-Caveat Lector-
Something odd going on here...
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"Lewis's co-authors are A. Wayne Garrison of the U.S. Environmental
Protection Agency Ecosystems Research Division in Athens, along with Eric
Wommack of the National Research Council Fellowship Program and the
University of Georgia; Alton Whittemore of the Senior Environment Employment
Program at EPA; and Paul Steudler and Jerry Melillo of the Ecosystems Center
at the Marine Biological Laboratory at Woods Hole, MA. Until recently,
Melillo served as associate director for the environment in the White House
Office of Science and Technology Policy.
"Lewis is employed by EPA as well but is temporarily assigned to the
University of Georgia as part of a legal settlement with EPA over concerns
he raised about EPA science in a 1996 Nature commentary. He is assigned to
the department of marine sciences at UGA"
EMBARGOED FOR RELEASE: 27 OCTOBER 1999 AT 14:00 ET US
Contact: David Lewis
[EMAIL PROTECTED]
706-542-7370
University of Georgia
New study claims data on pollutants worldwide are unreliable, and
that some may be less--or more--harmful than thought
ATHENS, Ga.-- Much of the information on pollution world-wide is
flawed at best and could be entirely wrong, according to a just-published
study, led by a visiting scientist at the University of Georgia. The
consequences of this oversight are beginning to threaten public health and
the environment, according the paper's senior author, research
microbiologist David Lewis.
The research specifically deals with chirality, a characteristic
exhibited by chemicals with asymmetric molecules. This asymmetry causes
molecules of the same chemical pollutant to exist as mirror images of one
another. Since many of the building blocks of living organisms, including
certain sugars, amino acids and proteins, are also chiral, the effects of
chiral pollutants depends on how well the toxic portions of the pollutant
fit together with molecules of living things.
"Our study emphasizes the fact that much of the historical
environmental data collected on pollutants is unreliable because so many of
the chemicals are chiral, and the data do not distinguish which
mirror-images of certain chemicals were present and which were harmful,"
said Lewis. "The good news is that many environmental pollutants including
some DDT derivatives, PCBs and plasticizers aren't as bad as previously
thought. On the other hand, steps taken to protect the environment, such as
using treated sewage sludge as a commercial fertilizer, will likely increase
the persistence of the more toxic forms of some pesticides."
The study was published today in the British journal Nature.
Lewis's co-authors are A. Wayne Garrison of the U.S. Environmental
Protection Agency Ecosystems Research Division in Athens, along with Eric
Wommack of the National Research Council Fellowship Program and the
University of Georgia; Alton Whittemore of the Senior Environment Employment
Program at EPA; and Paul Steudler and Jerry Melillo of the Ecosystems Center
at the Marine Biological Laboratory at Woods Hole, MA. Until recently,
Melillo served as associate director for the environment in the White House
Office of Science and Technology Policy.
Lewis is employed by EPA as well but is temporarily assigned to the
University of Georgia as part of a legal settlement with EPA over concerns
he raised about EPA science in a 1996 Nature commentary. He is assigned to
the department of marine sciences at UGA.
The entire issue revolves around molecular shapes and how the
environment affects the persistence of pollutants. When molecular shapes do
not permit a close fit, they cannot interact very well, and thus chemicals
with these molecules pose a less-serious threat to living things.
"It's like trying to shake someone's right hand with your left
hand," said Lewis.
The knowledge of which molecules are ill-fitting mirror-images or
enantiomers, as scientists call them, can be extremely helpful. Lewis points
out that 50 of the top 100 best-selling drugs (including barbiturates,
Ritalin and ibuprofen) are marketed after separating out the enantiomers
with harmful side-effects, such as the birth defects found three decades ago
with the drug thalidomide.
Many pollutants are also chiral, including some pesticides,
plasticizers and polychlorinated biphenyls--chemicals once used as
electrical insulators and which are now pervasive in the environment. The
problem, according the study, is twofold: first, very few chemicals now
considered major pollutants have been evaluated for their chirality at all,
and second, environmental changes appear to alter which mirror-images
persist in the environment by affecting soil microbes responsible for
breaking down the chemicals.
"In general we concluded that global environmental changes, such as
tropical deforestation, nutrient pollution and global warming will
significantly alter the risks posed by many pollutants--making the effects
of some worse and some less harmful," said Lewis. "Without knowing how
chiral pollutants will be affected, environmental measures aimed at reducing
the effects of pollution are being formulated virtually in the dark."
Since Lewis estimates that about one-fourth of all pesticides are
chiral, the scope of the problem could be large, he said. The high cost of
separating mirror images is currently prohibitive for most pesticides and
industrial chemicals, though there are two notable exceptions--the
herbicides dichlorprop and mecoprop, in which a limited portion of the total
worldwide production includes single enantiomers.
To assess the persistence of different pollutant enantioners and the
possible influence of large-scale environmental change on that persistence,
the research team studied soils collected in three areas: an upland plateau
in Norway; an 80-year-old mixed deciduous forest in the U.S.; and in an area
near the city of Porto Velho in Brazil.
The scientists amended the soil samples with herbicides dichlorprop
and methyl dichlorprop, and with ruelene, which is an insecticide banned in
the U.S. but still sold in other countries.
In tests designed to study the effects of long-term increases in
soil temperature, the addition of fertilizers and of tropical deforestation,
the researchers found that different soils and their associated
microorganisms reacted in different ways. For example, the addition of
inorganic fertilizers to forest and pasture plots in Brazil had no
measurable effect on enantioselectivity for methyl dichlorprop or to plots
in North American fertilized since 1988.
On the other hand, laboratory enrichments with organic nutrients,
such as those present in sewage, caused a strong shift in which mirror-image
molecules were preferred by microorganisms in samples from North America and
Brazil but did not have the same effect in samples from Norway.
The study also used buried electrical lines used for warming to
assess the potential effect on chiral chemicals of global warming and
studied the genetic diversity and biogeography of bacteria capable of
changing chiral chemicals.
"It appears that different kinds of environmental changes turn on
different genetically related groups of microorganisms," said Dr. Eric
Wommack, who carried out the genetic experiments in the study. This may
explain why environmental changes affect which mirror-image molecules
persist in the environment."
The results, the authors said, indicates a complexity that means
current methods of determining which chemicals pose threats to the
environment may be worthless in many cases.
"The differing effects of inorganic and organic nutrients on
enantioselectivity, for example, raise new questions with respect to land
application of processed sewage sludge," said Lewis. "This sludge transforms
pollutants enantioselectively. Thus, the sludge may increase microbial
transformation rates of some of the enantiomers of pesticides and diminish
their effectiveness in the field. On the other hand, some enantiomers may
persist longer under these conditions, posing a risk to public health and
the environment."
Lewis said the uncertainly about the mirror-image effects of
pollutants could also raise questions about so-called
endocrine-disrupters--chemicals in the environment that allegedly interfere
with the endocrine systems of animals.
Meanwhile, Lewis said, changes in understanding the chirality of
pollutants must occur if global environmental policies are to have proper
scientific weight.
"I don't think it's so expensive to create single-enantiomer
pesticides that it couldn't be done," he said. "I believe in some
Scandanavian countries that they are marketing them already. More and more,
it will become technically feasible, but first we must understand the
toxicity associated with them, and right now we don't even know that."
###
(Editors: A high-resolution illustration for news media coverage of
this article can be downloaded from
<http://photo.alumni.uga.edu/photohome.htm>. When prompted for search
information, search for "David Lewis," and when prompted for user name enter
"guest." For password, use "photo33." The photo is of David Lewis, lead
author of the Nature article, with potted plants showing how molecules of an
herbicide are toxic, while their mirror-image [enantiomer] forms are not.
Copies of the paper are also available from Dr. Lewis by calling the number
above.)
=======================
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