Researchers have found male fish with eggs in their testes and female sex traits off the coast of Southern California and believe that chemicals in sewage may be the cause, an author of two studies said on Monday.

The two reports found the changes in fish such as English sole and California halibut, both of which are bottom dwellers, in water near where sewage is released, said Dan Schlenk, an environmental scientist at the University of California, Riverside.

High levels of estrogen, both natural and man-made formulations used in birth control pills, are thought to cause such abnormalities in fish. Estrogen makes its way into sewage water and then the ocean through women’s excretions.

Compounds that act like estrogen, found in certain industrial chemicals, have also been blamed for such changes.

But in this instance, Schlenk said higher levels of the egg protein were found in male fish in areas with lower levels of estrogen and estrogen-like chemicals in the sediment. The cause of the female characteristics, therefore, could be unknown chemicals in the sediment, he said.

“We might have other players in this game,” Schlenk said in an interview on Monday. “We would guess they are primarily coming from waste water.”

He said the sewage contained natural and man-made chemicals that was deposited in ocean sediment.

One of the culprits could be DDT, Schlenk said, a pesticide banned in the United States in 1972 after it was shown to cause reproductive damage to birds. DDT is no longer used but can remain in the environment for a long time.

Los Angeles County’s sewage outfall, Schlenk said, “has probably one of the most contaminated DDT sites in North America, and these responses are fairly consistent with that kind of exposure.”

Shall we reconsider all those healthy seafood meals in California?