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译文 城市空气污染损害胎儿智商 摘要：本文探讨了孩子的智商降低与母亲接触矿物燃料燃烧产物之间的关联。该研究提供了证据显示出生前暴露于空气污染会对儿童认知发展产生不良影响。多环芳烃、铅、汞、烟草烟雾毒素,可以破坏全身多器官系统进而损害胎儿的大脑发育。 关键词：空气污染物；化石燃料燃烧；汽车尾气；多环芳烃；铅中毒 波兰克拉科夫的一项研究证实了纽约的发现，孩子的智商降低与母亲接触化石燃料的燃烧产物有关。 回溯到1999年一个闷热夏天的纽约，尤兰达鲍德温怀上她的第一个孩子已经八个月了。她住在一个加油站附近，马路对面的十字路口挤满了排着尾气的大大小小各种汽车和巴士。有时候污染的空气浓厚到她可以看得到，呼吸到，闻到，甚至尝到。她常常想她未出生的孩子可能会受到伤害。 现在鲍德温和几百个其他儿女的母亲经过参与完一个长达十年的跟踪监测后终于知道：婴儿甚至在第一次呼吸之前，母亲吸入的各种常见空气污染物就可能损害了孩子的智商。 两个城市超过400位妇女参与的一系列研究发现，5岁的孩子如果在胎儿时期接触超过平均水平的多环芳香烃即PAHs，在IQ测试中得分较低。这些化合物由化石燃料燃烧产生，在城市环境中随处可见。 在纽约市的非洲裔美国人和多米尼加社区，有249名儿童被监测环境污染对他们的影响直到11岁的时候。同时在大西洋彼岸波兰的克拉科夫，另外214个孩子也参与了平行调查。 春天在波兰发的研究与纽约的极为相似：母亲接触PAHs量高于平均值的孩子，在IQ测试中得分要比母亲接触PAHs量低于平均值的孩子低4分。 智商的差异虽然是适度的，但是专家说这足以妨碍孩子在学校的表现，甚至是终生的学习能力。这些影响与低水平的铅暴露基本相当，而铅导致儿童智力下降早已广为人。 “我们认为这是一个值得关注的发现，因为孩子的智力是预测日后学业表现的一个重要因素，”Perera Frederica，纽约市哥伦比亚儿童环境健康中心的高级科研作者及主管说。 这两个研究“为接触环境毒物可能阻碍儿童智力发展，增加注意力不足、多动症和行为障碍的风险提供了更多文献，”Bruce Lanphear说，他是英国哥伦比亚西蒙莎菲大学的儿童环境健康学教授，虽然没有参与这项研究。 胎儿暴露于污染的环境与认知发展之间的关联是一个发展中的研究领域，“越来越受关注”，哈佛医学院环境流行病学家及神经学教授David Bellinger说。 哥伦比亚大学研究的优势之一就是科学家能确切了解母亲怀孕期间接触了多少的污染。 1998年到2006年之间，该研究共招募了来自纽约和克拉科夫的鲍德温和其他462名怀孕妇女，她们携带一个装有PAHs检测仪的背包48小时。然后她们的孩子被分为高吸入量和低吸入量两组——标准是高于与低于平均值——当他们长到5岁时，他们接受了标准化的测试来衡量他们的认知能力。 “我们生活在一个到处都是污染却没有察觉的社会是令人震惊的，”鲍德温说，她现在是五个孩子的母亲。“我现在知道我们所做的可以影响我们的未来。我们吃的东西或呼吸空气时，我们所处的环境，它会影响孩子。” 在克拉科夫，大多数化合物来自家庭暖气和工厂的煤燃烧，而在纽约，汽车、卡车和公共汽车排放的尾气是主要来源。 四月在波兰发表的研究结果，支持了纽约一年前发表的数据，在世界不同地区不同生活条件的儿童智力受污染物的影响是相同的。 纽约的实验组——来自哈莱姆区，南布朗克斯区以及华盛顿高地——包括非洲裔和多米尼加裔妇女。所有的波兰妇女都是高加索人。 “我们在不同群体、不同设定、甚至是不同的接触程度下了这一发现，巩固了在纽约得到的最初发现”Perera说。“研究提供了进一步的证据胎儿在产前时期吸入的空气污染对孩子的认知能力产生不良影响。” 在克拉科夫，女性平均接触到的PAHs浓度是纽约女性接触量的8倍。（克拉科夫污染物为每立方米17.96纳克；纽约则是2.26） 一些专家说这些研究结果出现了问，因为智商损失相近而两个实验组接触的污染物水平相差八倍。 “这是令人吃惊的发现在两个实验组存在许多差异的情况下，”Jennifer Adibi说，她是加州大学旧金山分校的流行病学家，研究环境对于胎儿发育的影响。“在确定它们之间的联系之前，我们希望在其他的实验组中可以看到相同的结果。” Adibi还补充了在纽约市与克拉科夫之间许多不同的因素——例如饮食习惯，生活习惯，种族划分及其他的污染物。 “直接比较这两项有差异和不同样本数的实验组是非常困难的，”Negin Martin补充道，国家环境健康科学研究所的一项主要是研究污染物怎样对大脑发育产生影响的研究。 不过Martin认为两项研究结果相一致仍然是值得注意的；它们分别发现了“可被测试出的、在统计上有意义的IQ下降，”她说。当科学家比较了两个城市中污染接触量相似的150位妇女，IQ的差异确实被发现。 研究者们也调整了一些会影响到儿童智商而导致实验结果产生偏差的因素，例如孕妇的受教育程度和二手烟。有一个可能造成干扰的因素就是儿童幼年期的铅吸收量没有被检测。他们只在胎儿时期被检测过，胎儿时期通常不造成影响。分析这些因素是“一个非常大的挑战，并且这也是哥伦比亚的研究小组做的非常好的一点，”尽管没有参与此项研究的Bellinger说。 研究者们现在已经将几种会影响大脑发育的环境污染物联系起来了。 在早前的研究中，哥伦比亚大学的实验小组发现低智商的孩子的母亲对一种杀虫剂毒死蜱的接触量较大，这种杀虫剂过去被大量使用于日常生活中，直到2001年才被禁止家居使用。相似的结果也被发现在二手烟对胎儿影响的研究中。而且近二十年以来，科学家们在位于北大西洋的法罗群岛上，已经发现从水产品中摄入的汞一样可以损害孩子的智力。 Lanphear指出PAHs、铅、汞、烟草烟雾等都是全身性中毒毒素，可以破坏身体内的多个器官系统。 “已广为人知的空气污染物——各种各样类型毒素的混合体——与新生儿体重过轻，肺功能减弱，肺癌以及哮喘有关联。所以虽然这些研究（与儿童IQ相关的研究）是非常新奇的，但得出的结果一点也不让人惊讶，”他说。 科学家们知道许多种化学物质包括PAHs在内都可以穿过胎盘，但是他们还不了解这些物质是如何干扰胎儿发育中的大脑的。 大脑形成中有些敏感的过程，Bellinger说，在这里有很多东西可能出现问题。 “很多东西都快速的变化着，它们应该以一个特定的方式以一个特定的顺序发生，”他说。“构造大脑几乎就像编排好的舞蹈的结果，”这段舞蹈由几百个“演员”组成，每个都按照化学信号的指令。污染物会产生“噪音”干扰这个过程，就像静电干扰一个电台一样。 而且，PAHs可能会直接影响胎儿的DNA。当一个母亲吸入了PAHs，这些化学物质能被转化成副产物随着血液的流动，穿过胎盘的边界直接与胎儿的DNA结合，Susan Edwards解释道，伦敦帝国理工大学的研究生，在波兰研究的的第一作者。 在纽约和克拉科夫与空气污染相联系的四个百分点的IQ损失是相当微妙的；父母与老师不太会注意到它，因为大多数孩子会下跌是在正常范围内。 虽然如此，“三四个百分点的IQ损失是重要的吗？当然重要，”Lanphear说道，他的研究主要集中在铅暴露和儿童的神经发育。 他说了一个最近的分析发现，每投资一美元在减少铅污染上，社会就能实现17至220美元的收益。“大多数收益来源于通过提高儿童智力后他们一生收入的提高，”Lanphear说。 “有的时候，我们不应该总是责怪父母和老师因为孩子们学习和学业上的失败，而把我们的注意力集中在减少他们接触到大范围的神经毒素上，”Lanphear说。 好消息是，Perera说，纽约市的PAHs水平正在逐渐下降。通过妇女们的背包装置收集到的数据，研究者们报告说空气中污染物含量下降了超过百分之五十在1998年到2006年期间。 Bellinger说我们应当采取步骤来减少儿童接触污染物，同时注意其他一些对他们认知能力保持影响的重要因素。 “重要的一点就是虽然这些污染物接触与健康有关联，它们不是最主要的决定因素。父母怎样与他们的孩子互动，他们提供的各种鼓励，解释了更多的问题，”他说。 住在纽约华盛顿高地的30岁的已有了5个年龄从2岁到10岁孩子的Baldwin。她在1999年带上了空气检测背包，那个时候她正怀着她最大的孩子Patience已经到了晚期妊娠。 和其他参与实验的孩子一样，Patience从出生开始就被一组科学家们监测。Baldwin分娩时，一个哥伦比亚大学的研究者就在医院里来采集新生儿的脐带血进行检测。作为研究的一部分她的女儿在两岁时进行了第一次IQ测试，从那以后又参加了一系列的其他测试，包括对她大脑的一个近期CT扫描。 没有证据证明她女儿的IQ受到了PAHs的影响。Baldwin说这个小姑娘在学校表现很不错，也没有学习问题，不过她患有中度哮喘。Baldwin也不知道她怀孕期间吸入的PAHs水平是高是低。 Baldwin说由于参与了这次的研究，使她“深刻意识到”污染物和杀虫剂的风险了。当她的一个儿子还是婴儿时被诊断患有铅中毒，他显然是接触到了剥落的油漆。 但她尽量不去想这些各种各样污染物接触可能对她的孩子造成的影响在她怀孕期间。“我不喜欢去细想那些无法改变的事情，”Baldwin说。 相反，她试图是自己。她会避免经过汽车排放的尾气，不使用杀虫剂，买有机食品，关上窗户将空气污染阻挡在户外并且在家里使用空气过滤器。 “也许这项研究可能会改变我们对环境的认识，以及未来对待环境的方式，”她说。“无论是个人还是小团体我们都能期盼着这种改变。” 原文 Urban Air Pollutants Can Damage IQs before Baby's First Breath Abstract: The paper focuses on the children's lower IQ scores with mothers' exposure to compounds created by burning fossil fuels.The study provides evidence that prenatal exposure to air pollution adversely affects children’s cognitive development.PAHs, lead, mercury, tobacco smoke are systemic poisons that can damage multiple organ systems that can damage a fetus’ developing brain. Key words: Air pollutants；Fossil fuel burning；automobile exhaust；PAHs；lead poisoning A study in Krakow, Poland, corroborates New York City findings that link children's lower IQ scores with mothers' exposure to compounds created by burning fossil fuels. In a sweltering summer in New York City back in 1999, Yolanda Baldwin was eight months pregnant with her first child. She lived near a gas station and across the street from an intersection choked with exhaust-spewing cars and buses. Sometimes the air was so thick with pollution that she could see it, breathe it, smell it, even taste it. And she often wondered what it might be doing to her unborn child. Now Baldwin and several hundred other mothers whose sons and daughters have been monitored for a decade have an answer: Before children even take their first breath, common air pollutants breathed by their mothers during pregnancy may reduce their intelligence. A pair of studies involving more than 400 women in two cities has found that 5-year-olds exposed in the womb to above-average levels of polycyclic aromatic hydrocarbons, or PAHs, score lower on IQ tests. The compounds, created by the burning of fossil fuels, are ubiquitous in urban environments. In African American and Dominican communities of New York City, 249 children are being monitored for the effects of environmental contaminants until the age of 11. And across the Atlantic, in Krakow, Poland, another 214 children are participating in a parallel study. The findings in Poland, reported this spring, are strikingly similar to New York City’s: The children whose mothers had above-average exposure to PAHs scored about four points lower on IQ tests than children whose mothers had below-average exposure. The difference in IQs is modest, but experts say it is enough to hamper school performance and perhaps lifelong learning. It is about the same deficit linked to low-level exposure to lead, a well-documented cause of reduced IQs in children. “We think that this is a finding of concern because child intelligence is one of the predictors of how well a child will do in the academic setting later on,” said Frederica Perera, the senior author of the studies and director of Columbia Center for Children’s Environmental Health in New York City. The pair of studies “adds to a growing literature implicating exposures to environmental toxicants with stunting of children's intellectual abilities and increased risk for attention deficit hyperactivity disorder and conduct disorders,” said Bruce Lanphear, professor of children’s environmental health at British Columbia’s Simon Fraser University. He was not involved in the research. The link between prenatal exposure to pollutants and cognitive development is a growing area of concern “that's been getting a lot more attention,” said David Bellinger, an environmental epidemiologist and professor of neurology at Harvard Medical School. One strength of the Columbia University research is that the scientists know precisely how much pollution the mothers were exposed to during a brief period of their pregnancy. Recruited for the study between 1998 and 2006, Baldwin and the other 462 pregnant women in New York City and Krakow carried backpacks for 48 hours that contained equipment for measuring PAHs. Then their children were divided into high and low exposure groups – those above the median and below –and when they reached the age of five, they underwent standardized tests to measure their cognitive skills. “It’s scary and alarming that we can live in a society where these things are happening and they go unnoticed,” said Baldwin, now the mother of five children. “I know now that what we do can affect us in the future. The things we eat or breathe in, our environment, it does affect the children. In Krakow, most of the compounds come from coal burning for home heating and factories, while in New York City, exhaust from cars, trucks and buses is the major source. The results in Poland, published in April, bolster the New York City findings, which were published a year ago, because they found the same effect on IQs of children living in different conditions, in different parts of the world. While the New York City group – from Harlem, the South Bronx and Washington Heights included only African-American and Dominican women, all the women in Poland were Caucasian. “We’re confirming a finding in a different population, a different setting, even a different gradient of exposure, and that reinforces the initial finding in New York,” Perera said. “The study provides further evidence that prenatal exposure to air pollution adversely affects children’s cognitive development.” In Krakow, the women on average were exposed to eight times higher concentrations of PAHs than the women in New York City. (In Krakow, 17.96 nanograms per cubic meter; in New York City, 2.26) Some experts say the findings raise questions because the IQ losses were similar in the two groups despite the eightfold difference in their average level of exposure. “It is a striking finding given the many differences in the two cohorts,” said Jennifer Adibi, an epidemiologist at University of California, San Francisco who studies how environmental exposures affect fetal development. “We would want to see this association replicated in other cohorts before we attribute a causal relationship to it.” Adibi added that many factors are different in New York City and Krakow - such as diet, lifestyle, ethnicity and other contaminants. “Direct comparison between the two studies, given their differences and the sample sizes, is extremely difficult,” added Negin Martin, a research fellow at the National Institute of Environmental Health Sciences who studies how pollutants affect brain development. Nevertheless, Martin said it is notable that the studies were consistent; they each found “a measurable and statistically significant decrease in IQ,” she said. When the scientists compared only the 150 women who had similar exposures in the two cities, IQ differences were still found. The researchers also adjusted their data to consider some factors that could influence a child’s intelligence and skew the results, such as maternal education and second-hand smoke. One possible confounding factor, however, is that the children were not tested for lead exposure when they were toddlers. They were checked only for prenatal exposure, which is normally less of a problem. Accounting for such factors is “a pretty big challenge, and it's one that Columbia's group does very well,” said Bellinger, who was not involved in the study. Researchers have now linked several environmental contaminants to effects on developing brains. In earlier work, the Columbia University team found lower IQs in children whose pregnant mothers were exposed to high levels of a pesticide, chloropyrifos, which was widely used in households until it was banned for residential use in 2001. Similar results were reported in children with prenatal exposure to secondhand smoke. And for more than two decades, scientists in the Faroe Islands, in the North Atlantic, have reported reduced IQs in children exposed in the womb to mercury in seafood. Lanphear said PAHs, lead, mercury, tobacco smoke are systemic poisons that can damage multiple organ systems. “It is well known that airborne pollutants – a soup of various types of toxicants – are associated with low birth weight, diminished lung function, lung cancer and asthma. So while these studies [of children’s IQ] are novel, the results shouldn't surprise us,” he said. Scientists know that many chemicals including PAHs can cross the placenta, but they don’t understand how they may interfere with a fetus’ developing brain. In the sensitive process of brain development, Bellinger said, there are a lot of things that can go wrong. “Things are changing very rapidly and they're supposed to happen in a particular way, in a particular sequence,” he said. “It's almost like a choreography of events that go into building a brain.” This choreography is made up of hundreds of “performers,” each taking instructions from chemical signals. Pollutants introduce noise to this process, like static over a radio station. Also, PAHs may affect the fetus’ DNA directly. When a mother breathes in PAHs, those chemicals are changed into byproducts in the bloodstream that can cross the placental boundary and bind directly to a fetus’ DNA, explained Susan Edwards, a graduate student at the Imperial College in London, and the lead author on the Poland study. The four-point drop in IQs linked to the air pollutants in New York City and Krakow is fairly subtle; parents and teachers wouldn’t notice it because most children would fall within normal ranges. Nevertheless, “is a three or point IQ-point decrement important? You bet,” said Lanphear, whose research has focused on lead exposure and children’s neurodevelopment. He said one recent analysis found that for every dollar invested in reducing lead exposure, society would realize a $17 to $220 benefit. “The bulk of the benefit was from increased lifetime earnings by enhancing children's intellectual abilities,” he said. “At some point, we will cease blaming parents and teachers for children's failure to learn or thrive in academics and focus our attention on reducing their exposure to widespread neurotoxicants,” Lanphear said. The good news, Perera said, is that levels of PAHs are declining in New York City. Using data from the women’s backpacks, researchers reported that airborne levels dropped by more than 50 percent between 1998 and 2006. Bellinger said while steps should be taken to reduce children’s exposure to pollutants, other factors remain more important for their cognitive development. “An important point is that while these exposures are associated with health outcomes, they aren't the major determinants. How parents interact with their children, and the kinds of stimulation they provide, explains a lot more,” he said. Living in New York City’s Washington Heights, Baldwin, 30, now has five children between the ages of 10 and two. She wore the air-monitoring backpack in 1999 when she was in the third trimester of her pregnancy with her oldest child, Patience. Like the other children in the group, Patience has been monitored by the team of scientists since she was born. When Baldwin gave birth, a Columbia University researcher was at the hospital to collect the newborn’s cord blood for testing. Her daughter had her first IQ test as part of the study when she was two and has undergone an array of other tests since then, including a recent CT scan of her brain. There is no evidence that the PAHs affected her daughter’s IQ. Baldwin said the girl has thrived in school and has no learning problems, although she has moderate asthma. She does not know whether her exposure to PAHs during the pregnancy was classified as high or low. Baldwin said her role in the study has made her “hyper aware” of the risks of pollutants and pesticides. One of her sons was diagnosed with lead poisoning when he was a toddler; he apparently was exposed from peeling paint. But she tries not to think about what effects her various exposures during her pregnancies might have had on her children. “I don’t like to dwell on something I cannot change,” Baldwin said. Instead, she tries to empower herself. She avoids walking through exhaust, doesn’t use pesticides, buys organic foods, shuts her windows to keep air pollution outdoors and uses air filters in her home. “Maybe this study will potentially change the way we see the environment and treat it in the future,” she said. “Individually and in small groups we can invoke change.” This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company. 08环工吴迪 200809201134