Abstract

Eight ospreys (Pandion haliaetus) were hacked and released at The Wilds (Cumberland, Ohio) in June 2003 as part of a statewide reintroduction program initiated by the Ohio Department of Natural Resources. Through the Department of Wildlife and Conservation Medicine at The Wilds, a toxicologic risk assessment was performed to evaluate the potential for exposure of the released birds to contaminants and to provide a predictor of success for the reintroduction plan. Two species of fish, bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides), were taken from local ponds and lakes and tested for organochlorine pesticides, polychlorinated biphenyls (PCBs) and heavy metals. No pesticide contaminants or PCBs were detected, and heavy metals were found to occur at subthreshold levels. Mercury and other mineral contaminants were still present, however, and remain a cause for concern. Continued monitoring is warranted.

Introduction

In conjunction with an ongoing Ohio Department of Natural Resources (ODNR) Division of Wildlife reintroduction project, eight nestling ospreys (Pandion haliaetus) were transported to The Wilds for hacking and release in June 2003. Similar releases are planned to continue annually through 2006. The suitability of The Wilds as osprey habitat has been debated. The Wilds property comprises a vast expanse of reclaimed land and many of its ecological components are yet to be thoroughly investigated. Following decades of surface mining for coal, the reclamation process resulted in a large system of ponds and lakes extending throughout the property and surrounding area. There is no federally mandated biomonitoring of soil, water or fish in the region due to local restrictions on public access, and little is known regarding local ecosystem health. Through ongoing ecological and conservation medicine studies at The Wilds, efforts are being made toward developing a greater understanding of this unique habitat.

Prior to the initiation of the current reintroduction plan, the last known osprey nest in Ohio was abandoned in 1941. Ospreys were listed as endangered in this state in 1977 and were granted protected status in 31 states by the year 2000. Like many birds of prey, ospreys suffered major declines following exposure to environmental contaminants such as DDT, PCBs and mercury, which negatively impacted reproduction.¹⁵ Given their piscivorous diet, ospreys are particularly susceptible to contaminants that biomagnify through the food chain.⁷ Although the reintroduction project has been met with initial success (40 birds hatched from 22 nests this year), the distribution of the returning birds has been limited to the northern half of the state for reasons yet to be determined. The Wilds was therefore requested to support a release site in 2003 based on (1) the longstanding partnership between ODNR and The Wilds, (2) the southeastern location and excellent potential osprey habitat in The Wilds environs, and (3) the local expertise.

The Wilds staff recently participated in an investigation of African fish eagles (Haliaeetus vocifer) as biomonitors of environmental contamination in Uganda.¹² This, and similar research on bald eagles (Haliaeetus leucocephalus) in the United States,² prompted a more comprehensive approach to the health aspects of osprey reintroduction at The Wilds. Based on the uneven distribution of osprey return within the state of Ohio, the known ongoing effects of contaminants on osprey reproduction in some areas of the United States^5,11 and the unknown status of contaminants at The Wilds, a specific toxicologic investigation was indicated. Whereas exposure to contaminants that ospreys encounter during their southern migrations cannot be controlled, environmental investigations allow the suitability of the release site to be maximized.

Materials and Methods

Environmental Suitability Assessment

When addressing potential risk factors in the reintroduction of ospreys to The Wilds, persistent organic pollutants (POPs) were considered a significant non-infectious disease threat based on preliminary information including the following:

• Ospreys disappeared from Ohio due to heavy exposure to POPs such as dichlorodiphenyltrichloroethane (DDT), polychlorinated biphenyls (PCBs) and heavy metals. Mercury, PCBs, and DDT have proven to be among the most toxic contaminants to raptors due to bioconcentration, bioaccumulation and biomagnification processes.⁷
• The process of surface mining for coal and the resulting acid mine runoff can facilitate accumulation of disproportionately high levels of several heavy metals in the environment.¹
• Ohio is a largely agricultural state, and agricultural runoff has been associated with increased environmental burdens of chlorinated pesticides such as DDT.
• Coal plants such as those upriver of the watersheds of The Wilds are a potential source of contamination with PCBs, arsenic, cadmium, lead, mercury, and selenium.⁴
• POPs bioaccumulate in fish. While many POPs are being detected in decreasing levels in fish in Ohio and surrounding regions, in some areas contaminants such as mercury and lead have been found in slowly increasing levels.^3,13
• Ohio has widespread POP-based fish consumption advisories.
• Dietary contamination has proven to be the primary source of exposure to POPs in piscivorous raptors such as ospreys.⁷

Fish Collection

Bluegill and largemouth bass were selected for study because they are the prevalent fish species found at The Wilds and consequently will comprise the main prey base of resident ospreys. Fish samples were collected by hook and line and consisted of two same-species fish of similar size (<10% length disparity) per sample. Collection parameters were based on the upper end of the length range for typical osprey acquisition (bass 30–35 cm; bluegill 17.5–22.5 cm). A total of 18 samples were collected from 9 different lakes. Length and weight measurements were recorded, and whole-body composites were frozen within 4 hours of collection.

Sample Analysis

Samples were analyzed for contaminants at Michigan State University Animal Health Diagnostic Laboratory. Tissues for analysis of chlorinated pesticides (DDT and metabolites, aldrin, α-BHC, β-BHC, hexachlorocyclohexane, dieldrin, endrin, heptachlor epoxide, lindane, nonachlor) and PCBs (total aerochlors) were extracted and purified using procedures previously described.¹⁰ Linear standard curves at 0.002–0.5 ppm range for pesticides and 0.05–2.0 ppm range for PCBs were used for quantification. Concentrations were determined by gas chromatography with electron capture detector (Varian 3400 gas chromatograph, Varian Instruments, Walnut Creek, CA). The quantification limits were 0.001 ppm for pesticides and 0.01 for PCBs. The recovery rates were 70–100%. Samples were analyzed for mercury by cold vapor atomic absorption spectrophotometry at 253.7 nm with a quantification limit of 0.005 ppm. Accuracy was monitored by concurrent analysis of procedural blanks. Mineral panel analysis was performed with inductively coupled plasma-atomic emission spectrometry (ICP-AES) for the following elements: barium, iron, sulfur, copper, manganese, antimony, sodium, cobalt, molybdenum, arsenic, lead and potassium.

Results

Neither chlorinated pesticides nor PCBs were detected in any samples. Of 18 OSHA-regulated toxic metals measured, 11 were detected and are presented in Table 1. The following minerals were not detected at the corresponding quantification limits (ppm): selenium, 2.0; boron, 1.0; thallium, 2.5; antimony, 1.0; molybdenum, 0.2; arsenic, 0.5; and lead, 0.5. A literature review revealed proposed dietary risk thresholds for birds for eight minerals. Of these, cadmium, copper, manganese, arsenic and zinc were not detected at quantities above threshold. Levels of mercury and lead were found in subthreshold levels for most references,^6,14 but were above some U.S. EPA references for low toxicity values for dietary exposure in birds. The quantification limit for selenium was below the generally accepted threshold for dietary exposure in birds (3.0 ppm), but above a proposed threshold of 0.23 ppm found in one reference.

Table 1. Metals detected in largemouth
bass and bluegill at The Wilds, 2003

^aSamples below detection limit not included in mean

Discussion

Quantification limits for PCBs and chlorinated pesticides are well below both the critical toxic dietary thresholds proposed for reproductive failure in ospreys (0.5 ppm⁹ and 6.0–9.0 ppm ww,¹⁵ respectively) and the threshold for effects on shell thickness in birds (0.1 ppm ww⁸).

Heavy metal concentrations quantified in this study were similar to national averages reported in the early 1990s for freshwater fish from comparable areas. Little data is available regarding risk thresholds for many of these contaminants in birds. Of the minerals detected, mercury is of most concern. Mercury levels fell into the high-end range of those levels reported for southeast Ohio by the EPA in 1997; however, no sample exceeded the proposed risk thresholds for reproductive failure in osprey (dietary 0.5 ppm ww).¹⁴ Mercury levels have not appreciably declined across the country since 1974¹³ and have in fact increased in some osprey populations.³ Mercury is of particular concern because it readily bioaccumulates, bioconcentrates and biomagnifies as methlymercury⁷ which can reduce reproduction in birds with low-level chronic exposure.⁶ Furthermore, the majority of mercury that accumulates in eggs and offspring, and therefore presents the greatest risk to successful reproduction in adults, is acquired from the breeding area,⁶ which is typically within twenty miles of the male’s fledging site. Although mercury is ubiquitous, liberation of ecologically toxic methylmercury from the inert form may be exacerbated in this study area by mine runoff, coal-fired electric plants, seed treatment, and man-made lakes.¹³

Pre-introduction and translocation assessments are not new concepts. The variables and considerations, however, are ever expanding, and in the past decade the complexities associated with translocation have been increasingly revealed. While issues of disease spread and susceptibility were well discussed in the early 1990s (J Zoo Wildlife Med; Vol. 24:3), issues such as endocrine disruptors and unknown environmental toxicants as obstacles to successful animal movements have been introduced more recently.^2,7 The success of wildlife translocation is increasingly contingent upon interdisciplinary efforts and planning and the scientific community is responding with a broadened approach In regards to piscivorous raptors in particular, much has been learned from ongoing contaminant monitoring and individual species are becoming increasingly validated as contaminant biomonitors.^2,6,12 It is therefore prudent that the information be used as part of a preventive medicine regime for these birds as well.

Conclusions

The toxicologic analysis of local fish is considered a valuable determinant of risk associated with osprey reintroduction at The Wilds. In terms of known risk factors in food chain contamination, the results of this study indicate that The Wilds offers suitable habitat for an osprey reintroduction program.

The true extent of toxic risk from lead, cadmium and newer pesticide chemicals remains largely unknown, and further study is necessary. Newer, non-accumulating pesticide chemicals are showing increasing evidence of adverse health effects on wildlife, and expanded testing protocols are indicated. Mercury, PCBs and chlorinated pesticides represent a particular health hazard to osprey, and some of these chemicals are found in excessive levels in the Great Lakes region to the north of Ohio. Periodic monitoring of fish and possibly returning osprey or their offspring would be prudent.

Additional aspects of the merit of this reintroduction project warrant emphasis. The benefits go beyond those of a toxicologic risk assessment. This project offered a unique opportunity for public education and awareness. Through hands-on involvement with monitoring, feeding, banding and veterinary examination of the ospreys at The Wilds, dozens of Ohio children were directly involved with the reintroduction of an endangered species in Ohio. Furthermore, the hack tower could be seen from public tour routes, furthering public interest and education. Finally, the reintroduction strengthened ties between The Wilds and the ODNR as well as the Columbus Zoo, Muskingum College and the OHEPA.

Acknowledgments

This project was funded by the Columbus Zoo and Aquarium Conservation Fund. We gratefully acknowledge the Columbus Zoo for their support, Wilson Rumbeiha (MSU ADDL) for assistance with fish tissue analysis and interpretation, Dennis Mishne (Ohio EPA) for access to fish tissue contaminant data, and John Estinek (Ohio EPA) for toxicologic advice.

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