Microscopic pieces of metals in air pollution aggravate asthma and allergies, according to research by the U.S. Environmental Protection Agency and German scientists published this week.
The researchers concluded that people who live in areas with airborne soot that contains a lot of metals are prone to more severe bouts of asthma and allergic symptoms.
Evidence has been mounting in recent years that soot -- ultra-fine particles of pollution -- aggravates asthma and allergies. The new study implicates a specific ingredient of the soot -- metals, such as zinc, copper, tin and cadmium. The metals are most often found in emissions from factories and coal-burning plants.
Asthma is considered an epidemic in the U.S., afflicting an estimated 15 million people, including 5 million children.
For their study, EPA and German scientists examined air from two neighboring cities in East Germany, Hettstedt and Zerbst. Hettstedt, which has a high rate of bronchitis, allergies and wheezing among schoolchildren, is home to smelters and mines. It has several times more toxic metals in the air than the nonindustrial, farming area of Zerbst.
When lab mice with allergies were exposed to airborne particles from Hettstedt, they had more inflammation of their airways and worsened allergic symptoms than animals exposed to particles from Zerbst, according to the research, directed by Stephen Gavett of the EPA’s National Health and Environmental Effects Research Laboratory in North Carolina. Although the concentration of particle pollution was similar in both cities, the content of some metals in Hettstedt was as much as sevenfold higher.
Apparently, tiny pieces of metals cause airways to become inflamed, restricting the flow of air that reaches the lungs. Such symptoms can lead to asthma attacks. The metals also increased the animals’ sensitivity to common allergens -- substances such as dust or pollen that cause allergic symptoms.
There was no evidence, however, that soot causes the diseases in people who don’t already suffer them. When mice that were not allergic were exposed, they had no symptoms. Instead, the metals exacerbated symptoms in mice with existing allergies.
Gavett concluded that timing is critical to determine how severe someone’s symptoms will be. When mice breathed the metals right before being exposed to an allergen, their airway inflammation worsened.
Scientists have been trying to figure out why deaths from respiratory and heart diseases increase on days when particle pollution worsens. The phenomenon occurs around the world. Some researchers have suspected that metals in the air are responsible, and the new findings, published in the journal Environmental Health Perspectives, bolster that theory.
Scientists acknowledge that there are other causes of asthma and allergy symptoms.
Diesel exhaust and ozone, which is the main ingredient of smog, aggravate asthma and allergies. But diesel engines put out little, if any, metals.
The rate and severity of asthma among children, especially those under 5, has surged over the last 25 years in the United States and Europe, even though most forms of air pollution have declined. The reason for the increase is unknown. Officials are investigating several possible culprits, from sensitivity to indoor air allergens to a reaction of the immune system of infants to specific types of pollution, especially diesel exhaust and ash from coal plants.
Allergies have also increased dramatically. In 9 of every 10 cases, people with asthma also suffer allergies.