How the EPA assesses health risks after the Ohio train derailment
EMILY KWONG, HOST:
You're listening to SHORT WAVE from NPR.
So East Palestine is an Ohio town of about 4,800 people near the Pennsylvania border. And on February 3, just before 9 p.m. local time, a Norfolk Southern train derailed. Nobody was hurt in the accident, but 11 of the derailed train cars contained hazardous materials.
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UNIDENTIFIED REPORTER: New developments in the train derailment and toxic chemical spill in Ohio. The National Transportation Safety Board confirmed...
KWONG: Karen Dannemiller heard about the derailment from a news app on her phone.
KAREN DANNEMILLER: I think I felt the sense of uncertainty that a lot of people did at the time of just not knowing exactly what had happened and where a lot of these contaminants were going.
KWONG: And Karen understands chemical spills more than most. She's an associate professor at The Ohio State University and combines her training in engineering and public health to understand difficult questions, particularly around exposures in the built environment.
DANNEMILLER: I actually grew up in Northeast Ohio, not too far away, maybe about an hour away from where this happened.
KWONG: And there were multiple chemicals on board that train that were released onto the ground and waterways and into the air as the train cars caught fire. And one of the top chemicals of concern is vinyl chloride. That's a chemical used in manufacturing, often to create PVC.
DANNEMILLER: The compound tends to partition into the gas phase at room temperature. So I knew when this happened that a lot of this was probably going to end up into the gas phase.
KWONG: And vinyl chloride is also flammable. So officials were worried about the train cars exploding. So a few days after the derailment, they pursued a controlled explosion - first, evacuating residents within a one-mile radius and then intentionally releasing more vinyl chloride into the environment. Thing is, as vinyl chloride burns, it can form byproducts.
DANNEMILLER: And the two compounds that were of greatest concern at the time were hydrogen chloride and phosgene gas. And both of these can be acutely hazardous.
KWONG: And some residents who returned after the evacuations reported not feeling good - things like burning sensations in their eyes, nose and throat, as well as headaches, nausea and drowsiness. And these are known side effects from short-term exposure to vinyl chloride. But the real concern, especially for residents, is what this all means long term. Vinyl chloride is a known carcinogen, and long-term exposures have been linked to certain liver, brain and lung cancers.
DANNEMILLER: So we've now come to a point with this where we've transitioned from that acutely hazardous, dangerous phase at the beginning into this longer-term phase where people are going to start to worry about potential long-term health effects if there are exposures to these chemicals.
KWONG: As of February 23, when we're taping this, there are still a lot of open questions. The site is still being cleaned up. And with a chemical spill like this one, we wanted to know, how do you measure that long-term risk?
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KWONG: So today on the show, we're going to get into the nitty-gritty of how the EPA - the Environmental Protection Agency - answers this very complicated chemical question right now and years from now. I'm Emily Kwong, and you're listening to SHORT WAVE, the daily science podcast from NPR.
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KWONG: When a chemical spill like the one in East Palestine happens, the EPA springs into action and does what's called a Human Health Risk Assessment. This is to determine just how dangerous that spill is for the environment and the community. It's a four-step process that the EPA is doing right now and will be for the next several years. And it starts with identifying the hazards on board that derailed Norfolk Southern train that were then burned. Also, the burn itself.
DANNEMILLER: And then where these chemicals might end up in the environment, especially as we go to the long term.
KWONG: Like that vinyl chloride we were talking about earlier. But the train spilled other things, like butyl acrylate, a chemical used to manufacture paint. And the key question is, at what level would these chemicals negatively impact human health?
DANNEMILLER: So really, the goal of hazard identification is to be able to make a defensible judgment about whether exposure is going to potentially result in adverse health effects - sort of, do we need to look into this further?
KWONG: And as an indoor environmental quality expert, one of the tools Karen uses in her own assessments is public databases which contain detailed information on the toxicity of different chemicals.
DANNEMILLER: One of the databases that I look at a lot is the EPA IRIS database. In that one, you can go up and look up - so, for instance, vinyl chloride has an extensive summary sheet of all the studies that have been done that help tell us about hazards associated with vinyl chloride exposure.
KWONG: After identifying hazards, step two is dose response.
DANNEMILLER: And when I say dose, I'm talking about the dose of a chemical. And when I say response, I'm talking about a health effect that might occur from being exposed to that chemical at a certain dose.
KWONG: This is all about human health. And dose response is analyzed with graphs. So on one side of the graph - the horizontal axis - is the amount of exposure. And on the other side - the vertical side - is the measured health effect. For noncancerous effects, the graph tends to have an S shape.
DANNEMILLER: Where you have some low levels where you have no effect, it starts to increase and then it kind of levels off, at some effect.
KWONG: And on that S curve for noncancerous effects, the EPA zeroes in on two points of interest.
DANNEMILLER: One is the highest concentration at which we see no effect. Sometimes, people refer to that as the NOAEL, the no-observed-adverse-effect level - sort of the highest concentration you can have where you don't have any harmful effects. And then the LOAEL is on the opposite side of that, the lowest concentration when you start to see effects.
KWONG: And these two values - the NOAEL and the LOAEL - allow the EPA to calculate something really important - the reference dose. That's the maximum concentration an adult human can be exposed to any given chemical and be OK. Potentially dangerous chemicals tend to have a reference dose.
DANNEMILLER: A lot of times, they're based off of animal studies, of studies where rats or mice were exposed to these different chemicals, and then they basically measured what happened. And they do include uncertainty factors, as well. Humans and animals are very different. So usually, if we're basing these numbers on an animal study, they're going to include something like a factor of 10 buffer just to make sure and be absolutely certain that we're not going to actually see health effects. There's other safety factors that are often included, as well, like if, you know, some of the studies were done in adults, maybe we want to account for children, which might be another safety factor.
KWONG: And the other dose response curves they're paying attention to measure cancerous effects, like tumors. And those curves have a different shape.
DANNEMILLER: That's usually thought of as a straight line. And that's because for cancer, even a tiny, tiny amount could theoretically lead to cancer. It's just the risk might be infinitesimally small.
KWONG: And the EPA is using all these dose response curves for all these different chemicals to assess the long-term risk to residents of East Palestine.
Step three is exposure assessment. That's asking how much of these hazards got spilled into the environment - indoors, in the air, the water and the ground outside.
DANNEMILLER: A lot of the measurement numbers have been coming out of East Palestine. And we've seen that a lot of them have been nondetects, which is great.
KWONG: A nondetect, by the way, just means the concentration of the chemical, if not zero, is below the detectable level for assessors. Lastly is step four.
DANNEMILLER: Step four is putting it all together. Risk...
KWONG: Yes. Describing the whole picture.
DANNEMILLER: Describing the whole picture. Absolutely.
KWONG: And that picture shapes the EPA's description of what's going on and their safety guidelines. In East Palestine, these steps are happening all at once. As of this week, over 500 homes have been screened for indoor air quality, as well as the Ohio River and the wells people get their water from for water quality. And none of those screenings have exceeded residential air and water standards. They're all nondetects, as Karen said. The local government is still advising those with private wells to drink bottled water until more testing can be done. And in an interview with NPR, Michael Regan, the administrator of the EPA, says they would be offering additional testing for those that wanted it.
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MICHAEL REGAN: For anyone who has concerns about their indoor air quality, we're asking them to reach out to us. And we will come into their homes and test that air quality.
KWONG: For locals, the phone number to request free private testing in East Palestine is 330-849-3919. Though the EPA's risk assessment process will take years, what's important to Karen is that information is shared clearly with the community as soon as it's known. And it seems like the EPA is on the same page, wanting to make their data accessible and holding Norfolk Southern, the train company, accountable. Here's Administrator Michael Regan again.
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REGAN: And so what we're going to do is we're going to hold the company accountable to provide to us a workplan that lays out every single step for how they will clean up the soil, how they will clean up the water and how they will continue to pay for testing. If they do not do this, we can step in, provide those services to the community with no break in action. And we can fine this company up to $70,000 a day.
KWONG: With all of this in mind, I had one more question for Karen.
Well, the last thing I wanted to ask you is just simply, what do you want to see from this process for Ohioans, for Pennsylvanians who live close to East Palestine? What would you like to see from the science?
DANNEMILLER: There's going to be a lot of uncertainty at various times, and there's really nothing we can do to completely eliminate the uncertainty. But just, really, the communication around what we know, what we don't know, what the next steps are in the process. I think that's - that'll really be what we're looking for.
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KWONG: What government agencies like the EPA do on the ground and when an event like this trail derailment happens can feel really unknown, like one big black box. But in the background, this iterative risk assessment process is unfolding, those four steps of hazard identification, dose response, exposure assessment and risk characterization. All of this to build a scientific picture out of something that seems impossible to describe. For those of you interested in following the EPA's updates on the Ohio derailment case, we'll link to their website and the remediation plan in our episode notes.
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KWONG: Today's episode was produced by Margaret Cirino, edited by managing producer Rebecca Ramirez and fact-checked by Anil Oza. The audio engineer was Hans Copeland. Brendan Crump is our podcast coordinator. Our senior director of programming is Beth Donovan. And the senior vice president of programming is Anya Grundmann. I'm Emily Kwong. Thanks for listening to SHORT WAVE, the daily science podcast from NPR.
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