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PCB Concentrations in Birds Near Anniston Were Among the Highest Recorded in North America

Barn swallow nestlings and fledglings in a nest in Mississippi
Conservation · Threats

Eggs and nestlings from seven bird species collected along Snow Creek and Choccolocco Creek downstream of a former PCB manufacturing plant near Anniston, Alabama, contained some of the highest PCB concentrations recorded in North American birds. Most samples came from Carolina wren (Thryothorus ludovicianus) and barn swallow (Hirundo rustica). Based on the magnitude of the PCB and dioxin toxic equivalent (TEQ) concentrations, the authors considered adverse population effects highly likely in resident and migratory birds using the riparian corridors. TEQ combines several dioxin-like compounds into one value, weighting each compound by its relative toxic potency.

Seven Species Across Four Exposure Areas

Researchers collected 158 tissue samples in 2014 and 2015: 122 eggs and 36 nestlings from four exposure areas and a reference area in Talladega National Forest. The seven species were barn swallow, brown-headed cowbird (Molothrus ater), Carolina chickadee (Poecile carolinensis), Carolina wren, cliff swallow (Petrochelidon pyrrhonota), eastern bluebird (Sialia sialis) and tufted titmouse (Baeolophus bicolor). Carolina wrens accounted for 99 exposure-area samples and barn swallows for 36. The six reference eggs came only from Carolina wrens and eastern bluebirds, so there was no direct reference comparison for barn swallows.

PCB Levels Tracked Contaminated Floodplain Soils

Across eggs and nestlings from the exposure areas, total PCB concentrations ranged from 2 to 530 µg/g wet weight, compared with 0.08–0.45 µg/g in reference eggs. Dioxin toxic equivalents ranged from 83 to 21,000 pg/g in the exposure areas and 8–24 pg/g in the reference area. Egg concentrations of both total PCBs and TEQs were clearly higher in each of the four exposure areas than at the reference site. Total PCB concentrations in eggs also rose with PCB concentrations in floodplain soils within nesting home ranges; differences in soil contamination accounted for about half of the variation in egg concentrations. PCB congener patterns supported a common source in soils and sediments contaminated by historical releases from the Anniston facility.

Sensitivity and Exposure Routes Shaped the Risk Assessment

Dioxin-like compounds act through the aryl hydrocarbon receptor (AhR), a cellular receptor that can alter gene regulation when these chemicals bind to it. Differences in the receptor help explain why bird species vary in sensitivity and are used to classify that sensitivity. Published sequence information placed barn swallow, cliff swallow, eastern bluebird and tufted titmouse in the moderately sensitive Type 2 group. TEQ concentrations in these four species were clearly above the lethality thresholds used by the authors. Median total PCB concentrations in Carolina wren and barn swallow eggs and nestlings from the exposure areas exceeded tissue-based reference values for highly sensitive birds, and at least some samples from every exposure area exceeded reference values used for even relatively insensitive species.

Most of the sampled species were insectivores. The authors identified emergent aquatic insects as a likely route by which PCBs can move from contaminated sediments into riparian food webs. Barn swallows catch emerging insects over water and build nests from locally collected mud, so both food and contaminated nest material could contribute to exposure. Carolina wrens forage mainly for insects and spiders on the ground and lower portions of tree trunks, a habit the authors suggested could increase exposure to soil-borne contaminants. The study did not trace PCB movement through individual food items. Concentrations of lead and mercury were below the toxicity thresholds used in the assessment.

The study measured contaminant exposure rather than reproductive success, mortality or population trends. Its conclusion about likely population effects therefore came from comparing measured tissue concentrations with established toxicity reference values, not from observing a demographic decline directly. Even with that distinction, the authors concluded that the PCB concentrations in birds using the downstream riparian areas reached magnitudes associated with adverse population-level effects.

Sources and image credit

  1. Tillitt et al. (2026), Environmental Toxicology and Chemistry — Polychlorinated biphenyl (PCB) exposure assessment of Carolina wren and barn swallow eggs and nestlings near Anniston, AlabamaPrimary peer-reviewed open-access exposure assessment, published 1 July 2026. Researchers analysed 122 egg and 36 nestling samples from seven bird species collected in 2014–2015 at four exposure areas along Snow Creek and Choccolocco Creek downstream of a former PCB plant near Anniston, Alabama, plus a reference area in Talladega National Forest. Most samples came from Carolina wrens and barn swallows. Across exposure-area birds, total PCB concentrations ranged from 2–530 µg/g wet weight, compared with 0.08–0.45 µg/g in reference eggs; dioxin toxic equivalents ranged from 83–21,000 pg/g versus 8–24 pg/g at the reference area. The study measured tissue exposure and compared concentrations with established toxicity reference values; it did not measure population trends directly.
  2. Cleveland et al. (2026), U.S. Geological Survey data releasePrimary dataset supporting the contaminant measurements and analyses.

Image: Kati Fleming — barn swallow nestlings and fledglings in Mississippi, USA, 26 May 2012; Wikimedia Commons; CC BY-SA 3.0. Representative image, not birds from the Alabama PCB study. · CC BY-SA 3.0 · Source

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