<論説>鉛に曝されたこころ --近代イギリスにおける鉛製水道管の健康被害をめぐって-- (特集 : 病)

Abstract

一九世紀以降の西洋世界において、大気や土壌への放出量の増加、鉛を取り扱う労働現場の増加、食品加工時の鉛の利用、水道管への鉛の使用など、人は鉛への暴露の機会を大きく増やした。その結果生じる健康被害については、職業病や環境問題をあつかった諸研究で論じられてきた。また近年、社会経済史家W・トロスケンが、近現代の合衆国東岸やイングランド北部において水道水による鉛中毒が深刻だったことを論じている。一方、二〇世紀後半以降の医学研究は、低量の鉛暴露によって神経の発達や精神疾患への罹患リスクが高まることを主張してきた。本稿は、こうした諸研究をもとに、イングランド北部の西ヨークシャー、特にシェフィールドに絞って、精神疾患を中心とした健康被害の実態を検討し、同地域における深刻な鉛暴露の実態を明らかにした。ただし、人口統計や病院史料に基づく量的な分析においては、鉛暴露による健康被害は明確には認められなかった。

This paper aims to explore an environmental aspect to mental disease in modern England, paying particular attention to lead exposure through the water supply. People living in Western Europe were increasingly exposed to chemical materials to a great extent both in workplaces and at homes particularly after industrialization. Among them, lead, a poisonous heavy metal, has been widely employed from water pipes and cisterns, soldered cans, to colouring for ceramics and toys. Lead thus pervaded the lives of modern humans in numerous ways. However, lead could seriously affect human health, causing damage to nerves, blood cells, the liver, kidney and reproductive organs. If severely exposed to lead, human beings show symptoms such as anemia, abdominal pain, constipation, paralysis and mental depression and delusions, sometimes resulting in death. Even a small amount of lead exposure, such as 0.1 mg/Lin blood or 0.01 mg/Lin drinking water, would increase the risk of delays in nervous and intellectual development, of learning disabilities and of schizophrenia, as reported by medical reports published in the latter part of the twentieth century. Historians of the environment, occupational diseases, water supply and public health have referred to lead exposure, but most of them described it as a minor and temporal environmental problem that had been overcome in the past. This historical perspective was questioned by Werner Troesken, an American socio-economic historian. He argued in his seminal book The Great Lead Water Pipe Disaster published in 2006 that in modern Britain and the United States, lead exposure through leaden water pipes caused more serious health damage than had been thought, and its extent was particularly lethal in Massachusetts and northern England. As Erik Millstone, a well-known researcher of social policy in England, revealed, such serious lead exposure has continued in the British Isles. Meanwhile from the 1970s to 2010s, medical researchers paid more attention to the relationship between lead exposure and mental diseases. A particularly important study showed that prenatal exposure to lead, even at modest levels, would increase the risk of schizophrenia 1. 8 times. This finding remained outside the attention of historians, except David Healy, an eminent British psychiatrist and a historian of psychiatry. In his 2014 paper, Healy proposed historians shift their attention to environmental issues. Following Healy's suggestion, this paper attempts to study health damage caused by lead exposure, and the relationship between lead exposure and mental disease, in northern England, especially in the West Riding of Yorkshire (currently West Yorkshire), and its major city Sheffield between the early nineteenth century and the early twentieth century. The West Riding of Yorkshire has been known as an area in which lead poisoning spread significantly, and Sheffield was the heart of lead poisoning in the late nineteenth century. Historians have barely studied these events, nor examined the actual extent of lead exposure and its health effects. What was the extent of lead exposure through the water supply in nineteenth century Britain? How did people living in the West Riding of Yorkshire and Sheffield experience lead exposure? How serious was the lead exposure? Armed with these questions, this paper first inquires into the general history of lead exposure in Britain from ancient times to current times, and secondly introduces medical and psychiatric studies of lead exposure and its relation to mental diseases developed particularly after the late nineteenth century. It then refers to the history of water supply in England, including the popularization of leaden water pipes and its sub-effects on human health and focuses on local experiences in the West Riding of Yorkshire and Sheffield. Employing both qualitative documents (local newspapers and administrative reports) and a series of quantitative documents (Census and various statistics produced by the Registrar-General's Office, local governments and local mental hospitals), this paper concludes that on one hand people experienced serious, sometimes lethal, lead exposure through the water supply in the West Riding of Yorkshire and Sheffield in the late nineteenth century, and, on the other hand, that such serious exposure shows no clear correlation to the occurrence of mental diseases. This curious finding should lead us to a further research in the future because it suggests other factors are linked to mental disease. They would probably be poverty, living and working conditions, or nutrition, all of which seem to be related to modern ways of living.