However, public comment on this point was
requested, and promulgation of UCMR3 is not
expected until early 2012. Instead, EPA issued
guidance to water systems on voluntary
monitoring for Cr(VI). This guidance can
be found on the EPA Website. It includes
recommendations for sampling locations,
sampling frequency, and use of a modified
version of EPA Method 218.6.
In California, similar to the federal standard,
Cr(VI) is only regulated as part of total
chromium, though the MCL is lower at 50 ppb.
However, California’s Office of Environmental
Health Hazard Assessment recently published
a final public health goal (PHG) for Cr(VI)
at 0.02 ppb in July 2011. The California
Department of Public Health (CDPH) plans
to release a draft MCL within 18–24 months
of the PHG using the PHG as part of a cost-benefit analysis that also takes into account
occurrence, treatment feasibility and costs,
and setting the MCL as close to the PHG
as is economically and technically feasible.
CDPH is currently gathering information on
treatment technologies and costs to support
this analysis. Once the draft MCL is released,
CDPH plans to complete final rulemaking
within 12–14 months.
Hexavalent chromium is classified as a
known human carcinogen by inhalation
routes of exposure. For ingestion, the EPA
concluded in 1991 that the “body’s normal
physiology provides detoxification for Cr(VI),”
because Cr(VI) is reduced to Cr(III) in saliva
and in the digestive tract, and Cr(III) is a
required micronutrient with no carcinogenic
1 However, in 2008 the National
Toxicology Program (NTP) concluded there
was “clear evidence of carcinogenic activity”
in studies where rats and mice were exposed
to high doses of Cr(VI).
2 This NTP study
was used as part of the basis for California’s
PHG, but its conclusion was questioned by
the external peer review panel in EPA’s risk
The uncertainty surrounds the human health
effects of ingesting Cr(VI), particularly at low
concentrations. The main questions pertain
to whether the dose-response effect observed
at high doses in rats is linear or non-linear at
the low doses relevant to drinking water and,
thus, whether the mode of action of ingested
Cr(VI) is mutagenic or not. Studies conducted
by ToxStrategies, Inc., a scientific consulting
firm, are investigating the mode of action for
Cr(VI) and have shown non-linearity at low
doses. This data is important for low dose
extrapolation in the ongoing risk assessment.
Human epidemiology studies, as referenced
in the state of the science paper, have been
inconclusive due to various shortcomings.
There are several approved analytical
methods for measuring total chromium
in water. EPA Method 200.8, which
uses inductively coupled plasma–mass
spectrometry (ICP-MS), has the lowest
method detection limit (MDL), reported
as 0.08 ppb. However, research has found
problems with total chromium analysis in
real water samples using these methods,
which may be attributed to different factors.
Iron is one such factor, because particulate
iron can sorb chromium, and this particulate
chromium may not be measured.
Hexavalent chromium can be measured
by various analytical methods using ion
chromatography, high performance liquid
chromatography coupled with ICP-MS, or
field speciation. A complete list of available
methods is provided in the summary paper.
In general, analysis for Cr(VI) is more
sensitive than methods for total chromium,
but measurement of Cr(VI) is still a challenge
1. USEPA (1991)
Rule. Federal Register,
January 30, 1991, pp.
2. National Institutes
of Health (2008)
of Sodium Dichromate
Dihydrate, July 2008,