Now, scientists have discovered that much of the DDT — which had been dumped largely in the 1940s and ’50s — never broke down. He noted that the new science being shared this week is critical to answering one of the agency’s most burning questions: “Is the contamination moving? And is it moving in a way that threatens the marine environment or human health?”DDT was banned 50 years ago, but its toxic legacy continues to affect the California marine ecosystem and threaten various animal species. worked on the DDT problem since the 1990s, said that as he listened to the latest research discoveries, he couldn’t help but think that “our nation’s ocean dumpsites all have horrible contamination problems