As the region reckons with its toxic history of offshore dumping off the California coast, new findings raise troubling questions about whether the banned pesticide remains a threat to wildlife and human health.

In the 1940s and 1950s, the ocean off the coast of Los Angeles was a dumping ground for the nation's largest manufacturer of the pesticide DDT—a chemical now known to harm humans and wildlife. Due to the stubborn chemistry of DDT and its toxic breakdown products,