@2023 Pamela Ferris-Olson

Thrown Their Cares Away? - Cancer rarely occurs in wild animals yet one in four adult autopsied California sea lions have been diagnosed with urogenital carcinoma. The highest prevalence of this type of cancer ever observed in any mammal including humans. It took nearly 40 years to unravel the story of why. DDT, an insecticide originally developed in the WWII era, is the culprit. Its effectiveness in killing insect pests led to DDT being widely used for almost three decades. DDT is a lipid soluble toxin that accumulates in an animal’s fatty tissues. With time, research showed that the insecticide had adverse environmental effects. Its use is now banned in the US.

A while back a University of California Santa Barbara scientist using a deep-sea robot discovered upwards of 500,000 barrels of DDT dumped in the deep waters off the Channel Islands, an archipelago located about 20 miles off the coast of Los Angeles, California. This area is a primary breeding area for California sea lions. Even in the non-breeding season sea lions congregate by the hundreds on the islands beaches and rocks. The sea lions do not directly ingest the DDT; however, they eat the fish and squid that eat creatures that ingest the insecticide. Note: Humans eat some of the same seafood that sea lions eat.

Because the DDT hasn’t broken down in any significant way since the barrels were dumped decades ago, it continues to exist in a toxic form. It is unclear whether the toxins will ever be harmless and so there is no way of knowing how long the sea lions or any sea creatures are going to be exposed.  

The Marine Mammal Center in Sausalito, California cares for some of the sick sea lions and autopsies those that die, they were the first to make a link between the sea lions’ cancer and the DDT. They share their findings with researchers in hopes that together they may promote the health of the ocean and her creatures.