An elementary exchange is an Exchange between an Activity and the natural, social or economic Environment. This represents the boundary between the technosphere (human activities) and the environment, capturing flows that cross from human-controlled processes into or out of the broader environmental context.
According to ISO 14040, elementary exchanges encompass material or energy entering the system being studied that has been drawn from the environment without previous human transformation, or material or energy leaving the system that is released into the environment without subsequent human transformation. This definition establishes elementary exchanges as the fundamental building blocks of environmental impact assessment in LCA.
Elementary exchanges can be categorised into several types. Input elementary exchanges include unprocessed inputs from nature, such as raw materials extracted directly from the earth, water drawn from natural sources, or land occupied for specific uses. Output elementary exchanges typically consist of emissions to air, water and soil that result from human activities. Additionally, elementary exchanges encompass physical impacts on the environment, such as land transformation or occupation, and social exchanges such as working hours performed under specified conditions.
These exchanges form the basis of the Life Cycle Inventory (LCI) phase of an LCA study. During impact assessment, characterisation factors are applied to elementary exchanges to calculate their contribution to various impact categories. The comprehensive documentation of all elementary exchanges associated with a product system enables practitioners to evaluate the full environmental burden across natural, social and economic dimensions of the environment.
