Columbia River Basin State of the River Report for Toxics - Toxic Contaminants
Download the State of the River Report for Toxics
This diagram shows how persistent contaminants biomagnify (increase in concentration) up the food web. The highest biomagnification levels can be found in the eggs of fish-eating birds.
What are Toxic Contaminants?
Toxic contaminants (or toxics) are chemicals that when introduced to the environment can be harmful to fish, wildlife, and people. These chemicals can be concentrated to toxic levels in the environment. In the Columbia River Basin, toxics pollute streams and rivers from activities such as mining or wastewater treatment, storm water and agricultural runoff, and by natural processes like erosion.
Why are Persistent Toxics a Concern?
Persistent contaminants are chemicals that remain in the environment for a long time. Many contaminants break down slowly, so they accumulate and concentrate in plants, wildlife, and people. When persistent contaminants pollute food sources they can concentrate to toxic levels in fish and wildlife. The concentration of persistent contaminants through water, sediment, and food sources and within a plant or animal is called bioaccumulation. An example of a persistent chemical in the Columbia River is DDT and its breakdown product DDE, both of which are still present in the River nearly 40 years after DDT was banned.
Contaminants in water and sediment are absorbed by microscopic plants and animals at the bottom of the food web, called phytoplankton and zooplankton, as they take in food and water. As larger animals eat the plankton, the accumulated chemicals are absorbed into each animal’s body. Fish and other animals eat the plants, microorganisms, and small fish; the chemical moves into their bodies, and ultimately into larger fish-eating birds and mammals higher in the food web. This is how contaminant concentrations exponentially increase in fish and fish-eating animals at levels much higher than the concentrations found in the waters the fish live in. Through this biomagnification process, top predators, including birds of prey and humans, can accumulate contaminants in higher concentrations than those found in the plants and animals they consume.