How can pollutants affect food chains and ecosystems?

Human activity creates many harmful pollutants. These build up in the environment when decomposers are unable to break them down. Plants take up these pollutants. The pollutants are then transferred along the food chain until they reach the highest trophic level. Bioaccumulation refers to the gradual build-up of pollutants in living organisms. Biomagnification refers to the process in which pollutants not only accumulate, but also become more concentrated at each trophic level. Organisms at lower trophic levels may be affected by the pollutant, but primary, secondary, and tertiary consumers  will be more affected, because levels will build up in their tissues as they consume contaminated food. An example  of this is the PCB concentrations in the orca’s food web.  When orcas consume food contaminated with PCBs, they store some of the PCBs in their blubber. When salmon (their primary food) is not available, orcas use their blubber for energy. This releases PCBs into their system. Pollutants can build up to toxic levels in organisms at the top of the food chain. They can also affect entire ecosystems when keystone species, species that greatly affect ecosystem health, or the reproductive abilities of species are harmed.