Brady Ziegler

How an oil spill could cause arsenic to dissolve into your drinking water

If arsenic were introduced into your drinking water, the chances are high that you’d never know. Arsenic is difficult to detect since it’s tasteless and odorless. Even in very small concentrations, when frequently consumed over long periods of time its effects can be damaging, including skin and circulatory impacts and even cancer. It’s possible that arsenic might already be in your aquifer (a permeable geologic unit that contains and transmits groundwater), just not in a state that’s harmful—at least not right now.

Arsenic can often be found in aquifers associated with an immobile solid phase, safely kept from creeping into groundwater. But when an oil spill occurs, that arsenic may dissolve into the groundwater.

Brady Ziegler, a Department of Geosciences Ph.D. student in the College of Science who is advised by Professor Madeline Schreiber, has focused his research on how oil spills induce changes in chemistry that can cause naturally occurring arsenic found in sediment to become a dissolved contaminant in groundwater. Until recently, though, nobody was aware of this potential long-term consequence of subsurface oil spills.

“There are these things that we’re exposed to all the time that we have no idea that we’re exposed to,” Ziegler said. “The common phrase is ‘Oh, what’s in the water?’ Sometimes it actually has some very serious implications.” 

The process

So how does oil cause arsenic to be dissolved into groundwater? Arsenic can occur naturally in sediment, but it is often associated with a solid iron mineral phase and not in the groundwater.  The arsenic is associated with the iron mineral through a process called adsorption. In the solid phase, the arsenic isn’t a threat to drinking water. However, if an oil spill occurs, the oil can induce significant chemical changes.

“If conditions are oxygenated, meaning there’s a little bit of dissolved oxygen in the groundwater, then life is good and [arsenic] is going to stay on the solid phase,” Ziegler explained. “But if you introduce oil, bacteria can eat oil and breathe oxygen in the groundwater.”

Once the bacteria use up all the oxygen, however, they can move on to breathing (respiring) other things, called electron acceptors.

“One [electron acceptor] is iron, which acts as a host for arsenic,” Ziegler said, “but when they [bacteria] do that, the iron gets dissolved into groundwater, and since that’s the host, arsenic, too, goes into groundwater.”

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A figure displaying overlapping plumes of dissolved arsenic (top graph) and iron (bottom graph)—part of the evidence that where iron dissolves, arsenic can creep into groundwater. Credit: Arsenic cycling in hydrocarbon plumes: secondary effects of natural attenuation in Groundwater 2015, doi:10.1111/gwat.12316.

Part of what makes monitoring arsenic in groundwater so challenging is that it can go virtually unnoticed for so long, largely because arsenic is difficult to detect. Another contributing factor is that oil spills understandably attract attention to the oil itself and the long-term secondary effects, such as arsenic release, are not considered. Couple that with the difficulty in noticing when arsenic has dissolved into groundwater, and it’s not hard to see how the public might assume that once an oil spill has been cleaned up, the crisis is over and everything can return to background conditions. As Ziegler and others have discovered through their research, it can take a long time after an oil spill has been cleaned up for things to truly return to normal.

Why hasn’t this effect been noticed until just recently? It’s partially due to the fact that studying the long-term effects of oil spills is generally difficult. Ziegler is currently studying the site of an oil spill that occurred in 1979 in northern Minnesota.  The site is maintained by the U.S. Geological Survey. 

“When there’s an oil spill, people try to clean it up as best they can, and try to prevent any further contamination,” Ziegler explained. “This oil spill was so remote that it wasn’t affecting anybody, so they took this environmental accident and turned it into a national research site.”

This research site, the National Crude Oil Spill Fate and Natural Attenuation Research Site, is a prime spot to discover long-term or secondary effects like the ones Ziegler and his research group have recently uncovered.

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Ziegler with a sediment core.

It’s important that the public be made aware of research like Ziegler’s, because without knowledge of such harmful potential secondary effects, it’s impossible to accurately evaluate the risk of development projects that impact our environment. This is especially true when considering spills that tend to cause tunnel vision.

“In the past, if there’s been an oil spill, people’s main concern is ‘oh my goodness, the oil,’ but now what we’re seeing is the secondary effects,” said Ziegler. “Since we’re always concerned about the oil, people never look for these other types of contaminants that could be equally as harmful.”

Raising public awareness of such effects and promoting research like Ziegler’s is crucial to ensuring that the public can make informed decisions about projects with high environmental impact.

“Especially with the renewed interest in the development of oil pipelines in the country,” said Ziegler, “we’re putting potential oil spills all throughout our aquifer systems throughout the United States, so the fact that this is just now documented—that this process that occurs in oil spills can put arsenic into groundwater—it’s got pretty big implications for development of these major pipelines throughout the country.”

Policy implications

Ziegler pointed out that research like his may impact public policy, especially policy that’s based on some specific risk assessment. An interesting example stems from the recent increase in earthquakes in Oklahoma. In 2008, Oklahoma experienced fewer than two earthquakes that measured above 3.0 in magnitude; in 2015, Oklahoma suffered over 1,000 3.0-or-higher-magnitude earthquakes. This increase is connected to the disposal of wastewater from hydraulic fracturing. The increase in earthquakes may be occurring at a rate too fast for infrastructure regulations to keep up. Oil pipelines that met infrastructure regulations in 2008, before the increase in earthquakes, may not be built to withstand the new earthquake frequency or magnitude.

What role does Ziegler’s research play in this? If infrastructure regulations are adapted to reflect the need to withstand more powerful and frequent earthquakes, certain risks will need to be reassessed—for example, are oil pipelines more likely to rupture due to the increased frequency and magnitude of earthquakes? If so, there’s more risk to consider than we previously realized; not only is it important to consider the immediate harm an oil spill could cause, it’s now critical to also consider long-term impacts such as the ones Ziegler is researching. Public awareness of the increased risk associated with oil spills may well shape public policy and regulations.

What should the public know?

What should the public consider as they become aware of this research and its implications? First, it’s important not to panic.

“I would say if you find that there’s arsenic in the groundwater in the oil spill site, you shouldn’t immediately freak out,” Ziegler said. “Aquifers tend to have a pretty good capacity to mitigate any sort of human-induced effects like oil in the aquifer. Give it enough space and enough time and generally they can clean themselves up.”

In addition to the hypothesis that an oil spill won’t render an aquifer unusable forever, it’s also worth noting that the dissolving of arsenic into groundwater is fairly localized; the arsenic likely won’t travel for long distances through groundwater and spread to other areas.

However, while aquifers may potentially “clean themselves up,” this process, called natural attenuation, can take a long time. Ziegler mentioned that the oil spill in Minnesota occurred in 1979, and his research team has recently recorded concentrations of arsenic in the groundwater there that are still 23 times the drinking water standard. Therefore, the public should focus on action they can take in the meantime. If people live near the site of an oil spill and they are on a private well, one simple and effective action they can take is to have their groundwater tested for arsenic. Carefully monitoring the groundwater and testing it every few months after an oil spill ensures that individuals have information about the quality of their drinking water, and will allow them to switch to a new water source if arsenic or other contaminants are detected in their water.

Secondly, it’s important to be more aware of the potential secondary or long-term effects of disasters like oil spills.

“We need to have a broader scope beyond just the petroleum contaminants themselves,” Ziegler said. “We need to look at other things that might not even have been in the actual oil when [the spill] occurred. Because as we now know, the changes in chemistry from the reactions induced by the oil can lead to other naturally occurring contaminants in groundwater.”

This is good advice for those tasked with cleaning up oil spills, but more broadly, this research should encourage the public to pay close attention to research projects that explore other secondary effects, as that enhanced knowledge ensures that we can react appropriately in future crises. In Ziegler’s case, the research has gained some traction. Minnesota newspaper editorials have inspired discussion about the research and its implications, and some press releases helped raise awareness about the issue.

This increased awareness has even aided public activism regarding environmental issues, such as that surrounding the addition of a new pipeline through Minnesota.

“There was one that was planned to go through northern Minnesota, very near where this oil spill site actually occurred,” Ziegler recounted, “and the local newspapers picked up the paper that we published and they said, ‘Look at these problems that are created from oil spills!’ so there was a public response from what we had published. Now whether or not that’s actually going to lead to them stopping the pipeline, who’s to say?”

While it may not yet be clear how ongoing projects will be affected by this research, it’s evident that public awareness is critical to reacting appropriately in a crisis such as an oil spill. Such research ensures that, in the event of a spill, the public knows what action they can take to help keep their drinking water safe. A public understanding of the risks posed by oil spills and thoughtful discussion on the topic also aid regulators in performing accurate risk assessment. Research like Ziegler’s, and the awareness it provides, enable all of us to make informed decisions.

Article written by Josiah Pierce while participating in ENGL 4824: Science Writing in Spring 2017 as part of a collaboration between Fralin and the Department of English at Virginia Tech.