Expanded
Summary
Consumer panel estimates of odor thresholds
for crude 4-methylcyclohexanemethanol
MI CHAEL J. MCG U IRE , I. H . (M E L ) SU F F E T, A N D J EF F R EY R O S EN
http://dx.doi.org/10.5942/jawwa.2014.106.0129
On Jan. 9, 2014, a spill of “crude” 4-methylcyclohexanemethanol (MCHM) into the Elk River in West Virginia
contaminated the water supply for 300,000 people. The
crude MCHM caused an intense licorice odor in the
drinking water that supplied the area in and around
Charleston, W.Va. A sensitive analytical method
developed by a commercial laboratory was used to verify
the concentrations of crude MCHM presented to a
consumer panel selected using specific criteria. The
method used for the panel studies was ASTM E679-04,
which has been used to determine other odor thresholds
in water. The odor threshold and odor recognition
concentrations for crude MCHM in water were estimated
by the consumer panel to be 0.55 and 7.4 µg/L, re­­
spectively. Two estimates of the odor objection
concentrations were 7.7 and 8.8 µg/L.
On Jan. 9, 2014, approximately 10,000 gal (approximately 38,000 L) of “crude” 4-methylcyclohexanemethanol (MCHM) spilled into the Elk River from the
property of Freedom Industries 1.5 mi above the drinking water intake of the West Virginia American Water
(WVAW) treatment plant. Shortly after the spill began,
consumers located in the area served by WVAW
(Charleston, W. Va., and environs) began complaining
of a licorice odor in their drinking water.
Although the water treatment plant had several treatment systems available to deal with taste and odor problems, the high concentration of crude MCHM in the raw
water overwhelmed all attempts to remove the compounds
(McGuire et al, 2014). On Feb. 9, 2014, an expert team
was hired to help the state of West Virginia understand, in
part, the odor characteristics of the spilled chemical and
the reactions of the customers served by WVAW. The purpose of this article is to describe the methodology used and
the results determined for the odor thresholds for crude
MCHM in water using a consumer panel.
The crude MCHM used in this work was sampled from
a storage tank containing the material that spilled into
the Elk River on January 9 (McGuire et al, 2014). Crude
MCHM instead of pure MCHM was used in this work
because an odor assessment of the concentrated compounds in the mixture made it clear that the odor experienced by Charleston residents was far more complex
than the odor of pure MCHM. Crude MCHM is a mixture of organic compounds in which pure MCHM
accounts for approximately 80% of the mixture by
weight (Neslund, 2014).
All sample-spiking was done on a weight of crude
MCHM to a volume of the matrix water. A neutral-odor
spring water was used as the water matrix for this work.
A low-level analytical method (0.5-µg/L method detection limit) developed and used by the commercial laboratory was based on a methylene chloride extraction and
analysis by gas chromatography and mass spectrometry
(GC/MS). The GC/MS analytical system was based on
the US Environmental Protection Agency method
SW-846, 8270D for semivolatile organic compounds
(McGuire et al, 2014; USEPA, 2007).
The method used for the panel studies was ASTM
E679-04 (ASTM International, 2011). A marketing
research firm recruited the 60 panelists for this study. The
firm randomly selected a group of people from their
database of 85,000 respondents. Panelists had to be
untrained consumers between the ages of 18 and 65. The
panel was composed of equal percentages of men and
women. Pregnant women could not participate and only
nonsmokers could be panel members.
Concentrations of the spiked crude MCHM were
given to the panelists in an ascending order of concentration from 0.027 to 60 µg/L in eight logarithmic steps.
MATERIALS AND METHODS
In this work, the odor threshold (detection) concentration (OTC) is defined as the concentration of an
organic chemical that about 50% of a panel of consumers can detect simply by using their sense of smell. The
odor recognition concentration (ORC) for an organic
chemical is that concentration in which about half of
the panelists can recognize and accurately describe the
odor characteristic of the organic chemical. The odor
objection concentration (OOC) is defined in this study
as the concentration of the organic chemical that about
half of the panelists find objectionable using two assessment methods.
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The panelists were given three cups at each of the eight
steps. One cup contained the spring water spiked with
crude MCHM and the other two contained only spring
water. Panelists were instructed to choose the cup containing the odor that was different from the other two.
Next, panelists were asked to record on the score sheet
what they thought the water in the different cup smelled
like. They were told that they could use any terminology
that described the characteristic of the odor in the different cup. If the water smelled like nothing (had no odor),
the panelists could write “nothing” on the score sheet.
Panelists were then asked to rate how much they liked
or disliked the odor of the water in the different cup using
the degree-of-liking scale found in Standard Methods
(2012). If the odor in the different cup was objectionable
and the panelist would complain to their water utility or
bottled water company, they were instructed to answer
yes on the score sheet.
All estimates of individual and group thresholds were
calculated using the procedure described in method
ASTM E679-04.
RESULTS AND DISCUSSION
The odor threshold and odor recognition concentrations for crude MCHM in water were estimated by the
consumer panel to be 0.55 and 7.4 µg/L, respectively. Two
estimates of the odor objection concentrations were 7.7
and 8.8 µg/L.
Figure 1 shows the log concentration–cumulative percentage plots for all of the thresholds determined in the
consumer panel studies. The OTC plot appears to be a
straight line with the crude MCHM concentrations pre-
FIGURE 5
Cumulative percentage plot of individual
OTC, ORC, and OOC values
OTC—odor threshold concentration
ORC—odor recognition concentration
OOC liking—odor objection concentration based
on degree of liking
OOC complain—odor objection concentration
based on complaints
CONCLUSIONS
The ASTM threshold determination method (ASTM
International, 2011) was successfully used to determine
the OTC, ORC, and OOC values for crude MCHM in
water during the same panel session. A previous study
using an expert panel evaluated the procedures that were
used during the consumer panels. Estimates of the odor
thresholds for MCHM in water were determined by a
consumer panel to be 0.55 µg/L for the OTC, 7.4 µg/L
for the ORC, and 7.7 and 8.8 µg/L for the OOC using
two methodologies.
Consumers in the Charleston area could recognize and
object to the licorice odor caused by crude MCHM even
though the concentrations of MCHM in drinking water
were listed as nondetect by many labs at a minimum
reporting level of 10 µg/L. The low odor thresholds
reported by the consumer panel in this work confirm
what consumers in Charleston were experiencing.
REFERENCES
ASTM International, 2011. Standard E679-04, 2011. Standard Practice
for Determination of Odor and Taste Thresholds by a ForcedChoice Ascending Concentration Series Method of Limits. ASTM
International, Philadelphia.
McGuire, M.J.; Rosen, J.; Whelton, A.J.; & Suffet, I.H., 2014. An
Unwanted Licorice Odor in a West Virginia Water Supply. Journal
AWWA, 106:6:72. http://dx.doi.org/10.5942/jawwa.2014.106.0091.
Neslund, C., 2014. Eurofins Lancaster Laboratories, Lancaster, Pa.
Personal communication. Feb. 19, 2014.
Standard Methods for the Analysis of Water and Wastewater, 2012
(22nd ed.). APHA, AWWA, and WEF, Washington.
USEPA (US Environmental Protection Agency), 2007. Semivolatile
Organic Compounds by Gas Chromatography/Mass Spectrometry
(GC/MS)—Revision 4. www.epa.gov/osw/hazard/testmethods/
sw846/pdfs/8270d.pdf (accessed May 6, 2014).
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Panelists Correctly Identifying
Spiked Sample—cumulative %
sented on a log scale. The other three plots are not linear
and are indicative of cumulative percentages plotted for
higher threshold concentration levels. More data of this
type for other compounds are needed before results such
as these can be put into the proper context.
Comparing the results for OTC, ORC, and OOC values
for both expert and consumer panels showed that the
expert panel estimated values for all three of the aesthetic
response measures that were less than those estimated by
the consumer panel (McGuire et al, 2014).
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Corresponding author: Michael J. McGuire (to whom
correspondence should be addressed) is president of
Michael J. McGuire Inc., 469 25th St., Santa Monica,
CA 90406 USA; [email protected].
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40
20
0
0.01
0.10
1.00
10.00
100.00
Crude MCHM Concentration—µg/L
Journal AWWA welcomes comments and feedback
MCHM—4-methylcyclohexanemethanol
66
at [email protected].
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