Acute and Chronic Lead Exposure in Four Avian Scavenger Species in Switzerland

Effects of lead on avian thermoregulation in the heat: An experimental test with pied crows (Corvus albus)

Many of the negative physiological effects of lead involve the hypothalamus, but the possibility that thermoregulation is affected has received little attention. We tested the hypothesis that lead exposure reduces avian thermoregulatory performance under hot conditions in pied crows (Corvus albus) experimentally exposed to lead in their diet. Crows in our high lead treatment (blood [Pb] = 87.3 ± 44.7 μg dL-1) showed significantly higher air temperature (Tair) inflections for evaporative water loss (EWL) and resting metabolic rate (RMR) compared to control (6.4 ± 1.8 μg dL-1) or intermediate (53.9 ± 23.7 μg dL-1) lead groups, which did not differ. EWL, RMR and body temperature (Tb) all increased more rapidly at Tair > Tb in the high lead treatment. In contrast, neither maximum Tair tolerated by the crows nor maximum Tb varied with treatment. Our data reveal that water and energy balance during hot weather is affected by lead exposure.

Lead exposure of mainland Australia's top avian predator

Lead (Pb) toxicity, through ingestion of lead ammunition in carcasses, is a threat to scavenging birds worldwide, but has received little attention in Australia. We analyzed lead exposure in the wedge-tailed eagle (Aquila audax), the largest raptor species found in mainland Australia and a facultative scavenger. Eagle carcasses were collected opportunistically throughout south-eastern mainland Australia between 1996 and 2022. Lead concentrations were measured in bone samples from 62 animals via portable X-ray fluorescence (XRF). Lead was detected (concentration >1 ppm) in 84% (n = 52) of the bone samples. The mean lead concentration of birds in which lead was detected was 9.10 ppm (±SE 1.66). Bone lead concentrations were elevated (10-20 ppm) in 12.9% of samples, and severe (>20 ppm) in 4.8% of samples. These proportions are moderately higher than equivalent data for the same species from the island of Tasmania, and are comparable to data from threatened eagle species from other continents. Lead exposure at these levels is likely to have negative impacts on wedge-tailed eagles at the level of the individual and perhaps at a population level. Our results suggest that studies of lead exposure in other Australian avian scavenger species are warranted.

Lead, cadmium, and other trace elements in the liver of golden eagles and white-tailed eagles: recent data from Poland and a systematic review of previous studies

The golden eagle (Aquila chrysaetos) and the white-tailed eagle (Haliaeetus albicilla), being apex predators and facultative scavengers, can bioaccumulate different environmental contaminants, including toxic elements that may adversely affect their health. We analyzed the levels of cadmium (Cd), lead (Pb), and other metals and metalloids, including arsenic (As), barium (Ba), beryllium (Be), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), molybdenum (Mo), selenium (Se), thorium (Th), thallium (Tl), uranium (U), vanadium (V), and zinc (Zn) in liver samples taken from three golden eagles and 36 white-tailed eagles that were found dead across Poland to verify their exposure. We also used a systematic review to summarize the available literature data on Cd, Pb, and other studied elements in the liver of both eagle species. Analyses of trace elements in the liver samples of the Polish eagles revealed interspecific differences in Cd, Cu, and Mn and differences in Co, Mn, Tl, and Zn among study regions. All elements tested except Pb were below the suggested thresholds linked with adverse health effects in birds. The hepatic Pb found in almost half of all the tested individuals suggests environmental exposure to this toxic element. One of the tested white-tailed eagles had hepatic Pb above the threshold of sublethal poisoning. Although our results seem optimistic, as previous Polish studies showed a higher prevalence of birds with hepatic Pb exceeding the toxicity threshold, they indicate that exposure to this toxic metal could still pose an additional threat to the health of Polish eagles.

Identifying the origin of lead poisoning in white-backed vulture (Gyps africanus) chicks at an important South African breeding colony: a stable lead isotope approach

Elevated lead levels in scavenging raptors can originate from a variety of environmental and anthropogenic sources, including soil, water, mining activities and legacy lead from leaded fuel, but has mostly been attributed to fragments of lead-based ammunition embedded in the tissues of carcasses. To identify the origins of lead in the tissues of white-backed vulture (Gyps africanus) chicks at Dronfield Nature Reserve, South Africa, we used MC-ICP-MS to compare the isotopic composition of lead in blood samples to those of soil in the chicks' immediate environment, different mining activities in South Africa and lead ammunition commonly used in hunting and game management practices. The isotopic ratios in vulture blood samples ranged widely (207Pb/206Pb: 0.827-0.911), but fell within those measured for ammunition (0.761-0.938). Dronfield water can be excluded as a significant source, as the lead concentration for water was below detection limits. Uranium, coal, atmospheric Pb, legacy Pb from fuel and Pb mining can also be excluded as significant sources, based on the limited overlap with Pb isotopic ratios measured in vulture blood. Whereas 55% of chicks we sampled displayed isotopic ratios consistent with Dronfield soil, the low local Pb concentration and the low extractable Pb levels in South African soil in general, imply that soil Pb is unlikely the major source of Pb in WBV chicks, especially in birds with elevated blood Pb levels, i.e. > 20 µg/dL. Our results, when considered in the context of vulture feeding ecology and low Pb levels in non-scavenging birds in South Africa, imply the major source of elevated Pb levels in WBV chicks to be fragments of lead-based ammunition embedded in the carrion fed to them by their parents.

European mammal exposure to lead from ammunition and fishing weight sources

Ammunition and fishing weight usage is the greatest largely unregulated contributor of lead (Pb) deposition to the European environment. While the range of negative impacts of Pb exposure to humans and avian wildlife are relatively well documented, little is known about risks to wild mammals despite recent scientific interest and publications. A qualitative risk assessment of the potential Source-Pathway-Receptor linkages for European mammal exposure was conducted, based on literature reviews and existing evidence and discussions with experts from the fields of wild mammal feeding ecology, behaviour and health.

The assessment identified 11 pathways for mammal exposure to Pb, with all 243 European species likely to be potentially exposed via one or more of these. All species were identified as potentially exposed via ingestion of water with elevated Pb from degraded ammunition/fishing weights. Ingestion of vegetation with elevated Pb from degraded ammunition/fishing weights potentially exposed many species (158), 78% of which had a potentially high risk of exposure when feeding in areas of high Pb deposition. Ingestion of retained ammunition in previously shot prey and/or discarded kill/gut piles with embedded ammunition was another significant pathway, contributing to predatory and scavenging carnivorous mammal exposure where an individual exposure event would be expected to be high.

The mechanisms by which Pb from ammunition and fishing weight sources are moved up trophic levels and ‘transferred’ from areas of high deposition into wider food chains e.g. via water, flying invertebrates and herbivores being subsequently preyed upon requires further investigation.

In conclusion, there are multiple and diverse Source-Pathway-Receptors linkages for European mammal exposures to Pb and evidence of exposure, from Europe and elsewhere, exists for some herbivores, carnivores, omnivores and insectivores. Both fatal but more likely non-fatal chronic and acute exposures may be expected to occur in wild European mammalian species, including those in poor conservation status.

Small-Mammal Shooting as a Conduit for Lead Exposure in Avian Scavengers

Lead (Pb) exposure is a widespread wildlife conservation threat. Although commonly associated with Pb-based ammunition from big-game hunting, small mammals (e.g., ground squirrels) shot for recreational or pest-management purposes represent a potentially important Pb vector in agricultural regions. We measured the responses of avian scavengers to pest-shooting events and examined their Pb exposure through consumption of shot mammals. There were 3.4-fold more avian scavengers at shooting fields relative to those at fields with no recent shooting, and avian scavengers spent 1.8-fold more time feeding after recent shooting events. We isotopically labeled shot ground squirrels in the field with an enriched ¹⁵N isotope tracer; 6% of avian scavengers sampled within a 39 km radius reflected this tracer in their blood. However, 33% of the avian scavengers within the average foraging dispersal distance of nests (0.6-3.7 km) were labeled, demonstrating the importance of these shooting fields as a source of food for birds nesting in close proximity. Additionally, Pb concentrations in 48% of avian scavengers exceeded subclinical poisoning benchmarks for sensitive species (0.03-0.20 μg/g w/w), and those birds exhibited reduced δ-aminolevulinic acid dehydratase activity, indicating a biochemical effect of Pb. The use of shooting to manage small mammal pests is a common practice globally. Efforts that can reduce the use of Pb-based ammunition may lessen the negative physiological effects of Pb exposure on avian scavengers.

Lead contamination in tissues of large avian scavengers in south-central Europe

Lead poisoning from spent ammunition is known to affect many avian species. Birds of prey ingest lead when feeding on game shot with lead gunshot or bullets. Raptors with scavenging habits are particularly vulnerable to ingesting lead in areas with intensive hunting and are good indicators of the risk of poisoning from lead ammunition. To assess how much facultative and obligate avian scavengers suffer lead contamination in south-central Europe, between 2005 and 2019 we collected and analysed 595 tissue samples from 252 carcasses of 4 species (golden eagle, bearded vulture, griffon vulture, cinereous vulture). Lead concentrations in organs showed a similar pattern across species with long and small bones revealing the highest median values (5.56 and 6.8 mg/kg w.w., respectively), the brain the lowest (0.12), and the liver and kidney the intermediate (0.47 and 0.284). Overall, 111 individuals (44.0%) had lead concentrations above background thresholds in at least one tissue (i.e. >2 mg/kg w.w. in soft tissues, >8.33 in bone) and 66 (26.2%) had values indicating clinical poisoning (>6 mg/kg w.w. in liver, >4 in kidney, >16.6 in bone). Tissue lead concentrations and incidence of clinical and sub-clinical poisoning were higher in golden eagles and griffon vultures than in bearded and cinereous vultures, likely due to different feeding habits. In all species we found a rapid increase in lead values with age, but differences between age classes were significant only in the golden eagle. Birds with lead fragments in their digestive tract, as detected by X-rays, had higher median lead concentrations, suggesting that hunting ammunition is the main source of lead poisoning. Our results imply that lead impacts the demography of these long-lived species with delayed sexual maturity and low reproduction rate. A rapid transition towards lead-free bullets and gunshot is therefore required across Europe.

Integrating active and passive monitoring to assess sublethal effects and mortality from lead poisoning in birds of prey

The ingestion of lead (Pb) ammunition is the most important exposure pathway to this metal in birds and involve negative consequences to their health. We have performed a passive monitoring of Pb poisoning in birds of prey by measuring liver (n = 727) and blood (n = 32) Pb levels in individuals of 16 species found dead or sick in Spain between 2004 and 2020. We also performed an active monitoring by measuring blood Pb levels and biomarkers of haem biosynthesis, phosphorus (P) and calcium (Ca) metabolism, oxidative stress and immune function in individuals (n = 194) of 9 species trapped alive in the field between 2016 and 2017. Passive monitoring results revealed some species with liver Pb levels associated with severe clinical poisoning (>30 μg/g d.w. of Pb): Eurasian griffon vulture (27/257, 10.5%), red kite (1/132, 0.8%), golden eagle (4/38, 10.5%), and Northern goshawk (1/8, 12.5%). The active monitoring results showed that individuals of bearded vulture (1/3, 33.3%), Eurasian griffon vulture (87/118, 73.7%), Spanish imperial eagle (1/6, 16.7%) and red kite (1/18, 5.6%) had abnormal blood Pb levels (>20 μg/dL). Blood Pb levels increased with age, and both monitoring methods showed seasonality in Pb exposure associated with a delayed effect of the hunting season. In Eurasian griffon, blood Pb concentration was associated with lower δ-ALAD activity in blood and P levels in plasma, and with higher blood lipid peroxidation and plasma carotenoid levels in agreement with other experimental and field studies in Pb-exposed birds. The study reveals that Pb poisoning is a significant cause of death and sublethal effects on haem biosynthesis, P metabolism and oxidative stress in birds of prey in Spain.

High Frequency of Lead Exposure in the Population of an Endangered Australian Top Predator, the Tasmanian Wedge-Tailed Eagle (Aquila audax fleayi)

Lead poisoning, mainly through incidental ingestion of lead ammunition in carcasses, is a threat to scavenging and predatory bird species worldwide. In Australia, shooting for animal control is widespread, and a range of native scavenging species are susceptible to lead exposure. However, the prevalence of lead exposure in Australia's scavenging and predatory birds is largely unknown. We evaluated the degree to which the Tasmanian wedge-tailed eagle (Aquila audax fleayi), an endangered Australian raptor and facultative scavenger, showed evidence of lead exposure. We detected lead in 100% of femur and liver tissues of 109 eagle carcasses opportunistically collected throughout Tasmania between 1996 and 2018. Concentrations were elevated in 10% of 106 liver (>6 mg/kg dry wt) and 4% of 108 femur (>10 mg/kg dry wt) samples. We also detected lead in 96% of blood samples taken from 24 live nestlings, with 8% at elevated concentrations (>10 μg/dL). Of the liver samples with elevated lead, 73% had lead^207/206 isotope ratios within the published range of lead-based bullets available in Tasmania. These first comprehensive data on lead exposure of an Australian raptor are comparable to those for raptor studies elsewhere that identify lead-based ammunition exposure as a conservation threat. Our findings highlight the importance of further research and efforts to address lead contamination throughout the Tasmanian ecosystem and in other Australian regions. Environ Toxicol Chem 2021;40:219-230. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Lead contamination in raptors in Europe: A systematic review and meta-analysis

Lead contamination is a widely recognised conservation problem for raptors worldwide. There are a number of studies in individual raptor species but those data have not been systematically evaluated to understand raptor-wide lead exposure and effects at a pan-European scale. To critically assess the extent of this problem, we performed a systematic review compiling all published data on lead in raptors (1983-2019) and, through a meta-analysis, determined if there was evidence for differences in exposure across feeding traits, geographical regions, between hunting and non-hunting periods, and changes over time. We also reviewed the impact of lead on raptors and the likely main source of exposure. We examined 114 studies that were unevenly distributed in terms of time of publication and the countries in which studies were performed. Peer-reviewed articles reported data for 39 raptor species but very few species were widely monitored across Europe. Obligate (vultures) and facultative scavengers (golden eagle, common buzzard and white-tailed sea eagle) accumulated the highest lead concentrations in tissues and generally were the species most at risk of lead poisoning. We found no evidence of a spatial or decadal trend in lead residues, but we demonstrated that high lead blood levels relate to hunting season. Exposure at levels associated with both subclinical and lethal effects is common and lead from rifle bullets and shot is often the likely source of exposure. Overall, our review illustrates the high incidence and ubiquity of lead contamination in raptors in Europe. However, we did not find studies that related exposure to quantitative impacts on European raptor populations nor detailed studies on the impact of mitigation measures. Such information is urgently needed and requires a more harmonised approach to quantifying lead contamination and effects in raptors across Europe.

Feeding Ecology Drives Lead Exposure of Facultative and Obligate Avian Scavengers in the Eastern United States

Lead poisoning of scavenging birds is a global issue. However, the drivers of lead exposure of avian scavengers have been understood from the perspective of individual species, not cross-taxa assemblages. We analyzed blood (n = 285) and liver (n = 226) lead concentrations of 5 facultative (American crows [Corvus brachyrhynchos], bald eagles [Haliaeetus leucocephalus], golden eagles [Aquila chrysaetos], red-shouldered hawks [Buteo lineatus], and red-tailed hawks [Buteo jamaicensis]) and 2 obligate (black vultures [Coragyps atratus] and turkey vultures [Cathartes aura] avian scavenger species to identify lead exposure patterns. Species and age were significant (α < 0.05) predictors of blood lead exposure of facultative scavengers; species, but not age, was a significant predictor of their liver lead exposure. We detected temporal variations in lead concentrations of facultative scavengers (blood: median = 4.41 µg/dL in spring and summer vs 13.08 µg/dL in autumn and winter; p = <0.001; liver: 0.32 ppm in spring and summer vs median = 4.25 ppm in autumn and winter; p = <0.001). At the species level, we detected between-period differences in blood lead concentrations of bald eagles (p = 0.01) and red-shouldered hawks during the winter (p = 0.001). During summer, obligate scavengers had higher liver lead concentrations than did facultative scavengers (median = 1.76 ppm vs 0.22 ppm; p = <0.001). These data suggest that the feeding ecology of avian scavengers is a determinant of the degree to which they are lead exposed, and they highlight the importance of dietary and behavioral variation in determining lead exposure. Environ Toxicol Chem 2020;39:882-892. © 2020 SETAC.

Effects of lead from ammunition on birds and other wildlife: A review and update

Poisoning of wild birds following ingestion of lead from ammunition has long been recognised and considerable recent research has focused on terrestrial birds, including raptors and scavengers. This paper builds upon previous reviews and finds that both the number of taxa affected and geographical spread of cases has increased. Some lead may also be absorbed from embedded ammunition fragments in injured birds which risk sub-lethal and welfare effects. Some papers suggest inter-specific differences in sensitivity to lead, although it is difficult to disentangle these from other factors that influence effect severity. Sub-lethal effects have been found at lower blood lead concentrations than previously reported, suggesting that previous effect-level 'thresholds' should be abandoned or revised. Lead poisoning is estimated to kill a million wildfowl a year in Europe and cause sub-lethal poisoning in another ≥ 3 million. Modelling and correlative studies have supported the potential for population-level effects of lead poisoning in wildfowl, terrestrial birds, raptors and scavengers.

Wildlife, human and environmental costs of using lead ammunition: An economic review and analysis

A proposed European Union (EU)-wide restriction on the use of lead gunshot for shooting in and over wetlands estimated that the societal benefits of a restriction outweighed costs, despite few identified benefits being quantified economically. A subsequent Annex XV Investigation Report on the evidence of impacts of lead ammunition in terrestrial environments concluded that additional measures to control its use are warranted, although to date this has not been further evaluated. To help inform this process, we review the literature and undertake new analyses to estimate the costs of continued use of lead ammunition associated with impacts on wildlife, people and the environment. We estimate minimum annual direct costs across the EU and Europe of c. €383 million-€960 million and €444 million-€1.3 thousand million respectively. The value that society places on being able to avoid these losses, estimated using a 'willingness to pay' approach, was c. €2.2 thousand million for wildfowl alone. Our estimated costs of the continued use of lead ammunition across the EU appear to be considerably greater than the likely costs of switching to non-toxic alternative ammunition types, although these have not been formally estimated in full.

Blood and bone lead levels in South Africa's Gyps vultures: Risk to nest-bound chicks and comparison with other avian taxa

Poisoning, including secondary lead poisoning, is cited as the single most important cause of vulture mortalities in Africa. To evaluate the prevalence of lead poisoning among South Africa's Gyps vultures compared to other, non-scavenging birds, we obtained blood and bone samples from Cape (Gyps coprotheres) and White-backed (G. africanus) vultures. We found that 66% of White-backed Vultures (n = 110, including 85 nest-bound chicks sampled at Dronfield Nature Reserve) and 80% of Cape Vultures (n = 15) had blood [Pb] in excess of 10 μg/dL, the upper limit of background exposure. Average blood [Pb] were 15.4 μg/dL and 29.7 μg/dL for White-backed and Cape vultures, respectively. Bone samples revealed that 12% of White-backed Vultures (n = 18) and 9% of Cape Vultures (n = 75) suffered from subclinical to severe clinical lead poisoning upon their deaths. By contrast, none of the 40 blood, bone or liver samples obtained from non-scavenging bird species were found to exceed background exposure levels. Our results suggest that, unlike non-scavenging birds, the scavenging lifestyle of Gyps vultures subjects them to lead poisoning on a regular basis. Had environmental sources of lead (e.g., dust) been the source of the lead poisoning at the White-backed Vulture breeding colony at Dronfield, all the chicks would have displayed similar blood lead concentrations. Instead the values ranged from barely detectable to very high, leading us to conclude that metallic lead fragments regurgitated by parents during feeding are responsible for the elevated lead levels in some of the chicks at this site. We conclude the likely source of these particles to be fragments of lead ammunition embedded in the carcasses of hunted animals. These results add to a growing body of evidence underscoring the threat posed by the use of lead ammunition and its potential role in the declines of vultures and other scavenging taxa.