Mysterious chemical found in dead cat’s brain reopens debate over mercury poisoning disaster | Science
The metropolis of Minamata, Japan, is dotted with monuments commemorating victims of an industrial mass poisoning many years in the past. High in the hills, a small stone memorial honors different deaths—of cats sacrificed in secret to science. Now, after restudying the stays of a kind of cats, a staff of scientists is arguing, controversially, that the long-standing clarification for the tragedy is flawed.
No one questions the foundation explanation for the disaster, which at minimal poisoned greater than 2000 individuals: mercury in a chemical manufacturing unit’s wastewater that was dumped into Minamata Bay and brought up by seafood eaten by fishermen and their households. At first, the chemical type of the mercury, which finally killed lots of its victims and left many infants with extreme neurological problems, was unknown. But in 1968, the Japanese authorities blamed methylmercury, a standard byproduct of mercury air pollution. Many research supported that conclusion, discovering methylmercury spikes in shellfish, bay sludge, and even tons of of umbilical cords from infants delivered in the course of the time. But methylmercury is just not the perpetrator, says Ingrid Pickering, an x-ray spectroscopist on the University of Saskatchewan. “Our work is indicating that it’s something else”: an uncommon mercury compound which will say little concerning the broader menace of mercury air pollution.
Minamata has lengthy been a vivid case research of mercury’s risks. The metallic is poisonous by itself, however it turns into much more harmful when micro organism in pure environments convert it into methylmercury, an natural compound, readily absorbed by residing tissues, that may be concentrated and handed up meals chains. Since the 1990s, scientists have argued that the Chisso chemical manufacturing unit in Minamata produced methylmercury and dumped it straight into the bay.
The dead cat now difficult that image dates to 1959, when the then-mysterious neurological illness was sweeping by town. A physician working for the Chisso manufacturing unit combined wastewater with cat meals and fed it to cats, which began to convulse and had been paralyzed earlier than dying. He autopsied two of them, recognized solely as 400 and 717. Their habits and lesions in their brains steered the identical illness because the one raging outdoors. Factory supervisors hushed up the discovering.
The Chisso cats had been misplaced till 2001, when Komyo Eto, a pathologist on the National Institute for Minamata Disease, studied samples of the cats and the wastewater that had been found in storage at close by Kumamoto University—together with lab notebooks lent by the manufacturing unit physician’s spouse. His measurements confirmed that lower than half of the mercury in the cats’ brain samples occurred as methylmercury; the remaining was inorganic. Only a minuscule fraction of the wastewater’s mercury was methylmercury, however Eto thought that was most likely as a result of the compound had damaged down over the four many years for the reason that samples had been taken.
Now, Pickering and her colleagues have reanalyzed samples of cat 717’s cerebellum on the Stanford Synchrotron Radiation Lightsource, blasting them with x-rays and analyzing the ensuing spectrum for the fingerprints of particular molecules. The molecules that greatest match the spectrum don’t comprise any methylmercury in any respect, they found. Instead, three-quarters of the pattern’s mercury seems to be an obscure natural compound known as alpha-mercuri-acetaldehyde that seemingly got here straight from the wastewater, they argue. The relaxation was inorganic mercury.
The discovering suggests the Minamata disaster—and methylmercury poisoning extra usually—is due for a rethink, the researchers argue in their research, revealed in Environmental Science & Technology in January. Methylmercury performed no important function in the poisoning, says Graham George, Pickering’s husband and co-leader of the experiment, who can also be on the University of Saskatchewan. Because earlier research used much less delicate strategies, they missed the main type of mercury in Minamata samples, he argues. “Were there other more prevalent forms of mercury present that were not detected? Yes, we think so.”
But to different researchers, the staff could also be overstating its conclusions in the service of a bigger agenda. Many of the authors have downplayed the toxicity of methylmercury for years, says Philippe Grandjean, an environmental toxicologist at Harvard University. The work doesn’t do something greater than determine an uncommon chemical in one preserved cat brain, he says. “They did an admirable piece of chemistry, but it should not be interpreted beyond what it really shows.”
Charles Driscoll, an environmental scientist at Syracuse University, says the brand new mercury compound could be a product of the cat’s metabolism or an artifact of the pattern’s lengthy preservation. And even when it did spew straight from the manufacturing unit, the residents of Minamata had been uncovered to mercury from seafood they ate, not from manufacturing unit wastewater, he says. “Quite a few things in [the study] give me pause,” he says. “I was, frankly, surprised it would get published.”
The dispute displays a schism relationship to the 1980s, when dueling analysis groups appeared on the neurological penalties of methylmercury from seafood. One staff, on the University of Rochester, studied the brain growth of kids in the Seychelles islands, the place the food regimen is heavy in fish that may purchase methylmercury in the open ocean from pure and human sources of mercury. “We have not been able to confirm any adverse effects of methylmercury from fish,” mentioned Gary Myers, a University of Rochester neurologist who additionally participated in the research on cat 717. But a competing research by Grandjean and others in the Faroe Islands concluded methylmercury from seafood was harming youngsters.
In 2000, when the U.S. Environmental Protection Agency (EPA) outlined the utmost day by day quantity of mercury considered protected to ingest, the company found the Faroe Islands proof extra convincing and set a low restrict. In 2019, EPA started to reassess this restrict; Grandjean fears the brand new research might be used to help enjoyable the usual. At the identical time, the Trump administration is working to weaken a separate rule known as the Mercury and Air Toxics Standards, which limits mercury emissions from energy vegetation.
Last yr, Grandjean, Driscoll, and different mercury researchers submitted a remark to EPA as a part of the company’s reassessment. They identified that Minamata is just not the one instance of methylmercury toxicity; the compound prompted one other industrial poisoning in Iraq in 1971, and research of infants and youngsters around the globe have found that even low-level publicity can hurt brain growth, Grandjean says. Compared with previous many years, “We know better now.”
Eto, who loaned the samples and was credited as a research co-author, mentioned in an e mail that he nonetheless believes methylmercury was a very powerful explanation for the tragedy. But Pickering and George plan to maneuver past a single cat pattern to bolster their controversial declare. They have already borrowed preserved samples from human victims from the National Institute for Minamata Disease, and plan to check for a similar obscure compound.