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Duck Mortality at Wastwater Treatment Plants Report Now Available
Date Posted: July 29, 2010
The findings of a study investigating the cause of more than 1,000 duck deaths along the central Colorado Front Range near wastewater treatment plants are now available to the public. The study - "Adverse Effects to Northern shovelers from Exposure to Treated Wastewater from Central Front Range, Colorado, Wastewater Treatment Plants" - could not definitively identify a causative factor for the mortalities that occurred from January to February 2007, and again in January 2008, during unusually harsh winter weather conditions. However, polyethylene glycols (PEGs) were detected on feathers of birds in the study, and this class of chemicals has properties that can cause feathers to lose their water repellency. exposed to waters at area wastewater treatment plants.
The U.S. Fish and Wildlife Service (Service), U.S. Geological Survey (Survey), Colorado Division of Wildlife (CDOW), Metro Wastewater Reclamation District (Metro) and Chemir Analytical Services of Maryland Heights, Mo., collaborated on the study.
The study was prompted by the above-average number of duck deaths that occurred near wastewater treatment plants in the winters of 2007 and 2008. The extended periods of below-freezing temperatures for a few weeks in those winters froze most water bodies along the Front Range, making wastewater treatment plants some of the few remaining areas where open water was available to birds. At Metro, most affected birds were found in secondary clarifiers and in the chlorine contact basin.
Ducks that died were primarily northern shovelers (Anas clypeata). Tests immediately ruled out diseases that might be a threat to human health, avian flu and other toxic and infectious diseases as the cause. Likewise, no ducks died of cancer or poisoning from solvents. Most of the dead birds were very wet, suggesting that the ability of their plumage to repel water was compromised. Some also were emaciated, while others appeared in good body condition. The high number of mortalities ended as temperatures warmed in the metro area and birds began moving to other bodies of open water for food and shelter.
A team was formed to investigate the incidents that primarily consisted of staff from the Service’s Mountain-Prairie Region, CDOW and Metro. Initially, carcasses of dead birds were sent to the CDOW, USGS National Wildlife Health Center (Madison, WI), and the University of Wisconsin. Bird feathers were analyzed by scanning electron microscopy, which indicated structural anomalies in the feathers that may have been caused by a chemical. Follow-up chemical analyses conducted on samples washed from the feathers at the Mississippi State University Chemistry Laboratory could not detect a likely chemical agent, but researchers at that lab indicated that more sophisticated chemical analyses would need to be performed to detect certain sophisticated classes of chemicals, notably surfactants.
The team contacted Chemir Analytical Services, one of only a few labs in the U.S. that performs liquid chromatography-mass spectrometry analyses to detect specific classes of chemicals. Analyses by Chemir determined that a number of classes of surfactants, including polyethylene glycols (PEGs), were present in feathers from waterfowl collected during the mortality events.
In 2008, the team contracted with the U.S. Geological Survey, to conduct a live-waterfowl study at Metro’s facility in north Denver. The study exposed captive waterfowl to sources of treated wastewater to determine if these experimental birds were affected similarly to free-ranging birds that died at the plant. The study used mallards (Anas platyrhynchos) exposed to treated wastewater under controlled conditions from Metro’s secondary clarifiers and from the chlorine contact basin. A suitable group of control birds was also exposed to water from a source outside of Metro’s facility. Mallards exposed to treated wastewater from both the secondary clarifiers and from the chlorine contact basin lost buoyancy, became wetted to the skin, and exhibited signs of hypothermia in as little as three hours of exposure. Chemical analyses of feathers from both treatment and control birds and water samples are included in the study’s findings.
Although PEGs were detected in samples from the treatment birds, and these chemicals have characteristics that could cause the loss of water repellency from the birds’ feathers, PEGs also were found in samples from feathers of some birds that did not lose their ability to repel water, and those birds did not become hypothermic. Thus, the study could not definitively conclude that PEGs were the single causative factor in the wild bird mortalities. More experimental work is necessary to determine whether PEGs or some additional other factors are responsible for causing the symptoms exhibited by birds
Patty Stevens, U.S. Geological Survey, 970.226.9499