A wholesaler carries frozen tuna at Tsukiji Fish Market in Tokyo in July. In Japan, developmental problems were detected in children who ate a large amount of fish. (Koichi Kamoshida/Getty Images)

Molly Lutcavage thought she had a deal. For more than a decade, she had collected hundreds of tissue samples from bluefin tuna in hopes of settling a question that has long vexed pregnant women and the parents of young children: Should they eat the big fish, a beneficial source of protein and fatty acids? Or did mercury contamination make them too dangerous?

Lutcavage hoped to test the theory that selenium, a key chemical found in tuna, prevents mercury from being transferred to the people who eat them and that, therefore, the fish are safe to eat. So she gave her hard-won samples to a colleague, Nick Fisher, to analyze in his lab.

But Fisher, it seems, didn’t have as much interest in Lutcavage’s selenium theory. Two years later, he produced a study focused almost exclusively on his own hypothesis: that lowering pollution emissions from power plants reduced the levels of mercury in bluefin tuna.

Lutcavage was furious, and the two scientists went to war.

“We kept fighting on this,” said Lutcavage, a researcher at the University of Massachusetts at Boston. “I feel that the paper didn’t advance the issue whatsoever on this divide between scientists over methylmercury. I can’t tell you how much [my colleagues and I] agonized over taking our names off the paper.”

The battle, raging for two years, sheds light on the unsettled and contentious issue of seafood safety, particularly for large, long-lived fish like tuna and swordfish that tend to accumulate mercury.

Federal agencies such as the Environmental Protection Agency, the Food and Drug Administration and the National Institutes of Health urge caution for some types of fish, especially for pregnant women and young children, because high levels of mercury contamination can cause developmental disorders. But the agencies base their recommendations on a body of research that often comes to conflicting conclusions.

Tuna and seafood, in general, is delicious and healthy. Nutritionists emphasize that its nutrients are great for growing brains. But mercury contamination could potentially outweigh those advantages. So Lutcavage’s question about whether selenium could bind to mercury and protect people from its effects is a potentially important one.

But Fisher, a professor of marine science at Stony Brook University on Long Island, argues that it makes more sense to try to figure out how to keep the mercury out of the fish in the first place by keeping it out of the environment.

“We specifically did not address the toxicology of mercury in tuna,” he said, “only what the concentrations in tuna are and how they change over time.” At the start of the research, he said his team could not isolate enough selenium from the samples for a reliable test. But later, near the end, they did.

“When we generated some good selenium data, I said to Molly I would ship that data . . . and you can take the lead on publishing this. She chose not to do anything to do with that,” Fisher said.

Both Lutcavage and Fisher recalled her exact words: “I don’t want anything further to do with this.”

Mercury is released into the atmosphere from coal-burning plant emissions and other pollution sources around the world, and it settles on fresh and salt waters. Microbes convert it into methylmercury, which collects in small organisms and fish. Big predators, such as tuna, accumulate higher levels of methylmercury by gobbling hundreds of smaller fish.

Previous studies of how methylmercury affects people who consume large quantities of seafood have had mixed results. In Seychelles, off the East African coast, few harmful effects were found in mothers or children. In Japan, however, developmental problems were detected in children who ate a lot of fish. In a study from an island off the coast of Norway, results were mixed.

Lutcavage’s tissue samples came from 1,300 bluefin tuna collected over 14 years. Bluefin tuna isn’t canned or widely eaten by Americans — it’s favored for sushi and largely consumed in Japan. But the mix of methylmercury and selenium in their bodies could have shed light on what’s happening in other fish.

“The story of whether eating tuna is harmful is all over the media, but the science itself is rarely covered,” Lutcavage said. “The paper [from her collaboration with Fisher] does not discuss the very deep divide among scientists on whether methylmercury is dangerous to humans.”

Speaking for her other labs’ scientists, she said: “We’re very sad. We feel that the best possible science wasn’t used here and we lost a lot in terms of this research.”

Fisher was dumbfounded that his former colleague spoke so openly about their fighting, to the point of effectively disavowing their published study. “I’m not looking to pick a fight with her.”

The study had a single purpose, according to Fisher. “It simply shows that by implementing changes in mercury emissions, it could very rapidly result in changes in mercury concentrations in large fish like tuna. It did that effectively, showing that closing coal-fired plants that belch pollution reduces mercury in the environment and the ocean food chain.”

Conservationists, who are concerned about the environmental impact of overfishing, have taken up the issue of mercury contamination. They have squared off against the seafood industry for decades, with activists saying beware of eating fish and the industry saying there’s no solid evidence of harm.

Oceana, a nonprofit environmental group, launched a campaign to persuade grocery stores to place the FDA’s mercury warning on cans of tuna. Jointly with the EPA, the FDA says pregnant women should avoid such fish as orange roughy and bigeye tuna.

But the National Fisheries Institute, which represents the seafood industry, points out that the same agencies say eating a variety of crab, lobster, scallops, shrimp and fish, including canned skipjack tuna, is a good choice, even for pregnant women and children.

“The level of mercury in canned tuna remains . . . completely safe,” said Lynsee Fowler, a spokeswoman for the institute. Levels of mercury in seafood, she said, “are simply not making consumers sick.”

After three years of research yielded no evidence to contribute to the debate, Lutcavage now wonders why she bothered to contact Fisher and why she relied on only a verbal agreement.

“I blame myself,” she said. “Everyone has different ideas of what a collaboration might be. It’s like a relationship. Get it in writing, like a prenup,” she said.

Scientists who want to better understand the relationship between selenium and methylmercury will have to look elsewhere for answers.

“We fought as hard as we could for our points of view on the science,” Lutcavage said of her research team. “And we lost.”