Half of Piedmont drinking wells may exceed NC's hexavalent chromium standards

“Though often thought of as a by-product of industrial contamination, hexavalent chromium can form naturally in groundwaters, depending on the local aquifer geology and water chemistry,” said Avner Vengosh, professor of Earth and Ocean Sciences in the Nicholas School of the Environment at Duke.


Only a single North Carolina well in the study violated the maximum contaminant level for total chromium set by the U.S. Environmental Protection Agency of 100 micrograms per litre. But the NC Department of Health and Human Service’s much lower health advisory level – 0.07 micrograms per litre – is set to protect against a one-in-one-million risk of cancer over a 70-year life span. That level of hexavalent chromium was exceeded by 470 of the 865 wells for which the contaminant was measured.

“There is a huge gap between 100 and 0.07 micrograms per litre,” said Rachel Coyte, a doctoral student in Vengosh’s lab who was lead author on the study. “If you follow the EPA guidance, we have no problem. But if you look at the NC health recommendations, there is a significant population exposed to hexavalent chromium concentrations at or exceeding a one-in-one-million lifetime risk of cancer. Why is this gap not being addressed?”

The researchers used the large dataset to develop a model that predicts the occurrence of hexavalent chromium above the health standard in drinking water wells based on the well location’s geology, and on easily measured groundwater chemistry parameters such as water pH, oxygen content, and salinity. They also calculated the probabilities that a given well would exceed the 0.07 microgram per litre health advisory level for specific geologic belts in the state.

The occurrence of hexavalent chromium is predicted to be particularly high in wells located in the Piedmont region, where over 50% of the wells are expected to have concentrations of hexavalent chromium above the health advisory level, Vengosh said.

Statewide, nearly 4 million people rely on groundwater as their primary source of drinking water. "The areas where we see the largest number of groundwater users, like Wake and Mecklenburg Counties, coincide with some of the highest probabilities for the occurrence of hexavalent chromium above the health advisory level," Coyte said.

"Unlike public groundwater systems, private wells have no testing requirements and therefore many private well owners do not know the concentration of hexavalent chromium in their well water," Vengosh said. "Since we show that total chromium can be a good proxy for the presence of hexavalent chromium, homeowners can test total chromium, which is more common and cheaper."

While home water filtration for hexavalent chromium was not tested in this study, several technologies do exist to remove hexavalent chromium from drinking water, including reverse osmosis desalination.

The original study:

Rachel M. Coyte, Kristen L. McKinley, Sheng Jiang, Jonathan Karr, Gary S. Dwyer, Amy J. Keyworth, Christina C. Davis, Andrew J. Kondash, Avner Vengosh. Occurrence and distribution of hexavalent chromium in groundwater from North Carolina, USA. Science of The Total Environment, 2019; 135135 DOI: 10.1016/j.scitotenv.2019.135135

Related Studies:

Debra M. Hausladen, Annika Alexander-Ozinskas, Cynthia McClain, Scott Fendorf, Hexavalent Chromium Sources and Distribution in California Groundwater, Environ. Sci. Technol., 52 (2018) 8242−8251. DOI: 10.1021/acs.est.7b06627

Zoi Dokou, George P. Karatzas, Iraklis Panagiotakis, Dimitris Dermatas, Groundwater Modeling and Remediation Scenarios of a Hexavalent Chromium Plume Released from an Industrial Site, Bull. Environ. Contam. Toxicol., 98 (2017) 338–346. DOI: 10.1007/s00128-016-1951-z

Andrew H. Manning, Christopher T. Mills, Jean M. Morrison, Lyndsay B. Ball, Insights into controls on hexavalent chromium in groundwater provided by environmental tracers, Sacramento Valley, California, USA, Appl. Geochem., 62 (2015) 186–199. DOI: /10.1016/j.apgeochem.2015.05.010

A. Ramesh Kumar, P. Riyazuddin, Chromium speciation in groundwater of a tannery
polluted area of Chennai City, India, Environ. Monit. Assess., 160 (2010) 579–591.
DOI: 10.1007/s10661-008-0720-9

C. Bourotte, R. Bertolo, M. Almodovar, R. Hirata, Natural occurrence of hexavalent chromium in a sedimentary aquifer in Urânia, State of São Paulo, Brazil, An. Acad. Bras. Ciências, 81/2 (2009) 227-242. DOI: 10.1590/S0001-37652009000200009

A.R. Gonzalez, K. Ndung'u, A.R. Flegal, Natural Occurrence of Hexavalent Chromium in the Aromas Red Sands Aquifer, California, Environ. Sci. Technol., 39/15 (2005) 5505-5511. DOI: 10.1021/es048835n

David J. Gray, Naturally occurring Cr6+ in shallow groundwaters of the Yilgarn Craton, Western Australia, Geochem. Explor. Environ. Anal., 3 (2004) 359-368. DOI: 10.1144/1467-7873/03-012

Donatella Fantoni, Gianpiero Brozzo, Marco Canepa, Francesco Cipolli, Luigi Marini, Giulio Ottonello, Marino Vetuschi Zuccolini, Natural hexavalent chromium in groundwaters interacting
with ophiolitic rocks, Environ. Geol., 42 (2002) 871–882.  DOI: 10.1007/s00254-002-0605-0

D. Blowes, Tracking hexavalent Cr in groundwater, Sci., 295 (2002) 2024-2025. DOI: 10.1126/science.1070031

 Related EVISA Resources

 Link Database: Toxicity of hexavalent chromium (chromate)
Link Database: Legislation related to chromium
 Link Database: Methods for chromium speciation analysis 
Brief summary: ICP-MS: A versatile detection system for trace element and speciation analysis
Brief summary: LC-ICP-MS - The most often used hyphenated system for speciation analysis 

May 23, 2012: EFSA calls for scientific data on chromium speciation and nickel levels in food and drinking water 
April 11, 2012: EPA calls for more study on hexavalent chromium in drinking water
December 27, 2011: EPA ruling on hexavalent chromium in water expected soon 
May 26, 2011: Oral ingestion of hexavalent chromium through drinking water and cancer mortality
EVISA News, May 17, 2007: Hexavalent Chromium in Drinking Water Causes Cancer in Lab Animals

last time modified: September 22, 2024