| Researchers at the Woods Hole Oceanographic Institution have found that
two chemicals accumulating in the tissues of marine animals and
suspected to be manmade pollutants actually came from natural sources. Brominated
organic chemicals are used as flame retardants for electronics,
furniture, and textiles. In recent years, they have been found
throughout the environment, accumulating in fish and marine animals and
sometimes detected in human breast milk. Some researchers suspect that
these compounds may affect animal and human health, and several
compounds have been banned. By isolating 1 milligram of
(MeO-BDEs) from 10 kilograms (22 pounds) of whale blubber, Emma Teuten,
a postdoctoral fellow in the WHOI Department of Marine Chemistry and
Geochemistry (MCG), found that the MeO-BDEs in the blubber contained
carbon-14 (14C). This natural
radioactive isotope of carbon is incorporated into all living things,
but it would have long ago decayed out of the petrochemicals used by
industrial chemists. That means Teuten’s suspect chemicals were derived
from a natural, though still unidentified, source. “The
work shows that natural products with similar structures to industrial
compounds can also bioaccumulate,” said Teuten. “Consequently, animals
have been exposed to them for many years. The presence of natural
analogs may help toxicologists explain how and why enzymes have the
ability to metabolize industrial halogenated compounds, such as
polychlorinated biphenyls (PCBs).” The finding was published Feb. 11 in the journal Science.
The work was performed in the laboratory of Associate Scientist Chris
Reddy (MCG), who was a key contributor to the work along with Geology
and Geophysics Research Associate Li Xu. “The
accumulation of human-made chemicals such as PCBs and polybrominated
diphenyl ethers in whales and other top consumers has been known for
decades,” said Mark Hahn, a marine toxicologist in the WHOI Biology
Department. “The difficulty is that some anthropogenic compounds are
also made naturally by some organisms, and some anthropogenic compounds
can be biologically or chemically transformed in the environment to
derivatives that resemble natural products.” “Teuten
and Reddy have provided the first definitive evidence that specific BDE
derivatives are in fact naturally produced,” Hahn added. “They did this
by combining an elegant analytical method—analysis of radiocarbon
content—with the brute force purification of the compounds from large
amounts of whale blubber.” Wanted: dead or alive
It took 18 months, three blenders, and dozens of dulled knives to conduct this experiment. Proving the origin of the MeO-BDEs seems like a simple problem: Find 14C in a sample, and you know whether the chemicals came from the factory or Mother Nature. “In
the laboratory, we call this approach the ‘dead or alive theory,’” said
Reddy. “Petrochemicals are radiocarbon-dead and natural products are
radiocarbon-alive.” But to detect 14C, chemists require a sizable sample. To detect 14C within the scarce molecules of brominated compounds required a very large sample. The
first challenge was acquiring a large piece of whale blubber. Reddy
requested and received a permit from the National Marine Fisheries
Service, which limits the “take” of marine mammals for research. Teuten
then contacted researchers at various marine mammal stranding and
rescue operations to alert them that they needed a sample the next time
one was available. A new tool and a telltale clue
By
the fall of 2003, the unfortunate beaching and death of a True’s beaked
whale in Virginia turned into good fortune for the WHOI research team.
Teuten received a package from the Virginia Marine Science Museum
containing 10 kilograms of foul-smelling but scientifically precious
whale flesh. That’s when the brute force
portion of the experiment began. Teuten had to chop, cube, and blend
mounds of whale blubber, a task made even less appealing by the fact
that she is a vegetarian. “It was messy, oily
work, and I never thought working with blubber would be so nasty,”
Teuten said. She dulled many a knife and had to purchase three blenders
before moving on to more traditional tools of chemistry, such as
filtering, acid washes, dialysis techniques, and chromatography. “What
Emma did was heroic, like finding a needle in a haystack,” said Reddy.
“She removed 10,000,000 milligrams of other whale material—mainly
fats—to get our compounds of interest in very high purity.” “There
was no road map for this,” Teuten said. Most chemical extractions
involve work with 50 grams; Teuten started with 200 times that in order
to isolate just 1 milligram of the brominated compounds. “This kind of
thing just hasn’t been done much in radiocarbon analysis.” Teuten
and Reddy finally submitted their sample of brominated compounds to the
National Ocean Sciences Accelerator Mass Spectrometer facility (based
at WHOI) for analysis, where chromatography expert Li Xu became
involved in the effort. They found 14C. “This
radiocarbon technique is very exciting,” said Gordon Gribble, an
organic chemistry professor at Dartmouth College and a leader in the
study of halogenated compounds found naturally in the environment.
“There’s been no other way to distinguish the origin of the same
compounds that are produced both by nature and man.” Chemicals are everywhere, and they’re not all bad
In
recent years, polybrominated diphenyl ethers (PBDEs) have been found in
freshwater fish near industrialized areas of the Great Lakes and
Northern Europe, though there are no known natural sources for these
chemicals in fresh water. But natural PBDEs also have been found in sea
sponges off Australia and in the dolphins living nearby. Based
on preliminary findings of possible health risks linked to PBDEs, the
European Union and the state of California have banned certain
formulations of flame retardants. Industrial producers counter that the
compounds are non-reactive, do not degrade in the environment, and
therefore are safe. But no one really knows for sure. For
decades, environmental groups have said that nature would never make
brominated compounds or other halogenated chemicals, Gribble noted. But
in recent years, these compounds have been found in forest fires,
volcanic ash, soil, peat bogs, and myriad marine organisms. “It
appears that nature has been producing these chemicals since the first
forest fire and since life on Earth began,” he said. In the ocean,
where many of these compounds are ubiquitous, organisms have developed
ways of synthesizing these compounds from oceanic salt for use as
natural pesticides and repellents. “As we
design environmental laws for the regulation of chemicals, we have to
be aware of what nature is making,” said Gribble. “We have to evaluate
each chemical on a case-by-case basis.” “Many
people have the simplistic idea that synthetic equals bad and natural
equals good,” said Hahn. “Teuten and Reddy’s work shows that naturally
produced compounds can bioaccumulate to levels similar to those of some
notorious contaminants. Whether these natural compounds are affecting
the health of the whales or other animals that accumulate them is an
open question that needs to be addressed.” “These
sort of compounds are out there, globally distributed, accumulating in
wildlife and human tissues,” Hahn added. “We are still making some of
them, and our decisions about whether to continue or whether to
substitute other compounds should be based on knowledge about the
amounts and effects of both naturally produced and anthropogenic
compounds.”
-- Mike Carlowicz
The study was supported by the
National Science Foundation, The Camille and Henry Dreyfus Foundation,
Inc., the J. Seward Johnson Fund, and the WHOI Ocean Life Institute.
Posted: February 10, 2005 [top] |
