I grew up hearing about the Palos Verdes Shelf, where Montrose Chemical, once the country's largest DDT manufacturer, sent tons of the pesticide through the county's sewage outfall. That was bad enough. But in 2020, Rosanna Xia at the Los Angeles Times published an investigation showing the problem went much further out to sea. From the late 1940s into the early 1970s, waste from Montrose and other companies was loaded onto barges and dumped into the deep basin between the mainland and Catalina. Old shipping logs suggested the number of barrels could run into the hundreds of thousands. A year later, scientists from Scripps and UC Santa Barbara mapped the seafloor and found more than 25,000 barrel-like objects scattered across the dump site, with DDT contamination in the sediment around them.

The detail that stuck with me most was how casually it was done. When barrels floated instead of sinking, crews punched holes in them so they would go down. Sometimes they just dumped the waste straight over the side. Nobody expected anyone to look.

Montrose eventually paid into a settlement over the Palos Verdes Shelf, but the deep-water dumping has largely escaped that kind of accountability. So much time has passed that the companies involved have changed hands or disappeared, records are incomplete, and much of the dumping happened before federal ocean-dumping law took effect in 1972. The chemicals are still down there, though, and researchers have linked them to cancer in California sea lions.