On the left is a healthy eastern bluebird heart and on the right is a moderately deformed eastern bluebird heart. - Photo taken by Dr. Diane Henshel, Indiana University; taken fall 1997.

This is a picture of a series of house wren hearts, starting on the left with an example of what a healthy house wren heart might look like. The center heart and the ones to the right have significant deformities. - Photo taken by Dr. Diane Henshel, Indiana University, photo taken fall 1997.

This is a picture of a tree swallow embryo at approximately 3.5 days of incubation, showing a healthy developing heart. - Photo taken by Dr. Diane Henshel, Indiana University, in August 1996.

This is a picture of a tree swallow embryo at approximately 3.5 days of incubation, showing an abnormally developed "tubular" heart, likely a precusor to what is documented in the nestlings (note also cranial edema). - Photo taken by Dr. Diane Henshel, Indiana University, in August 1996.

In 1995, contaminants biologists from the U.S. Fish and Wildlife Service's Bloomington, Indiana, Field Office and researchers from Indiana University began studying songbirds at several PCB contaminated sites and at a reference site in Monroe and Lawrence Counties, Indiana.  Our preliminary evaluations of heart development in passerines from these PCB contaminated sites summarized in 1997 indicated that virtually all species studied (eastern bluebirds, Carolina chickadees, house wrens, red-winged blackbirds, and tree swallows) were sensitive to the cardiotoxic effects of PCBs.   This study was conducted to quantify and provide a detailed evaluation of the PCB-induced cardiac teratogenicity in the five passerine species exposed under field conditions.  Our goals were to systematically characterize a suite of necropsy observable cardiac deformities and changes in gross heart shape and size in avian wildlife; and to quantitatively correlate each deformity and change with total PCBs and dioxin-like toxic equivalent concentrations (TEQs) by species, establishing the relative sensitivity of each passerine species.

This work has just been published in the February edition of Environmental Toxicology and Chemistry, a publication of the Society of Environmental Toxicology and Chemistry.  This work is important for two reasons.  It was documented in the 1970s that these types of cardiac effects occurred in chickens fed PCB contaminated feed.  Laboratory chicken studies evaluating the effects of PCBs and dioxin also produced these types of cardiac deformities.  It has been widely accepted (and perhaps in error) that chickens must be more sensitive to these type of cardiac effects than other birds.  Prior to this study, none had looked for these cardiac effects in passerine field studies.  Secondly, this study confirms that significant adverse impacts can occur to passerines at concentrations below those known to cause a reduction in hatching success, a more commonly studied endpoint.