Air pollution: The time has arrived for the medical profession to take ownership of the problem and act
Air pollution: The time has arrived for the medical profession to take ownership of the problem and act
复制标题
DOI：
10.1111/resp.13690
复制
发表时间：
2019-09
期刊：
影响因子：
6.9
通讯作者：
S. Holgate
中科院分区：
文献类型：
--
作者：
S. Holgate
你看不见它，闻不到它，但在世界上大多数地方，“现代”空气污染是对公众健康的最大威胁。在过去的5年里，全球室外空气污染增长了8%，全球数十亿人暴露在危险的空气中。室外空气污染每年造成300万至450万人死亡，超过疟疾和人类免疫缺陷病毒/获得性免疫缺陷综合症（艾滋病毒/艾滋病），现在是世界上最大的单一杀手。到2050年，随着城市人口的增加和汽车数量接近20亿辆，这一数字预计将翻一番。与上个世纪与燃煤有关的污染相比，今天的空气污染是不同的。现代的空气污染物不是黑碳，它往往聚集成大颗粒，因此是可见的，也不是二氧化硫，它有自己独特的气味和味道，现代的空气污染物包括质量中值直径为2.5 μm（PM2.5）的较小颗粒，大量的颗粒在纳米尺寸范围内（超细颗粒（PM0.1或更小））。二氧化硫已被氮氧化物（NOx，最常测量为二氧化氮（NO2））取代。古代和现代空气污染的区别在于其来源--前者是煤炭污染，后者是交通污染。当然，在中国和澳大利亚等近年来燃煤发电迅速增加的国家，这两种污染并存。由于大气化学形成的二次空气污染物颗粒，包括来自农业的氨与氮氧化物和大气中的二氧化硫（如果存在）反应，使情况变得更加复杂。这种小颗粒的关键特征是，它们的行为几乎像气体一样，可以自由地穿过生物膜，如肺和嗅板，成为系统分散的，并找到进入细胞的方式，在那里它们破坏正常的细胞功能。超微粒子的另一个特性是它们的表面积很大，随着粒子直径的减小，表面积与粒子数量成比例地大大增加。由于这些颗粒在其基质中含有许多不同的有毒化学物质，并粘附在其表面，当它们进入人体时，它们就像“特洛伊木马”。虽然我们目前将所有颗粒物，无论其来源如何，都视为同样有毒，但情况显然并非如此。柴油发动机排气颗粒物的毒性得分最高，其次是汽油发动机排气颗粒物、生物质燃烧颗粒物、燃煤颗粒物和道路灰尘（包括刹车和轮胎磨损），这表明交通在增强细颗粒物的毒性效应方面发挥着最关键的作用。在这种情况下，似乎不寻常的是，几乎没有什么是已知的相对毒性的初级与二级PM。西班牙的一项研究表明，与二次颗粒物（PM）相比，短期接触初级PM对每日死亡率的影响更大。然而，在中国等国家，光化学反应导致二次PM中产生高羟基自由基，二次PM的毒性变得越来越重要。生物质燃烧现在被认为是低收入和中等收入国家、印度次大陆农村地区以及巴基斯坦和孟加拉国空气污染的主要原因，也是东南亚和亚马逊盆地森林火灾的主要原因。森林火灾和苔原燃烧是一个日益严重的问题，气候变化加剧了这一问题，因为大多数空气污染都是通过排放温室气体造成的。考虑到所有这些，在地球北方纬度的大片地区，令人担忧的大量强烈野火正在燃烧，这可能就不足为奇了。在2019年6月和7月，哥白尼大气监测服务已经跟踪了北极地区100多场激烈和长期的野火。仅在6月，这些火灾就向大气中排放了50公吨二氧化碳，更不用说前所未有的颗粒物了-相当于瑞典的年排放总量，超过了2010年至2018年同月北极火灾排放量的总和。反对者常说，今天的空气污染远没有上世纪那么严重。当然，在某种程度上，这对于悬浮颗粒和污染气体质量来说是正确的，但是工业和其他人使用的这种声明，既得利益是推动更严格的法规，很少考虑到现代空气污染不断变化的性质，它有能力成为系统性的生物可利用性，以获得大多数人体器官（图1）。污染物颗粒可以加速许多器官的老化过程，包括肺、心脏、大脑和内分泌系统，以及增加某些类型癌症的风险，如非吸烟相关的肺癌和乳腺癌，并在整个生命过程中产生累积效应，这一认识现在已经成为现实（图1）。在更小的区域范围内改善对空气污染的监测，导致全球估计增加880万人死亡（是以前认为的两倍），相当于每年比吸烟更多的死亡。然而，吸烟是可以避免的，但目前，空气污染不是。近年来，环境空气污染的焦点主要集中在死亡率上，但这掩盖了发病率和对儿童影响的巨大负担。
You cannot see it or smell it, yet in most parts of the world, ‘modern’ air pollution is the greatest threat to public health. Outdoor air pollution has grown by 8% globally in the past 5 years, with billions of people around the world now exposed to dangerous air. Outdoor air pollution causes more than 3–4.5 million deaths a year—more than malaria and human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS)—and is now the greatest single killer in the world. The toll is expected to double as urban populations increase and car numbers approach 2 billion by 2050. In contrast to the pollution related to coal burning in the last century, air pollution today is different. Rather than black carbon, which tends to aggregate in large particles and is therefore visible and sulphur dioxide, which has its own characteristic smell and taste, modern air pollution comprises smaller particles with a mass median diameter of 2.5 μm (PM2.5), with massive numbers being in the nanometre size range (ultrafine particles (PM0.1 or less)). Sulphur dioxide has been replaced by oxides of nitrogen (NOx, most frequently measured as nitrogen dioxide (NO2)). The difference between old and modern air pollution stems from its origin—coal in the former and transport in the latter. Of course, in countries such as China and Australia where coal burning to generate power has increased rapidly in recent years, both types of pollution coexist. The situation is made more complex by the formation of secondary air pollutant particles from atmospheric chemistry, including ammonia from agriculture reacting with Nox and, when present, atmospheric SO2. The key feature of such small particles is that they behave almost like a gas and can pass freely across biological membranes, such as the lung and olfactory plate, to become systemically dispersed and find their way into cells where they disrupt normal cell function. Another property of ultrafine particles is their great surface area, which—in proportion to the number of particles—increases enormously as the diameter of particles fall. Because such particles have many different toxic chemicals within their matrix and adhering to their surface, as they enter the body, they serve as ‘Trojan horses’. While we currently treat all particles irrespective of their source as being equally toxic, this is clearly not the case. The highest toxicity score has been found for particles from diesel engine exhaust, followed by gasoline engine exhaust, biomass burning particles, coal combustion particles and road dust (including brake and tyre wear), suggesting that traffic plays the most critical role in enhancing the toxic effects of fine particles. In this context, it seems extraordinary that almost nothing is known of the relative toxicities of primary versus secondary PM. One study in Spain indicates that short-term exposure to primary PM has a greater effect on daily mortality than secondary particulate matter (PM). However, in countries such as China, where photochemical reactions lead to high hydroxyl radical generation in secondary PM, the toxicity of secondary PM becomes increasingly important. Biomass burning is now recognized as the major cause of air pollution encountered in lowand middleincome countries; in rural settings in the subcontinent of India, in addition to Pakistan and Bangladesh; and forest fires in South-East Asia and the Amazon Basin. Forest fires and burning in the tundra is a rising problem exacerbated by and contributing to climate change as most air pollution is through emission of greenhouse gases. With all of this in mind, it should probably come as no surprise that a worrying number of intense wildfires have been blazing across vast stretches of the Earth’s northern latitudes. Over June and July 2019, the Copernicus Atmosphere Monitoring Service has tracked more than 100 intense and prolonged wildfires in the Arctic. In June alone, these fires emitted 50 mt of CO2 into the atmosphere, not to mention particulates at an unprecedented level—equivalent to Sweden’s total annual emissions and more than was released by Arctic fires in the same month between 2010 and 2018 put together. It is often said by the naysayers that air pollution today is not nearly as serious as it was in the last century. Of course, to some extent, this is correct in relation to the suspended particle and pollutant gas mass, but such statements used by industry and others, with a vested interest to push back tighter regulations, take little account of the changing nature of modernday air pollution, with its capacity to become systemically bioavailable to gain access to most human organs (Figure 1). The recognition that pollutant particles can accelerate the ageing process in many organs, including the lung, heart, brain and endocrine system, as well as being contributors to the increased risk of certain types of cancer such as non-smoking-related lung cancer and breast cancer, with accumulative effects across the life course, is now a reality (Figure 1). Improved monitoring of air pollution across smaller area scales has led to an estimate of 8.8 million extra deaths globally (twice as many as previously thought), amounting to greater extra deaths each year than tobacco smoking. However, smoking is avoidable, but currently, air pollution is not. Much of the focus of ambient air pollution over recent years has been on mortality, but this hides the massive burden of morbidity and effects on children.