From the Editor

Asparapee or aspara-EP?

Evan Zabawski | TLT From the Editor December 2018

Dinner conversation amongst tribologists.

During a dinner with colleagues a few weeks ago, the server brought the table a plate of asparagus to share. Its arrival immediately shifted the conversation to discussion about the well-known aftereffects of consuming asparagus, something we call “asparapee” in my family. Beginning with a humorous story about a friend’s first such experience, the topic was closed with a request to see if I could find a way to work the asparapee phenomena into my column. Challenge accepted.

Though not all people are affected by the distinctive sulfurous odor, it was only recently scientists determined why. In 1891 Polish chemist and doctor Marceli Nencki was the first to investigate the cause of the odor, which he concluded came from the production of methanethiol, but it wasn’t until 1956 that a Nature paper by Allison and McWhirter showed that not all people excrete methanethiol.

This characteristic is known as a polymorphism, a discontinuous genetic variation, which they showed occurred in 46 out of 115 subjects. This was later reconfirmed in a 1987 Experientia paper by Mitchell, Waring et al. that showed 344 out of 800 volunteers produced odorous urine after eating asparagus, reproduced over the course of a year, and proven through family studies to be inherited as an autosomal dominant trait (meaning either parent can pass it down with a 50% chance).

Another polymorphism was discovered by later research, which showed some people could not detect the smell in their own urine and some people could only detect the smell in other people’s urine. This proved that while some people really did not produce the odor, others simply cannot smell the odor independently of their ability to produce the odor. A 2016 study of the genetic data from 6,909 men and women narrowed the cause of the asparagus anosmia (specific loss of smell) to 871 different genetic alterations in the 4,161 participants who could not detect the odor.

For those of us who can smell the odor, we can all agree it is decidedly foul. A 1987 Xenobiotica paper from Waring, Mitchell et al. identified up to six sulfur-containing alkyl compounds responsible for the odor and suggested S-methylmethionine and asparagusic acid as the precursors. Other than the previously known methanethiol, the other five were dimethyl sulfide, dimethyl disulfide, bis-(methylthio)methane, dimethyl sulfoxide and dimethyl sulfone.

Half of these compounds have uses in food and pharmacological applications, but the other half have been used in relation to formulated hydrocarbon products. Methanethiol also is known as methyl mercaptan, the odorant added to natural gas to help detect leaks, and dimethyl sulfoxide has been used as the reaction solvent in the complexing of a metal salt from a fatty acid to produce antiwear additives.

Dimethyl disulfide (DMS), on the other hand, has been used directly as a lubricant additive—specifically for its antiseize and antiwear properties under extreme pressure conditions. One paper that investigated these properties, titled Surface Chemistry and Extreme-Pressure Lubricant Properties of Dimethyl Disulfide, was co-authored by one of TLT’s regular columnists, Dr. Eddy Tysoe.

Though DMS is produced commercially, it also is commonly found in nature and is the dominant source of sulfur in the atmosphere. Oceanic DMS produces that sweet/tangy smell landlubbers associate with the smell of the sea, whereas sailors would say it is the smell of the shore, and seagulls simply think of it as the smell of food. DMS is created when bacteria feed on dimethyl sulfoniopropionate, which is produced by the phytoplankton found in ocean water. The smell, noticeable by humans in concentrations as low as 0.02 ppm, telegraphs the location of plankton blooms to birds.

I neglected to mention the other side effect of consuming asparagus—aspara-gas; famously addressed in a satirical essay written by Benjamin Franklin proposing scientific testing of flatulence, and that other scientific investigations were “scarcely worth a FART-HING.”

Evan Zabawski, CLS, is the senior technical advisor for TestOil in Calgary, Alberta, Canada. You can reach him at ezabawski@testoil.com.