December 1, 2006 America's only dog that's trained to sniff mercury is able to detect as little as a half-gram, and is faster and cheaper than traditional lab analysis. Dogs' olfactory membranes are larger and 44 times more sensitive than humans'. Mercury contamination is frequent in schools: mercury spills are typical in science classrooms and labs where thermometers and barometers are used.
MINNEAPOLIS, Minn. -- It's not often that you see a four-legged student roaming the school halls, but this dog is on a mission. Clancy is the only dog in the United States trained to sniff out dangerous mercury.
"A lot of time the kids will break lab thermometers and try to sweep them down into the sink, and can continuously put out vapor that the students can breathe and the teachers can breathe," Carol Hubbard, a mercury specialist with the Minnesota Pollution Control Agency in St. Paul, tells DBIS.
She says breathing in that vapor can be dangerous. In young children, it can actually stunt their intellectual development.
But students at Patrick Henry High School in Minneapolis, Minn., have nothing to fear. Clancy can detect as little as a half a gram of mercury -- the same amount that spills out when a thermometer breaks. On command, he sits next to the hidden mercury and waits for his reward -- a tennis ball.
Student Andre Washington says, "If he's able to sniff out that stuff and save us from the mercury exposure, I think he's a really good dog!"
"He sniffs out mercury," David Hanvichid says. "That's an incredible ability that a dog can do!"
Incredible, but also in his nature. Dogs can detect odors 44-times better than humans. They pick up scents through folded membranes right behind their noses -- right in front of their brains. Humans' membranes are the size of a postage stamp, but dogs' are 50-times bigger.
Clancy finds unexpected mercury in a school supply room. Hubbard tests the area with her machine to make sure he's right. And he is!
"He is pretty reliable," Hubbard says. He's also quicker, cheaper and better company than her equipment. "We have gotten to be really good friends. He is my partner, so we have a lot of fun."
And they get a lot done! In the last five years, Clancy helped rid schools of more than 1,500 pounds of mercury.
Hubbard and her colleagues got Clancy from the humane society. They said they picked him because he was so responsive to tennis balls, indicating he'd work hard for his reward. It took her about two months to train Clancy. Both Hubbard and Clancy get their blood levels tested for mercury -- his every six months, hers every 12 -- and they've always tested normal.
BACKGROUND: Dogs have been used by law enforcement and military personnel for 30 years to detect narcotics and explosives because of their keen sense of smell. The Minnesota Protection Control Agency (MPCA) is now using specially trained dogs to check schools and other facilities for mercury contamination. The MPCA estimates that there is around two pounds of mercury "hidden" in most schools. The U.S. Environmental Protecton Agency is also conducting research on how to use dogs for detection of indoor air pollutants such as toxic molds, illegal pesticides, and gasoline vapors from contaminated ground water.
HOW DOGS SMELL: Dogs' noses are such sensitive chemical detectors that they can detect a target compound in the presence of other odors at much higher concentrations; they can even identify odors concentrated in a small object or piece of ground as small as a dime. They can even discriminate between a target odor and one that is closely related. Scent comes from an object in a plume that swirls and eddies so there are patches of dense odor and areas of faint odor. A dog will scan back and forth with its nose along those varying densities to try and locate the source of a smell.
INSIDE THE NOSE: When the dog inhales, a fold just inside its nostrils opens to allow air to flow through the upper part of the nose where mucus-covered scent receptors grow. Once inside the nose, chemical vapors dissolve in those receptors, and the chemical interactions are converted into electrical signals that travel along the olfactory nerve to the olfactory bulb and then to the dog's brain, which processes the data according to recognized patterns of odor signals. Dogs have around 220 million such receptors ý 40 times more than humans -- which can become sensitive to many different unrelated chemicals.
ABOUT MERCURY: Mercury, also sometimes called quicksilver, is an element that is just one of five metals that are liquid at room temperature. Mercury is used in thermometers and barometers, though recently alcohol has become more popular for oral thermometers. It is poisonous to humans when absorbed through the skin or in the stomach and intestines, causing brain damage, but it is still sometimes used in dental fillings because the amount absorbed may be low enough for humans to tolerate.