It became more and more concentrated as it went up the food chain through algae to small fish to large fish to cats or humans. So it happened with DDT through the soil, mosquitoes, birds, into bird's eggs and leading to near extinction of some bird species. Or with PCBs, polychlorinated biphenols, in your trout or milk or in your breakfast cereal. In most cases the offending chemical is carried in the last of our key natural cycling chemicals, water. And this is the final component of our air too.
Water moves into and out of all living systems.
So much so that the ancient philosophers thought all living things were made of water. We are made of over seventy percent water. And inside our bodies water is not only used directly in chemical reactions, it is also an essential carrier of all the other chemicals. Here you can see how the water cycle works on this spaceship. Notice that if you were to follow a single molecule of water it would make a fascinating world journey.