Plain Water: Mercury

Above the bay at Minamata, on the west coast of Kyushu, there is a terrace of grey stone looking out over the water, and set into it are polished steel spheres, each one for a victim, reflecting the sky. The bay below is calm and the fishing boats go out from it; the land along the shore, where the factory's drain used to run, is reclaimed ground, made in the 1980s by dredging the mercury out of the mud and sealing it under a park. Minamata was a company town with a chemical plant, and for thirty six years the plant discharged mercury into the bay, and the bay fed the town, and the town gave its name to a disease. It is the place where the world learned what mercury does in water, and in 2013 it was the place where the treaty to stop it was signed.

This article is about what mercury is, how water turns it into something worse, what happened at Minamata and why it took so long to stop, where the mercury in a tuna comes from now, what the drinking water limit covers, and what the convention is meant to end.

The metal that water changes

Mercury is an element, a heavy silver liquid that has been mined from cinnabar for three thousand years for mirrors, medicine, gold refining and, later, thermometers, switches, dental fillings and the cells that make chlorine. As a metal it is only moderately dangerous: swallowed, it mostly passes through; its vapour, breathed over years, damaged the hatters and the miners. In water it becomes a different substance. Mercury in a river or a bay settles into the sediment, and there the bacteria that live without oxygen attach a carbon atom to it and make methylmercury, which dissolves in fat, passes through every membrane in a body, and is held rather than excreted. Plankton take it from the water; small fish eat the plankton and keep all of their mercury; larger fish eat the small ones; and at each step the concentration rises by a factor of ten or so, so that at the top, in a tuna, a swordfish, a pike or a shark, the flesh carries on the order of a million times the mercury of the water. A person who eats that fish is the next step. Methylmercury crosses into the brain and across the placenta, and the nervous system of a child in the womb is the most sensitive thing it reaches.

Minamata

The Chisso corporation's plant at Minamata made acetaldehyde, a building block of plastics, from 1932, using a mercury compound as the catalyst, and it discharged the spent catalyst with its wastewater into the bay. The bay was a rich fishery and the town ate from it, more fish per head than almost anywhere in Japan. In the early 1950s the cats of the fishing villages began to convulse and die, and the crows fell from the sky; in 1956 a doctor at the company's own hospital reported a strange disease of the nervous system in children, with numbness, tremor, tunnel vision, loss of speech and, in the worst cases, convulsions and death, and the hospital's director began studying it. By 1959 the university at Kumamoto had found the cause, methylmercury in the bay's fish, and traced it to the plant, and the company denied it, produced its own experts, and went on discharging, with the government's acquiescence, because the plant was the town's employer and a pillar of the country's industry. It changed its process in 1968, when acetaldehyde was no longer made that way, and the government recognised the disease's cause the same year, twelve years after the first diagnosis.

The counting has gone on since. About two thousand three hundred people were certified as patients under the strict criteria the government set, and the court cases and settlements of 1995 and 2009 compensated tens of thousands more with milder damage; the children born with the congenital form, poisoned in the womb by mothers who had no symptoms themselves, became the disease's enduring image. A second outbreak, from another acetaldehyde plant on the Agano river in Niigata, was found in 1965. The dredging of the bay, which held hundreds of tonnes of mercury in its mud, took from 1977 to 1990 and cost more than the company was worth, and the mud is under the park by the shore. Minamata is the case the toxicology textbooks begin with, and the pattern it set, a known poison, a company that denies, a government that waits, a town that depends on both, is the one the arsenic and lead articles on this site have met since.

Where it comes from now

The mercury in the fish on a market slab today did not come from a factory drain. It came through the air. The largest source of human mercury to the environment is the gold pan: the small miners of the Amazon, West Africa and Indonesia, whom the gold article on this site describes, use mercury to bind the gold out of the gravel and then burn the mercury off, and the vapour, about two fifths of the world's emissions, goes into the air and comes down in the rain anywhere on Earth. The second is coal, which carries traces of mercury that leave a power station's stack unless it is fitted with the scrubbers that the richer countries required from the 2000s and China from the 2010s, about a fifth of emissions. Cement kilns, metal smelters and the burning of waste make up most of the rest. The mercury falls on the ocean and on the lakes, the bacteria in the sediments do their work, and the tuna of the Pacific and the pike of the Canadian shield carry it, which is why the advice to pregnant women in every rich country is to limit the large predatory fish, and why the Inuit, whose diet is the top of the marine food chain, carry more mercury than anyone.

There are places where the drain was the source and still is. In the north of Ontario, a paper mill at Dryden discharged mercury into the Wabigoon river in the 1960s, the people of Grassy Narrows downstream ate the fish and were poisoned, and the river's sediments still make methylmercury sixty years later, so that the community's mercury disease is a current condition rather than a historical one. Rivers below old chlorine plants, which used mercury cells until the 2000s, carry the same legacy in their mud, as do the reservoirs behind new dams, whose flooded soils release mercury into the fish for decades after the water rises.

The limit and the fish

The drinking water guideline for mercury, six micrograms a litre for the inorganic form in the WHO's standard and two in the United States, is one of the least often exceeded on this site, because mercury in a tap is rare: it binds to sediment rather than dissolving, and the water works' coagulation takes it out with the particles. The limit exists and is almost never the problem. The problem is the fish, which the water standard does not cover, and which the food standards cover with limits on the mercury in the flesh and advice on how much of which fish a person, and above all a pregnant person, should eat in a week. A litre of water at the guideline carries less mercury than a mouthful of swordfish. The plain water lesson is that the water can pass and the water's food chain can fail.

The convention

In October 2013 the governments of the world met at Kumamoto and Minamata and adopted a treaty, named for the town, to control mercury from the mine to the drain: a ban on new mercury mines and the phasing out of old ones, limits on the mercury in products, from batteries to thermometers to skin creams, which are the reason the thermometer in the drawer is now alcohol, controls on emissions from coal stations, smelters and cement kilns, and national plans to reduce mercury in small scale gold mining, which is the hardest part because the miners are poor and the gold is their living. It came into force in 2017 and has more than a hundred and forty parties. Its measure of success is the mercury in the tuna, which responds to the air over decades, and the children of the gold fields, who respond at once. The town whose name it bears took twelve years to be believed.

What it teaches

Mercury is the plain water article about the poison that water makes worse. The metal is almost harmless in a bead on a table and is turned, in the mud of a bay, into a form that climbs the food chain a factor of ten at a time and arrives in a child's brain before birth. Minamata is where that was learned, over a decade in which the people who knew denied it, and the lesson has had to be relearned in Niigata, in Ontario and in the gold fields. The tap is rarely the route; the fish is, and the fish carries what the air brought from a coal station and a gold pan on the other side of the world. The spheres on the terrace above the bay are for the people who ate from it.

A million fold up the food chain, twelve years from diagnosis to the end of the discharge, and a treaty named for the town that paid for the knowledge.