DENVER-Tiny black flecks as minute as a grain of sand. They may hold a key to a medical mystery that has researchers and immunologists baf-
fled-and frankly, worried.
Miniscule airborne residue from rubber tires-specifically radials-may explain why, over the past two decades, the prevalence and severity of asthma has steadily increased worldwide, with children living in urban areas affected most.
Despite improving U.S. air quality, due to more stringent testing of vehicle emissions, several preliminary independent studies have found the air we breathe thick with the tiny black particles produced by normal highway wear and tear on tires.
One minimum estimate states that ``60 percent of these fragments are small enough to be inhaled and retained in the lungs.''
But it's not yet a so-called ``smoking gun.''
One researcher cautioned that although allergists around the country are finding similar test results, they are still considered ``preliminary,'' and much more research needs to be conducted.
In a paper presented last January to the American Academy of Allergy in New York City, P. Brock Williams, Ph.D., who led a team of Denver researchers from the Allergy Respiratory Institute of Colorado, ``confirmed that a large number of respirable tire fragments are found in urban air.''
These particles ``could be partially responsible for the increase in latex sensitization, as well as the respiratory problems associated with air pollution.''
The Rubber Manufacturers Association has seen a copy of Mr. Williams' report. Peter Pantuso, the RMA's vice president of public affairs, said the RMA plans to monitor the situation, although ``there's nothing in his study, to our knowledge, that directly links'' the increase in asthma cases to particulate matter from tires.
For years, researchers testing air quality have dismissed the tiny black specks as fly ash, the pollution by-product of heavy industry and manufacturing. ``We've always looked for mold spores and pollens,'' Mr. Williams told TIRE BUSINESS. ``You can count them, then try to correlate them with various symptoms. But there's always this black stuff on the slides.
``We went to fairly extreme lengths to determine it's rubber. Actually, I wasn't very surprised-it looked like rubber and felt like it. There's little doubt a good proportion of this is rubber.''
There's ``literally tons of it in the air,'' said the molecular biologist, who in July became director of research for IBT Reference Laboratory Inc. in Kansas City, Mo., which specializes in clinical research and environmental allergen testing.
Several current studies-in Denver, Kansas City and Los Angeles-are trying to pinpoint what percentage of carbon in the air is from rubber particles.
In Kansas City, for example, Dr. Jay Portnoy, the chief of allergy and asthma for Children's Mercy Hospital, diligently gathers daily samples of the city's air from atop the hospital's roof. He has found that on weekdays particle levels rise both in the morning and in the evening, coinciding with rush-hour traffic, and are low on weekends when traffic slackens.
Tests in Denver by the respiratory institute produced similar results. Air samples were taken about 300 feet from a busy freeway where some 41,000 vehicles pass daily. Researchers observed ``a minimum of 60-120 times more rubber fragments than pollen grains during the allergy season.''
Tire abrasion occurs more readily in Denver in the winter, Mr. Williams explained, because gravel is used on highways there.
``We don't know what the health effects are from the rubber particles,'' Mr. Williams admits. ``I would predict they're subtle.'' Yet he acknowledges that, in some persons, a sensitivity to latex-the key ingredient of rubber-can trigger severe, even fatal allergic reactions as well as aggravate allergies to other substances.
Several studies have linked fine particulate air pollution to increased mortality rates in infants and in the general population in a number of U.S. cities.
The particles he described were ``black, fairly distinctive, irregular fragments that looked like they were abraded from a tire.'' In fact, Mr. Williams duplicated them in the laboratory by milling a steel-belted radial tire.
On the other hand, bias-ply tires, because of their construction, produce a different type of fragment. ``They seem to fall off in bigger chunks, and therefore a lot of that material ends up on the roadside instead,'' he said.
The steady rise in asthma cases has perplexed researchers, he said, as it comes ``in lieu of much better treatment, better-educated physicians and better medicine.
``And it keeps going up. Originally, it was thought to be due to auto emissions. But a lot of areas have cleaned up the air quite a bit, but that hasn't made a dent in this increase.''
Mr. Williams, himself a life-long asthmatic, said sensitivity to latex has created an ``epidemic'' in hospitals, where now up to 14 percent of the work force has been affected.
``When you've got a million health care workers sensitive to latex gloves,*.*.*.*that's a big problem,'' he said.
If that ultimate ``smoking gun'' linking rubber particles to the increasing worldwide occurrences of asthma is ever found, there may not be any ``silver bullet'' readily available to solve the problem.
Mr. Williams offered three possible solutions, two of which he admitted wouldn't be very palatable to the motoring public:
Slow down traffic-which goes against the grain because most people are driving faster, and legislation may soon do away with federally mandated speed limits;
Adopt alternative methods of travel-those generally have been a failure, declared by many to be too expensive; and
Change how tires are manufactured-``If a tire lasts longer, it doesn't wear as fast, thus producing fewer particles.''
The last remedy, Mr. Williams said, may be the most feasible, especially with the advent of 80,000-mile tires. The problem with this approach, he conceded, is that ``tire dealers won't sell as many tires.''
The irony in the entire predicament is that ``a lot of products developed to make our lives safer and better-such as radial tires-are in fact making us sick.''
In a somber tone, he added: ``I'm hoping these rubber fragments are not causing the problems that we think they may be, because I really don't see a lot of solutions.''