What term refers to the actual release or discharge of material from a source?

• A. The source.
• B. The exposure route.
• C. Advection or convection.
• D. Emission.

Answer: (D)

Emission is the term used for the actual release or discharge of material from a source into the environment. It captures the act of releasing a contaminant, whether into air, water, or soil, and is often described in terms of rate or quantity. This differs from the source itself (the origin of the material), from the exposure route (how people or receptors come into contact with the contaminant), and from advection or convection (the transport processes that move the released material through a fluid). For example, when wastewater leaves a pipe and enters a river, the release event is an emission; advection would describe how those contaminants are carried downstream, while exposure route would describe how someone might come into contact with them.