Minamata Disease

Hazy Sunset
Originally uploaded by FreeManWalking

Here's a brief paper I did for my Ecotox class. It was an interesting topic. I took the picture of the sunset there in sasebo and I can imagine such sunsets might be enjoyed around Minamata City despite the pall of the unfortunate heavy metal poisoning discussed in the paper below.

Introduction

In April 1956 a five-year-old girl was taken to a hospital in Minamata, Japan. She had difficulty walking, speaking, and was experiencing convulsions. Within a few days other patients were being seen and by October 1956 a total of 40 patients had been diagnosed with the mysterious disorder, fourteen of whom had died. Government officials investigating the outbreak of the disease found that affected individuals were often members of the same families, all of them living around Minamata Bay who ate diets high in fish and shellfish. Since all individuals affected by the disease (and animals eating table scraps) had been eating diets heavy in fish researches initially assumed some sort of food poisoning was to blame. But by early November researches from Kumamoto University had deduced that the victims were all suffering from heavy metal poisoning.

Investigators examined the effluent from the nearby Chisso Chemical plant and found it contained many heavy metals including lead, mercury, selenium, and arsenic. To further analyze the specific pollutant causing the disease researchers took hair samples from residents of Minamata suffering from symptoms and those that were symptom-free. They found that patients being treated for the disease had mercury levels of up to 705 ppm whereas subjects with no symptoms had mercury levels around 190 ppm. The mercury levels for the general population outside the Minamata area was around four ppm.

Physiological Impacts

Methylmercury ([CH3Hg]+) such as that found in people affected by Minamata disease is a heavy metal toxin that was once produced as a byproduct of industrial processes such as chemical production as was the case with the Chisso Chemical plant. Free mercury can also be methylated in the environment. It is associated with aquatic systems where methylmercury is produced by the anaerobic organisms.

Methylmercury causes sickness in people by combining with cysteine, an amino acid which readily binds with the poison, carrying it throughout the body. It can lead to blindness, deafness, loss of motor control, and reduced mental capacity. Fetuses subjected to methylmercury poisoning can be born with mental retardation, cerebral palsy, and microcephaly (small head).

In a study published in Environmental Research in 1999, researchers surveyed residents of a town (Town A) located next to Minamata City. As a control they also surveyed residents of another small town (Town B) located on the Ariake Sea but not associated with the methylmercury poisoning around Minamata. Residents of both towns were asked about general health complaints ranging from hearing loss, to arthritis, to loss of touch sensation. Forty years after the first reports of methylmercury poisoning residents of Town A had a significantly higher complaints across all categories of factor analysis than the residents of Town B (Fukuda et al. 1999).

Legacy

Over 2200 residents of Minamata, Japan have been certified as having Minmata Disease. As 2001 1,784 of them had died. A 1973 arbitration ruling ordered Chisso Chemical Company to pay approximately $60,000 to persons certified as having Minamata disease and $66,000 to the families of people who had died from the disease. Another 10,000 have shown symptoms of methylmercury poisoning and received financial reimbursement from the Chisso Chemical Company as well. Though the discharge of heavy metals into the Yatusushiro Sea stopped years ago, the study cited above shows many people still suffer from the lingering effects of the pollution both in their bodies and in the sea which provides the fish that are the staple of their diet.

Despite the public awareness that the Minamata disaster brought to methylmercury poisoning subsequent devastating pollutions have occurred. In 1965 another outbreak of Minamata disease occurred in Niigata, Japan and has affected nearly seven hundred people to date. In the early 1970’s Iraqis ate wheat and meat from cows that had been feed grain treated with methylmercury as a preservative. Over 6,500 cases of poisoning were reported and at least 459 deaths were associated with this event known as the Basra Grain Disater.

Sources:

"Basra poison grain disaster." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 27 May. 2009. Web. 29 Jan. 2010.

"Methylmercury." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 28 Jan. 2010. Web. 29 Jan. 2010.

"Minamata disease." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 3 Jan. 2010. Web. 29 Jan. 2010.

Fukuda, Yoshiharu, Ushijima, K., Kitano, T., Sakamoto, M., Futatsuka, M., 1999. An analysis of subjective complaints in a population living in a methylmercury-polluted area. Environmental Research Sec a 81, 100-107.