These Perfumers Are Analyzing the Stench of Toilets

As soon as you open the door, it hits you. The smell of a latrine or porta-potty can be overwhelming. But, what creates such putrid aromas?

The short answer is obvious. But the long answer involves a mixture of aromatic chemicals that produce a latrine's je ne sais quoi. Since the 19th century, scientists have had a general idea that sulfur and other fragrant compounds are likely at play. But, to make an odorless toilet, you have to know what makes it stink. Perfume researchers hope that if their techniques can suss out the chemicals behind the smells, they might be able to create an aromatic antidote.

Researchers in the R&D department of the fragrance company Firmenich first analyzed sludge from pit toilets in four countries in Africa and India. From sludge samples, they extracted and identified the key players. High levels of hydrogen sulfide, paracresol, indole and butyric acid, among other stinky compounds, all emerged from the sludge and likely contributed to its farmyard aroma, according to the results they published in 2013.

On some level, their results are not super surprising. However, every latrine is different, and that doesn't take into account the levels of such chemicals living in the latrine's "headspace" — the air above the toilet. Some volatile chemicals exist at really low levels in the air. Others are unstable as gases.

To analyze these gases, researchers trapped air from inside latrines or pit toilets in Kenya, India and South Africa in water. Expert perfumers verified analysis of the smells using an old fashioned form of odor measurement: the nose. All the latrines had similar levels of hydrogen sulfide, butyric acid, indole, and skatole, according to their findings in the May 19 Environmental Science & Technology.

The team also pinned individual toilet smells on specific compounds. For example, on the same block in India, one toilet smelled more like rancid vomit than another — probably because it had five times higher levels of the chemicals paracresol and a sulfur compound called methyl mercaptan which create that smell. Increased hydrogren sulfide pushed odor in a more sewage-like direction in the toilets of Behrampura Mohannathu, India.

The quality of the sanitation system also showed up in the smell. Well-maintained pit latrines in Nairobi, Kenya, had better ventilation and lower levels of sulfur compounds, producing more of a barnyard smell than a sewage smell. The type of toilet clearly mattered, too. In Durban, South Africa, and Nairobi, toilets that separated urine from feces had stronger smells than pit toilets.

Knowing the exact levels in latrine air could produce more effective odor fighting compounds. Worldwide, 2.5 billion people do not have access to a working toilet. Better ventilation in certain types of porta-potties or latrines can help control bugs and the smell to a degree, but poor sanitation has tangible fallout for public health. Bacteria from human waste can contaminate water sources, and kids can catch childhood diarrhea.

Much has been made of toilets of the future, but a truly odorless toilet is a long way away. That said, finding a way to control these odors based on their chemical profiles could pave the way towards a cheap, clean and perhaps even pleasant place to conduct one's business.

Helen Thompson | | READ MORE

Helen Thompson writes about science and culture for Smithsonian. She's previously written for NPR, National Geographic News, Nature and others.