Carpets as reservoirs of PAH-lution.

As concern about environmental carcinogens grows, researchers are attempting to home in on major sources of exposure. John W. Roberts, a Seattle-based consulting engineer, and his colleagues believe they have stumbled onto what may prove one of the less obvious reservoirs: residential carpets.

At the 6th International Conference on Indoor Air Quality and Climate, held this week in Helsinki, Finland, Roberts reported his team's analysis of data from a recent EPA study of eight homes in Columbus, Ohio. Dust vacuumed from carpets at each home contained detectable levels of seven potentially carcinogenic polycyclic aromatic hydrocarbons (PAHs) including benzo(a)pyrene, chrysene, and benz(a)anthracene.

Though these combustion pollutants occur in trace amounts throughout the environment, in six of the studied homes PAH levels in carpets equaled or exceeded -in some cases by up to 20-fold -- PAH levels in yard soil. At those homes, average carpet-dust PAH concentrations ranged from 1.3 to 12.1 parts per million (ppm). The other two homes were far more heavily polluted -- indoors and out. However, Roberts notes, total PAH levels inside even the less contaminated homes far exceeded the 1 ppm limit requiring cleanup of residential soil at hazardous waste sites in Washington state. (At present, there is no uniform federal limit for PAH contamination.)

No obvious trend linked severity of indoor PAH contamination with cigarette smoking or use of a fireplace. Because PAH concentrations in dust in outside doormats did "correlate strongly" with levels in carpet dust, Roberts now suspects residents tracked the pollutants in on their shoes.

Rugs shield chemicals from the sunlight, moisture, and microbes that can foster their breakdown in soil. That's why Roberts -- who has long studied pollutant buildup in carpet dust (SN: 8/11/90, p.86) - favors the bare-floor look. Carpet lovers can limit buildup by placing commercial doormats at all entries, removing shoes at the door, and vacuuming, he says.