Narrator: This is Science Today. In 1970, sea lions off the coast of central California had incredibly high amounts of DDT in their tissues. When researcher Wally Jarman of the University of California, Santa Cruz saw the figures from the same area 25 years later, he found the level of DDT had dropped dramatically.

Jarman: Probably as much or more than any other wildlife population that's ever been recorded.

Narrator: Jarman can pinpoint the exact reason for the drop.

Jarman: What we believe is, there used to be a manufacturing plant in Los Angeles that released a lot of its waste into the sewers and also dumped quite a bit of its DDT manufacturing waste out in the channel off Los Angeles.

Narrator: The plant was shut down in 1970.

Jarman: And I think that that is the major reason that we've seen these dramatic decreases, the stopping of DDT waste flowing into the Los Angeles basin.

Narrator: However, Jarman points out that the DDT isn't gone from the environment -- there's just less of it. And the plant has been closed for over 25 years. For Science Today, I'm Steve Tokar.