How does bioaccumulation occur?

Bioaccumulation occurs when an organism absorbs a substance, such as a toxic chemical or heavy metal, at a rate that exceeds the rate at which it is able to eliminate it. This means that the concentration of the substance in the organism's body increases over time, as the organism continually takes in more than it can expel.

This process is particularly concerning in ecological and environmental contexts because it can lead to significant toxin build-up in organisms, especially at higher trophic levels in food chains. For example, if a small fish absorbs a toxic pollutant from its environment and then is eaten by a larger fish, the pollutant can accumulate further in the larger fish. This chain can ultimately affect predators, including humans, who consume these higher trophic level organisms.

The other options describe processes that do not lead to bioaccumulation. If an organism absorbs a substance slower than it is eliminated, it will not accumulate that substance over time. Complete elimination of a chemical means there would be no accumulation, and lack of exposure to chemicals also negates the possibility of bioaccumulation occurring, as there would be no substance for the organism to absorb in the first place.