Shigeru Takaoka

Signs and symptoms of methylmercury contamination in a First Nations community in Northwestern Ontario, Canada

In 1970, fish caught in the English-Wabigoon River system in northwestern Ontario, Canada, were found to be contaminated with mercury coming from a chlor-alkali plant in the province. In the 1970s, patients exhibiting some of the symptoms of the Hunter-Russell syndrome (e.g. paresthesias, visual field constriction, ataxia, impaired hearing, and speech impairment) were reported by some researchers. However attempts to diagnose the patients as suffering from methylmercury poisoning proved to be controversial. In order to research the presence of methylmercury contamination, and show that the patients, through eating contaminated fish, were suffering from methylmercury poisoning, we studied the results of subjective complaints, neurological findings, and quantitative somatosensory measurements gathered in Grassy Narrows Indian Reservation, Ontario, in March, 2010. At that time, the population of the Grassy Narrows settlement was around 900. Ninety-one residents volunteered to be examined. From them, we selected 80 people who were older than 15 years old, and divided them into two groups. Canadian Younger (CY): 36 residents who were from 16 to 45 years old. Canadian Older (CO): 44 residents who were from 46 to 76 years old. We compared them to Japanese Exposed (JE): 88 methylmercury exposed residents from the Minamata district in Japan, and Japanese Control (JC): 164 control residents from non-polluted areas in Japan. Complaints and abnormal neurological findings were more prevalent and quantitative sensory measurements were worse in the two Canadian groups and the Japanese Exposed group than in the Japanese Control group. Complaints, neurological findings and quantitative sensory measurements were similar in Canadian Older and Japanese Exposed. The results for Canadian Younger fell between those of Canadian Older and Japanese Control. These findings indicate that the clinical signs and symptoms of the residents of Grassy Narrows are almost the same as those recorded for Minamata disease in Japan.

Survey of the Extent of the Persisting Effects of Methylmercury Pollution on the Inhabitants around the Shiranui Sea, Japan

In 1956 methylmercury poisoning, known as Minamata disease, was discovered among the inhabitants around the Shiranui Sea, Kyushu, Japan. Although about five hundred thousand people living in the area had supposedly been exposed to methylmercury, administrative agencies and research institutes had not performed any subsequent large scale, continuous health examination, so the actual extent of the negative health effects was not clearly documented. In 2009, we performed health surveys in order to examine residents in the polluted area and to research the extent of the polluted area and period of pollution. We analyzed data collected on 973 people (age = 62.3 ± 11.7) who had lived in the polluted area and had eaten the fish there and a control group, consisting of 142 persons (age = 62.0 ± 10.5), most of whom had not lived in the polluted area. Symptoms and neurological signs were statistically more prevalent in the four groups than in the control group and were more prevalent and severe in those who had eaten most fish. The patterns of positive findings of symptoms and neurological findings in the four groups were similar. Our data indicates that Minamata disease had spread outside of the central area and could still be observed recently, almost 50 years after the Chisso Company’s factory had halted the dumping of mercury polluted waste water back in 1968.

Accelerated functional losses in ageing congenital Minamata disease patients

Severe methylmercury poisoning occurred in Minamata and neighboring communities in Japan during the 1950s and 1960s. A considerable number of children were born with conditions resembling cerebral palsy, later known as congenital Minamata disease. Although surviving patients are now in their 50s or 60s, few assessments of functional capacities in daily living have been performed. We assessed the changes in Activities of Daily Living (ADL) status of 11 patients over a 10-year period. For assessment of ADL, we applied the Barthel Index (BI) and the Functional Independence Measure (FIM). We obtained the patients current and previous status information by interview of their caregivers or from medical records and then compared them using the Wilcoxon signed-rank test. Both ADL measures, including the status related with cognition, had significantly declined during the 10u202fyears. The same was true for the overall BI score (pu202f=u202f0.01). Similarly, all functions of the FIM scores declined (i.e., self-care, sphincter control, mobility, locomotion, communication, and social cognition), and for FIM physical and cognition subscores as well as FIM total score, the declines were statistically significant. The present study indicates that the ADL status of congenital Minamata disease patients, now in their 50s or 60s, has substantially declined during the last 10u202fyears; a decline that was much steeper in comparison with expectation in subjects of similar ages, but in agreement with accelerated ageing also reported in subjects with cerebral palsy, past polio infection, or epilepsy. While already incapacitated due to the prenatal methylmercury poisoning, their accelerated ageing may suggest that patients with developmental neurotoxicity have less reserve capacity to compensate for normal ageing. These patients will need continuous and increasing medical and welfare support in the community.