Teenagers in Los Angeles and New York City face a substantial -- and strikingly similar -- cancer risk from breathing the air, largely because of toxic chemicals inside their homes and schools, a new scientific study shows.
For the research, 87 high school students, including 41 from Jefferson High School in South Los Angeles, wore backpacks equipped with air monitors that measured what each was exposed to throughout the day.
Although outdoor air in both cities is heavily polluted, indoor air was responsible for 40% to 50% of the teenagers' cancer risk from the compounds measured.
The New York and Los Angeles teenagers were the only groups looked at in the study. They were exposed to virtually the same average concentrations of nearly all of the 19 carcinogens examined, according to the research by a Massachusetts consulting firm, Columbia University, UC Davis and the Harvard School of Public Health.
"Given that we spend most of our time indoors, we're really affected by indoor sources. We use a lot of cleaners and we're exposed to off-gassing from furnishings," said Sonja Sax, the study's lead researcher and an associate at Gradient Corp., which specializes in risk science.
"There were two contaminants driving the risk," she said, "and they were mostly coming from indoors."
Formaldehyde -- a colorless gas that wafts mostly from particleboard cabinets and shelving, plywood paneling and other pressed-wood furnishings -- was the biggest culprit by far, responsible for half of the Los Angeles teenagers' cancer risk.
A chemical called 1,4-dichlorobenzene, used in solid deodorizers and mothballs, also posed a substantial cancer risk. "Some households had very, very high concentrations and others didn't have much at all," Sax said. The researchers suspect that toilet deodorizers were to blame.
Only one outdoor pollutant, benzene, found in car exhaust, contributed significantly to the risk, and much less so than formaldehyde and dichlorobenzene. Although 42% to 48% came from indoor sources, 24% came from outdoor sources. The source of an additional 32% to 36% could not be determined.
The teenagers faced a risk from breathing the chemicals "in the same order of magnitude" as secondhand smoke, according to the study, published online last week in the journal Environmental Health Perspectives. In Los Angeles, 513 teenagers per million exposed (equivalent to 1 of every 1,949) could contract cancer from the pollutants, and in New York, 687 per million.
For the Los Angeles teenagers, the researchers reported that the cancer threat was seven times higher than an estimate for the city used by the Environmental Protection Agency, which does not include the effects of indoor air. Most of the chemicals exceeded the 1-in-a-million cancer threat considered acceptable for air pollutants.
Thirteen of the 19 carcinogenic chemicals measured in the study were volatile organic compounds, which are highly evaporative, petroleum-based solvents. Six were metals, which are predominantly found outdoors and posed a much lower cancer risk than the volatile organic compounds.
The study probably underestimated the threat because it did not monitor several dozen other air pollutants linked to cancer, including two major ones, diesel exhaust and gases called polycyclic aromatic hydrocarbons from vehicles.
Forty-one students at Jefferson High School and 46 New York teenagers, largely from upper Manhattan and the Bronx and attending a west Harlem magnet school, participated in the study, conducted in 1999 and 2000. All were between the ages of 13 and 17 and most lived in apartments. In Los Angeles, all but two were Latino.
The teenagers wore the backpack monitors for 48-hour periods on weekdays, during two seasons. Air samplers were also put in their homes and schools.
All the teenagers spent similar time indoors, on average 22 hours on weekdays. But while the New York teenagers commuted to school from around the city, mostly on subways, the Los Angeles teenagers lived within a few miles of Jefferson High and had little exposure to exhaust during commutes.
The major difference in the New York and Los Angeles exposures was chloroform, a gas that comes mostly from hot showers and other vaporization of chlorinated water. Its risk was nearly eight times higher for the New York City teenagers than the Los Angeles ones. The reasons are unknown; Sax said it could be differences in doses of chlorine added to water or in quantities of water used in the households.
The New York teenagers also were exposed to slightly more butadiene, from auto exhaust, and perchloroethylene, used in dry cleaning. California has the nation's strictest standards for auto exhaust and the Los Angeles region has regulations limiting drycleaners' perchloroethylene emissions.