Lead and mercury in fall migrant golden eagles from western North America.

Lead exposure from ingestion of bullet fragments is a serious environmental hazard to eagles. We determined blood lead levels (BLL) in 178 golden eagles (Aquila chrysaetos) captured during fall migration along a major North American flyway. These eagles spent the breeding season distributed over a large range and are the best currently available representation of free flying golden eagles on the continent. We found 58 % of these eagles containing increased BLL > 0.1 mg/L; 10 % were clinically lead poisoned with BLL > 0.6 mg/L; and 4 % were lethally exposed with BLL > 1.2 mg/L. No statistical difference in BLL existed between golden and bald eagles (Haliaeetus leucocephalus). Golden eagles captured on carrion had higher BLL than those captured using live bait suggesting differences in feeding habits among individuals. Median BLL increased with age class. We propose a conceptual model for the long-term increase in BLL after ingestion of lead particles. The mean blood mercury level in golden eagles was 0.023 mg/L. We evaluate a field test for BLL that is based on anodic stripping voltammetry. This cost-effective and immediate method correlated well with results from inductively coupled plasma-mass spectrometry, although results needed to be corrected for each calibration of the test kit.

Can a river heal itself? Natural attenuation of metal contamination in river sediment.

Sediment sampling of bed sediment from a large river contaminated by mining and smelting was used to determine rates of natural attenuation of metal concentrations. A "natural decay model" was developed from high-resolution temporal data and used to predict when restoration guidelines would be met without restoration and with various degrees of restoration success. The natural decay model estimates that in the most contaminated reaches it will take about 90 years for average concentrations of As, Cd, Cu, Pb, and Zn to fall below "probable effects concentrations" (PEC), i.e. levels above which we expect to see adverse environmental effects. At sites farther downstream, all metals will fall below PEC in <35 ± 8 years. It will take longer to reach "threshold effects concentrations" (TEC), i.e. concentrations at which no effects are expected. But, even in the most contaminated reaches, Cd, Pb, and Zn will reach TEC in <80 ± 57 years, while Cu and As will take ~200 years. Model simulations with different levels of remediation success show that recovery is highly dependent on source reduction and how far the goal is from the basin background concentration. Furthermore, beneficial effects of restoration may be unexpectedly small: for example a likely decrease of ~20% in the source concentration would shorten the time to reach the Cu PEC by only 13 years. We argue that conducting analyses like these can provide insight into remediation approaches and ultimately decrease the cost of restoration by identifying the role of natural attenuation in restoration design and implementation.

Mercury and other mining-related contaminants in ospreys along the Upper Clark Fork River, Montana, USA.

We investigated links between mining-related contaminants in river sediment and their occurrence in nestling ospreys (Pandion haliaetus) in the Clark Fork River Basin, Montana, USA. Blood and feather samples from 111 osprey chicks were collected during 4 years from nests along river sections with greatly different sediment concentrations of arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), zinc (Zn), and mercury (Hg). No significant differences between river sections were found among Zn (3,150 ± 160 µg L(-1)) and Cd (<5 µg L(-1)) concentrations in blood. Cu, Pb, and As concentrations in blood were significantly increased in chicks from the most contaminated river sections (mean values of 298, 8.9, and 100 µg L(-1), respectively). Cu, Zn, and Pb concentrations increased significantly during a year of above-average river runoff combined with high suspended sediment loads in rivers. Total Hg concentrations in blood and feathers were highly correlated and depended on the geographic locations of the nests. The lowest blood concentrations of Hg were observed in the most upstream river section (mean 151 µg L(-1)) where total sediment concentrations were increased (0.80 mg kg(-1)). River sections with intermediate blood concentrations (mean 206 and 303 µg L(-1)) were associated with low to intermediate sediment concentrations (0.058 and 0.46 mg kg(-1)). The highest concentrations of Hg in ospreys (mean 548 µg L(-1)) were observed downstream from a contaminated tributary (1-4 mg kg(-1) in sediment). In river sections with lower Hg concentrations in sediment, there was a negative correlation between blood Hg concentration and chick mass, presumably due to high deposition rates into growing feathers. This relationship was absent in sections of high Hg exposure. Osprey blood and feathers are suitable for monitoring Hg in aquatic ecosystems; however, responses of As, Cd, Cu, Pb, and Zn are more subtle.

Ecology of sulfate-reducing bacteria in an iron-dominated, mining-impacted freshwater sediment.

A legacy of lead and silver mining in its headwaters left Lake Coeur d'Alene, Idaho with a sediment body that is highly reduced and contains up to 100 g kg(-1) iron and a smaller fraction of chemically active sulfide phases. The dynamic character of these sulfides and their importance for the sequestering of contaminating trace elements prompted this study of the sulfate-reducing bacteria (SRB) involved in their production. We estimated parameters indicative of the distribution and activity of SRB in relation to season, site, and depth. Most probable number estimates and quantitative PCR assays of an SRB-specific functional gene, alpha-adenosine 5'-phosphosulfate reductase, indicated 10(3) to 10(6) cultivable cells and 10(5) to 10(7) gene copy numbers g(-1) dry wt sediment, respectively. Although culture-based estimates of SRB abundance correlated poorly with site, season, depth, total S, or pore water SO(4), non-culture-based estimates of SRB abundance were markedly higher at contaminated sites and positively correlated with pore water SO(4). Ex situ estimates of (35)SO(4) respiration and acid volatile sulfides abundance also showed strong among-site effects, indicating elevated sulfidogenesis at contaminated sites. These observations support the view that biogenic sulfides may act in concert with reduced iron to retain soluble metal(loid)s in the solid phase.