(AOLNEWS)  Already put off by the thought of oily gulf seafood? Well, it probably won’t help your appetite to know that the food is being smelled first.

But it should. Scientists say the skeptics just don’t know enough about their own noses. With many petrochemicals, humans will notice 1 part per million, or even less, of their smelly components in air. That’s like a few tablespoons in an Olympic-sized swimming pool (if you pretend those chemicals have the same density as water).

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That’s why the FDA says it’s very unlikely for tainted seafood to reach your plate after a battery of smell tests. And our sensitivity to such small traces of oil makes it even harder for higher, toxic levels to go undetected.

“The human sense of smell is more sensitive than many instruments that chemists and biochemists rely upon,” said Charles Wysocki of the Monell Chemical Senses Center, the world’s only think-tank on the subject.

People don’t think much about their sense of smell, Wysocki told AOL News. But we depend heavily on it, even from birth. One 1994 study found that one of babies’ first actions in life was to sniff out the location of their mother’s nipples.

Women are also more sensitive to smell than men, according to Gary Beauchamp, another researcher at the Monell lab. Witness the famous National Geographic photo of professional armpit-smellers: Women in lab coats lined up to judge deodorants on a row of sweaty men.

Nobody knows why women are better smellers, Beauchamp said, but one theory is that women have relied heavily on scent to choose good mates throughout human evolution.

More closely related to what’s happening now in the Gulf of Mexico, a local Chinese government used a team of 11 sniffers in 2007 to enhance its air-quality monitoring in a city with chemical, oil and rubber refineries, according to the newspaper China Daily. The team stayed in a lab all day, smelling noxious gases.

“Now we can differentiate between hundreds of smells that may make people ill, before making an assessment on their density,” a director at the environmental monitoring station told the paper.

A Complicated System

Wysocki said our olfactory system is a bit like a piano.

Humans have a dime-sized patch of smelling tissue way back in their nasal cavity, between the eyes. The patch contains 10 million nerve cells, but as they receive a smell, only 350 different types of receptors electronically transmit that information to the brain.

“You’ve got a very small repertoire of individual keys, but the skilled pianist can produce thousands and thousands and tens of thousands of different chords by pressing different combinations of keys,” Wysocki explained.

The brain combines all the different smell compounds of a substance and makes an overall judgment of what it is — coffee, for example, or garlic or gas.

There’s still a lot researchers don’t know about human smelling ability, but they have tested many of our smelling “thresholds” — the smallest concentration that we can smell, on average, of a certain food or chemical. It is often similar to the tablespoon-in-the-swimming-pool ratio, or even less.

For example, it would take only the tiniest drop of vanillin, the smell-causing substance in vanilla, to be smelled in that pool. People are also very sensitive to the smells of sulfur and green peppers.

In the case of petrochemical-oil products, people have a wide range of smell sensitivity to the different compounds they contain. We’re not particularly good at smelling some of the toxic components, like benzene, which we can smell at 97 parts per million.

But people like to classify smells according to what they’ve smelled before. They get unsettled, even panicked, if they can’t identify a new smell. Because we’re not used to the oily smells that mark contamination, especially in combination with food, they stand out, even to the average person.

Training Gulf Sniffers

Training also can increase your sensitivity. Just thinking about what you’re trying to smell can make you better at it. The two-day courses given at the gulf on behalf of the federal government taught people from five states to track the smell of oil, like giving a police dog the shirt of a missing person.

“Most of training involves learning to pay attention to a particular odor, to label them in your head, and to notice them against a background of other odors,” Beauchamp said.

Seafood is being tested twice, first by smell and then in a lab, according to CNN.

Still, some scientists would like better information about the seafood smell-testing to judge it for themselves.

For example, while NOAA has said it is training sniffers to identify a certain “oily, chemical mix,” it has not revealed what the human smell threshold is for that mix, said Miriam Rotkin-Ellman, a public health scientist at the Natural Resources Defense Council. That’s important, because hard-to-smell chemicals like benzene are part of the mix, along with easy-to-smell chemicals like ethylbenzene.

“I think that that is an important piece of information that should be revealed to the public that would help people understand better how sensory testing works,” Rotkin-Ellman said. “NOAA says that what the testers are able to smell in terms of an oily vapor or an oily smell would mean that chemicals like benzene are not present in unsafe levels. It would be in the mix of what they were smelling — it would be contaminated so heavily with benzene that they would pick it up.”

However, while all of the science behind their abilities isn’t known, the gulf smellers are given a final exam. It’s important to test individuals, the three scientists said, because the sensitivity of people’s noses varies widely. And, Wysocki said, each person has a couple of “blind spots” in their smell sensors that make them smell things a little differently from other people.

On their last day of training, gulf smellers are given fish, oysters and shrimp spiked with different levels of oil, according to Joan Bowman of the International Food Protection Training Institute, which held the courses.

“Some people were able to detect it easier in fin fish, some people weren’t able to detect it in oysters, et cetera,” Bowman said. “They were given kind of a rating for how sensitive their noses were.”

One of the trainees took an oyster out of its shell and held it up to his face as part of the final exam. He sniffed.

“If there’s any detection of oil, you’re gonna get a nasal sensation … or maybe a little gas smell,” he said, according to The Washington Post.

“This, believe it or not, smells like corn to me.”

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