Sensory survey of key compounds of toilet malodour in Switzerland, India and Africa

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.

Simulating latrine conditions to assess perfume performance against malodour

“…Our gas‐phase reconstitution of Mukuru UDT malodour was evaluated as strong and very faecal. This is in line with our previous work and with research showing the importance of butyric acid, p ‐cresol, indole, hydrogen sulfide, and methyl mercaptan as components of human faecal odour . Releasing the sulphur compounds stably is challenging because they are unstable gases.…”

“…This is in line with our previous work and with research showing the importance of butyric acid, pcresol, indole, hydrogen sulfide, and methyl mercaptan as components of human faecal odour. 2,3,17 Releasing the sulphur compounds stably is challenging because they are unstable gases. We overcame this problem by releasing mixtures of both compounds in nitrogen from pressurized cylinders.…”

“…Over the course of several field trips we analysed the sludge of toilets in Africa and India, and selected 19 molecules to prepare 40 reconstitutions of toilet malodour . Using ‘Sniffin’ Sticks’, pen‐like odour dispensers, we validated the most representative reconstitutions in sensory surveys with local people in India and Africa . We found that a mixture of only four compounds, butyric acid, p ‐cresol, indole, and dimethyl trisulfide, was necessary to evoke toilet malodour .…”

“…Using ‘Sniffin’ Sticks’, pen‐like odour dispensers, we validated the most representative reconstitutions in sensory surveys with local people in India and Africa . We found that a mixture of only four compounds, butyric acid, p ‐cresol, indole, and dimethyl trisulfide, was necessary to evoke toilet malodour . We used dimethyl trisulfide because it is a liquid at room temperature with an odour that approaches that of hydrogen sulfide and methyl mercaptan, two important components of toilet malodour .…”

“…2 We found that a mixture of only four compounds, butyric acid, p-cresol, indole, and dimethyl trisulfide, was necessary to evoke toilet malodour. 2 We used dimethyl trisulfide because it is a liquid at room temperature with an odour that approaches that of hydrogen sulfide and methyl mercaptan, two important components of toilet malodour. 3,4 We developed an analytical method to quantify hydrogen sulfide, methyl mercaptan, butyric acid, p-cresol, indole, and skatole in the headspace of latrines in Africa and India.…”