当Jane Horton于1975年购买了她梦寐以求的800平方英尺的农舍时，她认为街对面的半导体制造厂。即使在拆除公司的建筑物之后也拆除了一个连锁连锁围栏，她仍然没有了解潜伏在她脚下的有毒危险 - 更不用说他们正在入侵她家的事实。

直到2000年代初期，霍顿和加利福尼亚州山景的其他居民，听说过三氯乙烯的地下羽毛，或TCE - 在设施中使用的癌症液体清洁硅芯片。Horton了解到，从地下水和土壤中渗透到当地建筑物中的蒸汽。当调查人员于2004年测试了家庭房屋内的空气时，他们发现TCE的浓度超过了美国环境保护局设定的特定场地阈值。这是大约75％的污染后已经清理过清理。

“我们一直在困扰着羽毛，”霍顿说，当被发现的蒸气时，他们最小的儿子仍然在小学。“我记得如此愤怒，一切都花了这么久。我想知道：我的孩子们会去癌症吗？我的孩子会死吗？我怎么样？“

A venting system that the EPA installed in her cellar now sucks toxic gases up from the soil, sending them through pipes and out a rooftop stack into the air, where they would be quickly diluted to acceptable levels. Periodic monitoring by the agency has since shown that the TCE levels at the house are safe.

“It took them about a year to get the system working right,” Horton says. “It will be in the house until the house is no longer there.”

有毒蒸气的报告普遍存在

与此同时，侵入建筑物的有毒蒸气的类似故事继续在全国各地的表面 - 从圣地亚哥附近的移动房园到明尼苏达州的地点。

牵连的污染物 - 最令人惊奇的氯化溶剂，例如TCE和四氯乙烯（称为PERC）以及苯 - 可以通过土壤和地下水从它们从泄漏或泄漏渗入地球中迁移到地下。普通来源包括干净清洁剂，加油站，汽车维修店，军事基地和工业场所，即使是几十年前的门。

While exposure to high levels of these vapors can cause immediate effects, such as irritation and fatigue, breathing small amounts over a period of time is more concerning, according to Phil Landrigan, a pediatrician and epidemiologist at the Mount Sinai School of Medicine. “Babies and small children can especially be damaged by very low concentrations of some of these materials,” he says. Long-term exposure to TCE, perc or benzene is known or suspected to raise the risk of certain cancers and other health effects, although it still remains unclear if intruding vapors reach high enough concentrations to pose a significant threat to human health.

Research also hints at a link between a woman’s exposure to TCE during the first trimester of pregnancy and fetal heart malformations — a finding that has added considerable controversy and complication in addressing vapor intrusion.

Soil bacteria readily biodegrade benzene and other hydrocarbons into relatively benign products such as water and carbon dioxide, making these contaminants a lesser concern. The breakdown of chlorinated solvents, on the other hand, can be slow and generate even more toxic byproducts. Perc, for example, breaks down into TCE, which in turn creates dichloroethene and vinyl chloride, a potent carcinogen that is particularly persistent and mobile in the environment.

The extent of the problem is unknown

专家,包括EPA官员,不能estimate the full scale of vapor intrusion. But it is likely extensive. Amy Graham, an EPA spokesperson, noted 91 existing Superfund sites where unacceptable human health risks associated with vapor intrusion triggered mitigation. Nearly 4,000 other sites are regulated under the Resource Conservation and Recovery Act, of which the EPA previously estimated a quarter likely have some vapor intrusion.

The EPA does not track the occurrence of vapor intrusion for the estimated more than 450,000 brownfields, another category of contaminated properties, in the U.S. What’s more, in 2002, the U.S. General Accounting Office suggested that 200,000 underground storage tanks then in operation were not being managed properly and so could be at elevated risk for leaking. And an estimated 75% of the more than 36,000 dry-cleaning facilities currently operating in the U.S. have discharged solvents into the environment. “As more and more sampling is done, more and more vapor intrusion is found across the country,” says Lenny Siegel, executive director for the nonprofit Center for Public Environmental Oversight.

“The thing about vapor intrusion is that people are exposed in their homes, their workplaces, their places of worship, their schools without their knowledge and against their will to dangerous chemicals,” adds Siegel. “That’s intrusion.”

有毒蒸气的运动进入建筑物，而一般在公众关注的雷达下，吸引了环境健康专家，倡导者和机构的增加的审查。EPA在2011年出版了其毒性评估时，它认为安全的TCE暴露的水平降低。2015年，EPA发布了对州和部落机构进行评估和解决蒸汽侵入的自愿指导。在今年5月，原子能机构向确定网站是否有资格获得超级资金地位的标准，增加了蒸汽侵扰。尽管如此，全国仍然存在达成共识，但如何处理该问题。

吸尘蒸气

Regulators, as well as many scientists, didn’t take much notice of vapor intrusion until the 2000s. At that time, awareness had grown about the hazards of radon, a radioactive, carcinogenic gas that comes from the natural breakdown of uranium or thorium in the ground and was found to be leaking into basements. People had begun to connect the dots.

“氡问题基本上是相同的现象，除了自然而不是人造的来源，”棕色大学超级优惠基础研究计划的联合主任Eric Suuberg解释道。

As with radon, the average person is not likely to detect vapor intrusion. “You can’t smell it, you can’t see it,” he says. “You need sophisticated instrumentation to get to the kinds of low concentrations that are involved.”

氡和人造的蒸汽都可以以与吸尘器吸入真空吸尘器的方式相同的方式进入建筑物。当空气从高压区域移动到相对低的压力时，产生吸入。因此，就像通过真空吸尘器在地板上创建的吸入一样，在小颗粒中拉动并捕获袋子或隔间内，空气运动可以通过基础中的裂缝或其他开口将有毒蒸汽吸入房屋。

“这是基础物理学，”国家环境保健研究所超级资金研究计划总监William Suk说。“气体必须去某个地方，他们会找到一种方法来上升。”

In North Canton, Ohio, an even more direct connection between vacuums and vapor intrusion has emerged. The Hoover Company began making vacuum cleaners in the town during the early 1900s. Over the following decades, manufacturing led to releases of TCE and perc.

今天，大约85英亩（34公顷）胡佛地点的重建已经促使EPA促进监督，包括评估和解决现场历史污染的努力。

社区基督教教堂毗邻前工厂。William Henry“Boss”Hoover，该公司的创始人实际上担任了一个多世纪以前教会的主席，传教士和教师。2016年，当EPA承包商测试了教会内的空气，其中包括一个周日学校和幼儿院，他们发现了不可接受的高水平的TCE。

“在他们告诉我们我们出现问题之前，我们不知道我们出现了一个问题，”杰克哈特利说，他是教会的财务主管。

Hartley suggests that “not a lot of people” at the church know about the vapor intrusion, but adds that the discovery “wasn’t that alarming.” The bigger concern for the congregation at the time, he says, was keeping the sanctuary cool. The church needed to replace a 40-year-old air-conditioning unit, which they did with financial help from a Hoover trust. The Hoover property developer, meanwhile, paid for the installation of a mitigation system inside the church, and TCE concentrations subsequently dropped.

“没有人想承认或谈论它，”当地居民和活动家查克奥斯伯恩说。“这里的名字Hoover受到尊敬。人们很难想象他们让我们留下了一个有毒的受污染的混乱。“

狩猎危害

Horton, the Mountain View farmhouse owner, recognizes the conflicting social pressures, too. After the mitigation system was installed in her home, some parents would not let their kids come over to play with her sons. “We probably had the cleanest air in Mountain View,” she says, noting that many families remain in the dark about the air quality in their own homes because they’re concerned that having their air tested would lower property values.

Even with the cooperation of homeowners, regulators, polluters and other stakeholders, the challenges don’t cease. Difficulties remain in knowing where, when, and how to look.

Some states use the groundwater concentration of a contaminant to determine whether — and where — to investigate for potential vapor intrusion. But a plume doesn’t necessarily stay in place. It might drift north, south, east, or west from the source. Sewer lines can send vapors even longer distances. Companies have been known to empty chemicals directly into sewers, and cracks in aged lines can pick up vapors in contaminated areas. Concentrations at various depths can also change across seasons — or even days. A heavy rain might put a layer of relatively clean water on top of the contaminated water, explains Suuberg. “You can’t just willy-nilly drill a well, pull water up from any random depth and say that characterizes the problem,” he says.

如果地下水样品超过筛选水平 - 可以通过状态变化的值 - 下一步通常是为了测试水位上方的土壤中的气体。但是，这一深度可以波动。如果土壤 - 气体浓度超过另一个阈值，研究人员将在建筑物内部采样空气。一些调查员绕过土壤 - 天然气测试，立即在室内进行。

This step can be tricky, too. Consumer products, such as paints, gasoline, and dry-cleaned clothes, can emit the same vapors and so can obscure results. Further complicating matters, concentrations of contaminants in indoor air can swing by an order of magnitude or more, depending on air pressure, temperature, and circulation, explains Laurent Levy, a senior project manager at Gradient, an environmental and risks sciences consulting firm. Taking one 24-hour sample, as is classically done, may miss variations across days and months. Developers are looking into affordable continuous monitoring tools. The EPA now also recommends multiple rounds of sampling.

The indoor air concentration that will trigger a response varies widely by state — despite the finalized 267-page federal guidance and updated toxicity assessments for TCE and perc. When a specified level is reached, even just how to respond is not always clear. However, it usually involves some form of ongoing monitoring or mitigation similar to systems installed at the Hortons’ and Community Christian Church.

从行动到预防

In the face of regional inconsistencies, as well as pushback from litigation-weary companies and fearful families, Levy suggests the need to “switch from reaction to prevention.” A tax credit, he says, might help incentivize preemptive installation of mitigation systems in circumstances where there is potential for vapor intrusion — avoiding the need to spend time and money on an investigation. The EPA’s Region 9 now requires that new buildings constructed over the Mountain View Superfund site include vapor intrusion control measures.

Still, he says, it’s important to remember that vapor mitigation measures do not make the problem go away. “You’re just cutting the pathway,” says Levy. “You still need to go back and address the source.”

专家说，抵消可能导致蒸汽侵入的更具可预防措施的污染也是至关重要的。山景从清理开始，因为饮用水法规已经促使EPA授予超级资金状态。2017年5月的蒸汽侵入到国家优先事项列表的资格标准，有资格在超级资金计划下进行长期清理的危险废物现场可能导致更多来源的修复。

专家说，抵消可能导致蒸汽侵入的更具可预防措施的污染也是至关重要的。更新的法规详细说明了地下储罐的正确使用和维护，这可能有助于防止泄漏。和EPA，在奥巴马政府的最后几个月，拟议的禁令是某些用途的TCE。但是，虽然人们继续雇用罪魁祸首化学品，但完全停止不受欢迎的入侵者仍然不太可能。

“我们还在使用汽油。我们还在使用氯化溶剂。TCE仍然是一个好的枪支清洁剂，“Suuuberg说。“这些不是任何意义的化学物质。”

Beyond keeping vapor-emitting products out of their home and complying with vapor intrusion testing and mitigation, individuals can further lower their risks with some due diligence.

“正如我们建议人们警惕的含铅油漆and asbestos when moving into a new house or apartment, people also need to look at the surroundings,” says Mount Sinai’s Landrigan. “Are they buying a home next to where there used to be a dry-cleaning shop?”

Lynne Peeples是一名自由职业者科学记者。这篇文章最初出现在网站上Ensia。