Which route is used for exposure where a chemical is often delivered directly into the bloodstream?

• A. Ingestion
• B. Inhalation
• C. Absorption
• D. Injection

Answer: (D)

Direct entry into the bloodstream happens when a chemical is introduced by injection, especially intravenously. This route bypasses barriers like the gastrointestinal tract and the lungs, so the substance reaches the circulatory system immediately and distributes quickly throughout the body. Ingestion requires swallowing and passage through the digestive system, where the chemical must be absorbed into blood, often with variability due to metabolism. Inhalation delivers substance to the lungs and then into the bloodstream via the alveolar membrane, but it still involves a transfer step rather than immediate blood entry. Absorption is the process by which a substance crosses body barriers, applicable to dermal or mucosal exposures, whereas injection is the direct route into circulation.