Final answer:
Biomagnification is the increasing concentration of toxic substances as they move up the food chain, with apex consumers experiencing the highest levels, which can lead to severe health and reproductive issues.
Step-by-step explanation:
The term that describes the process whereby toxic substances increase along trophic levels of an ecosystem is biomagnification. This phenomenon occurs when organisms at each trophic level consume prey from the lower level that already contains accumulated toxins, leading to even higher concentrations in their bodies. Over time, apex consumers at the top of the food chain exhibit the highest concentration of these toxic substances. A classic example of this is the biomagnification of the pesticide DDT, which led to significant declines in bird populations due to the thinning of eggshells, as highlighted in Rachel Carson's Silent Spring.
Apex consumers like birds of prey, large fish, or mammals are most at risk due to biomagnification, as they end up with the greatest concentration of these nonbiodegradable substances in their systems, leading to harmful effects on their health and reproduction. As these toxic substances are fat soluble and persistent, they become more concentrated as they move up the food chain due to processes such as assimilation and the limited ability of organisms to excrete them.