What is the term for the biological sequestering of a substance at a higher concentration than its surrounding environment?

The term that describes the biological sequestering of a substance at a higher concentration than its surrounding environment is bioaccumulation. This process occurs when organisms absorb toxic substances, such as heavy metals or persistent organic pollutants, faster than they can eliminate them. As a result, the concentration of these substances increases in the organism's tissues over time. This phenomenon often poses significant risks to aquatic life and ecosystems, as well as to animals and humans that consume those affected organisms.

While bioremediation refers to the use of living organisms to clean up contaminated environments, and biodegradation involves the breakdown of organic substances by microorganisms, biomagnification deals with the increase in concentration of a substance up the food chain, rather than within a single organism over time. Bioaccumulation specifically addresses the accumulation process in individual organisms, which is why it is the correct choice in this context.