“Chromium in aquatic systems occurs
as either as the Cr3+ cation or Cr(VI) oxyanions”, aka hexavalent
chromium (Vengosh et al, 2016). Cr(VI) is a pulmonary carcinogen that poses a
threat to human health. Most often associated with anthropogenic releases, as
in the famous 2000 Erin Brockovich case in California, Cr(VI) can also occur
naturally in aquifers with ultramafic rocks that are enriched with Cr. When
exposed to manganese oxide minerals, Cr undergoes oxidation and leads to the
presence of Cr(VI) in aquifers.
State officials tested wells near
Duke Energy’s coal ash basins last year. When they found elevated levels of
Cr(VI) in the drinking water, local residents were worried that the coal ash
was the culprit. The North Carolina Department of Environmental Quality (DEQ)
and Department of Health and Human Services (DHHS) recommended that residents
within 1500 feet of a coal ash basin, and whose drinking water had a
concentration of 0.07 ppb hexavalent chromium do not drink their water (CWNC,
2016). Five million people in North Carolina (roughly half of the population)
rely on well water. The state of North Carolina spent the better part of a year
in turmoil over these findings, with many residents condemning the Duke Energy
coal-fired power plant.
The
Charlotte Observer, a newspaper in Charlotte, North Carolina, published an
article on October 26, 2016 entitled “Coal ash not the source of well
contaminant, Duke University study finds” (Henderson, 2016). The article
reviews the study published by researchers at Duke University on October 26,
2016 (web version) in the journal, Environmental
Science and Technology Letters. The news article summarizes the results of
the study, along with quotations from the lead author, a state toxicologist,
and a representative from Duke Energy. The author explains two different
methods that the researchers presented as evidence that the Cr(VI) present in
the wells was not from coal ash. First, the research team used tracers to
identify the source of the hexavalent chromium by looking at the geochemical
profile of boron, strontium and arsenic. Because coal ash contaminants have
their own distinctive signature, the research team was able to examine the
water samples to see if they matched the typical profile of coal ash. It was determined
that the water samples containing Cr(VI) had a geochemical profile that was distinctly
different than that associated with coal ash. Secondly, the researchers found a
high level of Cr(VI) pollution in wells measured over a large area. If the coal
ash had been the source, researchers would have expected to find an elevated
concentration in wells closest to the coal ash, and a lower concentration in
wells further away. This was not the case, suggesting that a more uniform
source was at play. The article summarizes the public health implications of
these findings. The most concerning detail is that hexavalent chromium does not
have a standard associated with it outside of the level set for total chromium.
This is an issue because hexavalent chromium is toxic at lower levels than the
total chromium threshold, and Cr(III) is less of a health threat than Cr(VI).
The purpose of the study carried out
by researchers at the Duke was to determine whether the Cr(VI) contamination of
aquifers was caused by the coal ash ponds or if it was a naturally occurring
phenomenon. The authors were looking for geochemical signatures that matched
those known to be associated with coal ash ponds, including elevated levels of
Strontium and Boron, along with distinct ratios of Sr isotopes. The authors hypothesized
that the geochemical signatures found in the aquifer would match those of coal
ash ponds. Water samples were taken from 376 groundwater wells in central North
Carolina. Of these samples, 77 were tested for Cr(VI) and Sr isotopes. All
samples were analyzed for major and trace elements. For the 77 samples, the
results ranged from below the reporting limit (0.0016 µg/L) to 33.8 µg/L, which
a fairly big range. Results showed that Cr(VI) accounted for nearly all of the
dissolved Cr in groundwater. Additionally, the concentrations of B and Sr, as
well as the isotope ratios for Sr, did not match those associated with coal
ash. Lastly, Cr(VI) concentrations
were not correlated with distance from coal ash ponds, suggesting that the
source of Cr(VI) is more likely natural. Using the California Maximum
Contaminant Level (MCL) for hexavalent chromium, and assuming that Cr(VI) is
the predominant species in drinking wells, 90% of the wells sampled had detectable
levels of Cr(VI), all of which are above the California Public Health Goal
(PHG) of 0.02 µg/L. An increased screening program was suggested.
Overall, I think that The Charlotte Observer article did a
very decent job. Some of the concepts in this study could be overwhelming to
the lay population. For example, instead of talking about isotopic ratios, the
author explained it as looking at the unique “fingerprints” of elements. I
think that the important points were covered, and the author suggested the
implications for public health, which is the next step. One major error I found
in the popular article was that the authors stated that 376 water samples were
taken, and that 90% of the samples contained elevated levels of Cr. This shows
that the author did not carefully read the study, as only 77 of the water
samples were actually analyzed for Cr(VI) and the isotopes. The author missed
an important point in the results section: “…indicates that Cr(VI) is the
predominant species of dissolved Cr in groundwater and accounts for nearly all
of the dissolved Cr.” (Vengosh et al, 2016).
Rating:
9.5/10
Henderson, Bruce. (26 October 2016). "Coal
ash not the source of well contaminant, Duke University study finds."
<http://www.charlotteobserver.com/news/local/article110465702.html>
Clean
Water for North Carolina (CWNC) (14 March 2016). “State reversal on hexavalent chromium
in well water an outrage.” Clean Water
for North Carolina.
<http://cwfnc.org/drinking-water/state-reversal-on-hexavalent-chromium-in-well-water-an-outrage/>
Vengosh, A., Coyte, R., Karr, J., Harkness, J.S., Kondash, A.J., Ruhl, L.S., Merola, R.B., Dywer, G.S. (2016). Origin of hexavalent chromium in drinking water wells from the Piedmont Aquifers of North Carolina. Environmental Science & Technology Letters
http://pubs.acs.org/doi/abs/10.1021/acs.estlett.6b00342
Very interesting article, Aubrey! I took a look at the Charlotte Observer article, and agree with your rating. The article did a good job using more lay terms to describe some of the more technical concepts of the study. I also liked how they added the background on how hexavalent chromium came to public notice via a movie. It reminds me of how Rachel Carson's Silent Spring brought DDT to public notice and catalyzed the environmental movement in starting in the 1960's.
ReplyDeleteI actually think, compared to other articles from popular media websites, this article did an exceptional job summarizing the findings from the study (besides the error you stated). The title wasn't catchy or click-bait or inflammatory, and neither was the content. It just states the findings of the case that are of most concern to the public. It'll be interesting to see whether the EPA sets a separate standard from hexavalent chrome.
That's an insightful parallel you drew to Rachel Carson and DDT. If you haven't seen the Erin Brockovich movie, I highly recommend it!
DeleteNice work Aubrey! I agree with your evaluation of the article. Although the author did make a critical misinterpretation, they covered important aspects of the study as well as implications behind it. Something I'd like to point out is that Cr(VI) can affect many other systems of the body such as the reproductive system. Because of this, it seems strange to me that the EPA does not control for Cr(VI) alone like Kesiree mentioned. Because it is possible to test for Cr(VI) isotopes like in this Duke study, why would there be no regulations on the allowable level? Especially considering that this form of chromium is fairly toxic. Just some general curiosities I had; great post!
ReplyDeleteThis is a good point, especially considering that Cr(VI) can be tested for using ion chromatography, which is less expensive than isotopic speciation methods. I think it is strange that the EPA does not control for Cr(VI) independently of total Cr, too. On the EPA website, it states that some public water providers are required to monitor for Cr(VI) for a one-year period, but this is much different than an enforced standard. It appears that the EPA will be considering adding a MCL for hexavalent chromium in the near future.
DeleteGreat post! I really liked how you summarized the results of the study. I found it easy to read. I also really liked the article you chose. I thought it was well written and easily understandable for people who aren't scientists which is important because this seems to be a big public health issue in North Carolina. I was curious about it there is a way to remove Cr(VI) from well drinking water or a way to purify it. The article mentioned that people who rely on these wells are being provided different drinking water. But I wonder if the wells will ever be safe to drink from again. I also found it disappointing that North Carolina's DEQ won't set their own standard for Cr(VI) since it is a big problem for them. They just plan to adopt any changes that the federal government does and there's a change no new standard will be made.
ReplyDeleteGreat point, Stacey. I was curious about removal options as well. After a quick google search, it appears that there are options available, such as an ion exchange filter or reverse osmosis. However, because these are individual wells and not a community water source, household filters would be needed. Both of the two above options can be expensive and require installation and maintenance. Because they are not designed specifically for Cr(VI) removal, careful research would be needed to ensure that the selected model removes the target contaminant.
DeleteThe chromium levels from these samples had a huge range and I'm curious how that could be? Were the wells perhaps at different depths and the higher chromium was found in the deeper wells? I think knowing why the levels were higher in certain wells would be important for identifying people at most risk to chromium exposure.
ReplyDeleteIdentifying people at risk is very important, and given the high variability it would probably require testing each individual well. From my interpretation of the ESTL journal article, the high variability is due to the underlying rock formation. It is possible that different wells tapped into different aquifers, which may have different containment sediments/formations with different chemical properties. But even the same aquifer can have very localized properties, leading to different geochemistry and therefore different levels of Cr(VI).
DeleteOne thing that does concern me with this study, as nice as it is that the authors cannot link Cr(VI) levels to the local mines, is that there will be folks who are non-scientifically literate and will try to use these results to say that there is no link anywhere between coal mines and groundwater contamination. We have to make sure that people with the wrong agenda of advancing their own interests don't manipulate the data. I think though that EPA should be taking more heat in this regard as they don't have set regulations for Cr6+ levels in drinking water (only the Cr3+ and Cr6+) combined. One only has to look to Norman, Oklahoma (city with the highest Cr6+ level in drinking water) and their history of Cr6+ levels in drinking water and it is easy to see where the EPA has failed. Who knows...maybe the Cr6+ levels in Norman are a result of the mining in that state?
ReplyDeleteI strongly agree with your point about the EPA not taking more heat for this issue. After all, we have known about the dangerous health effects of hexavalent chromium for decades, and the EPA just reviewed the total chromium guidelines in 2010 (perfect opportunity to make the addition!?). I did not even think about your second point, but you are right. I would not be surprised if people, particularly industry, look to the results of this study in the future to try to generalize the effects of coal ash on all cases of hexavalent chromium levels.
DeleteGood job, Aubrey! I totally agree with your opinion that the Charlotte Observer article did a very decent job. And you chose a quite interesting topic that you find the relationship between coal ash and well contamination. As we all know, Cr(VI) is a pulmonary carcinogen that poses a threat to human health. And the research is of great significance. And I am looking forward to hearing more advanced researches on Cr(VI) in groundwater and well contamination.
ReplyDeleteThank you, Qi! I am glad you enjoyed the article.
DeleteGreat article! I did not realize that the EPA does not have standard regulations set for Cr(VI) in drinking water, which is very alarming. I hope that high levels of Cr(VI) seen recently in drinking water will promote further efforts in establishing regulations as well as understanding where the source of Cr(VI) is coming from.
ReplyDeleteI agree, Amie. As I replied above, I am also surprised by the lack of Cr(VI) regulation. There was even a very popular movie (staring Julia Roberts) released in 2000 called "Erin Brockovich" which was premised on the poisoning of a community by Cr(VI). This has been no secret health threat, and I think the EPA has failed in this aspect.
DeleteNice job, Aubrey! You mentioned that the article tested Boron and Strontium in the water samples to try to see if the coal ash was the source of the water pollution. Did they include the quantity of these other elements found in the water? I know Boron can form a weak acid in solution, which could possibly affect pH levels and thus lead to health and environmental concerns. Did the authors of the study seem concerned at all about the level of these contaminants in the water?
ReplyDeleteInteresting idea, Annabel. The article states that there were "low" levels of boron in the aquifers, so this was likely not a problem. The authors did not present information on Sr and B as if the levels were of concern. They also reported Ca levels in the results, I am not sure how Ca might interact with any weak acid.
DeleteThanks for the post! I liked the articles and was not aware this was going on. What a serious and wide spread problem for the people of North Carolina to be dealing with. I googled a little and Cr(IV) isn't removed by most filters- only reverse osmosis. I wonder how they'll tackle it with such a large proportion of people using well water! It will be interesting to keep an eye on this in the future.
ReplyDeleteThe fact that half of North Carolina's population relies on well water makes this issue all the more difficult to combat. Many residents have been drinking from water bottles since the State tested high levels of Cr(VI) last year. A sustainable solution will surely be a challenge, and may take an engineered solution to properly and cost-efficiently filter individual wells.
DeleteInteresting article. I certainly do know how toxic Cr(IV) can be as it is a common reagent in synthetic organic chemistry. It is a bit nerve-racking to think that it is in some peoples drinking water. Is Cr common in this region of the world and/ or how dies it compare to other Cr levels throughout the country with respect to well water? Also, is there anything that can be done in these communities to treat the well water?
ReplyDeleteAccording to the authors, Cr(VI) is common in areas with aquifers composed of ultramafic rocks (NC, CA, AZ) or in areas with anthropogenic inputs (Chicago, IL, St. Joseph, MO, etc.). Brazil, Argentina, Italy, Mexico and Greece also have elevated levels of Cr(VI) due to ultramafic rocks (In Vengosh et al, 2016). It is possible to remove Cr(VI) using reverse osmosis, however it would need to be installed for each well and would need to be a system capable of removing Cr(VI) as not every RO system would.
DeleteInteresting article! I was not aware that this was a problem in North Carolina and I did not know so many residents rely on well-water. While it was good for the research group to confirm that the majority of the Cr(VI) wasn't coming from the coal ash due to the distinct chemical composition of the contaminated water, I also wonder if any of that data can be used to determine if coal ash is contributing any pollutants to well-water outside of Cr, B, and Sr. I think it will be interesting to watch how this story further develops after these early findings and if the geological source of the Cr(VI) will be more concretely identified.
ReplyDeleteGood point, Taylor. It would have been interesting to see what, if any, contaminants from coal ash could be found in the aquifer. Coal ash contains a slurry of highly toxic chemicals, including vanadium, arsenic, mercury, lead, cadmium, selenium, radioactive elements, etc. It would have been a great opportunity to test a plethora of wells for all of these contaminants. However, given the urgency in North Carolina and the anger of the public, I think the authors were very focused in their study. This is also evident in the fact that they published in Environmental Science and Technology Letters, which is designed for stream-lining temporally relevant papers.
DeleteNice Post Aubrey! I think that the different studies that they have done are incomplete. In addition to the metals that they mentioned in the article they could also have analyzed other components that can cause worse health problems to the population. Normally metals such as mercury, nickel, lead, silver and cadmium should also monitored because they are known to be toxic to the environment. Waste created by coal plants and gas factories can contain these compounds and can poison drinking water or kill fish and other wildlife.
ReplyDeleteGood point, Maria. As I replied to Taylor, I think the authors were looking to publish data specific to hexavalent chromium as quickly as possible given the high degree of stress in North Carolina over the State findings of Cr(VI) in water. This is a "hot topic", and had the authors findings suggested that Duke Energy's coal ash was responsible, there would have been a very large community response. The fact that the authors published in Environmental Science and Technology Letters is further evidence of the authors' immediate intentions, as this journal is meant to publish papers as soon as accepted for timeliness. Corporations like Duke Energy undergo routine monitoring by state and/or federal agencies (the initial Cr(VI) testing was performed by the state). Part of the issue in this case is that Cr(VI) is not regulated; only total Cr.
DeleteThat being said, the Duke Energy coal ash ponds in question are unlined ponds, allowing them to leak into the aquifers. So it would be a good idea to monitor the well water in the region regardless. As a side note, Duke Energy has recently stated that it will be "safely" closing the coal ash ponds in the area, which makes me a little suspicious given the timing.