How Can Toilet Odors Be Reproduced? Developing Sources for Deodorizing Tests

To compare toilet deodorizing performance, is it enough to introduce the same amount of odor into a test room? In practice, the route matters too: odor originates inside the bowl and spreads through the gap between a seated person’s body and the toilet seat.

A 2012 study explored ways to reproduce this pattern of odor release experimentally. Researchers made simulated fecal sources containing ammonia, a device supplying controlled amounts of gas, and an emission-source strip attached to the toilet rim, examining what each method could readily reproduce.

Standardizing the source before comparing deodorizing products

The authors’ concern was that tests distributing gas uniformly throughout a room do not adequately represent emissions from a toilet bowl. Immediately after excretion, odor compounds escape from warm waste. Between uses, deposits adhering to the toilet can become sources. Test methods need to accommodate both short-term changes and sustained emissions.

The researchers installed a toilet in a temperature- and humidity-controlled experimental room of approximately 4.98 cubic meters. The main conditions were a room temperature of approximately 25°C, relative humidity of approximately 50%, and 0.5 air changes per hour. Air sampled from the room’s center was analyzed for ammonia, and a separate instrument tracked concentration changes over time. The target was ammonia, not the entire mixture of toilet odors, and this was not a sensory test of perceived unpleasantness.

The gap between seat and body varied greatly between people

First, 10 men and 10 women aged 20–22 sat on the toilet seat while researchers measured the opening bounded by their thighs, crotch, and the seat. Its mean area was 39.2 square centimeters, with a standard deviation of 32.6 square centimeters, indicating substantial individual variation. Measurements ranged from 0 to 157 square centimeters.

The authors suggest that sitting position and leg opening, as well as body build, contribute to this variation. They therefore constructed a sliding device placed over the seat with an adjustable opening. Subsequent comparisons standardized it to the mean area of 39.2 square centimeters. This was an attempt to reduce the changing conditions caused by having a person sit on the seat each time.

Concentrations change over time with actual urine and feces

Separately from the opening-area survey, urine and fecal samples were collected from six men aged 20–24 and placed in the toilet immediately after excretion. Urine and feces were measured separately rather than mixed.

For example, for feces from one participant whom the authors considered representative, ammonia concentration was 1.8 mg/m³ during the first five minutes, reached 1.9 mg/m³ after 12 minutes, and then fell to 1.2 mg/m³ after 24 minutes. For the same person’s urine, it rose from an initial 0.35 mg/m³ to 0.68 mg/m³ after 18 minutes, then reached 0.56 mg/m³ after 24 minutes. A test at a constant concentration alone would struggle to represent this initial increase followed by a decline.

Longer observation of another sample showed high concentrations again around 120 minutes. The authors suggest that sample temperature may contribute initially and bacterial decomposition later. This is an explanation for the concentration changes, not a mechanism established by directly manipulating bacterial activity in this study.

Sponge and clay sources produced a rise followed by a fall

The simulated sources were a sponge soaked in aqueous ammonia and paper clay kneaded with the solution. Clay has the advantage of being readily shaped and weighed to resemble feces.

With the sponge, room concentration rose from an initial 0.28 mg/m³ to 0.39 mg/m³ after 120 minutes, then fell to 0.21 mg/m³ after 480 minutes. With clay, it similarly rose from 0.33 mg/m³ to 0.41 mg/m³ after 120 minutes, then fell to 0.22 mg/m³ after 480 minutes.

Both produced an increase followed by a decline. Under the preparation conditions used, however, initial and attained concentrations were lower than with actual feces, and neither was suitable for long-lasting, constant emissions. Making a source look similar does not necessarily reproduce the amount of gas released or its changes over time.

The gas-supply device and source strip serve different situations

The next device pumped ammonia gas stored in a bag into the toilet bowl. The flow was controlled, and the supplied gas was warmed to approximately 36°C, close to the temperature of freshly excreted samples. Adjusting the gas supply allowed control of initial concentration and its subsequent changes, and supported relatively long emission tests.

Across three repeated measurements, the standard deviation of concentration at individual measurement times was 0.01–0.06 mg/m³. The authors concluded that, among the methods examined, this produced stable emissions and could be used to test products such as deodorizing toilet seats. However, the apparatus costs more than sponge or clay sources.

Another main component of the study was a strip simulating emissions between toilet uses. A strip-shaped sponge containing ammonia solution was attached beneath the toilet rim. The purpose was to simulate odor emitted from deposits on the bowl, including the location of the source.

This method reached 1.5 mg/m³ after 480 minutes, or 2.10 ppm using the original paper’s conversion, approaching the range of between-use concentrations the authors took from previous reports. It suggested a possible source for simulating emissions between uses, but the amount of ammonia released at each time interval could not be determined and remains a topic for further work.

Summary

Reproducing toilet odors requires standardizing not only the substance and concentration, but also where in the bowl it emerges and how emissions change over time. In this study, sponge and clay sources produced a rise followed by a decline, but initial concentrations were lower than with real samples. The gas-supply apparatus allowed easier adjustment of emissions and was stable across repeated measurements.

The strip attached beneath the rim was also a candidate for simulating continuing emissions while the toilet was not in use. Mixed urine and feces, and the strip’s emission rate over time, were not tested. Refining these conditions can help bring deodorizing tests closer to everyday settings.

Research affiliations and assistance: At the time of the research, two authors were affiliated with LIXIL and one with the Life Science Research Laboratory. The acknowledgments mention assistance from the Life Science Research Laboratory and describe the study as part of the social activities of an indoor environmental technology research group. No separate research-funding or conflict-of-interest declaration was found.

Reference

Nishina H, Sugiyama N, Suzuki A, Narita Y, Nozaki A. Studies on the Odor Substance Pollution in the Toilet Space (Part 1): Ammonia Emission Method from Toilet Bowls. Indoor Environment. 2012;15(1):15–25. doi:10.7879/siej.15.15