750 Introduction to Industrial Hygiene

Routes of Entry

How Can Chemicals Enter the Body?

In industrial hygiene, hazardous substances enter the body through four primary routes: inhalation, skin (dermal) absorption, ingestion, and injection. Below are the standard routes of entry with examples:

Inhalation: The most common type of exposure occurs when you breathe a substance into the lungs. The lungs consist of branching airways (called bronchi) with clusters of tiny air sacs (called alveoli) at the ends of the airways. The alveoli absorb oxygen and other chemicals into the bloodstream.

Sometimes a chemical is present in the air as small particles (dust or mist). Some of these particles, depending on their size, may be deposited in the bronchi and/or alveoli. Many of them may be coughed out, but others may stay in the lungs and may cause lung damage. Some particles may dissolve and be absorbed into the blood stream, and have effects elsewhere in the body.

Absorption: Absorption is the process by which hazardous substances enter the body through direct contact with tissues such as the skin, lungs, eyes, or digestive system.

• Dermal Absorption: Some chemicals can easily pass through the skin and enter the bloodstream. If the skin is cut or cracked, chemicals can penetrate through the skin more easily. Also, some caustic substances, like strong acids and alkalis, can chemically burn the skin. Others can irritate the skin. Many chemicals, particularly organic solvents, dissolve the oils in the skin, leaving it dry, cracked, and susceptible to infection and absorption of other chemicals.
• Example: Benzene from solvents absorbed through the skin during cleaning, causing toxicity. A farmworker handling liquid pesticides without gloves absorbs the chemicals through the skin on their hands and forearms.
• Ocular Absorption: Hazardous substances enter the body through the eyes, typically via splashes or vapors.
• Examples: Ammonia vapors from cleaning agents contacting the eyes, causing irritation or chemical burns. A janitor splashes cleaning solution into the eyes while mixing chemicals, allowing harmful ingredients to be absorbed through the eye’s mucous membranes.

Ingestion: Swallowing chemicals is the least frequent form of workplace exposure. However, chemicals can still be ingested inadvertently by coming into contact with them on hands, clothing, or beards. Additionally, chemicals can contaminate food, drinks, or cigarettes. In the workplace, metal dusts like lead or cadmium can easily be ingested when they are present in the form of dust.

Injection: Hazardous substances enter through cuts, punctures, or broken skin, often via needles or sharp objects.

• Examples: Accidental needle sticks in healthcare settings exposing workers to bloodborne pathogens like hepatitis B. A cut from contaminated sharp metal in a manufacturing plant.

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