It happens that those who are most susceptible
[to air pollution] are the very young and the very old--not,
as some would suggest, particularly squeamish groups whose
interests the society can afford to compromise if it begins
to look like it might be expensive to protect them.
Lois Jeffrey, speech, University of North Carolina
1 November 1973
New Model for Ozone Transport
With the EPA proposing more stringent standards for ozone, understanding how this air pollutant is formed and transported is of major importance to creating effective ozone controls. Ozone is produced when volatile organic chemicals (VOCs)--both natural and manmade--combine in the presence of warm sunlight with nitrogen oxide emissions from vehicle exhaust and smoke stacks. While local production of ozone is a problem, newly developed computer modeling and data analyses have shown that ozone may also travel from distant locations to damage air quality and harm lungs.
Until relatively recently, ozone was regarded primarily as a local problem for cities, according to Michael Koerber, technical director of the Lake Michigan Air Directors' Consortium and a member of the Ozone Transport and Assessment Group's (OTAG) ozone modeling task force. Representing 37 eastern states affected by ozone, OTAG is an ad hoc group of EPA and state environmental officials, industry representatives, and environmental groups working to better understand ozone's formation, accumulation, and movement through the lower atmosphere of the eastern United States.
Ozone plagues many eastern and midwestern cities, exceeding levels set by federal ozone standards under the Clean Air Act. But as Koerber notes, the cities aren't solely to blame. For example, the air coming into Chicago on a hot summer day contains ozone levels already approaching the federal standard, says Koerber, "which means [the addition of] just a few urban emissions in a city like Chicago is enough to put it into nonattainment [status]. There's no way Chicago will ever be able to attain the ozone standard without some reduction in these high incoming ozone levels." Moreover, he notes, OTAG models have shown that the Lake Michigan region occasionally receives ozone from as far away as Kentucky and Tennessee.
Ozone model 1
. An OTAG modeling plot shows the change in aloft ozone concentrations resulting from NOx emission reductions. Emission reductions produce decreases in ozone over a broad area of the eastern United States and, in some cases, extend far downwind of the source area.
Ozone model 2
. An OTAG modeling plot shows peak ozone concentrations predicted for the July 1995 episode. Because of transport, high ozone concentrations occur over a broad area of the eastern United States.
The OTAG computer models reveal that ozone affects air quality as much as hundreds of miles from where its precursors are emitted, says Koerber. This shows, he says, that ozone is a regional, not just a local problem. Critics say, however, that even if ozone travels such distances, the impact of transported ozone on local air quality is greatly exceeded by that of closer, local sources.
The OTAG modeling region breaks up the eastern United States into grids measuring 144 square kilometers on the ground and extending 4 kilometers into the atmosphere. The model is made up of three basic parts, explains Rudolf Husar, a Washington University atmospheric scientist who is a member of OTAG's air quality analysis group. One part is emissions of ozone precursors from natural sources like isoprene, which some trees and plants produce, as well as manmade VOCs and NOx. A second part is meteorology, including winds and temperature. The third part is the highly complex chemistry that produces ozone. To verify the model, OTAG scientists matched the model's predictions against measured data for four hot, muggy, several-day periods in July of 1988, 1991, 1993, and 1995, during which there were high ozone concentrations across broad, multistate regions in the eastern United States.
John Jansen, principal scientist with Southern Company, a Birmingham, Alabama, holding company for five electric utilities in four southern states, offers a note of caution on the nature of ozone transport and the application of the OTAG model: "It's probably a fairly decent model, but it has its weaknesses." According to Jansen, studies sponsored by Southern Company and others indicate that the OTAG model overestimates the amount of isoprene by a large degree, compared with the amount actually found in the air. "This finding demonstrates that the [OTAG] model overestimates the amount of ozone reduction one gets from a [NOx] reduction and underestimates the amount of reduction one gets from a VOC reduction," he says. NOx is the limiting factor in ozone production if the VOC level is high.
Large NOx reductions would mean controls on utilities, many of which burn huge amounts of coal. "That could be very costly, and people are going to be disappointed in the actual result," Jansen says. He also argues that research done for his company finds that in a number of major southern cities, ozone levels that exceed current standards are caused primarily by local, not regional, emissions.
"I haven't seen any technical indication to say that this modeling system overestimates the benefits of NOx control," says EPA meteorologist Norman Possiel. "If the Southeast is not necessarily impacted by transport from other areas, that does not mean that ozone formed from emissions in [an] area does not impact other areas downwind."
The OTAG modeling information will be sent next to top environmental officials in the 37 OTAG states for use in developing plans to reduce regional ozone. Such plans will then go to the EPA for evaluation and approval.
Biocultural Perspectives onWomen's Health
In a session on biocultural perspectives on women's health in developing countries at the recent American Association for the Advancement of Science annual meeting in Seattle, a growing subdiscipline of anthropology addressed how cultural and ethnic practices interact with medical and biological factors in women's lives. "The biocultural perspective is coming out of the same sort of concern as [that] about the environment and the decline in biodiversity. People are interested in studying the biology of indigenous groups before these groups are lost," said David Tracer, an assistant professor of anthropology at the University of Washington in Seattle.
Bettina Shell-Duncan, also an assistant professor of anthropology at the University of Washington, emphasized that, too often, the study of women's childbearing role focuses more on the welfare of the child than that of the mother. Because women serve not only as reproducers but also as economic and cultural producers, Shell-Duncan said, women's health is important in itself. Shell-Duncan described female circumcision among the Rendille people of Kenya. As part of the traditional wedding ceremony, the bride's clitoris and labia minora are excised. Short-term health risks associated with excision include infection and hemorrhage, which are substantially reduced when sterile cutting instruments, antibiotics, and tetanus vaccine are used. Shell-Duncan noted that female circumcision marks a major status transition for women and makes their families eligible for bridewealth payments. Although Rendille culture is modernizing, almost all informants indicated that they will have their daughters circumcised. However, some women told Duncan that if they were convinced of its harmful effects, they would consider stopping the practice.
Worldwide women's health
. A growing subdiscipline of anthropology is looking at how culture and environment interact with women's biology and health in developing countries.
|
Joanne Leslie of the Pacific Institute for Women's Health discussed how sociocultural factors such as premarital sex, early childbearing, educational level, and attitudes about sexually transmitted diseases affect the health of West African adolescents. In a series of focus groups conducted in 1996 in Cameroon, Leslie found that adolescents are aware of the risks of pregnancy and sexually transmitted diseases, but not concerned enough to stop having unprotected sex. Girls see trading sex for gifts or money as one of their few sources of income in a money economy; boys believe most girls want a premarital baby as proof of the girls' fertility. Traditional cultural norms work synergistically with the country's state of economic upheaval to maintain very high adolescent fertility rates, while higher educational levels correlate with lower fertility.
Kathleen O'Connor, a researcher in the department of anthropology at Pennsylvania State University at University Park, and Tracer discussed women's health during pregnancy and lactation. O'Connor and Tracer based their presentation on 1993 field research in a village in Bangladesh in which they collected twice-weekly urine samples and questionnaires from 493 women in all reproductive states, including regular menstrual cycling, pregnancy, lactation, and amenorrhea. In all, about 19,000 paired questionnaires and urine samples were obtained.
O'Connor studied the relationships between pregnancy-related sickness (PRS)--the nausea, vomiting, and food and smell aversions associated with pregnancy--and levels of hormones such as estrogen, progesterone, and human chorionic gonadotropin (hCG). She also looked at possible correlations among PRS, maternal age, and fetal loss in 203 pregnancies. The hormonal results are preliminary, but the results so far suggest an association of PRS with high hCG levels. "A popular belief, based on the scientific literature, is that nausea and vomiting during pregnancy is good because it is associated with a lower risk of early fetal loss," O'Connor said. "Our results suggest that that is incorrect. If you control for the effects of the increase in the risk of fetal loss with maternal age, there is no association between PRS itself and fetal loss."
Darryl Holman, a research associate in the Population Research Institute at Pennsylvania State University, presented evidence on whether women in developing countries experience earlier menopause than women in more developed countries. Holman's research was also based on data obtained in the Bangladesh village study. Holman notes that the previous estimate of the median age at menopause in Bangladesh is 43.6 years, some eight years earlier than for U.S. women. After better statistical treatment, the difference is less than two years, which Holman suspects is a result of stress-related anovulation that resembles menopause.
"Everything we think we know about menopause in developing countries is probably wrong," Holman said. He believes stress-related anovulation among Bangladeshi women is probably related to their high fertility and the fact that they breast feed longer than most other cultures. They also have chronic high disease loads, Holman suggests, and are "some of the most nutritionally marginal people in the world" by most anthropometric measures.
Although biological anthropologists are interested in the effects of environmental factors such as phytoestrogens, pesticides, fertilizers, and pollutants on women's health, little direct study of this issue has yet been done, according to the session speakers. However, Holman and O'Connor's preliminary literature review assessing the amount of phytoestrogens in Bangladeshi women's diets revealed that lentils, the staple food, do not contain significant phytoestrogens.
Session presenters stressed that better knowledge of biocultural factors can lead to more effective medical treatment both in developing and more developed countries.
Children and the Environment
The first national conference addressing the latest research findings in pediatric environmental health convened 21-23 February 1997. The conference, "Children's Environmental Health: Research, Practice, Prevention, and Policy," was held in Washington, DC, and hosted by the Children's Environmental Health Network, a national nonpartisan project to protect the environmental health of children. The conference focused on five priority research areas: asthma and respiratory diseases, endocrine disorders, childhood cancer, neurodevelopmental effects, and cross-cutting issues.
"The conference has produced at the federal level a whole new commitment to focusing on children and that's a big change," says conference chair Joan Spyker Cranmer, professor of pediatrics and toxicology at the University of Arkansas for Medical Sciences. EPA Administrator Carol Browner announced plans to create a new center for children within the EPA to bring together work on children and to integrate policy making with research findings. Among other new federal efforts, the Agency for Toxic Substances and Disease Registry will also launch a new children's health initiative.
A World Safe for Children? New research programs are focusing on the impact of environmental agents on the world's most vulnerable population.
"Someday we'll be able to look back at this conference as . . . a cornerstone in addressing the needs of the most vulnerable among us--our children," Browner said in her keynote address. "Protecting our environment is critical to protecting the health of our children. It is just that simple."
For the first time, "we got the message through to policy makers that children are not just little adults," Cranmer says. But there is work to do. The federal government, which funds more than 90% of all research on children, spends less than 5% of its overall research budget on children, according to a study by Lynn R. Goldman, assistant administrator in the EPA's Office of Prevention, Pesticides and Toxic Substances. In addition, less than 1% of the $500 billion the nation now spends annually on the health and welfare of children is dedicated to research, she reports.
The well-attended conference reached more than just the federal sector, of course, bringing together people from all over the environmental health community. According to Philip J. Landrigan, a key speaker and chair of community medicine at Mount Sinai Medical Center, "The conference expanded the reach of the [CEHN] and rallied people around the mission statement," which is to promote a healthy environment and to protect the fetus and the child from environmental hazards.
The main goals of the multidisciplinary and multicultural conference were to provide a national forum to present and discuss the latest research findings on pediatric environmental health, to stimulate collaborative and innovative research efforts among a variety of research disciplines, to raise the next set of research questions to be investigated and develop research recommendations, and to encourage further research in the field of children's environmental health. The conference's sponsors included the NIEHS, the Environmental Hazards Assessment Program of the Medical University of South Carolina, the EPA, the National Center for Environmental Health at the Centers for Disease Control and Prevention, the Division of Cancer, Epidemiology, and Genetics at the National Cancer Institute, the National Institute for Child Health and Human Development, the Public Health Institute, and the Environmental Health Investigations branch of the California Department of Health Services.
Generally, conference speakers called for more and better information, research, and testing on exposures and susceptibility of children to environmental events; better use of and access to existing information; and increased cooperation at all levels of society from clinical researchers to policy makers to the community. A postconference report, which will be published in
Environmental Health Perspectives
, will specify the research areas and gaps that the conference identified as priorities for the 21st century.
Among exciting future research projects to emerge from the conference, Kenneth Olden, director of the NIEHS, unveiled his plan to create the Environmental Genome Project, a broad, multicenter effort to learn how genetic variances in individuals and populations account for differences in susceptibility to diseases with environmental triggers. The project would sequence about 200 known environmental disease susceptibility genes from five main categories: genes controlling the distribution and metabolism of toxicants, genes for the DNA repair pathways, genes for the cell cycle, genes for the metabolism of nucleic acid precursors, and genes for signal transduction systems controlling expression of genes in other classes.
New Questions on Genomic Instability
Cancer researchers have long been puzzled by the discordance of two related observations: that perhaps as many as eight distinct genes must be somehow mutated or altered in order for cancer to occur, and that such mutations appear to occur very rarely and are normally patched up quickly by DNA repair enzymes. The question, then, is how can it be that, out of the 100,000 or so genes in the human genome, the precise mutations needed to transform a normal cell into a cancer cell occur so frequently.
The answer may lie in the relatively new field of genomic instability. Recent research from several laboratories in the United States and abroad indicates that cells exposed to certain carcinogens, particularly radiation, appear to enter a state in which the rate of mutation increases and may stay elevated for 50 or more cell generations following exposure. This state of increased genomic instability may provide the conditions under which cells accumulate the number of mutations necessary to progress to cancer.
John Little, chairman of the Harvard School of Public Health's department of radiobiology, was one of the first researchers to see evidence of genomic instability. In the early 1990s, Little found that some irradiated cells that appeared to have escaped the effects of radiation retained a susceptibility to unexplained gene mutations. Not long after, Eric Wright of the National Research Council in England found a similar elevated rate of chromosomal abnormalities in the progeny of irradiated cells.
Relationships between these two types of genetic disruption may help elucidate this phenomenon. Recently, Little selected slow-growing HPRT gene mutants from cells that had been allowed to divide 25 times after radiation exposure. Over the following 20 cell generations, 10-40% of the offspring of these HPRT mutant clones contained chromosomal aberrations, compared to only 2-3% among progeny of non-HPRT mutants.
"The classical view of gene mutations is that each is independent, and that the probability of there being two multiple mutations in a cell is just a computation of the frequency of each," Little says. "Our results could mean that, among cells exposed to radiation, there's a range of induced instability. Perhaps, during the growth of cells, a change takes place that makes some daughter cells more unstable than others."
When Andy Grosovsky, associate professor of environmental toxicology at the University of California at Riverside studied genomically unstable cells that failed to express the thymidine kinase gene on chromosome 17, he found two different causes: a point mutation in the gene, and a chromosonal deletion or recombination resulting in loss of heterozygosity and slow growth of the cell.
"This would indicate that instability is likely to have an effect on genes that are sensitive to inactivation by loss of heterozygosity," says Grosovsky. "Many tumor suppressor genes, such as the gene for retinoblastoma and the
p
53 gene, are recessive, and could be inactivated in this way."
Thea Tlsty, director of molecular pathology at the University of California-San Francisco, has been investigating the role of
p53
, a gene already implicated in many cancers, in genomic instability. The
p53
gene is responsible for shutting down cell growth during DNA repair, and Tlsty has shown that
p53
's absence is associated with increased mutation and chromosomal abnormality.
"Think of the cell like a car," says Tlsty. "In a cell that has a mutation in
p53
, there's no way to put the brakes on. So normally, for example, if a cell gets irradiated,
p53
puts on the brakes and the cell repairs the lesions caused by radiation. If the damage gets repaired this way, you're okay, but if you don't have brakes, you're in trouble."
"It's a very interesting phenomenon, and the emphasis is on 'phenomenon,' because the underlying mechanisms aren't at all understood," says Richard Pelroy, the radiation effects branch program director at the National Cancer Institute's divison of cancer biology. In 1996, the NCI and NASA jointly earmarked $2 million for further study of this genomic instability, and 34 grant proposals are currently under consideration.
The NCI/NASA project will focus on understanding the relationship between high energy particles and genomic instability. Little has observed a "bystander effect" that occurs when cell cultures are exposed to high-density radiation particles, such as alpha radiation. Although only a few cells are actually traversed by alpha particles, many adjacent cells appear to exhibit signs of genomic instability for many generations afterward. Astronauts on extended space flight undergo increased exposure to heavy particles, which may likewise render cells unstable.
How instability might be communicated from cell to cell within one generation and between generations of cells is an important area for investigation. Wright has observed an increase in free oxygen radicals, normal by-products of human metabolism that can bind and break DNA, in genomically unstable cells. Several laboratories are investigating this as a possible pathway for the propagation of genomic instability.
"If it's true that bystanders to irradiated cells are unstable, it could have a major effect on our understanding of the effects of low-dose radiation," Little says. "This field has the potential to significantly change the way we look at cancer induction."
Priorities for Endocrine Disruptor Research
Concerns that some chemicals may disrupt the endocrine system causing cancer and reproductive problems prompted the creation of a federal working group in late 1995 to evaluate research needed to understand what threat endocrine disruptors pose. That group has since identified nine research priorities and inventoried federally funded studies of endocrine disrupting chemicals. This inventory identified nearly 400 projects and revealed an excessive emphasis on studies of PCBs and dioxins, said Lawrence W. Reiter, director of the EPA's National Health and Environmental Effects Research Laboratory, who chairs the group.
Reiter spoke in Seattle at an American Association for the Advancement of Science session devoted to efforts by the White House's Committee on Environment and Natural Resources (CENR) to develop coordinated research strategies in five areas: national environmental monitoring and research; natural disaster information and mitigation; seasonal-to-interannual climate change; North American research on tropo-spheric ozone; and endocrine disruptors. The first four areas include established threats to human health; not so endocrine disruptors. "The verdict is still out on how important this [area] is," said Jerry Melillo, associate director designate for environment at the White House Office of Science and Technology Policy.
Nonetheless, evidence that domestic animals and wildlife have suffered adversely from chemicals that interact with the endocrine system, and fears that humans might also, stimulated the CENR's attention. Its endocrine disruptors working group has identified three categories of research needs--methods, models, and measurements--divided into nine subcategories.
Concerning methods, researchers need bioassays that can identify endocrine disruptors and characterize their effects, and biomarkers that can look at both exposures and outcomes.
Scientists need models to better understand endocrine-system regulation across species and how chemicals might disrupt hormonal functions. Risk models are also needed for both exposures and outcomes, as well as models to assess biological interactions of mixtures of chemicals.
Measurement needs include better exposure-determination requirements and follow-up; multidisciplinary research and better coordination between laboratory and field work; developing sentinel species; and databases for consolidating bioassay results, looking at spatial and temporal trends in environmental chemicals, assessing field data on hormonal and endocrine disruptor levels, and tracking ongoing research.
The working group identified 394 endocrine disruptor projects funded by 14 federal agencies. The NIEHS topped the list with 93 studies, the National Cancer Institute had 59, and the EPA had 51. In all, 272 projects focused on human health, 70 on ecology, and 52 on exposure. Of the nine subcategories of research needs, four--biological interactions of mixtures, multidisciplinary research, sentinel species, and database development--account for only 6% of the projects. "Clearly, these four are underrepresented," Reiter said.
By topic, 178 studies looked at reproduction and development, 97 at carcinogenesis, 83 at neurologic effects, 37 at immunologic questions, and 98 at other issues. This ranking generally "follows the recommendations forwarded by a variety of workshops
that have looked at the research in this area," Reiter said. Seventy-one percent of the studies focused on PCBs, dioxins, and DDT and its main metabolite. A clear need exists, Reiter said, "to move away from the preoccupation" with these three chemical classes and "to begin to look at other environmentally relevant chemicals."
Both the research needs and inventory lists are accessible on the Internet at (
www.epa.gov/endocrine
).
For the first time in 10 years, the EPA is revising and updating the Clean Air Act, placing stronger limits on ozone and particulate matter emissions. The proposed rules, which the EPA plans to formalize in June 1997, are designed to reduce the concentration of smog-forming ozone in the atmosphere and to limit emissions of particulate matter smaller than 2.5 microns in diameter (PM
2.5
), a pollutant particularly harmful to human health.
By the EPA's own estimation, nearly 122 million Americans live in counties with air quality that will be considered unsatisfactory under the new ozone standard. This number does not include additional counties that will be out of compliance with the new PM
2.5
rule.
The EPA maintains a site on the World Wide Web that deals specifically with issues surrounding the proposed air standards, located at
http://ttnwww.rtpnc.epa.gov/html/ozpmrh/facahome.htm
. The site, which is maintained by the Subcommittee for Development of Ozone, Particulate Matter, and Regional Haze Implementation Programs, connects users to resources ranging from EPA press releases to original scientific data. The subcommittee is a part of the Clean Air Act Advisory Committee that the EPA established in 1990 to assist the Office of Air and Radiation on policy and technical issues associated with implementation of the Clean Air Act in that same year.
For a basic introduction to the EPA's national ambient air quality standards (NAAQS) and the process through which they are revised and implemented, users should follow the Background link on the home page. The EPA Announces Proposed New Ozone and Particulate Matter Air Quality Standards link is connected to pages that describe the newly proposed standards. Some of these pages contain press releases and general information on when and how the standards will be implemented, including how the EPA will monitor ozone and PM
2.5
levels. Other pages discuss the health effects of air pollutants and describe what areas of the country will be affected by the new rules. The site also provides links to directions for commenting on the revised standards, including mailing instructions, a toll-free telephone number, and several e-mail links.
Under the Maps and Data link on the home page, maps show which areas of the United States would be out of compliance under different averaging time scenarios for the proposed PM
2.5
and ozone concentration standards (for example, whether the EPA bases ozone exceedances on average concentration over one hour or eight hours). The data used to create these maps can be downloaded from the EPA site by clicking on icons near the maps. The Regional Haze and Visibility section at the bottom of the Maps and Data page shows where in the United States ozone pollution has significantly decreased people's ability to view and enjoy the landscape.
Other links on the home page connect users to resources that provide a more in-depth view of the revision process. The Issues link is the doorway to a collection of original papers used by the EPA in drafting the new standards. Some papers discuss how boundaries should be drawn separating different compliance zones, while others discuss implementation dates and the economic incentives and sanctions that will be used to enforce the new PM
2.5
and ozone limits. The Schedules link on the home page provides meeting dates and a timeline for the activities of the Subcommittee for Development of Ozone, Particulate Matter, and Regional Haze Implementation Programs, while the Participants link lists the members of each subgroup involved in the NAAQS revision process.
Last Update: April 9, 1997