EDITOR’S NOTE (September 11, 2020): Following the article’s publication, some of the interviewees have personally requested to have their names omitted from the story.
Located nearby UPLB, Sacay Grand Villas residents were bothered by a sulfur-like smell two weeks prior to August 31. However, they are soon relieved when they found out that the cause was anything but volcanic.
In actuality, the cause was a blooming Callery Pear tree, located within the campus’ Palma Bridge.
This is otherwise known as the “Sperm Tree.”
The stench of dread
Residents were worried when initial speculation pointed to the scent being a sign of possible volcanic activity. Specifically, from Mt. Makiling, where active hot springs could be found.
According to the Philippine Institute of Volcanology and Seismology (PHIVOLCS), however, no volcanic earthquakes were recorded in the area. The agency described Mt. Makiling as an inactive volcano.
“An ina[c]tive volcano has no recorded eruptions, its physical form has been intensively weathered and eroded, and bearing deep and long gullies. For the past several weeks, no significant earthquakes have been monitored in the area,” the agency said through Messenger.
PHIVOLCS also assured that the steams and hot springs are normal for inactive volcanoes, adding that some areas of the Makiling Mud Spring were barricaded to avoid coming into contact with people.
Residents described the odor as resembling sulfur, specifically sulfur dioxide, which is released when magma nears the surface. It can be likened to that of a rotten egg.
“Parang super lalang amoy bulok na itlog na amoy damo at lupa,” one Sacay resident said.
Her mother, meanwhile, found the smell indescribable, adding that it was noticed by everyone else in the community.
“Naku ‘di ko ma describe. Masakit sa ilong at throat,” she explained.
Their family driver, Zyril Dumbrique, said that the smell was pungent near the Saint Thérèse of the Child Jesus Parish.
Chancellor candidate Dr. Jose Camacho, Jr., vice president of the homeowners association, has also been observing the smell.
“I think I and my neighbor including the security guard and caretaker are aware of the smell. It’s not yet alarming,” Camacho said.
Nature at work
The Callery Pear, also known as the Pyrus calleryana, is a flowering tree usually found in China and Vietnam. It is widely planted in the United States but is considered as an invasive species.
Its smell is the reason why the Palma bridge in UPLB is known as the “Sperm bridge” by students due to the prominence of the tree’s odor in the area.
According to Dr. Glenn B. Gregorio, the director of the Southeast Asian Regional Center for Graduate Study and Research in Agriculture (SEARCA), the tree emits a foul odor like semen to attract an insect to pollinate for its flower.
“It’s the flower of a sperm tree near Palma bridge. It emits a foul odor like semen to attract a specific inse[c]t pollinator of its flower,” Gregorio said in an interview with the Perspective.
Comparing the stench to that of a Dama de Noche‘s (night-blooming jasmine) or a Sampaguita, both smelled during nighttime, Gregorio explained that it was amides behind the scent.
“Ang sulfur kasi para siyang itlog diba? Parang utot gano’n, which is the borderline between the sperm and the rotten egg or rotten fish, kaya parang may Sulfur siya. But it’s amides, because of the ammonia. Ammonia iyon eh. Ma-free radicals, which is a volatile substance, kaya yon ang naamoy nila,” he said.
An amide refers to a nitrogen-carrying chemical compound that is derived from ammonia by replacing hydrogen with any other element. Ammonia can be traced to decaying remains of organic matter, such as dead animals or rotting plants.
On why they only smell during evenings, as confirmed by residents, Gregorio explained that at sunrise, the pollen would no longer shed.
“Every specific oras, alas nuwebe (nine o’clock), alas otso (eight), alas siyete hanggang gabi. Tapos pag-araw wala na ulit. Kasi pag may sun hindi na nagsheshed ang pollen niya. May specific time kasi pag nagsheshed ng pollen ang halaman,” Gregorio discussed.
According to him, this was because the plants only had a specific time to do that.
“Like rice, nagbubuka lang ang bulaklak niya from nine o’clock to 11 o’clock in the morning. Ang mais ganun din,” he added.
Residents reassured
On whether or not the stench is harmful, Gregorio believed that while it takes time to get used to it, some people might be allergic to it.
“I think hindi naman siya harmful, pero may iba, I think, na allergic doon. Yung iba allergic sa amoy, pero ako sanay na ako,” he said.
Gregorio added that the tree deserves to be studied further.
“Maganda isya pag-aralan kasi may social aspect at scientific aspect siya. It’s like kapok dahil during gradutaion lumalabas ang kapok. Kung ako magstudy niyan aalamin ko yung method of propagation niya, may seedling ba noon,” Gregorio said.
The residents were relieved to find out that the smell was coming from a Sperm Tree near Palma bridge.
“Thank God at hindi yung worst na naiisip namin. Sabi ni Pareng Glenn [Gregorio], pag mag -O-October, nangangamoy daw talaga yan pero hindi every year,” another resident said.
On what might happen had there been an actual volcanic eruption, a resident explained that things would have been extremely difficult.
“Malaking problema yon like kahit lockdown, walang students sa campus[. H]owever, may mga residents pa din. So if ever nga ganon (buti nalang at hindi) dapat immediate evacuation,” she said. [P]
Photo from Tucson.com
UPLB Perspective 
“At sunrise, the pollen would shed” and “Kasi pag may sun hindi na nagsheshed ang pollen niya” are contradicting statements.