquid particles.

Chemicals or hazardous substances which penetrate the skin may form temporary reservoirs so that delayed absorption may occur. Even the vapor of some volatile chemicals and agents can penetrate the intact skin and intoxication may follow. Wounds or abrasions (even minor injuries caused by shaving or by chemical depilation) present areas which are more permeable than intact skin. Chemicals and hazardous substances may contaminate food and drink and so be absorbed by the gastrointestinal tract. The penetration of chemicals and hazardous substances by these various routes may not be accompanied by irritation or damage to the surfaces concerned.

Methods of exposure to these chemicals are called routes of entry. They are:

  1. Absorption
  2. Ingestion
  3. Injection
  4. Inhalation
1. Absorption (through the skin or eye)
  • If a child were to walk barefoot through contaminated soil, the contaminant would contact the skin of the foot. This could cause mild skin irritation, or more serious problems like burns, sores, or ulcers on the outer layers of the skin. Contact with a substance may also occur by spilling it on the skin or brushing against a contaminated object.
  • Depending on the substance and the condition of the skin, the contaminant might also be absorbed through the skin and poison the body. While some chemicals are not absorbed easily unless the skin is cut, others are absorbed quite readily regardless of the skin’s condition. When you are using a material that bears instructions recommending the use of gloves, this is to prevent skin contact or absorption through the skin (also called dermal exposure).
  • When you work with chemicals, it is particularly important never to put your hand to your eye. Eyes are particularly sensitive to toxic substances; since capillaries are near the surface, the substance can enter the bloodstream more readily. Eye contact with toxic substances can cause irritation, pain, or even blindness.
2. Injection
  • The most familiar example of injection is that of shots given to administer medicine, in which the skin is punctured with needles so that a substance can enter the body. Injection can also occur accidentally. For example, if a contaminated can or a piece of glass that had been in contact with a contaminant cut the skin, the contaminated substance could be injected into the body. This is a very powerful means of exposure because the contaminant enters the bloodstream immediately.
When we ingest (eat) or inhale a substance, the body tries to filter it out through internal defenses. If there is enough of the substance, these filters are overwhelmed.
3. Ingestion
  • If we eat a substance that contains a harmful material, that substance enters our bodies by means of our digestive system. An example of inadvertent ingestion is a battery factory employee who eats lunch in the work area and ingests inorganic lead that has contaminated a sandwich. A more common instance is the child who puts a toxic substance in his or her mouth out of curiosity. We may also ingest residue from chemicals that have been added to our food to kill germs or parasites.
4. Inhalation
  • It is also possible to be contaminated by toxic substances when we breathe them into our lungs. The amount of air inhaled in a workday can be extremely large, so if we work or live in a contaminated area, we can be exposed to significant quantities of a substance in this way.
  • Some chemicals have excellent warning properties that let us know when they are in the atmosphere. There is the well-known “rotten egg” smell of hydrogen sulfide, for example. But at high concentrations of this gas, our sense of smell is quickly lost. Many toxic substances, such as carbon monoxide, are both colorless and odorless, providing us with no sensory clues that we are being exposed to anything unusual.