The greatest danger for whales used to be harpoon-wielding Ahabs, but, according to Yale researchers, their gravest threat today may be a common chemical painted on the bottoms of boats.

In a study to be released in the March issue of Biophysical Journal, Yale researchers determined that tributylin oxide — a toxic chemical commonly painted on the bottom of large ships and vessels to protect against barnacles — can have harmful effects on the sense of hearing in whales and other marine mammals.

“TBT is clearly a very toxic chemical, and we’ve determined that it is an environmental hazard,” said Joseph Santos-Sacchi, the senior author of the study and a professor of surgery and neurobiology at the Yale School of Medicine. “This issue is a big concern in the marine environment, as [TBT] might affect other kinds of ocean mammals and the food chain.”

The research was focused on hearing organs’ outer hair cells, which move in the presence of sound energy and amplify the sound for the inner hair cells, Santos-Sacchi said. The inner cells have many neural connections, which allow for hearing and sound perception.

The motor activity of outer hair cells is vital for sensitive hearing. Mammals are the only kind of species that have these outer hair cells, so the discovered effects of TBT could affect all kinds of aquatic mammals, especially whales.

The severity of the effect depends greatly on the degree of exposure to the chemical. Whales that come in close contact with TBT sediment from boats more often have a higher risk of developing hearing problems.

“Everything depends on the dose, but TBT is a very strong agent,” said Lei Song, a post-doctoral associate and co-author of the study.

Humans are not threatened by TBT and are therefore not susceptible to any sort of harm from contact with the chemical, Song said. He said even people who swim frequently are not in any danger.

Santos-Sacchi said there is a history of legislation banning TBT, and the chemical has already been proven to inflict damage on marine mammals’ immune and hormonal systems.

“TBT was banned a long time ago on small ships, but there is a treaty on the table to ban it outright,” he said.

Despite restrictions on its use, Santos-Sacchi said TBT is still applied to the bottom of many boats, though many boaters now use a safer, copper-based paint.

Santos-Sacchi, who has been working at Yale since 1991, said he hopes that the conclusions of his study will lead marine biologists to conduct further testing on TBT levels and their effects on dolphins and whales. He said he plans to work toward understanding the effect TBT could have on marine mammal communication.

“Further research will either support or reject my hypothesis,” he said. “This basic research has been going on for years, but this whale stuff is recent.”