Scent is a powerful thing for many species. For humans, scent impacts taste on our tongues, and it’s even been linked to memory recall.

For wildlife, smell is even more critical, essential to survival.

According to Jordanna Sprayberry, a professor at Stony Brook University on Long Island in New York, people are messing with the “smellscape,” as it’s known, leading to odor pollution.

She told The World’s Host Marco Werman that there are actually two kinds of odor pollution.

“One is what I would call additive odor pollution. And those are things that human beings put into the world that are pretty stinky,” Sprayberry said. “Think of your diesel exhaust or chemical fertilizers and chemical fungicides. These are artificial chemicals that we make that have really strong odors that we are putting into the environment. The other kind is subtractive odor pollution. So, when we have car exhaust, your nitrous oxides, your ozone radicals, those actually can interact with the molecules that make up floral scent and turn them into a different kind of molecule and pull them out of a blend. So if, say, canola flower has eight molecules, when it gets run through the ozone, it drops down to seven and then six and then five, and suddenly it doesn’t smell like what an insect is expecting anymore.”

Marco Werman: And what does that mean in the long run for, like, canola oil?

Jordanna Sprayberry: What it means is that certain crops, like canola oil, are going to be potentially much harder for insects to find from a distance. Modeling studies show that when odor plumes travel short distances, the ability of a searching insect to find food goes down. That means that odor is going to be really important for a searching insect to find its way to enough flowers in order for it to get enough resources to lay enough eggs for the species to persist.

And there have been studies done by a really great group of folks in the UK indicating that the presence of ozone is reducing pollinator visitation to some of these agricultural crops because of the way that it’s interacting with floral scents.

Well, we’re speaking with you, Jordanna, as a growing number of scientists are documenting how humans are changing the chemical signals of plants and animals. Where in these various studies is there pretty much unanimous agreement?

Where there is unanimous agreement is that there is cause for concern. There are very few studies that show us there’s nothing wrong. Almost every study shows that odor is changed, and many studies that look at how odor is changed show a change in behavior. And if we’re changing behavior and we’re changing the landscape, we could be disrupting conservation stability.

Where are we seeing this in the world? How widespread is it?

Well, human activity has changed the atmosphere over the entire globe. So, anywhere you are seeing ozone, anywhere you are seeing nitrous oxide. It’s going to be much more concentrated in industrial sections, and it’s going to be more concentrated in agricultural areas. So, anywhere you’re seeing a lot of vehicular exhaust or industrial exhaust. And some crops are really reactive, have molecules that are really reactive to ozone, and they appear to be very susceptible to things like industrial air pollution or human-based activity creating modifications in floral scents. Others seem to be really stable. So apples, that scent really doesn’t seem to be impacted by ozone at all.

You spoke about the canola flower, the source for the cooking oil.

It’s clear how this is primarily an issue for insects and wildlife, but generally, what does it mean for human beings?

At the beginning of your segment, you talked about the role of scent in memory, and human health is not just physiological. It’s cognitive. And our experience of the world shapes our emotional reaction to the world and our well-being. And scent is deeply embedded in the human experience, right? You will see poets talk about it as the root of memory. You will have all of these scented products. Like, why are there so many scented soaps and candles? So, as we changing the sensory landscape that we live in, we’re actually changing how we interact with the world, which means we’re going to be having impacts on our own cognitive and emotional health in ways that we don’t fully understand. What we do know is that odor perception is a predictor of cognitive decline. It’s one of the first symptoms of things like Parkinson’s or Alzheimer’s. What we’re less clear on is whether or not there’s a causative relationship between things like pollution, olfactory epithelium inflammation, and the development of some of these cognitive disorders. That’s a piece of the puzzle that scientists are actively trying to decode right now.

As you said earlier, Jordanna, with odor pollution, there is cause for concern. What efforts are underway to address this?

Outside of dealing with clean air regulation, not many. One of the most important things we can do in a landscape where odor pollution is reducing the distance traveled by floral odor is to put flowers in shorter distances from each other. So, if my signal travels, say, 100 meters (328 feet) instead of 500 meters (1,640 feet), if I put plants every 100 meters, well then the animal is going to be able to find it. So, some of the same conservation initiatives that, in some sense, are just good logic can help us through these moments when maybe we don’t have all the experimental data that we want to make the perfect decision.