Using air data to estimate your health risks
What does this article cover, and why should I read it?
In February 2016 news broke that dangerously high levels of airborne heavy metals had been detected in areas surrounding Uroboros and Bullseye glass factories in North and Southeast Portland. (See “Can you remind me how we got here…?” below.)
This article is intended to help individuals assess the health risks they may face as a result of having lived or spent extensive time in these heavy metal “hot spots.” Specifically, it explains how to use historic air test data, information about where you’ve lived and spent your time, and basic toxicological models to estimate your individual cancer risk.
This article also addresses gaps and flaws in health risk assessments provided by Oregon Health Authority (OHA) and by Safer Air Oregon, the joint public information campaign of OHA, Multnomah County Health Department (MCHD) and Oregon Department of Environmental Quality (DEQ).
In other words, it answers basic questions such as these:
- In February and March, I read advisories from OHA stating that long-term health effects from exposure to glass factory emissions were “relatively low.” How and why did the agency change its risk assessment in late April?
- Public health agencies have shared two maps estimating glass factory neighbors’ location-specific cancer risks due to cadmium exposure. But these risk estimates assume 70 years of continuous exposure. How do I adjust those estimates if I’ve lived near a glass factory for less than 70 years?
- What is my cancer risk from long-term exposure to arsenic, which exceeded state safety benchmarks by 159 times at Bullseye’s property line—more than three times cadmium’s exceedance?
- What is my cancer risk from combined arsenic and cadmium inhalation?
- What do these cancer-risk numbers mean? For instance, how does my cancer risk from arsenic and cadmium inhalation compare to my cancer risk overall?
Can you remind me how we got here—and say more about those “gaps and flaws” in the public health response?
How we got here: In 2015 U.S. Forest Service scientists in Portland completed an innovative moss study. Moss accumulates air pollutants. Preliminary results of the study pointed to several areas of the city where sampled moss tissues contained unusually high levels of heavy metals, including cadmium and arsenic. (See “What about the moss study?” below.)
Alerted to this information, Oregon Department of Environmental Quality (DEQ) searched for emissions sources and found that two of the heavy-metal hot spots centered on colored glass factories: Bullseye Glass, in Southeast Portland, and Uroboros, in North Portland.
In October 2015 DEQ conducted air tests at the property line of Bullseye. Test results, which came back in January 2016, showed cadmium and arsenic levels averaging 49 and 159 times state safety benchmarks. These benchmarks, also called ambient benchmark concentrations, or ABCs, are goals set to limit cancer risk from any single air toxic to one excess cancer case per one million people.
The other factory, Uroboros, was close to Harriet Tubman Middle School, where EPA air tests in 2009 and 2011 had previously detected high levels of cadmium. Both factories had been operating without stack filtration for roughly 40 years.
Portlanders learned about the glass factory emissions in a February 3 Portland Mercury report. Later that month, responding to pressure from residents and from DEQ, both Bullseye and Uroboros agreed to temporarily stop using the three metals of highest concern, arsenic, cadmium and chromium. DEQ is presently establishing new rules for controlling glass factory emissions (a process EPAC is intensely watch-dogging).
Gaps and flaws in the public health response: Despite the significant exceedances of air-toxics safety benchmarks, OHA issued advisories stating that long-term health risks to glass factory neighbors were “relatively low.” The advisories didn’t make clear that this assessment was based on air tests conducted after February 2016, when glass factories had already stopped using arsenic, cadmium and chromium.
In late April, after EPAC raised questions to OHA staff, OHA revised its assessment to address health risks from past exposure, as well. But OHA still hasn’t provided the public with (a) an explanation of the data and interpretive methods used to make its qualitative assessments or (b) answers to the basic questions listed above. (OHA technical staff have responded directly to individuals, however; OHA toxicologist David Farrer was the source for critical information in this article.)
I want answers to those basic questions listed above, and I don’t want to read this whole thing.
Go to the end of this article.
You said this article deals with evaluating cancer risk from past exposure to heavy metals. Should I also be concerned about my current and future exposure, even though OHA has indicated I shouldn’t be? And should I be concerned about health risks other than cancer?
Yes and yes.
As Safer Air Oregon’s press releases have emphasized, OHA’s risk models indicate that Bullseye and Uroboros neighbors aren’t currently being exposed to airborne arsenic or cadmium at levels high enough to cause acute short-term effects, such as respiratory or skin irritation.
However, there are questions as to whether these risk models adequately account for the full range of health effects, both short-term and chronic, that could be caused by low current levels of exposure to heavy metals, especially for individuals exposed to multiple toxicants. These are questions worth exploring.
Additionally, as of this posting in early May 2016, monitoring stations in Southeast Portland are still measuring arsenic and chromium VI at levels that exceed state health safety benchmarks for lifetime cancer risk. (After EPAC raised questions to OHA staff, OHA alerted the public to this fact on April 29.) Since Bullseye has stopped using these substances while it works on installing a filtration system, the metals are believed to be coming from another source or sources. OHA and DEQ are investigating.
We plan to address these topics more thoroughly in the future; look for updates.
What about health risks associated with emissions from other hot spot polluters, and from air pollution in general—including glass factory emissions of substances other than cadmium and arsenic?
Good questions. Join our Facebook group to connect with ongoing conversations and organize with your neighbors to take action on these issues.
Is OHA concerned about residents’ health risks caused by past exposure to heavy metals?
Yes. Though the Safer Air Oregon public information campaign hasn’t emphasized this (as of the writing of this article in early May), OHA staff have told EPAC representatives that OHA is working on a broad-based study to better understand residents’ risks from past exposure to unfiltered glass factory emissions. A brief mention of the study was recently added to Safer Air Oregon’s “long-term health effects” statement.
The study will look not just at historic air testing data, but also at Bullseye’s and Uroboros’s historic production records, historic wind and weather patterns, ongoing soil tests, moss data and other evidence. It will involve intensive community input and is expected to be released in the fall of 2016.
What health effects could I experience as a result of past exposure to airborne heavy metals?
There are serious potential health effects associated with exposure to the heavy metals detected in the air near Bullseye and Uroboros glass factories. The health testing page on this site summarizes the health effects that can result from exposure to cadmium and arsenic, two of the metals of highest concern; Safer Air Oregon also provides a brief description of health effects. We hope to provide more details, including health effects associated with chromium VI exposure, in the future.
Knowing the broad scope of health effects that could result from heavy-metal exposure doesn’t tell you what specific health risks you may face as an individual, though. Long-term arsenic inhalation can cause lung cancer, for example. But your chances of getting lung cancer due to arsenic inhalation depend on many factors, such as precisely how much arsenic you’ve been breathing over how long a period of time, what other lung-cancer risk factors you’re being exposed to, and your genetic makeup.
To understand your risks, a good starting point is to assess your level of exposure.
How can I assess my past exposure to airborne heavy metals?
We’ll to get to the calculations soon. First, a reminder that there are several types of data to consider:
- Environmental monitoring data. You can estimate the level of your exposure based on available environmental (air, soil, etc.) monitoring data in the areas where you live and spend time, and compare your level of exposure to safety-based “screening” levels established by the EPA or other authorities.
- Epidemiological data. You can look at whether your neighborhood (or community or workplace) has any unusual incidences of disease, such as cancer clusters.
- Health testing data. You can get your body tested for specific contaminants.
This article deals specifically with air data. Our health testing page deals with health testing data. We hope to address epidemiological and soil data in the future.
What air monitoring data do we have?
As far as data that’s relevant to assessing your long-term past exposure to glass factory emissions, it consists primarily of three sets of air test results.
- The first test was done by the EPA in August through November of 2009 at Harriet Tubman Middle School. This site was chosen because the EPA was studying air pollution in communities close to highways, and Tubman School is near a highway. It also happens to be near Uroboros glass factory.
- EPA did a second test at Tubman School in July 2011 to follow up on high levels of cadmium found in the first.
- The third test was done by Oregon Department of Environmental Quality (DEQ) in October 2015, on a property 120 meters from Bullseye Glass factory. The test was done because of concerns raised by the U.S. Forest Service moss study (see details below). The air samples were collected 18 times, in 24-hour cycles, over a period of a month.
Starting in February of 2016, DEQ did additional air monitoring in several locations near the two glass factories. But these tests were done after Bullseye and Uroboros agreed to temporarily suspend use of cadmium, arsenic and chromium, so they are not relevant for assessing your past exposure to those pollutants.
What about the moss study?
It’s really important. Moss accumulates pollutants from the air. U.S. Forest Service researchers gathered moss samples from different parts of the city and tested them for air pollutants known to exist at concerning levels, including certain heavy metals and polycyclic aromatic hydrocarbons, or PAHs. It turned out that moss sampled from several areas in Eastside Portland contained unusually high levels of cadmium, arsenic and other heavy metals. Graphed onto a city map each of these heavy-metal hot spots took the form of a concentric circle (or splotch), with concentrations highest at the center, lowest at the edge.
The moss data enabled DEQ personnel to pinpoint Bullseye and Uroboros as probable sources of two of the hot spots, prompting DEQ’s October 2015 air testing at Bullseye’s fence line.
With regards to cadmium only, USFS and DEQ scientists were also able to establish a correlation between the moss data and historic air data that had been gathered at several sites around the city. This correlation has made it possible for scientists to estimate cadmium air concentrations in areas of town where (expensive, scarce) air tests haven’t been done, and to produce these two maps showing estimated cadmium air concentrations and associated lifetime cancer risk on a block-by-block basis in the areas surrounding Uroboros and Bullseye.
A similar correlation could not be established for arsenic; USFS scientists are continuing to work on that.
Note that while the moss study provides excellent clues about relative concentrations of air pollutants in different areas of the city, it doesn’t tell us the actual air concentrations of these pollutants. Only air monitoring can do that.
Ok, what did the three air monitoring tests show?
Air concentrations are given below in nanograms per cubic meter, or ng/m3.
The October 2015 air samples collected next to Bullseye were tested for chromium, cobalt, arsenic, selenium, cadmium, lead, nickel, manganese and beryllium. Following is a list of the metals that exceeded state safety benchmarks, their average air concentrations over the month and, in parenthesis, the safety benchmark. We also did the math to show how much the measured levels exceeded the safety benchmarks. (For more on safety benchmarks, see “Can you say more about how the safety benchmarks are set?” below.)
- Cadmium, 29.4 (0.6) = 49 times the safety benchmark
- Arsenic, 31.7 (0.2) = 159 times the safety benchmark
- Nickel, 5.4 (2) = 2.7 times the safety benchmark
The state has not established a safety benchmark for unspeciated chromium, which averaged 71.5 ng/m3.
The 2009 air samples collected at Tubman School were tested for pollutants associated with highway traffic, including butadiene, acetaldehyde, benzene and others. The only pollutant found at levels that were concerning* to the EPA was cadmium.
The 2011 air samples collected at Tubman School were tested for cadmium. Cadmium concentrations averaged 1.24 ng/m3. This number looks low compared to the 29.4 ng/m3 measured next to Bullseye, but remember that Tubman School is not at the center of the hot spot described by moss data. Moss sampled at the center of the Uroboros hot spot had cadmium levels comparable to those sampled at the center of the Bullseye hot spot, correlating to air concentrations of 30 ng/m3 or higher. Nonetheless, the concentrations measured at Tubman School were double the state safety benchmark of 0.6 ng/m3.
*Note that the EPA reported its results against a screening level of 30 ng/m3, a level it defined as safe for children and adults to be exposed to for a period of “a couple of weeks.” Why the EPA used this period of exposure is unclear to this author.
Can you say more about how the safety benchmarks are set?
Also called ambient benchmark concentrations, or ABCs, the safety benchmarks are clean air health goals set at a level that would be expected to produce one additional case of cancer per one million people if people were exposed 24 hours per day, 7 days per week, for 70 years. For non-cancer-causing air toxics, the benchmarks are set at levels that could be breathed in for a lifetime without any non-cancer health effects. DEQ’s Air Toxics Scientific Advisory Committee has set ABCs for 52 air toxics of concern in Oregon.
You just said there’s no safety benchmark for unspeciated chromium. Should I be concerned about being exposed to levels of 71.5 ng/m3, potentially over a long period of time?
That’s an important question with a complicated answer. We plan to provide more details soon. Short answer: yes, this is concerning.
What do these air test numbers tell me about my health risks?
There are many ways you could interpret the air test numbers to assess your risk for different health effects. This article addresses the limited question of how to extrapolate individual cancer risk due to arsenic and cadmium inhalation based on lifetime cancer risk estimates provided by OHA. (Roughly speaking, OHA’s estimates come from inserting assumed exposure levels into EPA risk models, which come in part from actual epidemiological studies.)
Assessing the reliability of OHA’s estimates, addressing non-cancer risks, and addressing health risks from air toxics other than arsenic and cadmium are all outside the scope of this article.
Here are the OHA risk estimates we’ll start with:
Inhaling cadmium at concentrations of 29.4 ng/m3—the level measured near Bullseye and indicated by moss data to potentially exist at the center of the Uroboros hot spot—24 hours a day, over a period of 70 years, would result in…
- A 50 in 1 million (or 1 in 20,000) excess risk of contracting cancer.
Inhaling arsenic at concentrations of 31.7 ng/m3 (the level measured near Bullseye) 24 hours a day, over a period of 70 years, would result in…
- A 100 in 1 million (or 1 in 10,000) excess risk of contracting cancer. (Source: David Farrer, Oregon Health Authority.)
Inhaling both arsenic and cadmium at the above concentrations 24 hours a day, over a period of 70 years, would result in…
- A 150 in 1 million (or 1 in 6,667) excess risk of contracting cancer.
Of course, no one in Portland has lived next to a glass factory for 70 years—Bullseye and Uroboros started operating in the 1970s—and few people live so close to a glass factory that they would have been exposed to air concentrations this high.
So, below we’ll show you how to adjust these risk figures based on where you live and how much time you’ve spent there.
A note on what’s meant by “excess” risk: These risk models are telling you how much your lifetime cancer risk would increase, due to cadmium/arsenic inhalation, relative to your background lifetime cancer risk. Your background lifetime cancer risk is actually really high. For men, it’s one in two. For women, it’s one in three. (That’s the observed risk: what really happens, not what is likely to happen based on models.) Of course, that high background risk is all the more reason to be concerned about excess exposure to carcinogens.
I noticed you simply added the cancer risks from cadmium inhalation and arsenic inhalation to get a total cancer risk (100 in a million + 50 in a million = 150 in a million). Can you really do that?
There are different views on this.
According to David Farrer at OHA, you can and should. It’s not a perfect method, but it’s the best one to use in this case.
The way toxicologists look at it, toxics interact in the body in three different ways. The interaction can be additive, meaning the effects of one substance simply add to the effects of another; synergistic, meaning each substance increases the other’s effects; or antagonistic, meaning the substances counteract each other’s effects.
Farrer couldn’t immediately point to any scientific studies looking specifically at the interaction between cadmium and arsenic in the human body, but he said studies do exist that indicate interactions among heavy metals in general are often antagonistic, because the metals compete for the same transporters to get through cell membranes.
(The same goes for calcium and lead, which is why people exposed to lead are told to eat calcium-rich leafy greens—except when those leafy greens have been grown in an urban garden, where lead particles abound. As in human tissues, plant tissues may absorb lead particles in place of calcium. Ugh.)
Because the interaction of cadmium and arsenic in the body may be slightly antagonistic, adding together cancer risks from cadmium and arsenic exposure may produce a slightly high (conservative) risk estimate.
Others, including some naturopathic physicians, take a more holistic and conservative approach to evaluating health risks that might lead to an even higher assessment of risk. Roughly stated, this view holds that it you’re already loaded down with toxics, or if you’re genetically predisposed to process toxics inefficiently, it may take just a small amount of additional exposure to create negative health effects. In that case the interaction of heavy metals in the body might be seen as, to some degree, synergistic.
Farrer’s approach has the advantage of simplicity, and we’ll use it for now.
I live a quarter-mile from a glass factory, not right next to it. I’ve lived there for 20 years, not 70, and breathed the air for about 18 hours per day, not 24. How does that change my risk, compared to the numbers above?
It changes it a lot.
Distance impacts risk. Air pollutants dissipate with natural ventilation. So if you live/work/go to school even a few blocks from Bullseye or Uroboros, you will have breathed less arsenic and cadmium than someone who lives right next to the factory. Unfortunately, there’s no simple formula that can tell you what air concentrations you’ve been exposed to, based on your distance from the source and from the nearest air monitoring site. But, in the case of cadmium only, we can use moss data to make an estimate—see next question. (Also see “What about the moss study?” above.)
Time impacts risk. According to OHA’s David Farrer, standard toxicology models assume your cancer risk from exposure to airborne toxicants varies in direct proportion to the duration of your exposure. You can make this adjustment using the simple calculation method below (“How do I adjust my estimated cancer risk if the duration of my exposure was less than 70 years?”).
How do I adjust my estimated cancer risk based on my distance from the factory?
To do this, you need to use one of two maps published by Multnomah County Health Department (see links below).
As indicated on the map labels, the figures provided on these maps are not certain or precise. They are based on limited data sets and use a new and still-developing method of correlating cadmium concentrations measured in air with cadmium concentrations measured in moss. Additionally, they assume that cadmium air concentrations near the factories have been constant over the given exposure period, based on measurements taken in October 2015.
If you’re okay with accepting these uncertainties and assumptions, continue as follows.
Step 1: Get your location-adjusted cancer risk for cadmium. If you live near Bullseye, you can find your location-adjusted estimated lifetime cancer risk from cadmium inhalation on this map. If you live near Uroboros, you can find your location-adjusted estimated lifetime cancer risk from cadmium inhalation on this map. (Example: If you live a quarter-mile from bullseye, your cadmium-related cancer risk would be between 9 and 20 in a million. To be conservative, you could use the higher figure.)
Step 2: Get your location-adjusted cancer risk for arsenic. There is no similar map for arsenic, because a moss-air correlation for arsenic has not been established. So, if you prefer, you can be conservative and assume your cancer risk from arsenic inhalation is just as high as it would be if you lived at Bullseye’s fence line (100 in a million). Or, for lack of a better method, you could assume your cancer risk from arsenic inhalation drops proportionately to your risk from cadmium inhalation as you move away from Bullseye’s fence line. That’s a two-part calculation.
- Part A: Divide your location-adjusted cadmium risk from Step 1 by the fence-line cadmium risk (50 in a million) to get the multiplication factor. (Example: 20 in a million / 50 in a million = 0.40.)
- Part B: Multiply the fence-line arsenic risk (100 in a million) by the multiplication factor you calculated in Part A. (Example: 100 in a million x 0.40 = 40 in a million.)
Step 3: Add your cadmium and arsenic risks together. Example: 20 in a million + 40 in a million = 60 in a million (or 1 in 16,667).
How do I adjust my estimated cancer risk if the duration of my exposure was less than 70 years?
First, a quick reminder that, following OHA’s lead, our estimates for long-term past exposure assume that air concentrations of cadmium and arsenic have been constant based on measurements taken near Bullseye in October 2015. This is purely a hypothetical assumption, not based on Bullseye’s actual production history (though OHA is investigating that history).
To adjust your lifetime cancer risk by the duration of your exposure, start with the “base” time in hour-years: 24 hours per day x 70 years = 1,680 hour-years.
Step 1: Multiply “your” hours and years together. (Example: 18 hours per day x 20 years = 360 hour-years.)
Step 2: Divide your hour-years by the base hour-years. (Example: 360 hour-years / 1,680 hour-years = 0.2143.)
Step 3: Multiply your location-adjusted cancer risk by the factor you just calculated. (Example: 60 in a million x 0.2143 = 13 in a million.)
I’ve used your calculation methods to determine my estimated cancer risk from long-term past exposure to airborne cadmium and arsenic. Based on this risk figure, should I be freaking out? Should my family and I get tested?
Only you can answer that question, in consultation with your health care provider if you have one. We can say that, driven by a combination of public demand and scientific concern, OHA is embarking on a large-scale study to better understand residents’ exposure over the past 40-plus years. But no matter the results of that study, what constitutes an acceptable level of exposure is really up to you to decide.
Putting your risk in context…
- 1 in a million: the maximum excess lifetime cancer risk that it’s acceptable for Oregonians to face as a result of exposure to any one hazardous airborne pollutant, as determined by rule makers who set Oregon’s ambient benchmark concentrations (ABCs). ABCs are clean air health goals set at a level that would be expected to produce one additional case of cancer* per one million people if people were exposed 24 hours per day, 7 days per week, for 70 years. (For more details on ABCs, see “Can you say more about how safety benchmarks are set?” above.)
- 13 in a million (1 in 76,923): the estimated excess cancer risk from combined cadmium and arsenic inhalation for a person who has been living about a quarter-mile from Bullseye for 20 years, and breathing the air 18 hours a day, assuming (a) emission levels have been constant over those 20 years compared to October 2015 measurements, (b) location-specific air concentrations of cadmium really do follow the pattern described on MCHD’s moss-correlated map (see “How do I adjust my estimated cancer risk based on my distance from the factory?” above), and (c) arsenic air concentrations of arsenic follow a similar pattern.
- 40 in a million (1 in 25,000): the excess cancer risk faced by the average American from breathing air toxics from all outdoor sources, according to the EPA’s 2015 estimate based on data from its 2011 National Air Toxics Assessment (NATA).
- 90 in a million (one in 11,111): the excess cancer risk from combined cadmium and arsenic inhalation for a person who has been living right next to Bullseye for 42 years, and breathing the air 24 hours a day, assuming emission levels have been constant over those 42 years compared to October 2015 measurements.
- 270 in a million (1 in 3,704): the excess lifetime cancer risk the average Multnomah County resident faces from breathing diesel particulate matter, based on air concentration estimates in the 2011 NATA, and on the State of California’s diesel PM cancer-risk model. (The EPA does not classify diesel particulate as a known carcinogen, though California an and Oregon do.) http://portlandcleanair.org/files/Multnomah%20Air%20Pollution%20-%20Cancer%20Risk%20Maps%20-%20PCA.pdf
- 1,200 in a million (1 in 833): the excess lung-cancer risk faced by a 50-year-old woman who has smoked 10 cigarettes a day for 25 years, according to Memorial Sloan Kettering Cancer Center’s smoking-caused cancer prediction tool.
- 333,333 in a million (1 in 3): the observed risk you have of developing cancer in your lifetime if you’re a woman.
- 500,000 in a million (1 in 2): the observed risk you have of developing cancer in your lifetime if you’re a man.
These risk models seem kind of crude, don’t they? It makes me wonder if the resulting numbers really mean anything.
Yeah, we kind of wonder the same thing. At the same time, we feel like a crude interpretation of the data is better than no interpretation. And we think there’s something empowering about better understanding what’s known and unknown, knowable and unknowable, and to set individualized assumptions about key risk variables. If you want a more direct indication of your exposure, you can get your body tested (see our health testing page). But be forewarned, there are lots of weaknesses in those tests, as well.
I want to channel my frustration into cleaning up our air and creating a regulatory system that truly protects the health of Oregonians. Where do I start?
Volunteer with one of EPAC’s action groups to help with things like scientific research and legislative strategy.
Make a donation to help EPAC with printing, web hosting and other costs.
Can I get help with some other questions?