Long-term Studies Examine Contaminant Exposure and Reproduction of Ospreys Nesting in Two Large United States Estuaries

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In a series of studies from 2010 to 2018, U.S. Geological Survey (USGS) scientists detected low levels of legacy contaminants and pharmaceuticals in osprey (Pandion haliaetus) and their food chain within the Chesapeake and Delaware River estuaries. Osprey reproductive success increased during the same period and was determined to be adequate to sustain a stable population in both estuaries.

Two of our Nation’s largest estuaries—Delaware Bay and Chesapeake Bay—serve as important habitat for fish and bird populations for hunting and other recreational activities. Numerous species of birds depend on the estuaries, which are part of the Atlantic flyway and are critical staging sites for a large population of fish-eating birds.

The Delaware Bay and Chesapeake Bay Estuaries are areas of historical and current contamination from agriculture, industry, and domestic wastewater sources. During the mid- to late 1900s, osprey and other fish-eating birds suffered population declines related to eggshell thinning associated with exposure to dichlorodiphenyltrichloroethane (DDT) metabolites—primarily dichlorodiphenyldichloroethylene (p,p’-DDE), and to a lesser degree polychlorinated biphenyls.

Recently hatched osprey nestling and an unhatched egg in the Delaware Estuary

Recently hatched osprey nestling and an unhatched egg in the Delaware Estuary.

(Credit: Rebecca S. Lazarus, USGS. Public domain.)

During 2010–2018, USGS scientists and other collaborators used environmental sampling and modelling approaches to determine if legacy contaminants and more contemporary contaminants, such as active pharmaceutical ingredients, are in osprey and associated food webs. Scientists also used these approaches to determine if osprey reproductive success was stable compared to previous measurements in the 1970s through the early 2000s.

Scientists frequently visited osprey nests and used onsite cameras to monitor reproductive activity and osprey food selection.  They collected eggs and nestlings for analyses, measured osprey egg shell thickness, and counted osprey nests to determine osprey population stability. In some areas, water and fish were also collected for analyses to examine food web transfer of legacy and contemporary contaminants. An exposure model to understand trophic transfer of active pharmaceutical ingredients was created, tested, and improved using field data from the Chesapeake and Delaware Bays.

Scientists reported that concentrations of legacy contaminants in osprey were lower than values measured in the 1970s through early 2000s in both estuaries, with the exception of some historically contaminated areas.

Biomagnification factors from fish to osprey eggs for p,p’-DDE and total polychlorinated biphenyls were generally similar between the two estuaries. No relation was determined between legacy contaminants with egg hatching, eggs lost from nests, nestling loss, or fledging and nesting success. Osprey eggshell thickness recovered to pre-DDT era values and osprey reproductive success increased during that same period and was
determined to be adequate to sustain a stable population in both estuaries. 

Active pharmaceutical ingredients were detected in osprey, fish, and water in both estuaries. Acetaminophen was detected in 22 of the 29 osprey plasma samples in the Delaware Bay, whereas diltiazem was detected in all 69 osprey plasma samples in the Chesapeake Bay.  The levels detected in osprey plasma were less than the therapeutic plasma level for humans. Effect thresholds for the active pharmaceutical ingredients detected are unknown in ospreys at this time.

Questions remain about the transfer of pharmaceuticals and other contaminants through food webs from water and sediment to fish, other fish-eating birds, and humans that consume them. Future research could focus the scope of these studies on understanding geographic locations where pharmaceuticals and other contaminants may represent the greatest exposure
potential and the greatest health risks.

This research was funded by the USGS Contaminant Biology Program, the Delaware Department of Natural Resources and Environmental Control, the Chesapeake Bay Program, and by a grant to the Texas Sea Grant College Program from the National Sea Grant Office, National Oceanic and Atmospheric Administration.


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