Ex situ bioremediation, possibly with a first round of phytoremediation to clean any heavy metals. On the long run this would be the most beneficial process. The displaced contaminated soil can eventually (after initial phytoremediation) be used for conventional agriculture.
The energy costs of this are the initial superficial excavation of contaminated soil from beaches and marshland, transportation to a suitable location for processing, seeding with air, fertilizer and microorganisms, building infrastructure to prevent leakage of toxins into environment, mixing with existing soil, and, possibly, desalination for irrigation if the location does not have a freshwater supply. If i am not mistaken desalination is a process that has been discussed in this forum before.
