Which are the four routes of exposure to toxic substances?

• A. Inhalation, Dermal contact, Injection, Ingestion
• B. Inhalation, Ingestion, Dermal, Transdermal
• C. Inhalation, Ingestion, Injection, Oral
• D. Inhalation, Dermal, Injection, IV

Answer: (A)

Exposure to toxic substances occurs through four primary pathways: inhalation, dermal contact, ingestion, and injection. Inhalation means the substance is breathed in as gases, vapors, or airborne particles, reaching the lungs and then the bloodstream. Dermal contact involves the substance touching and penetrating the skin or mucous membranes, potentially entering the body at the site of contact. Ingestion covers anything swallowed, whether from contaminated food, drink, or hand-to-mouth transfer, allowing the toxin to pass through the digestive system. Injection refers to entry through puncture of the skin or mucous membranes, such as needle sticks, delivering the substance directly into the body or a body compartment.

This set captures the broad routes used in toxicology and risk assessment. Some terms in the other options are either synonyms for these routes (oral equals ingestion, IV is a specific type of injection) or subdivisions that don’t change the fundamental pathway. Transdermal, for example, describes a delivery system over time rather than a distinct primary route, and IV is just one injection route, not a separate category.