Classification of Pollutants

In terms of how an ecosystem processes them, pollutants fall into two basic groups: degradable and non-degradable. Degradable pollutants are further split by how long they take to break down into harmless components.

1. Rapidly degradable or non-persistent pollutants are broken down quickly by natural processes such as microbial decomposition -- domestic sewage and vegetable waste are typical examples, since bacteria and other decomposers can metabolize them within days to weeks under normal conditions.
2. Slowly degradable or persistent pollutants remain in the environment for many years in essentially unchanged form and take decades or longer to break down; the pesticide DDT is the textbook example, remaining active and toxic in soil and water long after it was applied, which is exactly why it is able to accumulate in food chains and cause biomagnification. …