Are flame retardants the next DDT?
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Fernie, KJ, J Laird Shutt, RJ Letcher, IJ Ritchie and DM Bird. 2009. Environmentally relevant concentrations of DE-71 and HBCD alter eggshell thickness and reproductive success of American kestrels. Environmental Science and Technology 43(6):2124–2130. |
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| ER Post, Flickr |
Flame retardants weaken American kestrel eggshells. |
Context
Chemicals that can reduce flammability of products which readily burn are called flame retardants. They have been used since the 1970s in furniture, carpeting, clothing, electronics and other consumer products. Because of their persistence and popularity, they are widespread in the environment.
Similar to many chemical contaminants–such as the insecticide DDT–flame retardants can travel long distances in air and water, ending up in remote environments, such as coastal areas, mountain tops and the Arctic regions of the world.
Two common types are polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane
(HBCD). The chemicals contaminate people and are consistently found in fat, blood and breast milk. Exposure most likely occurs through food, water and household dust.
Wildlife harbor the chemicals, too. Levels of flame retardants in fish and fish-eating birds are increasing in North America, despite recent bans of some commercial mixtures. The chemicals can move from prey to predator, concentrating with each move up the food chain.
Researchers have measured very high levels of the chemicals in top avian predators, like the American kestrel, China's common kestrels and Sweden's peregrine falcons. Females can deposit the contaminants in their eggs, exposing their growing chicks to highly elevated levels of the contaminants. Levels found in peregrine eggs in the US exceed those measured in Europe.
Animal laboratory and wildlife studies find that PBDEs can affect behavior, thyroid hormone, sperm production, and number of offspring. Like DDT, PBDEs and other flame retardants may be affecting raptor populations in similar ways as DDT did in the mid-twentieth century. The pesticide congregated in peregrine falcons, eagles and other predatory birds where it caused egg shell thinning that led to species declines.
Decreasing numbers of American kestrels across North America -- especially in the eastern US and Canada -- have left researchers wondering why.
What did they do?
Researchers fed 31 pairs of captive male and female kestrels a diet with one of three concentrations of a commercial flame retardant mixture (D-71). D-71 contains individual flame retardants commonly found in the environment.
The birds were fed either none (control), 0.3 ppm (low dose) and 1.6 ppm (high dose) of D-71 daily for 3 weeks before breeding began and during courting, mating and egg laying. The birds ate the diet until the eggs hatched, about 75 days in total.
The researchers measured the time it took the kestrels to lay their eggs and counted the total numbers of eggs laid. Shell thickness, weight and flame retardant levels (14 PBDE types and total HBCD) were measured in the first eggs. The rest were allowed to hatch to gauge effects on the fertility of the eggs and the survival of the chicks.
What did they find?
As expected, female kestrels deposited the flame retardants into their eggs.
Eggs from kestrels fed the control diet had 3 ppb of measured flame retardants (total of 14 PBDE types) while eggs from birds fed the low and high doses had an average of 288 and 1130 ppb, respectively. These levels were within the range of what has been measured in eggs from wild kestrels and peregrine falcon from the northeastern US and Sweden.
Reproduction in the kestrels was affected by the chemicals in their diet. Egg laying in the birds exposed to the highest dose of flame retardant was delayed by 10 days. Egg laying delays increased with exposure to higher levels of four types of PBDEs. The delays and the contaminant exposure went hand-on-hand with fewer fertile eggs, hatchlings and fledglings from the exposed pairs.
Eggs with higher levels of flame retardants also had thinner and lighter shells, were smaller and lost more weight during incubation than the control eggs. More specifically, adults given the high flame retardant diet laid eggs that were 8 percent thinner than those laid by unexposed pairs.
What does it mean?
The results show that reproductive success of the birds was lower when their exposure to flame retardants was higher. Several individual flame retardants were linked to egg laying and eggshell changes and may indicate which of the varieties pose the biggest threats to wildlife, and possibly people.
The increasing levels of flame retardants in wild bird eggs coupled with the new evidence that these chemicals affect reproduction in kestrels may, in part, explain the declining numbers of this species in North America.
According to the authors, this may be the first study "to demonstrate cause-and-effect mechanisms of PBDE exposure on avian reproduction at PBDE concentrations that are currently found in the eggs of terrestrial and aquatic bird species."
In this study, the chemical mix had broad ranging effects on both the adults and the eggs. It influenced egg laying, egg integrity and egg viability. Any one of these alone could affect reproductive success in wild animals.
The amounts of the chemicals found in the study's kestrel eggs were similar to what is found in wild birds, such as kestrels, herring gulls and peregrine falcons. The most common type in peregrine eggs is called BDE-153, which was associated in this study with a number of problems, such as delayed egg laying, reduced eggshell quality and poorer fledging success. Based on this, wild populations, then, could have common reproductive troubles as the study animals, although no field studies have been done to show this is the case.
This story parallels what happened when the pesticide DDT was heavily used in North America. DDT concentrated up food chains and into fatty tissues of organisms. Birds were exposed to high levels of DDT in their diets. The pesticide caused a decline in raptors like the eagle and the peregrine falcon because the birds were laying eggs with shells that were too thin.
Previous studies on DDT in wild raptors found that their populations could not be sustained when eggshell thinning exceeded 18 percent. This study found an 8 percent reduction in eggshell thickness from exposure to flame retardants.
The new evidence that these chemicals affect reproduction in kestrels may, in part, explain the declining numbers of this species in North America and adds to the growing concern over the presence of these chemicals in the environment.
ResourcesAmerican Kestrel. Canadian Biodiversity Web Site. Fernie, KJ, JL Shutt, RJ Letcher, JI Ritchie, K Sullivan and DM Bird. 2008. Changes in reproductive courtship behaviors of adult American kestrels (Falco sparverius) exposed to environmentally relevant levels of the polybrominated diphenyl ether mixture, DE-71. Toxicological Sciences 102(1):171-178. State of North America’s Birds of Prey. 2008. Ed. KL Bildstein, JP. Smith, ER Inzuna and RR Veit. American Ornithologists’ Union/Nuttall Ornithological Club, Series in Ornithology Number 3, 466 pp. ToxFAQs™ for DDT, DDE, and DDD. 2002. Agency for Toxic Substances and Disease Registry. US Environmental Protection Agency. Polybrominated diphenylethers (PBDEs). |
PBDEs
