Trivalent versus Hexavalent Chromium: Why Total Chromium Doesn't Tell the Whole Story
When laboratory reports mention chromium, they often refer to total chromium, which includes both trivalent chromium (chromium-3) and hexavalent chromium (chromium-6 or Cr(VI)). These two forms differ significantly in chemical properties and health considerations. A total chromium measurement cannot specify how much chromium(VI) is present, which is the form often discussed regarding water quality concerns. Therefore, relying solely on total chromium results obscures the specific presence and concentration of chromium-6.
The UCMR3 Nationwide Survey: Its Purpose and Household Limitations
Between 2013 and 2015, the Environmental Protection Agency (EPA) conducted the third Unregulated Contaminant Monitoring Rule (UCMR3) survey. Portsmouth Waterworks, serving approximately 33,000 people in Rockingham County through surface water sources, participated by providing chromium-6 data. The survey detected chromium(VI) in most samples, with the highest measurement at 0.46 micrograms per liter (µg/L or parts per billion). However, these measurements represent the public water system’s average and sampling points, not individual household tap water. To know specific chromium-6 content in your home, a direct test of your water is necessary.
Chromium-6 Versus Commonly Confused Water Problems
Chromium-6 differs from other water issues often raised by households such as iron, hardness, or microbial contamination. It is neither a taste nor odor problem but a specific chemical form of chromium requiring chemical analysis to detect. Unlike iron or hardness, hexavalent chromium does not cause staining or mineral buildup. Understanding the unique nature of chromium-6 helps focus on correct water treatment approaches if needed.
Ruling Out Other Factors: From Simple Checks to Laboratory Testing
Households concerned about chromium-6 should first verify if any visible signs or taste changes exist, although these are rare with chromium-6 alone. Following this, reviewing recent municipal water quality reports is useful. The Portsmouth Waterworks has no recorded health-based violations and maintains chromium concentrations well below total chromium standards. Ultimately, an accredited laboratory test on your specific water sample is the definitive step to determine your home's chromium-6 levels.
Oxidation State Changes in Water Distribution: From Source to Tap
Chromium's chemical form can change in the water supply chain. Hexavalent chromium (Cr(VI)) can be altered to trivalent chromium (Cr(III)) under certain chemical conditions, including pH, oxygen levels, and presence of reducing agents. These changes may occur between the water source, treatment facilities, distribution mains, and household plumbing. This dynamic nature affects what a tap water test reveals compared to source water data, adding complexity to assessing household chromium-6 exposure.
Distinguishing Aesthetic Secondary Standards from Health-Based Limits
Water quality regulations distinguish between health-based maximum contaminant levels (MCLs) and aesthetic secondary standards that address taste, odor, or appearance. For chromium-6, there is no current federal MCL, although total chromium has a 100 µg/L limit related to health-based criteria. Some states or agencies may set advisory levels or aesthetic guidance for chromium-6, but these do not signify a health violation. Understanding this helps households interpret monitoring data without undue alarm.
In summary, public water monitoring in Portsmouth’s Rockingham County detected chromium-6 consistently but at levels below any federal health-based standard. Determining your household’s chromium-6 requires testing your own water. If elevated levels are a concern, the Pentek Chromium-6 Filter ships ready to configure and is documented as an effective solution for reducing chromium(VI) in water.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2015-04-07. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR3 monitoring (2013-2015) for Portsmouth Waterworks (NH1951010), NH: 36 results across 2 listed contaminants, 31 detections above the reporting level; no federal MCL for hexavalent chromium; total chromium MCL 100 ug/L
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