Bioaccumulation is an ecological phenomenon where certain substances, particularly non-biodegradable toxins, gradually build up within the tissues of living organisms. This process typically occurs due to these toxins being fat-soluble, allowing them to nestle themselves into the fatty tissues of an organism and remain there, thereby increasing in concentration over time.

Here's a real-world example: let's imagine a pond where a factory has been discharging harmful chemicals. The smallest organisms, like algae and tiny aquatic insects, will ingest these chemicals. When small fish feed on these organisms, the toxins now transfer and accumulate in the bodies of the fish. As the chemicals are non-biodegradable, they can't be broken down, leading to an increase in toxin concentration in the fish, demonstrating bioaccumulation.

While bioaccumulation refers to toxin build-up within a single organism, biomagnification deals with the escalation of toxin concentration up the food chain. This is often seen in ecosystems with distinct food chains where top predators sit at the highest trophic level.

In a continuation of the pond example, a larger predatory fish might eat the smaller fish. Now, the toxins that have been bioaccumulated in the smaller fish are transferred to the predator. This increases the concentration of the toxins in the predator's body - the process of biomagnification.

Top carnivores often bear the brunt of bioaccumulation and biomagnification. With a build-up of toxins in their system, these organisms are at high risk of facing health complications, some of which can be fatal. This could lead to a decline in their population, destabilizing the ecosystem as a whole.

The Bald Eagles DDT crisis is an infamous example. DDT, a pesticide, was accumulating in the fatty tissues of small organisms. Through the process of biomagnification, DDT reached dangerous levels in bald eagles, leading to significant population declines.

Similarly, mercury in swordfish is a concern for marine ecosystems and humans alike. Human activities like mining and fossil fuel combustion have resulted in mercury pollution. When mercury settles on land or water, it's absorbed by small organisms. It then moves up the food chain, concentrating in top predators like swordfish.