The Dog That Was A Canary

A 60 year old factory worker was seen at the Yale Occupational and Environmental Medicine Program for an elevated urine mercury level. He worked in a factory making mercury vapor light bulbs. The company doctor had removed him from work because of a high mercury level, but even staying home the level of mercury in his urine continued to rise. The workman’s compensation carrier had questioned whether there could be a problem with his urine mercury testing results.

During the clinical evaluation, the patient recalled that he had brought his work boots home and had been using them for the past several weeks. When he had checked inside his boots, he found beads of mercury under the soles.

As part of his evaluation, the clinic’s industrial hygienist performed a site visit to his home, in conjunction with the State Dept of Public Health. Real time measurement of mercury vapor in the house showed a number of slightly elevated areas. At the site visit, it was also noticed that the patient had a 3 month old German shepherd puppy. Since there was still a question about whether the house was sufficiently contaminated with mercury to cause the patients elevated level, the dog’s veterinarian was contacted (with the owner’s permission) to arrange for mercury testing of the dog. The dog’s urine showed a mercury level that was five times normal!

Both the man and his dog were advised to move out of the apartment, and the apartment was cleaned of mercury. After a month, dog and human returned to the house, and the man’s mercury levels continued to return towards normal.

Mercury is an important toxic exposure in both workplaces and the environment. Elemental mercury (quicksilver) vapor can be inhaled and cause toxic effects to the brain, kidney, and developing fetus. Workers can bring home mercury from work on shoes and clothes and contaminate a home, as in this case. Lead can also be tracked into a house by workers who are exposed at their job.

This case illustrates that pets and other animals can serve as “sentinels” for toxic exposures in the home, just as canaries once warned miners about dangerous gases. In particular, household dogs and cats have provided warning to nearby humans in the household about lead poisoning as well as carbon monoxide poisoning as well as other toxic hazards. Communication between veterinarians and physicians may help detect hazardous exposures affecting both animals and humans. The Yale Human Animal Medicine Project  maintains the “Canary Database” of evidence about animals as sentinels of human environmental health hazards (
See for example the Canary summary for animals as sentinels of lead poisoning: 

and the following papers in the database: 

Childhood plumbism identified after lead poisoning in household pets.

"Veterinary" diagnosis of lead poisoning in pregnancy


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