First the mink and the otter began to disappear. Then the local people started noticing something odd about the way the eagles and turkey vultures were flying overhead. One man watched his kitten walking in circles, salivating and convulsing.

These were the early warning signs around 1970 that something sinister was happening at Grassy Narrows along the Wabigoon River in northwestern Ontario.

The mink, the otter, the eagles and the vultures had mercury poisoning from eating contaminated fish. The cat’s brain, later analyzed, revealed full-blown Minamata disease, the twitching tremors and stumbling gait associated with extreme exposure to the heavy metal.

Those details are preserved in the research papers of Dr. Masazumi Harada, a Japanese scientist who never stopped tracking the effects of mercury contamination on the people at Grassy Narrows, long after Canadian researchers closed their files.

Even though Harada died a few years ago, his research on the community northeast of Kenora continues to this day. A Japanese team is just wrapping up the fifth visit since the research began in 1975.

They’ve spent the last week doing physical examinations, looking for evidence of brain and central nervous system damage from one of the most infamous examples of environmental mercury poisoning.

Sixty years ago, the world was oblivious to the hazards of the raw mercury that industries were dumping into lakes and rivers, unaware that bacteria were transforming the inorganic metal into methyl mercury, an organic pollutant that accumulates in the food chain, contaminating fish and poisoning people.

In the late 1950s, more than 100 people died in Minamata, Japan, and many more suffered devastating brain damage after eating fish contaminated with mercury that had been released into a lake by a chemical company.

Contaminated fish

But it took another decade to recognize the emerging disaster in northern Ontario, just downstream from the Dryden pulp mill, where mercury used in the bleaching process was being flushed into the Wabigoon River.

By the time government scientists arrived in 1970 to do some testing, the people at Grassy Narrows and neighbouring Wabeseemoong First Nations had already eaten dangerous amounts of contaminated fish. The first tests revealed extreme levels of mercury in hair and blood.

The community of Grassy Narrows, northeast of Kenora, Ont., is built along the same water system that makes the people sick. Mercury contamination from the 1960s and '70s has never been cleaned up. (Jody Porter/CBC)

But human health effects were not diagnosed until Harada showed up in 1975, tipped off by a Japanese photographer that there was a mini-Minamata happening in Canada.

Using his expertise from studying the Japanese victims, Harada diagnosed at least 60 cases of Minamata disease in Grassy Narrows, another 54 cases of Minamata-with-complications and a further two dozen suspected cases.

Yet, to this day, Canadian officials have never admitted to a single case of Minamata disease.

A small number of the people in the Grassy Narrows region who have applied for compensation have received money, based on neurological symptoms consistent with mercury poisoning. But there has long been a reluctance to confirm an official diagnosis.

And the full extent of the human health effects of the mercury poisoning at Grassy Narrows has never been systematically investigated.

There has been no epidemiological study to establish the scope of the Grassy Narrows exposure, and no long-term tracking of what are now recognized as the life-long effects of ingested mercury, although an expert review by Canadian scientists in 2010 stated "there should have been extensive examinations and followup of these communities."

Fading interest

Instead, scientific interest in the Grassy Narrows story faded. Over the decades, as the levels of mercury in hair and blood tests began to fall, government monitoring tapered off. The hand-bound copies of research reports now gather dust on library shelves.

There have been some recent surveys of environmental contamination in First Nations communities, which have included testing for mercury in hair and blood, but those tests reveal only recent exposure. They do not shed light on the effects of past exposures or the ongoing damage from the toxic metal now embedded in the cells and tissue of the brain.

Margaret Wanlin, chair of the Mercury Disability Board, right, listens as Dr. Kazuhito Tsuruta presents his research on mercury poisoning at the trappers hall in Grassy Narrows. (Jody Porter/CBC)

"You can’t put a thermometer in the brain," says Donna Mergler, an environmental scientist and University of Quebec in Montreal biologist who has studied the effects of mercury on people living in the Amazon forests.

"Often you won’t see effects in early adulthood, but they will come out later on, if you have had high exposure, because the nervous system does age and mercury appears to accelerate this aging process," she says.

Another lingering question from Grassy Narrows is the effect on the next generation, on the children whose mothers ate contaminated fish while they were in the womb.

It has long been known that the dangers of fetal exposure to mercury can be severe, resulting in long-term neurological damage.

Yet research on the influence of prenatal mercury exposure "has been pervasively delayed," Harada wrote in 2011.

"It is regrettable to think that a systematic investigation in Canada’s Grassy Narrows and [Wabaseemoong First Nations] would have yielded a precious resource for humanity."

Limited scope

As it is, Harada’s research is the only ongoing study of the clinical effects of mercury poisoning on the people of Grassy Narrows.

But as field studies, they are limited in scope, and Mergler says they should be seen as preliminary investigations that demonstrate the need for more comprehensive epidemiological research.

It was the science of Grassy Narrows that has drawn the Japanese researchers back over the last 40 years.

The current team leader, Masanori Hanada, said what they learn here can be applied to the Japanese victims back in Minamata and to other victims of mercury poisoning all over the world.

It is research that grows more acute because the mercury is still there, in the English-Wabigoon River system and in the fish at Grassy Narrows, and in waterways all over the world.

And every day, mining, logging and the combustion of fossil fuels release more, to begin the dangerous ascent through the food chain.