ST. LOUIS (AP) -- About half of the ground-feeding songbirds collected from lead-mining regions of southeast Missouri had extremely high levels of lead in their blood, kidneys and liver, according to a survey released Tuesday by the U.S. Geological Survey.
Lead mining and smelting have been going on in portions of southeast Missouri since the early 1700s. The region contains the world's largest deposit of the lead mineral galena.
USGS performed the study at the request of the U.S. Fish and Wildlife Service as part of an assessment of potential damage to wildlife from exposure to lead-contaminated soil. USGS scientists in 2009 and 2010 captured 34 songbirds in the region known as the Old Lead Belt, portions of the Big River flood plain and in an area within the Mark Twain National Forest.
"We knew mining had gone on there for many years," said Nelson Beyer, author of the study. "We knew the area itself was very contaminated but there hasn't been a lot of work done on songbirds."
Tested birds — mostly cardinals, robins, blue jays and eastern towhees — had eight times the normal amount of lead in their blood, 13 times the normal amount in their liver and 23 times the normal amount in their kidneys, according to the survey that compared the Missouri birds with birds captured elsewhere.
Lead poisoning in birds can cause abnormal muscle function, kidney and liver failure, decreased fertility and anemia, wildlife experts say.
Beyer said contamination levels were particularly bad in robins. Some had lead levels 50 times higher than robins sampled in other areas.
"It's very clear that robins stand out, and it's because of their habit of eating things in the ground such as worms," Beyer said.
Elevated lead levels were also found in soil and earthworms in the region. Some soil had lead levels 40 times above normal. Testing also found cadmium 25 times higher than normal, and zinc eight times higher than normal, the USGS said.
The study found high levels of cadmium in the birds. Concentrations of zinc were not found to be elevated.
Fish and Wildlife Service spokeswoman Georgia Parham said the survey is part of an effort to assess damage in southeast Missouri caused by lead mining. The study will eventually be part of settlement negotiations once responsible parties are determined.
Parham said there was no timetable for how long that process could take. She said that eventually, the settlement money could be used for things such as restoring habitat used by songbirds.
The region has been dealing with lead-related problems for years. Studies have found high levels in some yards and along roadways where trucks containing the lead come and go. Huge piles of chat — mine waste — are part of the landscape in some towns in the Old Lead Belt area of St. Francois County.
Experts say the lead gets into the environment through erosion from the chat, smelting and dust. Flooding has transported some of the lead and caused it to get into waterways.
Among humans, children are at the greatest risk from lead exposure. It can affect their cognitive function and can cause anemia, decreased muscle and bone growth, hearing loss and even brain damage in extreme cases.