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低濃度の鉛でも長期間暴露で心血管疾患と関連か：海外専門家コメント

シンシナティ大、カナダ・サイモンフレーザー大などの研究グループは、アメリカに住む現在44歳以上の約14,000名を対象にした過去20年に渡るデータを元に、水道管や塗料、有鉛ガソリンからの微量の鉛に長期間暴露したことで心血管疾患による死亡者数がどの程度増えていたか見積もる研究成果を発表しました。分析では、比較的若く心血管疾患で死亡した症例のうち28.7%が鉛への暴露によるものだとしています。著者らは、今回の調査対象はまだ鉛の規制がそれほど厳しくない時期に若年期を過ごした世代であり、今日の状況とは異なるとコメントしています。論文は3月12日付のThe Lancet Public Health に掲載。この件についての海外専門家コメント（原文）をお送りします。

論文リンク（抜粋）

The Lancet Public Health

Historical lead exposure may be linked to 256000 premature deaths from cardiovascular disease in adults the USA each year

https://www.thelancet.com/journals/lanpub/article/PIIS2468-2667(18)30025-2/fulltext

Dr Paul Harvey

Postdoctoral Researcher at Macquarie University

原文 

"The current research detailing lead exposure as a risk factor for cardiovascular diseases brings once again into the research and public realm, the notion that there is no safe level of lead exposure.

 

Although the study was conducted in the USA, this work has implications in Australia where we often see lead exposures in a number of inner city areas, for example in Sydney and Melbourne, as well as in mining communities and also nationally through drinking water fixtures and fittings.

 

While the data and evidence is strong in the USA for a link between lead exposure and cardiovascular disease, there would need to be a similar study conducted in Australia to determine the extent of the association and correlation of lead exposure and cardiovascular disease here. This is due to the slightly different exposures pathways, population demographic, health care and lifestyle habits in Australia as compared to the USA."

Stuart Khan

Professor of Civil & Environmental Engineering at the University of New South Wales (UNSW). His expertise include the detection and management of trace chemical contaminants in drinking water

原文

“In decades past, drinking water was seen to be a comparatively minor source of exposure to lead for most people in Australia. That’s because there were other much more significant sources including leaded petrol and paints. However, since lead has been largely phased out for those uses, exposure through drinking water may be much more significant than it was. With the focus now on low-level exposure, I think the onus will increasingly be on Australian drinking water quality managers to ensure that safe levels are not exceeded.

 

The city of Flint, Michigan in the USA has been dealing with a major water quality crisis regarding lead contamination since 2014. This crisis has reminded Australian water quality managers that lead is a contaminant, which we cannot afford to become complacent about. The Australian water industry has long recognised lead as an important water quality contaminant, but in many water supplies it requires constant vigilance to control. 

 

Although lead can enter drinking water from contaminated supplies, a more common problem involves lead being leached from pipes and other plumbing materials. This is particularly common where poor procedures have been used for welding and soldering. Household tap fittings, such as some water filters, can also contain lead-based components, which can leach lead into the water. Australian cities have a very wide variety of materials, which have been used for drinking water supply pipes and plumbing. As a result, we can expect that low levels of lead will continue to be detected in some Australian drinking water samples from time to time. 

 

Experiences with the commissioning of the water supply system for the new Perth Children’s Hospital reinforce just how difficult lead can be to manage in some systems. In that case, the construction company spent more than a year trying understand and resolve the lead contamination that was being measured in the hospital drinking water. Many techniques, including flushing the pipes, we tried to reduce the contamination, but were mostly unsuccessful. That issue is still not fully resolved.

 

Lead contamination in school plumbing systems is also something I believe we should be paying closer attention to. I think this is of particular concern when the students come back to school after a long summer break. Under those circumstances, there is potential for water to have sat stagnating, with warm summer temperatures, in the school plumbing system. These are ideal conditions for lead to be leached from the pipes to the drinking water. Such a scenario is all the more significant when we consider that many of the risks around which lead exposure is controlled are considered to be greatest for children, compared to adults. In my opinion, state governments should mandate that all schools develop water quality management plans and ensure that such plans are effectively implemented.”

Dr Ian Musgrave

Senior Lecturer in the Discipline of Pharmacology at the University of Adelaide

原文 

Lead is a well known persistent environmental toxin. While most Australians would be aware of chronic exposure to lead's effects on brain development and behaviour in children, fewer will be aware that long-term exposure to relatively low levels of lead increases blood pressure and the risk of heart and blood vessel disease.

 

This new paper in The Lancet “Low-level lead exposure and mortality in US adults: a population-based cohort study” extends our knowledge of the kinds of lead levels that increase risk, and the degree to which the risk is increased.

 

The study looked at a representative sample of the adult US population. After measurement of blood lead and other baseline health measures, the subjects were followed for 17-22 years. Blood pressure and other health information, as well as causes of death, were followed over this time.

 

The study's strength is that it was able to follow a defined population over a sufficiently long time. However, the study only measured blood lead once, at the beginning of the study, and although they tried to correct for other causes of heart disease such as smoking and obesity, they may not have been able to correct all for possible contributory causes of death and so may overestimate the risk due to lead. In this study subjects with the highest levels of blood lead had a 37 per cent greater risk of premature death from any cause and a 70 per cent greater risk of death from heart disease.

 

The study suggested that almost one-third of deaths due to heart disease was attributable to lead exposure. This estimate is about ten times higher than previous estimates, but the careful measurement of blood lead and the long-term followup make this estimate plausible.

 

The other main finding is that lead levels generally considered to have minimal health impact were associated with higher death from heart disease. This suggests that lead has a larger public health impact than previously recognised. Even if the risks found in this study are an overestimate.

 

Most of the focus on lead in Australia has been in towns near lead mining and smelting facilities, where public health approaches may need to be reevaluated in the light of these findings. However, urban settings may also be impacted. While lead petrol was phased out in the 1970s, as was lead paint, recent studies show that some urban areas in Sydney and Melbourne have high soil lead levels, exceeding the Australian regulatory guideline of 300 mg/kg.

 

This could potentially lead to exposures that will have adverse effects on heart health. Again, public health approaches may need to be re-evaluated in urban areas in the light of these findings.

Ivan Kempson

Associate Professor of Biophysics and a Foundation Fellow at the Future Industries Institute, University of South Australia

原文

The data are cause for concern. Many toxic effects of lead have been known for decades but it is only with studies, such as this, of increasing rigour, that the longer term effects and more subtle effects are being identified.

 

Research, especially over the past decade, have been indicating that the acceptable degree of exposure to lead is progressively less and less.

 

This latest study drives home the long term impact that lead exposure, even below previously accepted levels, has significant impact on public health.

 

Australia has had a long history of lead mining and smelting which supports many of our technological advances. Lead pollution in various centres around Australia are well known. There have been many excellent initiatives from councils, governments and industries to reduce lead pollution and conduct remediation.

 

The data from this study show that past initiatives to reduce lead exposure in Australia will have significant benefit for current and future generations of Australians in terms of health and well-being.

 

However, this new insight into the impact of low lead level exposure should direct more efforts into the remediation of polluted sites around Australia and reduce our current definition of what is considered safe.

Professor Mark Patrick Taylor

Macquarie University

原文 

This new study confirms earlier, emerging views that lead is a significant contributor to heart disease in exposed populations. There is no reason to assume that Australia has been immune to the consequences of lead exposure as detailed in the new Lancet study.

 

In Australia, we released more than 240,000 tonnes of lead from petrol over its 70 years of use in motor vehicles, causing elevated blood lead levels, particularly in major cities.

 

Other recent research has confirmed that previously elevated lead-in-air exposures were associated detrimental outcomes and anti-social behaviours, including increased rates of aggressive crime and death by assault.

 

Blood lead levels in major cities declined rapidly following the removal of lead from petrol and are now low (i.e. typically < 2 µg/dL). However, the best available estimates indicate that up to 100,000 Australian children may have a blood lead level at some time in their first five years exceeding 5 µg/dL, the Australian guidelines for intervention.

 

Sources of lead exposure for most Australian children today are from legacy lead that have been deposited in garden soils and dusts or come from the former use of lead in paints.

 

However, some lead mining and smelting communities are still subject to significant environmental injustices due to the massive lead exposures they continue to be subjected to. The communities most exposed are Broken Hill, (NSW), Mount Isa (Qld), and Port Pirie (SA).

 

For example, recent data shows that the average lead in air in the lead smelting town of Port Pirie is the worst in Australia being some 200 times higher than that in Sydney.

 

Broken Hill lead in air levels are around 40 times higher than those in Sydney and Mount Isa lead in air levels remains elevated at approximately 20 times those in Sydney.

 

Thus, it is not surprising that the most recent data shows that approximately 50 per cent of all children under five years of age in these three communities have a blood lead level > 5 µg/dL (the upper acceptable level in Australia). Indigenous children are more greatly impacted, with approximately 70 per cent of Indigenous children in Broken Hill having a blood lead > 5 µg/dL. Similar disparities occur in Mount Isa and Port Pirie.

 

As one of the top 15 nations in terms of GDP, the Australian public should be incredulous that we have permitted such blatant injustices to be imposed upon sensitive populations (children), for which the effects will not fully bear fruit until their later years.

 

Moreover, while the lead-related decrements due to lost IQ, behavioural problems and missed life opportunities will impact those most exposed, all of society will pay via economic losses and societal costs.

Prof Kevin McConway

Emeritus Professor of Applied Statistics at The Open University

原文 

“The researchers make a very important point in their report – that it is more accurate to view this study as estimating how many deaths might have been prevented if historical exposures to lead had not occurred.

 

“In other words, they aren’t saying that current exposure to lead in the environment is the main thing here, as much of the exposure would have been in the past when regulation was much less strict than it is now.  The lead author does state, however, that action needs to continue to reduce exposure.

 

“Lead tends to stay around in the body once it has entered it, so the blood lead levels of the people in this study will have been affected by exposure to lead throughout their lives: including exposure to lead in petrol before it was banned, and exposure from lead-based paint or lead drinking water pipes when those were more common than they are now.

 

“People starting their lives in the UK or USA now will, very likely, have lower blood lead levels when they grow up than did the people in this study, because several sources of lead pollution have been reduced.  Assuming that the researchers’ statistical models are valid, numbers of cardiovascular deaths will decrease in the future because of those reductions in blood lead levels across the population.

 

“But, if lead has as strong a relationship to cardiovascular disease as these researchers describe, then changes in the level of lead in people’s blood in the past would have had major effects on numbers of deaths from cardiovascular diseases, particularly heart attacks.

 

“How much of the rise in deaths from heart disease over the past century might have been due to lead pollution, rather than all the other causes that have been put forward? Heart disease has been reducing in the UK and similar countries in recent decades; might this have more to do with reductions in lead levels than has been thought? I don’t think those questions can be answered in detail from this study alone, though the study may well lead to change in the way we understand trends in cardiovascular disease. Indeed, as the linked editorial by Landrigan points out, there may well be similar issues about several other pollutants.”

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