MERCURY POLLUTION IN THE AMAZON BASIN, BRAZIL

- MERCURY CONTENTS OF SCALP HAIR AND HEALTH EFFECTS -

Masazumi Harada¹⁾, Junko Nakanishi²⁾, Eiichi Yasoda²⁾, Maria da Conceição N. Pinheiro³⁾, Teiichi Oikawa³⁾, Gerald de Assis Guimarães³⁾, Bernardo da Silva Gardoso³⁾

¹⁾ Department of Social Welfare Studies, Kumamoto Gakuen University, Ooe, Kumamoto 862-8680, Japan (e-mail: mharada@hi-ho.ne.jp)

²⁾ Institute of Environmental Science and Technology, Yokohama National University, Yokohama, Japan

³⁾ Nucleo de Medicina Tropical, Universidade Federal do Para, Belem, Para, Brazil

Abstract

Authors have investigated the level of Hg in scalp hair of garimpeiros and fishers in the Amazon Basin and the effects of Hg contamination on health since 1992. Symptoms caused by inorganic Hg poisoning were confirmed in the garimpeiros. In the fishers in the Tapajos Basin, the mean was as high as 10.2 - 35.9 ppm. In November 1998, clinical examination was performed in 50 subjects in whom the level of Hg in scalp hair was higher than 20 ppm. Of the 50 subjects, 3 should be diagnosed as having mild Minamata disease (M.d.) because of high levels of Hg in scalp hair and the absence of other causes. In 4 cases, the main symptom was glove and stocking type’s sensory disturbance, which may have been caused by MeHg, considering the high levels of Hg in scalp hair. In one case with cerebral palsy, congenital (fetal) M.d. was suspected, but not confirmed.

Introduction

Reports on Hg pollution in the Amazon Basin were published between 1988 and 1990 and have drawn attention ¹⁾. Authors first examined Hg contents of scalp hair of garimpeiros (gold miners) and gold brokers in 1989, and found that a large amount of Hg was used for gold refining and that high levels of Hg were accumulated in scalp hair of the garimpeiros, most of which was inorganic Hg. Based on the level of Hg in scalp hair, inorganic Hg poisoning was anticipated in the garimpeiros, and environmental pollution was also suspected^{2, 3)}.

In February 1992, authors visited places in the Amazon Basin to investigate Hg pollution and then monitored the level of Hg in scalp hair of garimpeiros and fishers in the Tapajos and Madeira Basins in the Amazon Basin 3 times before February 1994^{2, 3, 4)}. There were some people with levels higher than the temporary safety level of Hg in scalp hair (50 ppm) (Harada, M. et al.²⁾, Akagi, H. et al.^{3, 4)}). Nakanishi et al. periodically monitored the level of Hg in scalp hair in people of 3 fishing villages in the Tapajos Basin 5 times between February 1994 and February 1998, and confirmed that the level of Hg in scalp hair remained high.

To confirm the presence of chronic M.d. by long-term Hg pollution and to clarify the earliest effects of MeHg poisoning on human bodies, we performed clinicoepidemiological investigation in the 3 fishing villages where the level of Hg in scalp hair had been examined by Nakanishi et al., in collaboration with them in November 1998.

Methods and results

1. Investigation was performed by collecting scalp hair samples together with examination using a questionnaire and clinical examination to check symptoms. Based on the above investigations and results, the level of Hg in scalp hair was measured in 108 fishers in 3 fishing villages (Barreiras, Rainha, Sao Luiz do Tapajos) in the Tapajos Basin. In this investigation, the total Hg level alone was analyzed, because the percentage of MeHg contained in scalp hair had been known. The mean Hg level remained high to be 14.1 - 20.8 ppm (highest, 53.8 ppm).

2. In these 3 fishing villages, levels of Hg in scalp hair higher than 20.0 ppm were observed in 18 of the 42 subjects (42.8%) in March 1994, in 22 of the 65 subjects (33.8%) in March 1995, in 31 of the 63 subjects (49.2%) in August 1996, in 13 of the 48 subjects (27.0%) in October 1996 and in 65 of the 236 subjects (27.5%) in February 1998. Of the fishers in whom the level of Hg in scalp hair had been higher than 20.0 ppm, 50 consented to be clinically examined.

In the 50 subjects, subjective symptoms, intake of fish, malaria, drinking history, anamnesis, internal examination, sensory disturbance, ataxia, tremor, hearing (tuning fork), visual field stricture (facing method), walking and speech were examined.

3. Various subjective symptoms and neurological symptoms were observed in this group. The symptoms were numbness in 17 cases, dizziness in 12 cases, headache in 12 cases, weakness in 11 cases, arthralgia of limbs in 9 cases, dorsalgia in 7 cases, reduction of vision in 7 cases, tremor in 6 cases, dysthymla in 6 cases, reduction of hearing in 5 cases, forgetfulness in 5 cases, and slow action and clumsy of hands in 5 cases.

Objectively, sensory disturbance was observed in 16 cases. Of the 16 cases, 9 had monoplegic sensory disturbance, 7 had glove and stocking type’s sensory disturbance, and 1 had prioral sensory disturbance. Orthostatic and balancing failure was observed in 6 cases, disturbance of coordination in 5 cases, reduction of hearing in 5 cases, tremor in 4 cases, hyperreflexia in 4 cases, lateral visual field stricture in 1 case, hemiplegia in 1 case, and cerebral palsy in 1 case.

In this examination, the number of adult subjects was small, and 15 subjects were children under 10 years of age. Because neurological symptoms and subjective symptoms are limited in children with M.d., the incidence of neurological symptoms in the subjects was notably high in this region.

4. Neurological symptoms of the subjects in whom the level of Hg in the scalp hair was higher than 20 ppm were non-specific but similar symptoms are observed in M.d.^{5, 6)}. Judging from the observed combination of symptoms, the hair Hg level and the presence or absence of other diseases, Case 1, 2 and 3 should be diagnosed as having mild M.d.. The effects of MeHg was suspected in 4 cases. One case was diagnosed as having cerebral palsy, fetal M.d. was also suspected, but no confirmed.

Case 1: A 56-year-old fisherman. The level of Hg in the scalp hair measured 6 times was 41.8 - 79.0 ppm. He had eaten less than 1 kg of fish (about 500 g) every day, and had had symptoms such as numbness, reduction of manual dexterity, dropping stuff and shoulder pain for about 10 years. Glove and stocking type’s sensory disturbance, 2-point discrimination failure, tremor, oculomotor disorder, adiadokokinesis, failure in the finger-nose test, and Mann’s phenomenon positivity were observed. He was not alcoholic and had not had malaria, and worked in a garimpo for 3 months in 1960.

Case 2: An 18-year-old male fisher/farmer. Because the level of Hg in the scalp hair of his father was 21.3 ppm, he would have been examined in this investigation, but he died one month before examination. The hair Hg level of this young man was 16.0 - 27.1 ppm. He had eaten about 500 g of fish per day, and had had numbness of hands and feet, tremor and weakness for about 2 years. Glove and stocking type’s sensory disturbance, 2-point discriminaiton failure, tremor, adiadokokinesis, failure in the finger-nose test and failure in the knee-heel test were observed. Reduction of right hearing was caused by injuries. He had no drinking history.

Case 3: A 23-year-old fisherwoman. The level of Hg in the scalp hair was 30.0 - 35.6 ppm. She had eaten about 300 g of fish per day, and had recently had various symptoms such as dullness, dropping stuff, numbness, headache, reduction of vision, tinnitus, tremor and weakness. Glove and stocking type’s sensory disturbance in extremities, 2-point discrimination failure, balancing failure (Mann’s phenomenon), failure in the finger-nose test, failure in the knee-heel test, mild tremor, reduction of hearing and muscular weakness were observed. Left visual field stricture was suspected by the facing method. She was highly hypochondriacal and had no drinking history.

Discussion

A large amout of Hg has been used and disposed of in the Amazon Basin, and fish and fishers have been contaminated with Hg^{1, 7)}. It was reported in the late 1980s that Hg levels in fish and in scalp hair of fishers were high ^{1, 3, 7)}.

Because a large amount of Hg has been disposed of in the natural world, authors were concerned about changes in the level of Hg in scalp hair, and began to investigate Hg-pollution in the Amazon Basin in 1992^{2, 3, 4)}.

The level of Hg in scalp hair recorded in the Amazon Basin was clearly higher than that in the control group consisting of residents in a city, farmers and native people, and even higher than that of fishers in Shiranuikai sea area where M.d. occurred⁶⁾.

M.d. progresses according to the following stages.

Stage 1: inorganic Hg poisoning occurs orally and transcutaneously in garimpeiros who are directly exposed to Hg. The level of Hg in scalp hair is sometimes high, and most of the Hg is inorganic^{1, 2, 8)}.

Stage 2: Hg released into the environment pollutes the atmosphere, soil and water, and methylation occurs^{1, 7)}.

Stage 3: Methylated Hg is ingested by organismus such as fish and shellfish, resulting in concentration and accumulation via the food chain. The level of MeHg in fish and shellfish becomes high^{3, 4)}.

Stage 4: MeHg is accumulated in human bodies by ingestion of contaminated fish and shellfish, resulting in high levels of Hg in scalp hair, blood, urine and the umbilical cord. Of the total Hg, MeHg accounted for more than 85%^{2, 3, 4)}.

Stage 5: Minamata disease occurs^{5, 6)}.

Authors were concerned about the minimum symptoms in Stage 5. The chief purposes were to investigate Stages 1, 4 and 5.

In 1988, L. A. Martinelli et al. found that the highest level of Hg in scalp hair was higher than 241 ppm, and reported that 21 subjects with hair Hg levels higher than 50 ppm had some symptoms⁹⁾. And Label et al. in 1996, reported neurological symptoms in MeHg contaminated fishers¹⁰⁾.

In this investigation, general sensory disturbance was observed in 16 of the 50 subjects (32%) in whom the level of Hg in scalp hair had been higher than 20 ppm. Of the 16 subjects, 7 had glove and stocking type’s sensory disturbance in extremities (14%). In the subjects older than 10 years, the incidence was as high as 20%. This glove and stocking type’s sensory disturbance is sometimes observed with other diseases, but its incidence was unusually high in Minamata where MeHg pollution had occurred^{5, 6)}. Furthermore, from symptoms such as tremor, 2-point discrimination failure and mild balancing failure, the absence of other diseases found by health examination, high intake of fish, and high levels of Hg in scalp hair, symptoms were very mild but considered to be cauesd by MeHg. Although this investigation was performed only in a limited number of regions in the very large Amazon Basin, these results suggested that the health of many fishers and family members is being affected by MeHg. Therefore, authors advised people, women within childbearing years or pregnant women in particular, not to eat much fish.

References

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