Final answer:
The principle of lifetime dose refers to the total amount of a substance that an individual is exposed to over their lifetime, taking cumulative exposure into account.
Step-by-step explanation:
The principle of lifetime dose is best explained by the statement that it is the total amount of a substance that an individual is exposed to over their lifetime. Unlike a single instance or daily exposure, lifetime dose accounts for the cumulative effect of a substance throughout an individual's life. This concept is especially relevant in environmental health and toxicology, where the cumulative exposure to toxins, chemicals, or radiation may result in different health outcomes than those predicted by only considering single or daily exposures.
In practical terms, the lifetime dose can help assess the risk associated with substances such as radiation, where it is understood that the biological effects are not only dose-dependent but also time-dependent. For instance, a person exposed to a high dose of radiation in a short period has a different risk profile compared to someone exposed to the same dose over an extended period. The principle of lifetime dose assists in considering how the body's ability to repair damage over time affects the severity of the health outcome.