Organic Contaminant Levels and the Reproductive Success of Ospreys in Chesapeake Bay

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Changes in the regulation and use of some organic chemicals have caused environmental concentrations to stabilize or decline during the past 35 years coincident with a rebound in the osprey (Pandion haliaetus) population of the Chesapeake Bay.

Game camera image of an osprey taken on Poplar Island, Maryland

Game camera image of an osprey taken on Poplar Island, Maryland. Game cameras were used to identify species of fish fed to osprey nestlings. Photo Credit: Game camera placed by Rebecca S. Lazarus, USGS.

The U.S. Environmental Protection Agency (EPA) classifies more than 70 percent of Chesapeake Bay tidal waters as impaired by toxic contaminants. To track these contaminants and their effects on bay ospreys, water, fish, osprey eggs, and blood samples from osprey chicks were sampled along Chesapeake Bay tributaries in Pennsylvania, Maryland, and Virginia, including several sites the EPAconsiders "Regions of Concern." These findings were published in three manuscripts, with the article published in the journal Integrated Environmental Assessment and Management, being named the Best Student Paper published in a Society of Environmental Toxicology and Chemistry journal for 2015.

Results from samples collected during the summer nesting season from 2011 through 2013 were compared to results from a 2000–1 study that showed levels of polychlorinated biphenyls (PCBs) had not changed significantly, not only in the last 10 years, but during the past 35 years. Residues of the pesticide dichlorodiphenyltrichloroethane (DDT) and the related compound, dichlorodiphenyl-dichloroethylene (p,p'-DDE), had decreased by approximately 80 percent during the same period of time to concentrations below the levels that caused the eggshell thinning responsible for osprey and bald eagle population declines in the 20th century. Although polybrominated diphenyl ethers (PBDE) flame retardants (also potentially toxic to wildlife) had declined slightly, samples from nests located near wastewater treatment plants (WWTPs) indicate that hotspots remain. Although Bay osprey populations have rebounded, one marker of genetic damage in osprey chick blood samples from some Regions of Concern and WWTPs was elevated compared to samples taken at a relatively uncontaminated reference site, which indicates the ongoing effects of these contaminants.

U.S. Geological Survey scientists monitoring an osprey nest on Back River, Maryland

U.S. Geological Survey scientists monitoring an osprey nest on Back River, Maryland. Photo Credit: Peter C. McGowan, U.S. Fish and Wildlife Service.

Currently used (2016) pharmaceuticals were also evaluated in this study to assess their bioaccumulation potential. The bioaccumulation potential was calculated by determining the concentration of these contaminants in prey fish and water near nesting sites to predict uptake in fish and ospreys. To complement the exposure model, water, fish, and osprey nestling blood were analyzed for 23 active pharmaceuticals or their metabolites and an artificial sweetener. Of the 18 analytes detected in water, 8 were found in fish blood but only 1 in osprey nestling blood (antihypertensive diltiazem). Although all of the detected compounds were well below the human therapeutic concentrations, their effects at the observed concentrations (or of their metabolites) are unknown.

Overall, the osprey population is thriving in the Chesapeake Bay. Their population has increased from 1,450 pairs in the 1970s to 3,500 during the mid-1990s. Recent observations in several tributaries indicate that the Chesapeake Bay osprey population may be approaching 10,000 pairs, which is more than 6 times greater than their nadir during the DDT-use era.

This study was funded by the U.S. Geological Survey (USGS) Chesapeake Bay Program, USGS Ecosystem Mission Area's Environmental Health Program (Contaminant Biology Program and Toxic Substances Hydrology), and Texas Sea Grant Program.