Heavy metal: Some airborne particles pose more dangers than others
By Lindsey Konkel
Environmental Health News
December 17, 2009
Lippmann, a scientist at New York University who has studied the effects of air pollution for over 50 years, couldn’t explain it. During those two weeks in October, 2004, air pollution levels were lower than average at his laboratory in Tuxedo, New York, 30 miles north of New York City.
But Lippmann soon learned that concentrations of tiny particles of nickel were the highest he’d ever seen. He tracked them all the way to a nickel smelter in Ontario, Canada, about 500 miles away.
Now Lippmann and his colleagues have gathered evidence suggesting that it’s not just mice that are affected by the metallic particles. They observed that both concentrations of airborne nickel and daily deaths from heart disease were much higher in New York City than any other city in the United States.
Around the world, fine particles – smaller than a few microns in diameter – have been linked to increased hospitalizations and deaths from cardiovascular and respiratory diseases within hours to days of exposure.
But new evidence is emerging that some particles in the air may be more dangerous than others.
A growing body of animal and human research suggests that breathing metals may put acute stress on the lungs and heart, resulting in illnesses and deaths at particulate levels below national standards.
“There’s all kinds of evidence that the toxicity and composition of airborne particles vary from one city to another. In New York, airborne nickel, present even at a small concentration, is particularly influential,” said Lippmann, a professor of environmental medicine who directs the federally funded Particulate Matter Health Effects Research Center at NYU.
Residual oil, known as bunker fuel, is the main cause of New York City’s high levels of nickel and another metal, vanadium. Space heaters in older apartment buildings often burn the cheap form of crude oil, which also is used to fuel ships.
”Although the metals may be highest in New York, studies show that hospitalizations across the country increase with metals in the air.
These findings may help regulators identify which particles are the most important to control from vehicles, factories and fuels.
“A better understanding of what particles in the mixture are most harmful would aid decision makers in developing the most effective policies to protect human health,” said Michelle Bell, a Yale University environmental health scientist.
“We have evidence linking nickel, vanadium and elemental carbon in the air to wheeze and cough in inner city children,” said Rachel Miller, an allergist and immunologist and co-deputy director of the Columbia University Center for Children’s Environmental Health.Inhaling metal and carbon particles may be a risk factor for respiratory problems in children as young as two years old, Columbia University researchers found in a recent study, released this month in the American Journal of Respiratory and Critical Care Medicine.
The researchers followed more than 700 children between birth and two years of age living in northern Manhattan and the south Bronx. Every three months, parents filled out a questionnaire about respiratory symptoms. The study controlled for factors such as seasonal trends, ethnicity and exposure to tobacco smoke.
After comparing the questionnaire results with weekly pollutant data at several sites in the community, the researchers found that children exposed to nickel and vanadium were more likely to wheeze. Exposure to carbon particles, a byproduct of diesel exhaust, was associated with coughing during the cold and flu season.
Total levels of particulates were not significantly associated with wheeze or cough, suggesting that individual ingredients – not fine particles as a whole – may be harmful.
This study was the first to investigate the health effects of specific airborne components of heating oil and traffic exhaust.
Nickel and vanadium measurements are highest in the winter and vary throughout the city, figuring more prominently in neighborhoods with older buildings and those closest to ports, according to Lippmann.
Traffic also may be an important source of metal and carbon particles from tailpipe emissions, brake and tire abrasions, and roadway dust.
Though the New York City study looked at the long-term effects on children’s health, many other studies have documented the short-term risks in adults.
Bell and a team of researchers looked at respiratory and cardiovascular hospital admissions of patients 65 years or older associated with same-day exposure to airborne metal components of fine particulate matter in 106 U.S. counties.
Counties with higher nickel, vanadium and elemental carbon were found to have higher risk of hospitalizations associated with short-term particulate exposures, according to the study, published in March in the American Journal of Respiratory and Critical Care Medicine.
In another study, nickel concentrations and cardiovascular deaths in New York City varied widely from neighborhood to neighborhood and were also higher in the winter due to the combustion of residual heating oil. On average, nickel was 9.5 times higher than the average for 60 other U.S. cities, according to the research by Lippmann and colleagues, published this year in the Journal of Exposure Science and Environmental Epidemiology.
Researchers are not sure why certain components of fine particulate matter are more dangerous than others. “It’s a pretty open question right now,” said Miller.
Miller and others suspect the tiny particles, which can settle deep in the lungs, trigger an inflammatory response by the immune system.
“Mid-range atomic metals (such as nickel and vanadium) may be more reactive than other particles,” said Lippmann.
Chronic inflammation in the lungs can cause respiratory symptoms in children or a deadly response in older adults. For individuals with cardiovascular conditions, lung inflammation can increase heart rate. This puts additional stress on the lungs and heart and can lead to heart attacks and stroke.
The Environmental Protection Agency set health-based standards for fine particulates in 1997 and began wide enforcement in 1999. But the standards do not take into account new research on the composition of the particulate mixture or the toxicity of its components.
Some states are taking matters into their own hands. A bill in the New York State Senate would require that most heating oils meet refining standards for ultra-low sulfur fuel.
Though this legislation would reduce particulates, it would not cover the heavier, residual heating oil used in 10 percent of buildings in New York City. Compared to other heating fuels, residual heating oil emits disproportionately high levels of heavy metals and other pollutants.
“Over the past year the City has been evaluating several options to further reduce pollutants from the burning of residual oil,” said Carter Strickland, senior policy advisor for air and water at the New York City Mayor’s Office of Long-term Planning and Sustainability.
According to Meredith Franklin, an environmental health scientist at the University of Chicago, a greater understanding of the sources of particles, as well as the body’s response, are necessary to create effective public health policy.
“The more you know about the cause of health effects, the more you can target certain sources and really do something about it,” Franklin said.