Toxic pollutants are different from conventional pollutants such as sediment and bacteria in that they can cause biological impairment at low concentrations due to their high toxicity. Many toxic pollutants tend to bioaccumulate, in other words, their concentrations will increase along the food chain. Many are persistent and tend to attached onto suspended and bedded sediments, therefore the period of impact can greatly exceed the period of discharge.
The Santa Ana Regional Water Quality Control Board is currently dividing the Toxics TMDL into five separate TMDLs based primarily on chemical class, and developing individual implementation plans for each TMDL. These TMDLs include:
Development of the selenium TMDLs and selenium site-specific objectives (SSOs) are being supported by the efforts by the Nitrogen and Selenium Management Program (NSMP), which is a watershed-wide collaborative effort to address nitrogen and selenium issues. The County of Orange is responsible for administering and managing the NSMP, as well as serving as Chair of the program. As the NSMP continues, it will be the primary mechanism for achieving compliance with the nitrogen and selenium TMDLs for Newport Bay.