Final answer:
Biomagnification refers to the increasing concentration of toxic substances in organisms at each trophic level, from primary producers to apex consumers. It leads to the accumulation of toxins in fat reserves, affecting the health and survival of species at higher trophic levels.
Step-by-step explanation:
The term that describes the process whereby toxic substances increase along trophic levels of an ecosystem is known as biomagnification. This process involves the increasing concentration of persistent, toxic substances in organisms at each successive trophic level. These substances are typically fat-soluble, allowing them to accumulate in the fat reserves of organisms. A classic example of this phenomenon is seen with the pesticide DDT, which led to the bioaccumulation of toxins in apex consumers such as birds that feed on affected fish. The result was a detrimental effect on bird eggshell strength and significant population declines. Biomagnification is an important environmental issue, as it can lead to dangerous levels of toxins in species at the top of the food chain, including humans.