What term describes the quantitative relationship between dose and harmful biological effects?

• A. Toxic index
• B. Exposure limit
• C. Dose-response relationship
• D. Hazard quotient

Answer: (C)

Understanding how the amount of substance someone is exposed to translates into harm is described by the dose–response concept. It captures how increasing dose changes the probability and/or severity of adverse effects, usually shown on a curve with dose on the x-axis and response on the y-axis. The curve reveals potency and whether there's a threshold: many non-carcinogens have a threshold below which little or no harm occurs, while carcinogens are often modeled as risk increasing with dose, sometimes without a true threshold. This relationship underpins how toxicology data translate into exposure guidance and safety decisions. The other terms refer to regulatory limits or risk metrics rather than the actual relationship between dose and effect: exposure limits are permissible levels, hazard quotient compares exposure to a reference dose, and toxic index is not a standard concept in this context.