Ready to sand and refinish wood floors in your mid-20th century house? Do you assume your old house is "safe" from toxic chemicals because they've had time to "gas out"? Confident your old hard wood floors are ecologically sound and couldn't possibly pose a health risk? Think again.

A new study published in the journal Environmental Health reveals older wood floor finishes in some homes from the l950s and l960s may be an overlooked source of exposure to the cancer-causing environmental pollutants known as polychlorinated biphenyls (PCBs).

These highly toxic chemicals are particularly dangerous because they linger in the environment for countless decades and are associated with an increased risk for a host of serious health problems - from thyroid toxicity to reproductive, nervous, and endocrine systems disorders. Perhaps most worrisome, they are also known carcinogens and are especially linked to an increased risk of breast cancer.

Before they were finally banned in the 1970s, PCBs were used in a huge array of housing and domestic products, including varnishes, caulking material and cooling and insulating fluids. However, the toxins are such persistent organic pollutants they are still documented worldwide as human blood and breast milk contaminants.

Now scientists say some people may be getting a big dose of PCBs from their current exposure to old wood floors sealed with products like "Fabulon", a popular PCB-containing floor finish used in the 1950s and 1960s.

In l999 through 2001, researchers Ruthann Rudel and Julia Brody of the Silent Spring Institute and Liesel Seryak, of the Ohio State University studied PCBs in indoor air and dust in 120 homes in Cape Cod. They documented detectable levels of PCBs in about 1 out of 3 houses and 2 houses had particularly high amounts of the chemicals.

To retest the initial findings, the research team retested the 2 highly contaminated homes. Then they took samples of the blood of the homes' residents to check for PCB concentrations.

The results? Over the past 5 years, the PCB-laden air and dust of PCBs remained high. Most concerning, the people who lived in the 2 highly contaminated homes also had very high levels of PCBs in their blood - more than the 95th percentile of a representative sample of the US population.

Unfortunately, it isn't only older homes that may be exposing Americans, including children, to cancer-causing polychlorinated biphenyls. The researchers point out that many public buildings, including schools, from the middle of the last century may well contain PCB-loaded floor finishes or other products. "Our findings suggest that the exposure potential posed by historic use of PCBs in building materials may be significantly underestimated," the researchers conclude.