About half of ground-feeding songbirds collected from a historic lead mining district in southeast Missouri contained toxic levels of lead in their blood and internal organs, according to a new U.S. Geological Survey study. Elevated lead levels were also found in soils and earthworms in the lead district sites examined, which included the “Missouri Mines” in the Old Lead Belt; “Washington State Park,” on the Big River floodplain; and the “Viburnum Trend,” within Mark Twain National Forest.
Tested birds had lead concentrations exceeding those of reference birds by factors of 8 in blood, 13 in liver, and 23 in kidney samples. Soils in the study exceeded background levels for lead nearly 40 fold, for zinc 8 fold, and for cadmium 25 fold.
Southeast Missouri contains the world’s largest deposit of the lead mineral galena. The area has a long history of lead mining and smelting. Lead has been mined in the region since 1721. Previous studies have measured elevated lead in floodplain soils, stream sediments, fish, invertebrates, amphibians, other birds and wildlife in the area. Lead has been released from the erosion of tailings, mine waste, smelting, and dust. Periodic flooding has also transported lead in the environment.
Cadmium levels in birds from the mining study sites were several times those in reference birds, but concentrations of zinc were not elevated more than those in the reference birds.
Ground-feeding songbirds were selected for the study because they were more likely to be exposed to lead than songbirds feeding in shrubs or in the forest canopy. Cardinals, robins, blue jays, and eastern towhees were among the birds tested.
USGS completed this study at the request of the U. S. Fish and Wildlife Service as part of a natural resource damage assessment by the U.S. Department of the Interior to investigate whether wildlife might be adversely affected by exposure to lead contaminated soil.
Lead poisoning in birds can cause abnormal muscular function, kidney and liver failure, decreased fertility, and anemia. Songbirds poisoned by lead, however, generally do not show lesions. The exposure to lead is detected by chemically testing tissues or by measuring suppressed enzyme levels.
The study, “Toxic exposure of songbirds to lead in the Southeast Missouri Lead Mining District,” is available in the journal Archives of Environmental Contamination and Toxicology.