Natural sources of the toxic form of chromium appear in wells that provide drinking water to a large population in California, offering a new perspective on California’s groundwater management challenges.
(Image credit: Richard Thornton / Shutterstock) In a study that appeared online June 27 in Environmental Science & Technology, Stanford scientists used a statewide groundwater database and a new means of tracing sources to identify wells containing hexavalent chromium from industry versus those that became contaminated from naturally occurring sources – some of which may also have resulted from human activity.
“As we continue to push the need to use and manage groundwater, understanding how these naturally occurring contaminants can jeopardize water becomes really, really important.” Benign vs. toxic chromium The benign, natural form of the chemical, known as trivalent chromium, is needed to help people break down glucose.
(Image credit: Debra Hausladen and Scott Fendorf) The toxic form, hexavalent chromium, is very soluble and moves easily within the environment.
Industrial uses of hexavalent chromium include electroplating, steel manufacturing, leather tanning and wood treatment.
Drinking water that contains hexavalent chromium, also known as chromium-6 or Cr(VI), is considered a human health threat, increasing the risk for stomach and intestinal cancer.
Based on where they find the toxic form in the Central Valley and other regions, the study co-authors suspect human activities, such as groundwater pumping, could contribute to that transformation.
Of those, 15 percent contained higher levels of hexavalent chromium than the 2014 drinking water standard of 10 parts per billion.
The scientists determined which of the 234 other chemicals in the database were commonly found with hexavalent chromium and used that information to figure out where natural occurring chromium is threatening groundwater quality and which processes may be responsible.
“It’s really important to have this holistic view as we develop groundwater management strategies.” The researchers hope to create more detailed distribution maps of where naturally occurring contaminants can threaten groundwater and the pathways that would cause them to move into California’s water system.