Bird Hatchling Development Following Exposure to Environmentally Relevant Levels of Brominated Flame Retardants

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Scientists performed laboratory studies with American kestrels and zebra finch to determine the effects of brominated flame retardant exposure on hatchlings. They found evidence that exposure while in the egg disrupted thyroid function in female American kestrel hatchlings and affected nestling body condition in zebra finch hatchlings, but no other effects were detected.

 

Owing to increasing restrictions on the use of some flame retardants, there has been a shift toward use of alternative brominated flame retardants. These brominated flame retardants and their derivatives have demonstrated potential for bioaccumulation. However, very little is known of the metabolic processes or toxicological effects of brominated flame retardants, particularly for birds.

American Kestrel eggs

American kestrel eggs (Credit: Natalie Karouna-Renier, U.S. Geological Survey. Public domain.)

Therefore, the U.S. Geological Survey (USGS), along with partners from Environment and Climate Change Canada and academia completed two laboratory studies in which two brominated flame retardants were injected at environmentally relevant concentrations (at concentrations previously detected in biota) into fertilized eggs under controlled conditions. In one series of tests, American kestrel (Falco sparverius) eggs were exposed to tetrabromobisphenol A bis(2,3-dibromopropyl ether) (TBBPA-BDBPE) and 1,2-bis(2,4,6-tribromophenoxy) ethane (BTPBE) 5 days after they were laid and artificially incubated until hatching. Blood and tissues were collected to measure morphological and physiological endpoints. Although there was evidence of thyroid system responses to the brominated flame retardant exposures in female hatchlings only, the two brominated flame retardants had no effects on embryo survival through 90 percent of the incubation period, hatching success, body mass, organ size, or oxidative stress of hatchlings.

In the second study, zebra finch (Taeniopygia guttata) eggs were injected with TBBPA-BDBPE on the day they were laid. Subsequently, egg contents were collected throughout embryonic development and nestlings were observed. There were no effects on hatching success, nestling survival, growth, organ somatic indices, or thyroid hormone homeostasis; however, there was evidence that body condition declined at higher doses toward the end of the rapid nestling growth phase.

 

American kestrel

American kestrel  (Falco sparverius) (Credit: Natalie Karouna-Renier, U.S. Geological Survey. Public domain.)

The injections of brominated flame retardants simulate the exposure of hatchlings in a controlled manner and are a step to understanding the effect of contaminant uptake in wild bird populations. The results indicate that these brominated flame retardants may not be particularly toxic to American kestrels or zebra finch at environmentally realistic concentrations. However, the decline of the finch embryo condition later in the nestling growth phase could indicate that the breakdown products of these flame retardants are more harmful than the parent compounds.

The USGS Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology), in collaboration with partners from other agencies and academia, has a long-term research strategy to improve the understanding of contaminant exposure from source-to-receptor; that is, designing research to look at contaminants like flame retardants from their sources in household and industrial products and other materials in the environment down to individual organisms like birds. To accomplish this, scientists apply their expertise in avian toxicology, ecology, reproductive ecology, food web ecology, aquatic ecology, hydrology, and environmental chemistry. By combining these results with environmental studies, scientists strive to answer more source-to-receptor questions about contaminants in the environment.

The Environmental Health Program (Contaminants Biology and Toxic Substances Hydrology) of the U.S. Geological Survey Ecosystems Mission Area supported this study.