California's peregrine falcons, once driven to the edge of extinction by the pesticide DDT, now are contaminated with record-high levels of other toxic chemicals that may threaten them again.
State scientists have found that peregrines in Long Beach, Los Angeles and San Francisco contain the highest levels of flame retardants found in any living organism worldwide.
The findings parallel studies that have detected high concentrations of the chemicals, known as polybrominated diphenyl ethers, or PBDEs, in human breast milk, particularly in California women. The compounds, which mimic thyroid hormones and can damage developing nervous systems, have spread to wildlife and people worldwide, working their way up food webs.
The concentrations found in California's urban peregrines are similar to those that cause neurological damage in lab mice and rats, resulting in reduced motor skills and altered behavior.
Scientists said the peregrines, the fastest and most agile birds, are being contaminated with the industrial chemicals from eating urban pigeons that scavenge on city streets.
The chemicals are used as flame retardants on electronics and furniture cushions. They begin as indoor pollutants, building up in household dust, then migrate outdoors, where they pollute urban environments.
Kim Hooper, a scientist with the state Department of Toxic Substances Control's environmental chemistry laboratory who led the study, said the PBDE levels in the peregrines have doubled every 10 years, and might still be increasing.
Hooper and his colleagues suspected that because household dust contains PBDEs, top predators in big cities would have the worst contamination, so they tested the eggs of peregrines in 42 locations, including Los Angeles, Long Beach, Newport Beach, Coronado and the San Francisco Bay Area.
Their hunch was right. The eggs in rural inland and coastal areas had only trace amounts of PBDEs, but the urban eggs contained up to 52 parts per million, and one dead chick contained 95 ppm. Scientists consider those concentrations extremely high -- substantially higher than nearly any chemical measured in any species worldwide in recent years.
"We think urban wildlife are sentinels for exposure to indoor pollutants in big cities," Hooper said.
Hooper said a PBDE compound called deca is largely responsible for the birds' contamination. Deca, used in electronics since the 1970s, is produced in large amounts in the United States -- about 80 million pounds a year.
The peregrine is known for its torpedo-like dives, reaching speeds of up to 200 mph. Hunting from skyscrapers in large cities as well as from steep cliffs in rural areas, they inhabit much of North America. They normally shun prey on the ground, choosing to capture birds mid-flight.
One bird egg, taken from the Port of Long Beach, had the highest level of any egg -- 52 ppm. Other birds with highly contaminated eggs had nested on high-rises in San Francisco and downtown L.A., including the Union Bank building. Included was a popular pair that San Francisco residents named George and Gracie.
"We're always concerned when a high level of contaminants is found in a species," said Alex Pitts, a spokeswoman for the U.S. Fish and Wildlife Service. PBDEs "are showing up everywhere and they are more concentrated in urban areas, which is challenging for urban wildlife."
Because the levels have been increasing, "it's very possible they could reach levels in the food web that could be unsafe for predators such as peregrine falcons," Pitts said.
Janet Linthicum of the Santa Cruz Predatory Bird Research Group, said the high contaminant levels are "disappointing and disturbing" but she has "no idea whether there are any effects." The two dead chicks and 95 unhatchable eggs that were tested came from the Santa Cruz group's archive and had been collected at nesting sites between 1986 and 2007.
Avian experts say if a bird's nervous system is altered, it might change how it hunts and raises its young, and perhaps eventually reduce populations.
"Whatever happens to the peregrines, we will be surprised by it, just like we were surprised when DDT thinned eggshells," Hooper said.
A half century ago, peregrines, bald eagles and brown pelicans were nearly wiped out by DDT, an insecticide that weakened their egg shells and caused nearly complete reproductive failure.
Like DDT, the brominated flame retardants are slow to break down in the environment and build up in animal tissues, reaching high levels in species that top the food web.
PBDE levels in the birds' eggs are about a hundredfold higher than the amounts found in the breast milk of California women, who have among the highest concentrations of women tested worldwide, the scientists said. Children are five to 10 times more contaminated than adults because they are exposed to more dust from playing on floors.