Tracing toxic heavy metals in organisms using X-ray fluorescence (XRF)

Our worldwide community develops around industrial centers, as populations migrate to where opportunities exist.

And those centers often are characterized by major commercial enterprises. These sometimes employ materials suspected of being harmful to the health of living organisms. Exposure and health impacts are often geographically clustered.

Take hexavalent chromium, for instance. That’s the pollutant featured in the movie Erin Brockovich. It has many useful industrial purposes and is used in various industries for electroplating, welding, and chromate paint. But is known to be a widespread environmental contaminant. The substance is linked to a number of detrimental health effects, including lung cancer.

Toxin Sleuth

Aaron Specht devotes his career to investigating the pathways that these substances take through the body, which eventually helps reveal the effects the substances might have on public health.

And to do it, Specht uses X-ray fluorescence (XRF) as his main investigative tool.

XRF analysis provides non-destructive qualitative and quantitative information into the elemental makeup of samples based on the sample’s unique XRF spectra.

Specht, Ph.D., an Assistant Professor at Purdue University, was awarded his doctorate there and did post-doctoral work at Harvard University’s T.H. Chan School of Public Health, where he remains active as part of its Trace Metals Laboratory1.

His research centers around the development, application, and understanding of exposure assessment for elemental and radiation exposures in environmental and occupational health studies2.

Specht’s job is to localize where absorbed particles, the metals, are depositing, whether it be absorbed through inhalation, skin, ingestion, or other means.  In his latest publication, he and his group are looking at localization where inhaled particles are depositing in the lungs.

“In the future, I think we are going to be able to answer some more vital questions about how environmental contaminants are impacting things like brain development and Alzheimer's Disease,” he said, “and how the co-localization of metals within the brain might be potentially influencing different pathways. And those pathways are influencing dementia.”

When we can actually localize where the metals and these elements are, specifically in relation to other known organs, it gives us a better insight into how the body is functioning and how some of these environmental toxins that we deal with every day are impacting our health.”

In his current, soon-to-be-published study, tentatively titled Chromium distribution in an oropharyngeal aspiration model for hexavalent chromium in rats, the group used inhalation to deposit the hexavalent chromium in rat lungs.

“What we're hoping to do in the future with this (investigative) technology is to look at human samples,” he said. “There are biobanks across the world that have brain samples of people who have specific diseases. Those we can then look very, very specifically where the metals are localizing within the brain of someone who has a disease. And how is that different from someone who is not diseased?”

Many of these substances like hexavalent chromium are useful for industrial purposes but actually have toxic impacts. Specht’s team looks at how it relates to the human population. Lead is also one of these substances.

“It goes into the body and triggers oxidative stress mechanisms and can disrupt your hormones and endocrine discrimination.”

There are many different ways these chemicals initiate the problems that we see in human health. Sometimes it does this by mimicking different aspects of processes that are actually useful in the body.

“So, for example, a lot of heavy metals will go into the body and the body thinks that it's similar to calcium,” he said. “So if it's similar to calcium, it'll successfully move through a lot of different places. For calcium, it's normally, going through the body and it will disrupt those calcium channels. It will go through the blood-brain barrier, acting like calcium.”

“So there’s a need to balance the use of these toxic substances with the human health aspects that we can identify and make it so that we're not polluting ourselves to death.”

Much of Specht’s paper was focused on where the chromium was deposited within the lung, and then the downstream consequences of these deposits.

The researchers established a couple of different hypotheses about where the lung could be distributing the most chromium after an inhalation event, and what that would lead to in terms of dysfunction later on.

“But the toxicologists really are able to follow and pick up on where it is influencing cells and then understanding how those cells are impacted in a downstream effect within the body.

“Because everything within the body is this large cycling system, and it just depends on which portion of that cycle that you've disrupted that influences the downstream impacts of everything else.”

Much of what Specht does involves X-ray fluorescence, including micro-XRF and portable units.

“It makes it a lot easier to do community engagement projects because the alternative for XRF is some much more expensive chemical measures.”

XRF has other benefits.

“We have this micro-XRF, which actually makes it much more accessible to do these elemental mapping measurements because everything else that is used in elemental mappings is a destructive or semi-destructive process. When we can do this and we can have it accessible in our lab, it opens up the possibility of doing a lot of different studies than we never could have done, because the only other options for doing this kind of microscale XRF is going to big national labs. Normally you have to put in a proposal and maybe you'll get a weekend to go spend there to do these measurements. But now we have the technology to do this inside of a lab and do whatever we want when we want. It affords us the option to look at a bunch of novel scientific questions that otherwise wouldn't be looked at because we now have the access to this tremendous technology that do these analyses.”

Anatomy of XRF

XRF gives Specht and his team the ability to look at everything on the periodic table.

“When we're actually doing the measurements, it excites an atom in the sample that we're measuring. And from that excited atom, it de-excites and we collect a signal, but the signal is always reflective of whatever element that atom was.”

“So, whether it be chromium or lead or arsenic, you can capture all of it with the X-ray fluorescence device. And having it on the micro-scale, allows us to look at almost the cellular level with the device that we have. That gives us a lot of opportunities to be able to identify really interesting topics matching with histology of what the tissue is actually showing, and overlaying it with the known things within the tissue versus where the lead is actually going into these known sites. So are the astrocytes accumulating in the brain, or is, is the lead actually accumulating elsewhere? XRF gives us the ability to answer all of these questions, and it does so in a much more accessible way than some of the other lab-based methodologies, which are much less accessible.”

Worldwide Effort

Specht and his colleagues travel the world to trace these toxins. He’s done studies from Europe to Asia, all focused on this one aspect of how the environment is shaping our health.

Yet, different biological sites are key.

“In a lot of these studies, people collect different bio-specimens from a person in order to identify what they've potentially been exposed to. And all of those different bio-specimens can reflect a different amount of exposure at a different time that can be more or less helpful for what we're looking at in terms of human health.”

“For example, if we, if we measured someone's bone, we can do with this and can actually look at 20 to 30 years’ worth of exposure time all accumulated in that one measurement of the bone. But if we measure someone's blood, we’re looking at 30 days, give or take, of someone's exposure time. So if we're looking for someone's acute exposure, and how that's impacting their health right now, then we might choose different biological sites that we would actually measure. If we're looking at something that has really long symptomology, like a neurodegenerative disease, we'll be looking at the more chronic exposures that would be reflected in the bone.”

In the Erin Brockovich movie, exposure was due to the contamination of drinking water and the method of exposure was ingestion. Inhalation is common in industrial settings.

“There are specific sites that deal a lot with hexavalent chromium and those communities, in particular, are very heavily impacted by hexavalent chromium. You’ve probably heard of recycling sites in China and Ghana that deal heavily with hexavalent chromium.”

Community Engagement

One of the big aspects of Specht’s work is community engagement. Scientists often will go into communities and tell people what the scientists think that communities need to do. But one of the the big things within engagement, he says, is to just figure out what the community wants to do, and what the scientists can you bring to the table to help them solve these problems.

“That's normally what I'm trying to do when I'm doing my community engagement. If we have a specific cohort study that's large and people just sign up for research, then it's a different story and it's not normally about a specific community. But for specific communities, we try to make sure that we're not trying to take advantage of anyone for our own gain in terms of science. We're trying to make them part of the process and understand where they're coming from to try and solve the problems they are most interested in while keeping them engaged in the science.



Specht’s main tool is the HORIBA XGT 9000, a Micro-XRF X-ray Analytical Microscope. It features

  • <15µm probe size with ultra-high intensity without compromising sensitivity or spatial resolution
  • High-resolution cameras and multiple illumination modes to help capture images.
  • Dual types of detectors for transmission and fluorescent X-rays
  • Detectable element range down to carbon with a light element detector

But there’s something behind the specs that enticed Specht into getting an XGT 9000.

“First and foremost, HORIBA was very open to having an ongoing relationship. Within the samples that I'm measuring, there are a lot of questions that come up on how we do the measurements and what's the best way to proceed and do the analysis of the measurements. So when I reached out to HORIBA, it was very clear that they were more than willing to have an ongoing relationship and answer all of those questions as time went on. And I very much value that because I don't know everything. And I understand that the research and development people at HORIBA have a better understanding of their instrument at times than I will of their instrument.

Specht and his group should see their paper on hexavalent chromium published sometime early in 2023. And there’s no doubt that this team of scientists will benefit huge populations with their studies and community engagements to improve public health.


2 Idbid

Follow Us