commentary first appeared in the February
2002 edition of Our Planet, a publication of the United Nations
Environment Program, UNEP.
revolution in scientific understanding of the impacts of contamination
on health is underway. As it unfolds, it is likely dramatically
to alter our understanding of the consequences of pollutants for
human well-being, and to require fundamental changes in how chemicals
revolution arises from scientific discoveries which establish that
many chemicals - both from the natural world and synthesized in
laboratories - interfere with the natural chemical messaging systems
that direct the biological development of plants and animals, including
all biological development is under the control of various "chemical
messaging systems" that convey instructions from the genes
to their targets, thereby directing development. Hormones, neurotransmitters,
and growth factors, among others, are key elements of these message
systems. Their successful transmission of genetic instructions is
vital to normal, healthy development, as they control almost if
not every aspect of the process - from what sex a baby will become
to how many fingers it will have, to whether its brain is capable
of intelligent reasoning or whether its immune system will be able
to resist disease.
has now established that a wide array of chemicals can disrupt these
genetically-based messages without damaging the genes themselves.
Much attention has focused on disruption of hormonal signalling,
which has become known as endocrine disruption.
roots of research in this arena go back to the 1930s, but it has
burgeoned in the last 10 years because of very significant investments
of funds by European, Japanese and North American governments. New
results are published virtually every week. These new findings are
rich in detail, fascinating in what they reveal about biological
mechanisms, and sometimes breathtaking in their implications.
example, a study published in July 2001 by the U.S. Centers for
Disease Control reported a strong relationship between DDE contamination
in mothers and the likelihood of pre-term birth of their infants.
Using biological samples stored since the 1960s, the authors report
that their findings indicate that the U.S. experienced an epidemic
of pre-term birth during the hey-day of DDT use, and that this persistent
pollutant may have caused up to 15% of infant mortality in America
during that period.
important broad trends in the pattern of research findings can be
identified from the thousands of studies on endocrine disruption
published since the early '90s
the research confirms that contamination by hormonally-active compounds
is globally ubiquitous. No one is unexposed, even in the womb. The
same is true for most, if not all living organisms, especially those
higher in ecological food chains and thus consuming foods in which
the contaminants have become concentrated by bioaccumulation. Contamination
is partly so widespread because of global redistribution of pollutants
transported through air and water. Inadvertent but pervasive inclusion
of hormonally-active compounds in consumer products - such as many
cosmetics and plastics - also contributes.
effects of exposure can be observed at levels dramatically lower
than those thought relevant to health a decade ago. Scientists are
measuring endocrine-disruption impacts of contaminants like arsenic,
dioxin, and bisphenol A (a basic component of polycarbonate plastic)
in the low parts-per-billion. This was unmeasureable two decades
ago-scientific instruments simply were not that accurate- and highly
controversial until recent review and empirical confirmation.
the findings indicate that virtually all chemical messaging systems
are vulnerable, in principle, to message disruption. Work in this
area focused for decades on interference with estrogen. As the focus
has expanded to other hormones, one or more disrupting contaminants
have been discovered for every system studied carefully, including
the thyroid system (crucial for brain development), the retinoid
system (involved in very basic control of development), and the
glucocorticoids (important for metabolism and tumor suppression,
among other things). In the summer of 2001, new results reinforced
this trend dramatically, with a report that the ecological symbiosis
between leguminaceous plants like beans and the bacteria responsible
for nitrogen fixation is vulnerable to disruption by contaminants.
This symbiosis, mediated by chemical communication between the plant
and the bacteria, is a vital component of the global nitrogen cycle.
the health effects of concern have expanded dramatically beyond
those of the traditional focus for toxicology. Laboratory studies
unequivocally demonstrate effects on disease resistance, cognitive
function and fertility resulting from low level exposures.
findings should be of deep concern to people, organizations and
agencies focused on human economic development and equity. It is
clear, for example, that background levels of contamination can
make children less resistant to infectious agents. Further research
in this area may force a radical reassessment of the toll of contamination,
as this implies that many deaths and diseases would have been avoided
had contaminants not reduced resistance.
the research suggests that widespread exposure to neurologically-active
contaminants-as might occur, for example, in agricultural areas
in the developing world with intensive pesticide use-may lead to
community-wide erosion of cognitive abilities. In a world in which
information is a key economic currency, this contamination burden
could consign those affected to the economic margins forever.
emerging trends are forcing toxicologists toward several conceptual
shifts that will lead to fundamental changes in the ways that chemicals
are managed. The most important of these involves a change in the
way that toxicologists think about what is relevant to human health.
toxicology focuses on damage, such as cell death, mutations, cancer
or genotoxicity. Message disruption can cause these, but the effects
may also be of a very different, but equally important, nature.
Most challenging to traditional toxicology, message disruption does
not work by overwhelming the body's (or the cell's) defenses. It
works by hijacking the developmental process, adding or subtracting
to the body's own control mechanisms at remarkably low levels of
exposure. By subtly (or blatantly) altering the path of development,
message disruption leads the victim to a different future. The difference
may be small, as in the loss of a few IQ points, or it may be large,
as in a completely dysfunctional immune system.
Toxicology has focused traditionally on the impact of high levels
of exposure on small numbers of people. This new approach requires
considering widespread, low level exposures experienced by many
people-exposure levels that many had come to write-off as "background"
and, by implication, irrelevant.
together, these new scientific findings add to growing pressure
to change the basic rules of chemical regulation. Once again, we
have been blind-sided. Our ability to synthesize chemicals got far
ahead of our scientific understanding of their impacts. Traditional
risk assessment allowed them to be commercialized and distributed,
causing pervasive contamination. Risk assessment's partner in developing
protective standards, epidemiology, by definition works only after
an epidemic. Even then, its tools are remarkably insensitive in
studies of the effects of endocrine disruption, and strongly biased
toward negative results even when there are real effects.
answer, still imperfect, lies in implementing precautionary measures
that impose far more stringent requirements on old and new products
alike. As the Swedish Chemicals Policy Committee has recognized,
certain attributes should be knock-out criteria. Persistent bioaccumulative
compounds, for example should be eliminated from use even without
demonstrating toxicological risk. Endocrine-disrupting materials
should be removed from consumer products and their environmental
release should be phased out. More generally, the demonstration
of potentially harmful biological impacts in laboratory studies
should reverse the burden of proof in developing regulations - from
one in which harm must be demonstrated before a product is withdrawn,
to an approach where safety is ensured beyond reasonable doubt before
widespread deployment is allowed. These steps will help ensure that
the benefits we all enjoy from modern chemistry do not come back
to haunt us.