The most challenging aspect of this problem is discovering how to eliminate these compounds from the environment and where to focus remediation efforts. Even pollutants no longer in production persist in the environment, and bio-accumulate in the food chain. An understanding of how these chemicals, once in the environment, move through ecosystems, is essential to designing ways to isolate and remove them. Working backwards through the food chain may help to identify areas to prioritize for remediation efforts. This may be extremely challenging for contaminated fish and marine mammals that have a large habitat and who consume fish from many different areas throughout their lives.