Men are like plants; the goodness and
flavour of the fruit proceeds
from the peculiar soil
and exposition in which they grow.
J. Hector St. John de Crevecoeur
Letters from an American Farmer, 1782
Environment and Infertility
Diane Aronson is often consulted by couples worried about whether substances they're breathing or eating may prevent them from conceiving a baby. Aronson is executive director of RESOLVE, a national organization for those who experience infertility, a condition that affects an estimated 5.3 million people in the United States. But in her review of the scientific literature on effects of environmental factors on the male and female reproductive systems, Aronson has yet to find a definitive connection between environmental exposures and infertility.
On October 20, Aronson assembled a group of researchers from the EPA, the FDA, the U.S. Public Health Service, and academia to examine the evidence for such a connection. The meeting, "The Environmental Impact on Fertility," held in New York during National Infertility Week, served to point out that, while reduced fertility has not been established as an effect of many perceived risk factors, researchers are looking closely at environmental impact. This emphasis on environmental factors began in Europe, where reduced sperm counts have recently been documented, and spread to the United States, where it has become a topic of discussion at scientific conferences and several federal studies are being developed. "There is a real commitment toward pulling together all the factors," says Aronson. "Just because the studies are inconclusive now doesn't mean that we should relax and say nothing is proven. We think there is enough sufficient evidence to inform people about these possible risks and allow them to make their own decisions."
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Empty cradles? Researchers are looking at whether environmental hazards may play a role in infertility.
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RESOLVE has published a free primer about potential environmental hazards to fertility. But the slate of unqualified risks seems enormous to any couple trying to modify their environment. About 60,000 chemical substances are used by commerce and industry in Western countries, and 1,000 are introduced annually, but only 5% have been investigated for reproductive effects. Although the EPA says at least 50 widespread chemicals affect reproduction in animals, only four workplace health hazards--lead, ionizing radiation, ethylene oxide, and dibromochloropropane--are regulated in the United States partly because of their effects on human reproduction. The opinion offered by many of the conference's speakers is that the inability to account for the origin of millions of cases of infertility leaves open the possibility that exposure to environmental hazards, from pesticides to household glue to computer display video terminals, may be to blame.
There is strong evidence that environmental estrogens such as DDT are responsible for infertility in exposed animal populations and that high levels of dioxin are toxic to humans. But whether these substances are harming the general population at current levels of pollution and exposure is still unclear, said conference speaker Michael Zinaman, assistant professor of endocrinology and reproduction at Loyola University Medical Center. Among the reasons previous research is inadequate, he says, is that it's not always possible to extrapolate animal studies to human fertility outcomes, exposure to toxicants is impossible to pinpoint, medical histories and working environments change, and sampling studies can't often establish linkages. For example, because none of the recent sperm count studies were designed to measure infertility, Zinaman is conducting an EPA-funded study to determine better ways to measure relative fertility in men. He will soon publish results of a study that sets a normal rate of male fertility to be used as a control population to determine when environmental agents may be producing poorer fertility. Such "normal" rates, however, may include confounding factors such as the impact of environmental estrogens, but, says Zinaman, they at least set a comparative standard. Once such as standard is created, the EPA will launch epidemiological studies to determine if certain chemicals or agents affect fertility. "EPA has a lot of things ready to go once a standard is created," says Zinaman.
But more can be done. The FDA is making progress on testing products with an estrogenic and/or androgenic bioassay. For example, recently, a simple assay found that some plastic baby bottles leach low levels of estrogenic compounds into infant formula. These bottles are no longer produced. "Some government scientists, as well as other researchers, are beginning to understand the importance of such studies," says Zinaman. "There is absolutely some light ahead in this field." However, there is still no mandate that new drugs and materials be tested for estrogenic/ androgenic activities.
At the conference, Mt. Sinai School of Medicine epidemiologist Maureen Hatch pointed to studies that raise infertility issues, including a 1994 Dutch study that implicated farm pesticide exposure and a 1992 Italian study that correlated exposure to high heat with a higher incidence of childlessness and self-reported difficulty in conceiving among ceramic oven operators. Hatch's own unreported research found that job stress and strenuous physical activity among 100 nurses has generally led to longer menstrual cycles of between 33 and 52 days, although a connection to fertility hasn't yet been made. Hatch trusts that such research will be continued and expanded. "The issue is definitely catching on," she says. "With so many people waiting so long to have children, and this narrowing the window of opportunity, they are looking for valid reasons for infertility other than age."
Australian Forum
Australia's health professionals, academic scientists, and health and environmental interest groups were recently urged to become more involved in environmental issues. In his address to the Australian Medical Association first national forum, Our Health, Our Environment--A National Stocktake, recently appointed AMA Federal President David Weedon called for the medical profession to serve as lobbyists to government on environmental issues, particularly global issues such as ozone depletion, global warming, sustainable biodiversity, and the use of toxic industrial, agricultural, and domestic chemicals. Pesticides, with their potential for suppression of the immune system, were targeted for particular attention.
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New developments down under. A recent national forum in Australia examined the impact of environmental issues such as global warming, ozone depletion, and hazardous chemicals on human health.
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The summit was a new direction for the AMA, which historically has maintained a low profile in the environmental debate. The summit was seen as repositioning the medical agenda away from a curative to a preventive, stance. This would help change Australians way of thinking about their environment, Weedon said.
The "greening" of the AMA's agenda with its strong focus on global issues would help to minimize adverse environmental impacts in Australia, said summit speakers. For example, while there have not been any major outbreaks of Australian encephalitis in the 1990s, the recent diagnosis, for the first time, of Japanese encephalitis in the indigenous people of Northern Queensland and the 1992-1993 epidemic of Ross River fever in South Australia emphasized the potential for new outbreaks of vectorborne diseases such as malaria and dengue.
The meeting focused on impacts of the environment on public health in Australia including lead pollution, ozone depletion, global warming, noise, air and water quality degradation, the inappropriate use of chemicals, and medical and hazardous waste management. Weedon particularly emphasized the potential impacts of ozone depletion in Australia, such as increased incidences of cataracts and skin cancers (140,000 cases per year) adding to the already high national incidence of these conditions.
The summit was opened by the Federal Environment Minister, Senator John Faulkner, and attended by about 170 participants including parliamentarians, leaders from all levels of government, industry, unions, environmental groups, professional medical bodies, and experts in environmental health. Faulkner warned that stressors on the environment were already compromising public health.
A number of national strategies are being developed in partnership with the states and local governments to address environmental health issues. A first national state of the environment report is expected to be available in early 1996 and will provide the necessary benchmarks to measure future progress. There have already been some successes. For example, through round table talks with stakeholders and extensive education campaigns, the lead task force has raised public awareness of the risks to sensitive populations, particularly children. The task force's "lead in petrol" initiative has resulted in more than half a million drivers switching to unleaded fuel within two years. A new phase of public education launched in November and developed in cooperation with state health agencies has targeted possible exposure from old and deteriorating lead-containing paint.
Degradation of the urban air environment is a key government priority addressed by the National Air Quality Management Strategy, which is modeled on the National Lead Abatement Task Force that was created by former Environment Minister Ros Kelly. Respirable particulates and photochemical smog will be the immediate targets of this program.
Patricia Caswell, former executive director of the Australian Conservation Foundation (ACF), focused on the need for community empowerment. Many communities, particularly those associated with the cotton industry and smelting, lack information and legal rights, according to Caswell. She described the Newcastle suburb of Boolaroo, a town adjacent to a lead smelter where about 85% of children had blood lead levels higher than 10 micrograms per deciliter (g/dl), with peak values approaching 40 g/dl--4 times the acceptable limit. In this suburb, soil samples contained up to 21,000 parts per million (ppm) of lead, and over 30% of samples taken exceeded 1000 ppm lead. Caswell's comments were expanded by Theresa Gordon of the "No Lead Group" in Boolaroo, who said that lead exposures in her area of Broken Hill and in other smelting towns created second-class citizens.
An AMA/ACF/Greenpeace coalition will raise the profile of environmental health. Within the political arena, the coalition will target community "right to know" issues, including a National Pollutant Inventory. Caswell said that prior to establishment of the coalition, "There was a lack of government commitment to address accelerating environmental degradation and a vacuum in public policy development to address long-term environmental degradation, particularly water resources and population issues."
The coalition, which toured "chemical hot spots," including cotton growing areas where pesticide use is heavy in New South Wales and contaminated land sites in Melbourne, Victoria, before the summit, endorsed the need for a national health effects reporting system for chemicals. The register would include agricultural, industrial, and household chemicals and, using coalition established criteria, would document instances where doctors believed patients had suffered adverse effects from exposures. Weedon said, "We are concerned that there are medical effects from exposures to chemicals following improper use and occupational or accidental exposures." The Australian Council of Trade Unions (ACTU) recently completed a study that indicates that chemical exposures are a major cause of workplace injuries (an estimated 2,200 deaths per year).
Senator John Coulter, a research scientist and environment spokesperson for the Australian Democratic Party, focused on degradation of national water resources, particularly overuse for irrigation, which has resulted in extensive salination of some of Australia's best agricultural land. "Australia has the unenviable reputation of the world's largest outbreak of blue-green algae in the Murray River system in 1993," Coulter said
John Donovan, principal medical advisor to the Australian Institute of Health and Welfare in Canberra, provided a summary of the results from the National Children's Blood Lead Survey. According to Donovan, more than 93% of the children sampled between April and June 1995 had blood lead levels lower than the National Health and Medical Research Council target for all children (below 10 g/dl by 1998). Donovan also indicated that for the remaining 7% of children, ambient air pollution and lead paint in housing could not adequately account for the observed levels. There was a strong correlation between blood lead levels and levels of household dust in homes of these children, with dustier homes associated with elevated blood lead values. Other significant correlations existed with childhood pica (hand-to-mouth behavior) and parental smoking in the home.
The Australian Capital Territory Government Environment Minister, Gary Humphries, identified arsenic as a new urban problem. Canberra, the national capital that was built on sheep country in 1901, has recently discovered old animal dip sites in residential areas. "The problem is much more than the physiological health of the residents," said Humphries, "the issue is clearly an emotive one and goes right to the heart of the community's perceptions of risk." Humphries stressed the need to maintain community involvement through information campaigns and close consultation and participation in the management of the remediation.
Erin Jackson, head of Greenpeace's Climate Impacts Unit, spoke of the increasing international concern that the long-term impacts of climate change represent one of the greatest challenges for humanity. Increased frequency, severity, and wider distribution of crop losses, spread of infectious diseases into new environments, heat waves, and flooding from rising sea levels will bring a generation of "environmental refugees," Jackson said.
The next major environmental health gathering in Australia will take place at the Intergovernmental Forum on Chemical Safety in Canberra on 3-8 March 1995.
Carbon Monoxide-Heart Failure Link
Every year, hospitals in the United States admit roughly a million patients with congestive heart failure, a condition in which the heart pumps less blood than normal. Researchers now think tens of thousands of these admissions may be linked to carbon monoxide (CO) in the air.
A study in the October issue of the American Journal of Public Health reports that increases in outdoor CO may cause shortness of breath in people with congestive heart failure, sending them to the hospital. "Across the country, with each day that showed an increase in carbon monoxide, we saw an increase in hospital admissions,'' says lead author Robert D. Morris, an epidemiologist at the Medical College of Wisconsin in Milwaukee. "The consistency was striking.''
Carbon monoxide, a common air pollutant, results from burning hydrocarbon-based fuels. According to the EPA, motor vehicles generate over 90% of urban CO pollution. Car tailpipes emit the gas directly into the air. Other CO sources include factory emissions, gas stoves, and tobacco smoke.
Carbon monoxide presumably aggravates heart disease by binding to hemoglobin, thereby hindering oxygen transport through the blood. "In particular, carbon monoxide appears to affect congestive heart failure patients who also have lung disease,'' says Morris. In the study, 15% of hospitalized patients had both lung and heart disease. Nationwide, an estimated 3 million people, most over the age of 65, suffer from congestive heart failure.
The study is one of the first to explore outdoor the effect of CO on heart disease. Morris and colleagues compared Medicare data on heart failure hospitalizations with air pollution readings collected by the EPA in seven U.S. cities: Chicago, Detroit, Houston, Los Angeles, Milwaukee, New York, and Philadelphia. Looking at data for 1986-1989, the researchers found that 3,250 (about 5.7%) of the cities' annual congestive heart failure hospitalizations correlated with an increase in air CO.
Thomas E. Dahms, a cardiovascular physiologist at St. Louis University who has studied CO, cautions that the study's retrospective approach is limited. "For one thing, congestive heart failure is a loosely defined diagnosis,'' Dahms says. "To validate its consistency between hospitals, you'd have to do some spot checking of patient records.''
Dahms also worries whether air pollution readings accurately reflect an individual's exposure to CO. "There have been a number of studies trying to relate personal CO exposure levels to air readings picked up at monitoring stations 50 to 100 feet off the ground,'' he says. "So far, there has been little validation in relating the two.''
But Joel Schwartz, an epidemiologist at the Harvard School of Public Health who wrote an editorial accompanying the study, says the work is informative. "There is certainly a chance for misdiagnosis when looking across cities,'' Schwartz says. "But within any one city's analysis, it shouldn't be a problem.'' Such misdiagnosis is absorbed during statistical analysis, he says. Schwartz adds that, despite inconsistencies, there is a clear link between personal exposure and air pollution readings: "The real question is, If I took everyone in this city, averaged their personal exposure to CO and correlated that, day to day, with the average outdoor air pollution readings, what would I find? Would the averages go up and down together? We won't know until we do more studies.''
Morris agrees his findings are preliminary. "Clearly, this study raises as many questions as it answers,'' he says. One question involves the amount of CO that exacerbates heart problems. The health effects cited in this study occurred below federally permissible CO levels. "From the lowest levels of carbon monoxide, we are seeing an increase in hospital admissions with rising pollutant,'' Morris says. "If future studies do establish a minimum CO effect threshold, that may impact EPA air standards.''
The EPA attempts to control CO pollution by regulating motor vehicle emissions. The Clean Air Act of 1990 strengthened tests for auto emission standards and required oxygenated gasolines, with additives to improve fuel efficiency, for metropolitan areas with high CO levels.
Morris next plans to study exposure to another common auto pollutant: fine combustion particles. "It's possible that this pollutant, along with carbon monoxide, contributes to the heart failure admissions we reported,'' Morris says. "Now we've got to separate the two pollutants and find out how important each one is.''
Barking up the Right Tree?
People may now have one more reason to save trees: they might someday save your life. In a recent study at the University of Illinois at Chicago, a compound called betulinic acid, derived from the bark of white birch trees, has been shown to halt the growth of melanoma cancer cells. More importantly, the compound selectively targets these cells, providing hope that a chemotherapeutic drug developed from betulinic acid will have very few side effects.
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Made in the shade. A substance isolated from the bark of white birch trees shows promise for treating melanomas.
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The compound was originally extracted from the bark of an African tree, Ziziphus mauritiana lam (Rhamnaceae). It was later found in the bark of the common white birch. Unlike extracting taxol, another chemotherapeutic substance obtained from tree bark, the process to extract betulinic acid is relatively simple, involving a chloroform extraction and crystallization process.
Betulinic acid was shown to be a highly effective antitumor agent in a study published in the October 1995 issue of Nature Medicine. The study reported on a successful series of cell culture experiments with four human melanoma cell lines (derived from lymph node, lung fluid, liver, and skin). The growth of the cell cultures was specifically inhibited using half the maximal effective doses of 1-5 micrograms per milliliter. Researchers tested the compound in immune-suppressed mice that had been induced to develop human melanomas. In these experiments, tumor growth was either inhibited significantly or halted in the treated group. A drug called DTIC (dacarbazine), commonly used to treat human melanoma, was used as one of the positive controls. The betulinic acid-treated mice showed three times greater tumor inhibition than the DTIC-treated mice.
"These results are very encouraging," says John Pezzuto, director of the Program of Collaborative Research at the University of Illinois. "Of the thousands of agents screened, betulinic acid is one of the best compounds to come out of our lab in the last five years." A potentially beneficial property of betulinic acid is that it does not appear to affect other human cancer cell types, suggesting a unique specificity for melanoma that may shed light on the mechanisms of this disease. Current antineoplastic agents such as captothecin, taxol, and vinblastine are toxic to multiple cell types, resulting in damage to normal tissue.
Several pharmaceutical companies have shown interest in funding the development of betulinic acid. According to Pezzuto, in vivo tests are continuing and will be followed by rigorous toxicity testing. If the results are positive, an investigative new drug application may be filed with the FDA as early as 1996, allowing human clinical trials to begin.
In addition to treating malignant melanoma, a disease that strikes 1 in 90 Americans, the compound may someday be used to prevent and treat other skin cancers. Skin cancers, with about 800,000 new cases per year, are the most frequent type of cancer in the United States. The compound's efficacy will eventually also be tested against a variety of other tumor types such as neuroblastoma, a type of brain tumor. In addition, because of its emerging excellent safety profile, Pezzuto envisions betulinic acid's potential usefulness in consumer products such as sunscreens.
According to one expert, it may be too soon to tell the real potential for this bark extract. Antonio Buzaid, a melanoma specialist at the University of Texas MD Anderson Cancer Center, recently commented in Science News that "in most cases, such effective drugs don't pan out in people." This caution is echoed by Don Morton, medical director and chief of surgery at the John Wayne Cancer Institute, who conducts research on melanoma vaccines. Morton, however, expresses optimism about the October study results and describes betulinic acid as one of the most exciting and unique compounds currently under investigation for treatment of melanoma.
An Environmental Nobel
Twenty years ago, when Mario Molina described his research to friends, they would look baffled, perhaps even a little worried about his state of mind. Then a postdoctoral fellow at the University of California, Irvine, Molina would explain how an invisible gas sprayed out of aerosol cans could float up to the stratosphere, about 8-12 miles above the earth's surface, and create havoc with the ozone, which protects living things on earth from shorter-wave length ultraviolet radiation. "Only a few people were aware of the ozone problem in those days, because it was such a specialized topic," says Molina, now a professor of environmental science at the Massachusetts Institute of Technology. "But a decade later, when the public had a better understanding of what humans can do to the planet, I became amazed at how many people were knowledgeable about the depletion of the ozone layer."
In 1995, Molina shared the Nobel Prize in Chemistry with colleagues F. Sherwood Rowland, professor of chemistry at the University of California, Irvine, and Paul Crutzen of Max-Planck Institute for Chemistry, in Mainz, Germany, for their work in atmospheric chemistry, especially on the formation and destruction of ozone. The researchers have made crucial discoveries showing how chemical emissions from air conditioners, aerosol cans, and fire extinguishers can dramatically increase the destructive processes of the sensitive ozone layer, our planet's "Achilles heel," said the Royal Swedish Academy in its award citation on October 11. As ozone is depleted, more of the sun's dangerous ultraviolet rays can reach the earth causing additional skin cancers, cataracts, and damage to the immune system, but also harming ecosystems. By sounding the alarm about ozone damage, the researchers "have contributed to our salvation from a global environmental problem that could have catastrophic consequences," the academy said.
In 1970, Paul Crutzen was the first scientist to identify one of the important processes that create a natural balance in stratospheric ozone. Crutzen discovered that when nitrous oxide, which is produced by soil bacteria, floats up to the stratosphere, the chemical demolishes ozone molecules. Crutzen's research led directly to discoveries on the relationship between ozone destruction and freon compounds manufactured with chlorofluorcarbons (CFCs), says Jack Calvert, atmospheric scientist at the National Center for Atmospheric Research in Boulder, Colorado. "When nitrous oxides get to the stratosphere, they start a chemical chain reaction that destroys ozone, in the same way that freon does," Calvert says.
In fact, small amounts of other natural compounds, hydrogen and chlorine, also migrate from the earth's surface and break down ozone molecules in the stratosphere. But until industrial chemicals changed the atmosphere's chemical mix, this destruction was generally balanced by natural production of ozone. That is, the sun's rays would split oxygen molecules and start a rapid chemical reaction, leading to the formation of ozone molecules. So the amount of ozone would increase or decrease by small degrees, depending on chemical influences from volcanic eruptions and seasonal changes, and on variations in the sun's intensity.
Crutzen was also among the first scientists to suspect that human-made chemicals could deplete ozone. In the early 1970s, Crutzen and Harold S. Johnston, a chemistry professor at the University of California, Berkeley, theorized that a new kind of commercial airplane called the supersonic transport (SST), which flew into the stratosphere and spewed nitrogen oxides from its exhaust, could accelerate natural destruction of ozone.
Meanwhile, by 1973, Rowland and Molina theorized that CFCs could migrate into the upper atmosphere and damage ozone. The researchers calculated that because CFCs are so stable and durable in the surface atmosphere, the chemicals can live for 50-100 years, but when they reach the stratosphere, they are disintegrated by shorter-wave ultraviolet radiation. As each chlorine molecule breaks down, it can destroy many ozone molecules, possibly depleting ozone, on a global average, by 7-13% over 100 years if CFC production continued at its rate of growth (at that time), Molina and Rowland theorized.
With further research, though, the scientists learned that ozone would be depleted in more complex ways. "Later, we realized that there would be large depletions of ozone at different latitudes, and more severe depletions at high latitudes," says Molina.
In 1975, researchers from the National Center for Atmospheric Research and the National Oceanic and Atmospheric Administration separately reported that instruments on balloons had detected abundant CFC-11 in the stratosphere. This was the first time that measurements had been made of any manufactured chlorine compounds in the upper atmosphere. The next year, a special National Academy of Sciences panel calculated that stratospheric ozone could be depleted by 7% over the long-term due to CFCs, within the range first estimated by Rowland and Molina. In presentations at scientific meetings, press conferences, and legislative hearings, Rowland and Molina began recommending a complete ban on the release of CFCs to the atmosphere.
By 1979, the United States and other nations had banned the sale of aerosol cans that contained CFCs, but companies continued to produce CFCs for other uses. Moreover, there was no urgency by the international community to ban CFCs outright, and researchers were challenged to prove that the observed ozone depletion was well beyond natural variations.
This challenge was answered in 1985 when British researchers announced that they had found a huge ozone hole above Antarctica. This hole confounded scientists until 1987 when Molina, Rowland, and their colleagues discovered that manufactured chlorine compounds initiated a chain of chemical reactions on the surfaces of extremely cold polar stratospheric clouds, accelerating the destruction of ozone in this area.
In 1987, through the United Nations' involvement, 24 industrial nations signed the Montreal Protocol, agreeing to set sharp limits on the use of CFCs and bromine-containing chemicals that also destroy ozone. The following year, DuPont, the world's largest manufacturer of CFCs, announced that it would begin moving toward discontinuing further production.
Calvert says, "DuPont scientists were a big help in proving the connections between ozone loss and CFCs. They honestly tried to find what the truth was." Michael Oppenheimer, an atmospheric scientist at the Environmental Defense Fund, agrees that ozone research has been "the best example of industry, government, and university scientists getting together and crafting a solution on an important environmental issue."
Under further tightening of the Montreal Protocol, the most dangerous gases will be totally banned by 1996, although developing countries have a few years to introduce substitutes for ozone-destroying chemicals. In 1995, however, Republicans in Congress introduced legislation that would stop the United States' participation in the ban on CFC production. But Oppenheimer sees "no ground swell of opposition" in Congress to the ozone treaty. Furthermore, the Nobel Prize in Chemistry shared by Molina, Rowland, and Crutzen "shows that the scientific basis for the Montreal Protocol is of the highest quality," he says. "On this issue, governments have been making policy based on the best science--period."
EHPnet
When the 1995 Nobel Prize in Chemistry was awarded to Paul Crutzen, Mario Molina, and F. Sherwood Rowland for their work in atmospheric chemistry, particularly concerning the formation and decomposition of ozone, the world's attention focused once again on ozone depletion. A World Wide Web site of the U.S. EPA (URL: http://www.epa.gov/docs/ozone/index.html) provides information on ozone depletion, regulations designed to protect stratospheric ozone, explanation of the UV index, and consumer information.
For novices in ozone research, the ozone depletion hyperlink is a good starting point. The questions and answers on ozone depletion section provides a layman's explanation of the concern about ozone depletion. More technical information on ozone depletion can be found under sections including a fact sheet, United Nations Environment Programme Common Questions about Ozone, and Current Reports on Ozone Depletion by the World Meterological Organization, NASA, and the British Antarctic Survey. To decipher some of the scientific jargon, many of the scientific terms used throughout the site are linked to a glossary.
One interesting feature of this Web page is the Ozone Depletion: Myth vs. Measurement hyperlink. Some of the most popular misconceptions about ozone depletion are dispelled here. The issues covered include CFCs, volcanoes, and whether a link exists between ozone depletion and higher UV levels. One of the newest additions to this site is an animated illustration of the ozone hole over the Antarctic. A series of images shows the change in percentage of ozone during the fall of 1995.
Users interested in the latest regulatory efforts by the EPA to prevent ozone depletion may access a hyperlink describing the methyl bromide phase-out. Methyl bromide is a pesticide used to control insects, nematodes, weeds, and rodents. It is also a significant ozone-depleting substance: recent scientific evidence indicates that bromine from this material is 50 times more effective at destroying ozone than chlorine from CFCs on a per-molecule basis. When this phase-out will occur, how it will affect current uses, and what alternatives exist for this pesticide are clearly outlined in this hyperlink. In addition, a hyperlink on the Montreal Protocol on Substances that Deplete the Ozone Layer details international actions to protect ozone.
Alternative products that consumers may consider that do not impact on ozone are provided in the Consumers and Ozone Protection hyperlink. Products discussed in this section include refrigerants, pesticides, solvents, halons such as aerosols, adhesives, and inks. This link also includes tips for how individuals can help protect the ozone layer. Users who are unable to access the Web site may obtain information about ozone depletion by calling the Ozone Protection Hotline at (800) 296-1996.
Last Update: May 6, 1997