By Sara Procacci
Heavy metal poisoning due to unsound environmental practices has been an issue for decades, increasingly a symptom of technological and scientific advancement. For example, in Minamata, a small city of southern Japan, toxic waste from a chemical plant starting in the 1950’s gave rise to a neurological disease which killed 1043 people by 1995.1 Similarly, though the health impacts of cobalt poisoning due to unsafe mining practices in the Democratic Republic of Congo (DRC) have not been studied extensively, urine analyses on exposed populations showed the highest ever recorded concentrations of cobalt, and evidence has been found of harmful genetic effects.2,3 Both cases highlight how neglecting the effects of industrial processes on environmental integrity can impact human health on a large scale.
Starting in the 1950s, and continuing through to 1968, a chemical factory belonging to Chisso Corporation, a Japanese chemical manufacturing company, released toxic effluents into Minamata Bay, causing severe heavy metal poisoning.1These effluents contained methylmercury, an extremely toxic by-product of the production of acetaldehyde using a mercury catalyst.4 The factory’s improper waste disposal systems caused the accumulation of methylmercury in the waters of Minamata Bay, and the consumption of contaminated fish lead to human poisoning.5 Hair sample surveys taken in 1960 from fishermen of the Shiranui Sea, which Minamata Bay is part of, showed median mercury concentrations ten times higher than controls (21.5 ppm vs 2.1 ppm).6 This evidenced the extent of methylmercury pollution, and increased the concerns associated with widespread heavy metal poisoning.
The first case of Minamata Disease (MD), the neurodegenerative condition that resulted from the ingestion and assimilation of methylmercury, was reported in 1956, though cases were misdiagnosed as early as 1953. MD is a disease caused by damage to neurons of the central nervous system, resulting in poor coordination, impaired vision and hearing, dysarthria, and tremor. MD also affects the peripheral nervous system, causing numbness and sensory disturbances.4 The regions of the brain affected include the motor cortex, and the occipital and temporal lobes (the visual and auditory centres of the brain).5 Chronic and acute forms of the disease may arise due to prolonged exposure and accumulation of methylmercury in the body, causing cerebral lesions and damage to nerves of the peripheral nervous system. 5,7 Congenital patients with MD can be born with cerebral palsy and often suffer the most severe symptoms as a result of in-utero poisoning through the placenta, such as retardation, ataxia, hyperkinesia, and limb deformity.7
Even though much research had been done into the causes and prevalence of MD, Chisso Corp. still vehemently denied polluting Minamata Bay; in 1959, they even halted further research into the effluents released by their industrial processes.4 A water purification system installed in the same year proved ineffective at filtering out harmful compounds, and in 1962, further evidence of methylmercury compounds were found in their wastewater.6
Lacking regulation and control in the industrial chemical sector led to a similar instance of mercury poisoning in Niigata, a larger city in central Japan, and further manifestations of MD; this finally prompted the construction of a closed waste water system which efficiently filtered out methylmercury.5 In 1968, by the time the government acknowledged the cases of methylmercury poisoning were due to the acetaldehyde plants, mercury had been phased out due to newer technology.4 More affirmative government action earlier on could doubtlessly have spared the lives of many and been more efficient in combating further environmental contamination. Though acute cases declined after the end of the polluting period, chronic cases increased with time.1
Recently heavy metal poisoning in DRC has become of relevance due to the importance of cobalt mines, and their unsafe working conditions for artisanal miners. Cobalt is an increasingly important element, due to its use in the manufacture of electric batteries for electronics and cars, and DRC supplies 60% of worldwide cobalt.2 However, the unsustainable practices of many of these cobalt mines and large metal furnaces for processing are causing environmental contamination. The contamination of surrounding rivers not only wreaks havoc on local ecosystems but is also incredibly harmful for the residents who rely on them as water and food sources. A study by Banze et al. shows the cobalt accumulation indexes for two affected rivers ranging from heavily to extremely polluted, with the amount of cobalt in the waters classified as extremely severe enrichment.8
Insufficient protection regularly exposes artisanal miners, including child labourers, to toxic levels of trace metals.8 Cobalt levels in blood and urine samples were 5 times higher in adults and 9 times higher in children living in contaminated areas compared to controls; in mineworkers it was 11 times higher.High levels of cobalt have been cited as being harmful to several vital organs, such as the heart, lungs, blood, and thyroid.9 Several papers point to the genetic and epigenetic changes such poisoning can cause. A study by Brusselen et al. showed that paternal occupation in cobalt mines is associated with birth defects, and congenital malformations occur in a higher frequency in areas closer to industrial mines and smelters. The former has been explained possibly due to mutations or epigenetic changes at the spermatozoid levels.8 An analysis of urine samples from children living close to mining areas found increased levels of 8OHdG, a biomarker for oxidative DNA damage; increased oxidative DNA damage could result in mutations and subsequent cancers.6,10
The cases of widespread heavy metal poisoning historically in Minamata, Japan, and currently in DRC highlight how the furthering of technology and economy may come at the cost of public health, especially when the latter is not prioritised. While in Minamata in the 1950-60s a lack of governmental interference failed in what was preventable and incredibly harmful pollution, a lack of regulation and legislation today in DRC is leading to the poisoning of artisanal miners and people who live near highly polluting mining sites. These instances reveal a critical intersection between environmental pollution and public health; going forward, it is essential to respect the environment to prevent similar threats on public health.
1. Harada, Masazumi. Minamata Disease: Methylmercury Poisoning in Japan Caused by Environmental Pollution. Critical Reviews in Toxicology. 1995; 25(1):1–24.
2. Banza Lubaba Nkulu C, Casas L, Haufroid V, De Putter T, Saenen ND, Kayembe-Kitenge T, et al. Sustainability of artisanal mining of cobalt in DR Congo. Nat Sustain. 2018;1(9):495–504.
3. Brusselen DV, Kayembe-Kitenge T, Mbuyi-Musanzayi S, Kasole TL, Ngombe LK, Obadia PM, et al. Metal mining and birth defects: a case-control study in Lubumbashi, Democratic Republic of the Congo. Lancet Planet Health. 2020;4(4):e158–67.
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8. Banze wa Mutombo A, Atibu EK, Mbuya wa Mutombo J, Kalonda EM, Bakatula EN, Kanda VN, et al. Contamination by heavy metals from mining activities: An ecological impact assessment of Mura and Kimpulande Rivers, Democratic Republic of the Congo. Watershed Ecol Environ. 2022;4:148–57.
9. Banza CLN, Nawrot TS, Haufroid V, Decrée S, De Putter T, Smolders E, et al. High human exposure to cobalt and other metals in Katanga, a mining area of the Democratic Republic of Congo. Environmental Research. 2009;109(6):745–52.
10. Valavanidis A, Vlachogianni T, Fiotakis C. 8-hydroxy-2′ -deoxyguanosine (8-OHdG): A Critical Biomarker of Oxidative Stress and Carcinogenesis. J Environ Sci Health Part C. 2009;27(2):120–39
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