Research article
Received: 18 August 2015,
Revised: 22 September 2015,
Accepted: 27 September 2015
Published online in Wiley Online Library: 2 November 2015
(wileyonlinelibrary.com) DOI 10.1002/ffj.3293
Sensory survey of key compounds of toilet
malodour in Switzerland, India and Africa
Charles Jean-François Chappuis,* Yvan Niclass, Isabelle Cayeux
and Christian Starkenmann
Abstract: Improving sanitation in developing countries is a key issue. New toilets must be clean and well maintained and must
present a pleasant olfactory experience. Knowledge about toilet malodour is crucial to create pleasant perfumes for toilets. To
identify the key constituents of toilet malodour, we created synthetic reconstitutions based on our previous analytical work,
and we performed sensory surveys in Switzerland, India and Africa to evaluate the efficiency of our synthetic reconstitutions
made of selected key compounds to evoke toilet malodor. The olfactory stimuli were two reconstitutions of faecal odours and
a reconstitution of stale urine odour. We also used three perfumes as controls: banana, lemon and lavender. Participants
from Geneva (N = 21, Switzerland) and from the slums of Ahmedabad (N = 105, India), Nairobi (N = 143, Kenya) and Durban
N = 144, South Africa) were familiar with all odours presented. They described banana, lemon and lavender as pleasant odours
and both faecal reconstitutions and stale urine reconstitution as unpleasant odours. Faecal reconstitutions were identified as
odours that emanate from faeces or latrines in all countries. These results confirm and consolidate those of previous studies
on faecal odours in identifying butyric acid, p-cresol, indole and dimethyl trisulfide as strong contributors to human faecal
odour. © 2015 The Authors. Flavour and Fragrance Journal published by John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: faeces; malodour; olfaction; perfume; toilets; urine
Introduction
* Correspondence to: Charles Chappuis, Firmenich SA, Corporate R&D Division,
P.O. Box 239, CH-1211 Geneva 8, Switzerland. E-mail: charles.chappuis@
firmenich.com
Firmenich SA, Corporate R&D Division, P.O. Box 239, CH-1211Geneva 8,
Switzerland
This is an open access article under the terms of the Creative Commons
Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is
non-commercial and no modifications or adaptations are made.
Flavour Fragr. J. 2016, 31, 95–100 © 2015 The Authors. Flavour and Fragrance Journal published by John Wiley & Sons, Ltd.
95
More than 2.5 billion people lack proper sanitation worldwide, leading to various diseases that contribute substantially to the global
burden of disease in developing countries. The improvement of
sanitation would not only reduce the transmission of diseases associated with human faecal material, but would also have a positive
impact on social and economic aspects of life.[1] The Bill & Melinda
Gates Foundation project, ‘Reinvent the Toilet Challenge’ (RTTC),
aims to implement sustainable sanitation facilities that are adapted
to different cultures and environments such as India and Africa. In
addition to the design of new toilet systems, including waste
management and cleaning cycles to maintain the toilets in hygienic
conditions, the Bill & Melinda Gates Foundation pays attention to
the olfactory experience during toilet use because the perception
of cleanliness is also driven by odour.[2] Thus, implementing
pleasant fragrances in clean toilets will communicate a message
of good sanitation in hygienic conditions and promote their usage.
In this context, Firmenich, a world leader in the fragrance industry, is
involved in the RTTC project to create the perfumes that will make
the use of toilets a pleasant olfactory experience.
In developing a perfume that is pleasant in the background of
toilet odour, it is critical to identify the molecules that create a negative perception and understand their volatility and odour threshold. Toilet malodour consists of a complex mixture of volatile
compounds arising from faecal material and stale urine. Analysis
of the odours emanating from human waste is a challenging task
because these odours change over time and can vary depending
on individual diet and health.[3–6] Moreover, faecal material and
urine are rich in volatile organic compounds (VOCs). Together, faecal and urine odours contain more than 200 VOCs from various
chemical classes such as carboxylic acid, sulfur compounds,
nitrogen compounds, aldehydes, alcohols, phenols, ketones, steroids, lactones, alkanes and terpenes.[7–10] The identification of
key compounds from such a list is difficult because of the lack of
information about the contribution of each compound to faecal
or urine malodour. Fortunately, recent publications showed that
only a small number of these compounds contribute to the odour
of both types of human waste. Headspace analysis and gas
chromatography-mass spectrometry equipped with sniffing ports
(GC-MS-O) revealed the importance of some phenols, indole, skatole, amines and sulfur compounds for stale urine odour.[11,12]
Using similar methods, Lin et al.[13] showed that the odour of pit
latrines in India and in Africa was mainly faecal and stemmed from
sulfur compounds, short-chain fatty acids, indole, skatole and
phenols. They identified important constituents of human waste
odour, but did not reconstitute the odour with synthetic compounds as the ultimate test. Knowledge of the key compounds
should make it possible to reconstitute toilet malodour by combining synthetic key compounds, resulting in stable and reliable
references for toilet malodour. This will be a strong asset in the development of perfumes, allowing testing of perfumes in a stable
C. J.-F. Chappuis et al.
age: 31.8 ± 12.8 years) and 144 from Durban (99 females and 45 males,
age: 37.4 ± 14.4 years).
background of toilet malodour. Moreover, using these reconstitutions instead of using unstable and contaminated toilet sludge will
help engineers to develop new ventilation or waste management
systems to reduce toilet malodours.
In this study, we performed sensory surveys in the field to evaluate the efficiency of synthetic faecal and urine reconstitutions made
of selected key compounds to evoke urine and faecal odours. In a
first step, we created more than 50 synthetic reconstitutions of stale
urine and faecal odours by combining the compounds found by
Troccaz et al.[11] and Lin et al.[13] With the help of a master perfumer,
we selected three reconstitutions that were the most representative of stale urine and faecal odours. We ensured that our mixtures
evoked stale urine and faecal odour by means of an internal
sensory panel of experts in Switzerland. In a second step, we
performed our study in the countries where RTTC implementation
projects took place. The RTTC project primarily aims to implement
toilets for people living in the slums of India and Africa, which
involve dissimilar cultures. Recognizing that the perception of an
odour can be influenced by cultural traits,[14–16] we interviewed
on-site participants from the slums of Ahmedabad (India), Nairobi
(Kenya) and Durban (South Africa). The participants smelled the
three malodour reconstitutions, as well as pleasant odours used
as controls. They were asked to rate the intensity, familiarity,
pleasantness and degree of association with eight descriptors.
Because we used the same experimental protocol in each country,
we were able to compare the data obtained from the sensory
surveys performed in Switzerland, India, Kenya and South Africa.
Stimuli
The participants were exposed to seven odors delivered by Sniffin’ Sticks[17]
that were loaded with 4 mL of diluted perfumes in triacetin, a non-odorous
solvent. We used three malodor reconstitutions: a reconstitution of stale
urine (named “stale urine”), a reconstitution of fecal odor (named “fecal
reconstitution”) and a more complex reconstitution of fecal odor (named
“latrine reconstitution”). We used three odors as controls: banana, citrus
and lavender.
The stale urine reconstitution was composed of trimethyl amine, indole,
p-cresol, dimethyl disulfide and 2-methoxy-4-vinylphenol. The fecal reconstitution was composed of butyric acid, indole, p-cresol and dimethyl
trisulfide. The latrine reconstitution was composed of butyric acid, 2methylbutyric acid, 3-methylbutyric acid, phenylacetic acid, indole, skatole,
p-cresol and dimethyl trisulfide. The concentrations and ratios were in the
range of the values found in the field by Lin et al.[13] The ingredients used
in this study and the banana, citrus and lavender perfumes were provided
by Firmenich (Geneva, Switzerland).
Questionnaire: scales and measures
We designed the test to be as simple as possible to avoid confusion and to
maintain the spontaneity of responses. The participants were interviewed
with the use of a questionnaire (Supplementary Figure 1). Participants were
asked to rate the intensity of the odor on a 5-point scale from “no odor” to
“very strong” and to rate the pleasantness of the odor on a 7-point scale
from “I don’t like” to “I like.” To rate the pleasantness rating, we presented
a picture with a scale showing seven smileys, representing a smile gradient
(Supplementary Figure 2). The familiarity was rated as a binary answer to
the question, “Have you ever smelled this odor?” We asked the participants
if they use toilets or defecate in the open. The participants were also asked
to rate the degree of association between the odors and eight pictures
(descriptors) on a 5-point scale from “does not correspond” to “corresponds
strongly” (Supplementary Figure 3). The pictures were presented in random
order and accompanied by a corresponding legend that had been translated into the local language of each country (Gujarati, Swahili, Zulu,
French). The gray-scaled pictures depicted human stool, a latrine, an open
sewer, a man urinating, bananas, lemons, leaves and a flower. The pictures
were discussed with our partners in each country to find an acceptable
trade-off for the choice of pictures and their respective labels. These
pictures were then presented to the participants and explained by the enumerators. The participants could rate the degree of association between an
odor and more than one picture or could reject all pictures.
In Ahmedabad, India, the participants were recruited by the Self Employed
Women’s Association (SEWA). In Nairobi, Kenya, the participants were
recruited by Mrs. Millicent Kasaya (freelance project coordinator). In Durban,
South Africa, the participants were recruited by Mr. Ngiyabonga Scelo Xulu
(Ethekwini Water). The age of the participants ranged from 18 to 80 years
and their level of education varied widely, some of them being illiterate.
All participants lived in informal settlements or slums. A total of 463 adult
participants were interviewed. Eight participants quit the interview; the
responses of 42 of the remaining 455 participants (9.2% of the total) were
discarded. In Switzerland, the 21 participants were from Firmenich
(12 females and 9 males, age: 41.6 ± 10.7 years). In the other countries,
we interviewed 105 participants from Ahmedabad (58 females and 47
males, age: 35.7 ± 15.1 years); 143 from Nairobi (85 females and 58 males,
Latrine
Urine
Banana
Citrus
Lavender
c
ac
a
ab
bc
ac
bc
1
de
de
e
de
e
e
e
−3
e
e
de
de
d
0
−1
−2
Pleasantness
c
2
ac
a
3
Faecal
ac
Participants
ac
Experimental
India
Kenya
South Africa
Switzerland
96
Figure 1. Mean ± 95% confidence interval (CI) of pleasantness ratings as a function of odor and country. Means with different letters are significantly different following a multicomparison test based on a generalized least squares model
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Sensory survey of key compounds in toilet malodour
A
1.0
0.6
0.4
lav:sa
lav:swi
lav:ken
lav:ind
0.5
ur:ken
ur:ind
flower
leaves
bl:ken
lemon
cit:ind
−1.0
−0.5
0.0
0.5
1.0
cit:sa
cit:swi
−1.0
−0.6
fec:swi
ban:swi
cit:ken
−0.5
faeces
lat:swi
−1.5
urine
bl:ind
ban:ken
latrine sewage
faecesban:ind
ban:sa banana
0.0
0.0
lemon
banana
flower
leaves
fec:ken
latrine sewage
lat:ind
lat:sa
lat:ken
fec:safec:ind
−0.2
Dim 3 9.38 %
0.2
bl:sa
−0.4
Dim 4 4.09 %
B
ur:sa
urine
ur:swi
1.5
−1
0
Dim 1 56.52 %
2
1
Dim 2 28.97 %
Figure 2. Results of the correspondence analysis with descriptors (triangle and italic labels) and odors for each country (dots). Fec, lat, ur, ban, cit, lav and bl
represent fecal reconstitution, latrine reconstitution, stale urine reconstitution, banana, citrus, lavender and blank, respectively. Ind, ken, sa and swi represent
India, Kenya, South Africa and Switzerland, respectively. The closer the odor to the descriptor, the stronger the association. (A) Descriptors and odors plotted
as a function of Dimensions 1 and 4 (Dim). The labels of the pleasant odors (ban, cit, lav and bl) associated with the descriptors “lemon,” “flower,” “banana”
and “leaves” are not shown for clarity. (B) Descriptors and odors plotted as a function of Dimensions 2 and 3. The three reconstitutions of malodors (fec, lat
and ur) are closely associated with the descriptors “feces,” “latrine,” “sewage” and “urine” (labels not shown for clarity)
questions under our supervision. They were trained to collect the data without influencing the participant’s answer. In Ahmedabad, the eight enumerators comprised four females and four males aged 30 to 40 years; in Africa,
the enumerators were younger, aged 20 to 30 years. We also asked that,
preferably, female enumerators interview females and male enumerators
interview males. This rule was not strictly followed, but when an enumerator interviewed a participant of the opposite gender, the participant had to
first agree.
Interviewing conditions
Participants were invited to be interviewed in a nearby building. In
Ahmedabad, the interviews were performed at the SEWA organization
headquarters. The temperature outside was 45 °C and we could maintain
an inside temperature of 32 °C with ceiling fans and air conditioning. In
Nairobi, we performed our survey in a church in the Mukuru slum. The temperature was not controlled and varied between 28 °C and 31 °C. In Durban,
the study was performed in a community building of Bester with a temperature of between 25 °C and 28 °C. In Geneva, the experiments took place in
ventilated cabins with a temperature of 22 °C.
Interviewing procedure
The enumerator read a consent form to the participant that had been translated into the local language that explained the study. The participant had
to sign the consent form or apply his or her fingerprints. The consent form
and the experimental protocol were approved by the internal review board
of Firmenich in agreement with the Declaration of Helsinki for Medical
Citrus
ghij
ij
hij
defj
befg
ac
ad
j
ij
ij
ij
bef
eh
adf
de
a
ac
cdf
cdef
4
3
1
2
Intensity
Lavender
cdefj
Banana
efj
Urine
adefi
Latrine
5
Faecal
abd
In each country, we trained eight enumerators. The training consisted of a
general introduction, after which they smelled the sticks and answered the
adef
Enumerator training
India
Kenya
South Africa
Switzerland
Flavour Fragr. J. 2016, 31, 95–100 © 2015 The Authors. Flavour and Fragrance Journal published by John Wiley & Sons, Ltd.
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Figure 3. Mean ± 95% CI of intensity ratings as a function of odor and country. Means with different letters are significantly different following a
multicomparison test based on a generalized least squares model
C. J.-F. Chappuis et al.
Statistical analysis
The data were analyzed with the statistical program R.[18] The intensity
and pleasantness data were analyzed by a generalized least squares
model to take into account the repeated measures and the
heteroscedasticity of variances.[19] Because the response variable familiarity was binary, a generalized linear mixed model (GLMM) with a logit
link function (binomial family) was used.[20] Non-responding participants
were added when the proportion was 100% to render the analysis possible. For GLMM, the individual variable was used as the random effect
and the variables odor, country and sex were set as fixed effects. To render possible the integration of the country variable in the models, we
discarded the results obtained with the blank, as no odor was found
with it in Switzerland. The multicomparison tests were achieved by
using the multcomp R package.[21] The data obtained for the association
between the odors and pictures were transformed into a binary variable,
as the distribution clearly showed a binomial distribution. The dependence between the descriptors (the pictures) and the odors was
2
assessed by χ tests and the results shown using factorial analysis. The
level of significance was set at 0.05.
Results
B
a
a
80
60
b
40
60
40
20
a
a
b
80
b
0
0
Familiarity, percentage
b
20
a
b
Familiarity, percentage
A
100
The participants in all countries perceived banana, citrus and
lavender perfumes as pleasant odors and fecal, latrine and stale
urine reconstitutions as unpleasant odors, showing that the reconstitutions were perceived as malodors (Figure 1). Moreover, the test
with pictures showed that the odors were not randomly associated
with the descriptors (χ 2 = 6007.36, df = 182, P < 0.0001) and revealed that the stale urine and both fecal reconstitutions were significantly associated with the descriptors “stale urine” and “feces” in
all countries (Supplementary Table 1). The association of the three
malodors with their respective pictures, however, was weaker than
the association of banana and lemon odors with their respective
pictures (Figure 2A and B, Supplementary Table 1). In fact, both
fecal reconstitutions were also significantly associated with the
descriptors “latrine” and “sewage” in every country except Switzerland, where no reconstitutions were significantly associated with
“sewage” (Figure 2A, Supplementary Table 1). The stale urine was also
significantly associated with the descriptors “latrine,” “sewage” and,
to a lesser extent, “feces” in some countries, although the stronger association was with the “stale urine” descriptor (Figure 2A,
Supplementary Table 1). Both fecal reconstitutions were not significantly associated with the “stale urine” descriptor in every country except Kenya (Figure 2A, Supplementary Table 1). The Kenyan
participants associated the fecal reconstitution with the “stale urine”
descriptor, but this association was weaker than the association of
the fecal reconstitution with the “feces” descriptor (Supplementary
Table 1). Although the participants used several descriptors for
the malodor reconstitutions, they could discriminate between
the stale urine and the fecal reconstitutions. They were not, however, able to discriminate between the fecal and latrine reconstitutions, because both produced similar results in every country
(Figure 1 and 2A, Supplementary Table 1). Like the malodor reconstitutions, the lavender odor was associated with more than
one descriptor. It was significantly associated with the descriptors “leaves,” “flowers” and, to a lesser extent, lemon in Kenya
and India (Figure 2B, Supplementary Table 1).
In India, Kenya and South Africa, both fecal and latrine reconstitutions were perceived as significantly stronger than odors such
banana, citrus and lavender (Figure 3). In Switzerland, no odor
was perceived to be significantly more or less intense except citrus,
which was perceived to be significantly less intense than the fecal
reconstitution. Stale urine reconstitution was perceived to have an
intensity that was between that of the pleasant and the unpleasant
odors. It was judged to be significantly weaker than fecal and
latrine reconstitutions only in India and in South Africa (Figure 3).
The familiarity ratings were less odor specific than were the
intensity or the pleasantness ratings. Although the proportion of
people who felt familiar with the banana and the citrus odors
was significantly higher than the proportions who felt familiar with
the other odors, the highest difference between proportions did
not exceed 8.1% (Figure 4A). More than 80% of the participants
overall (regardless of country) felt familiar with the odors (Figure 4A).
Participants in India felt less familiar with all odors compared with
participants in other countries (Figure 4B). No significant effect of
sex was found for the intensity, familiarity or pleasantness
ratings.
The blank was perceived at an average intensity ± 95%
confidence interval (CI) of 1.29 ± 0.12, 1.40 ± 0.13, and 1.60 ± 0.15
in India, Kenya and South Africa, respectively. In Switzerland,
no odor was perceived in the blank, whereas 30.7% of the
100
Research involving Human Subjects. All signed forms for India were kept by
Dr. Myles F. Elledge (RTI International, USA), whereas the forms from other
countries are being safely kept in Switzerland.
Each participant was interviewed only once by trained enumerators in
the local languages. The enumerators collected the data, explaining the
scales and the pictures if necessary. The enumerators used thirty sets of pictures that were placed in randomized order and numbered. Each questionnaire corresponded to a specific set of pictures. The participant was asked
to smell the seven Sniffin’ Sticks presented in random order and to rate
the measures described earlier.
Faecal Latrine Urine Banana Citrus Lavend.
India
Kenya South Africa Switzer.
98
Figure 4. Proportion of participants who felt familiar with an odor as a function of odor (A) and country (B). Proportions with different letters were significantly different following a multicomparison test based on a generalized linear mixed model
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© 2015 The Authors. Flavour and Fragrance Journal published by John Wiley & Sons, Ltd. Flavour Fragr. J. 2016, 31, 95–100
80
40
0
Percentage
Sensory survey of key compounds in toilet malodour
India
Kenya
South Africa
Figure 5. Proportion of participants using toilets for defecation by
country.
participants from other countries perceived an odor when
sniffing the blank. When the blank was described as an odorant,
the mean pleasantness ± 95% CI was 0.7 ± 0.88, 0.61 ± 0.54, and
0.78 ± 0.49 in India, Kenya and South Africa, respectively. The
percentage of participants who felt familiar with the blank
was 52.38% (n = 22), 83.78% (n = 37) and 80.36% (n = 56) in
India, Kenya and South Africa, respectively.
The proportion of people who reported using toilets to defecate
was lower in India than in Africa (Figure 5). As this proportion was
above 90% in Africa, we integrated this variable into the data from
India only to assess whether the use of toilets affects the perception of malodors related to toilets. No significant effect of the use
of toilets was found on the intensity, pleasantness or familiarity
ratings.
Discussion
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This study aimed to evaluate whether the synthetic fecal, latrine
and urine reconstitutions evoked urine and fecal odors and to
define the pleasantness or unpleasantness of these odors across
countries.
It was a challenge to set up a sensory survey in slums in three
different countries with participants who had different levels of
education. The interviewing room in Ahmedabad was hot, and
the air conditioning, in addition to the rotation of the ceiling fans,
made conditions difficult. In Nairobi, we were hosted in a church in
the slum, and so the participants were spread out around a large
space. In Durban, we were hosted in a community building, but
the survey created excitement in the community and noisy conditions. Thus, the participants in India and Africa were not isolated in
a booth with controlled temperature and ventilation, as was the
case for the internal panel in Switzerland. We maximized the
distance between each participant in the space available and,
despite the ventilation and the noise, we were able to collect
relevant data. The participants were not paid, but our partners in
India offered plastic lunch boxes, and in Africa, they offered a soda,
a chocolate bar and Jeyes Fluid, a multipurpose cleaner.
The picture choices were made after discussion with our partners from India, Kenya and South Africa. We used banana and
lemon odors as positive control of pleasantness and to estimate
the ability of participants to associate an odor with an image.
Bananas and lemons are common in these countries and we determined that the picture should be associated with these odors. We
also added lavender as a pleasant odor control that people from
slums of Africa and India should not be used. Finally, one stick filled
only with the solvent was used as a negative control, called the
blank. The background noise observed in the results obtained for
the blank can be explained by the difficult conditions; in addition,
the sticks were presented in random order and thus if a participant
started with the blank, they may have been confused and felt the
need to describe a smell. The presence of a background noise for
the blank was a good indication that the sensory survey was well
conducted and that the enumerator did not try to influence the
responses. The responses of 42 participants were discarded
because the participants failed to associate at least the banana
or the citrus odor with the respective picture. Eight participants
also quit the test because they were unable to smell the odor or
for other undefined reasons.
Despite these difficulties, we demonstrated that it is possible to
mimic the odor of human feces, the main source of pit latrine malodor, on three different continents by using only four molecules.
The fecal and latrine reconstitutions differed in chemical composition but produced similar results in terms of pleasantness, intensity
and familiarity and were similarly recognized as malodors emanating from feces, latrines or sewers. The fecal reconstitution
contained butyric acid, p-cresol, indole and dimethyl trisulfide,
whereas the latrine reconstitution contained these compounds
and additional four also found in the sludge of pit latrines and in
stools: 2-methyl butyric acid, 3-methyl butyric acid, phenyl acetic
acid and skatole.[7,8,13] Although the additional four compounds
changed the odor of the reconstitution, the results show that butyric acid, p-cresol, indole and dimethyl trisulfide contribute more
to evoke an olfactory experience of using latrines. These four compounds have previously been described as important components
of human fecal odor;[3,22] some of these compounds, namely,
p-cresol and indole, have been known as constituents of fecal
odor since the 19th century.[23] Butyric acid is formed by the fermentation of carbohydrates, principally starch,[24,25] p-cresol by
the fermentation of tyrosine, and indole by the fermentation of
tryptophan.[26] In the case of the sulfur compounds, we used
dimethyl trisulfide found in the sludge of pit latrines,[13] a good
alternative to gaseous hydrogen sulfide and methylmercaptan.
Hydrogen sulfide and methylmercaptan are produced from the
anaerobic decomposition of fecal material and sludge. They play
an important role in human fecal and pit latrine odors.[22,27]
The stale urine reconstitution was recognized as a malodor
emanating from urine in every country, but it was also associated,
to a lesser extent, with latrine, sewage or feces, depending on the
country. On the one hand, stale urine differs qualitatively from
fecal odor by the presence of a significant amount of trimethyl
amine and the lack of carboxylic acid,[11] which explains the strong
association of the stale urine reconstitution with the descriptor
“urine” in every country. On the other hand, the odor of stale urine
and feces share key compounds such as indole, p-cresol and
methylmercaptan. This could explain the association of stale urine
with the descriptors “feces” and “sewage,” as well as the association of fecal reconstitution with the descriptor “urine” in Kenya.
Our results show that some descriptors overlap, especially
those for malodors. The participants chose the descriptors
“feces,” “latrine” and/or “sewage” for the fecal and latrine reconstitution but discriminated much more between the banana
and citrus odors by choosing mainly the respective descriptor
for each odor. A similar overlap was obtained with the lavender
odor that was associated with the “leaves” and/or “flower” descriptors. This overlap can be explained by the proximity of
the olfactory experience that the descriptors can evoke. Indeed,
the odor of the flower and of the leaves contribute to the odor
of the entire plant, just as the odor of feces contributes to
latrine malodor.
The “sewage” descriptor is also close to the other descriptors of
malodors. The smell of sewage is due to sulfur compounds such as
hydrogen sulfide and methylmercaptan. We found that in some
slums in Africa and India, when the latrine has no pit but is
C. J.-F. Chappuis et al.
connected to a drainage system, the smell of sewage discharges
into the latrine. We can thus reasonably affirm that the olfactory
experience during the use of these types of latrines can be close
to that of smelling the odor of a sewer in India and in Africa. Alternatively, the overlap between the descriptors for malodors could
originate from the fact that malodors provoke an unpleasant experience and thus may reduce the time and attention required for an
adequate analysis of the odor, as proposed by Herz[28] and
Ferdenzi et al.[16] The perception of an odor is a complex process
in which sensory inputs and cognitive factors intervene.[29] Thus,
a superficial analysis of the odor can reduce the ability to discriminate it. The measure of time spent smelling an odor could be an
interesting variable to examine, as it may covary with pleasantness.
The differences in the perception of our reconstitutions were
limited across countries. This is in line with the fact that the perception of decomposing materials and waste, such as human or animal waste, has a certain level of consensus across different
cultures.[14,30,31] Moreover, the fecal and latrine reconstitutions
were recognized as malodors emanating from feces or latrines in
every country, although we can expect the odors of such material
to differ slightly with diet. This observation shows that the combination of key compounds in our reconstitutions evoked the odor
of a latrine worldwide.
The odor emanating from latrines is a complex mixture of
various compounds. Nonetheless, we demonstrated that a fecal reconstitution composed of only four molecules and the stale urine
reconstitution evoked fecal and stale urine odors, respectively,
the two sources of toilet malodor. The compounds described in
this paper were recently found in significant concentrations in
the headspace of latrines in India and in Africa,[27] supporting the
evidence that we identified the key odorants of toilet malodors.
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Funding
This research was equally co-founded by Firmenich and the Bill &
Melinda Gates Foundation.
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Acknowledgements
We would like to express our appreciation to the following people:
Dr. Myles F. Elledge, Senior Director of RTI International (USA), for
helping us organize the survey in Ahmadabad; Mrs. Ritu A. Sinha,
Head-Strategic Alliances, RTI India; the ladies team from SEWA (Self
Employed Women’s Association); and M. Sumeet Patil, Research
Director at Neerman, Environmental, Engineer & Economical Consultant, Mumbai, India. We would also like to thank the following
people: in Nairobi, M. David Auerbach, co-founder of Sanergy
and Peter Khaemba; in Durban, South Africa, Prof. Chris Buckley
of the University of KwaZulu-Natal for coordinating the odor sampling, along with Dr. Lungi Zuma from Ethekwini Municipality; the
perfumers Makarand Kamat from Firmenich India and Gary Marr
from Firmenich USA, for the selection and fine-tuning of the reconstitutions; and Dr. Laurent Wünsche, Director of the Analytical
Innovation team for his critical remarks, as well as Nadine
Gaudreau, Christine Saint-Léger and Pauline Lederrey for their help
in testing the protocol.
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