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    • Pesticide Warning Sign in front of agricultural field / iStockPhoto

Invisible Dangers


From the pesticides that protect our food supply to the particulate matter that comes out of our tailpipes, we are exposed to countless chemicals in our daily lives, some of which can be toxic. Fielding School researchers are identifying the risks and developing global solutions so that we can breathe more easily.


DR. YIFANG ZHU believes the on-board school bus air filtration system she and her Fielding School colleagues have been testing could be the solution to a safer ride for the 25 million children who commute on school buses in the United States nearly every day.

“School buses tend to be very leaky,” explains Zhu, associate professor in the Fielding School’s Department of Environmental Health Sciences. “When they are on freeways and busy streets, the emissions from the surrounding vehicles make their way inside the bus fairly easily, and the children on board can be exposed to significantly greater levels of air pollutants than a typical resident.” Studies have associated exposure to high levels of vehicle pollution with pulmonary and cardiovascular risks, and children are most susceptible because they breathe more quickly and their immune and cardiovascular systems are developing.

So, with funding from the California Air Resources Board, Zhu’s team studied a prototype high-efficiency cabin air (HECA) filtration system designed specifically to clean the air aboard school buses. The results, published in the journal Environmental Science & Technology, were highly encouraging. Vehicular pollutants inside the buses were reduced by up to 88 percent – with the greatest reductions occurring under freeway-driving conditions. The study found that the air inside buses with the HECA system was as clean as air near the beach in Santa Monica, CA.

“A reduction of nearly 90 percent in children’s exposure to pollutant levels on their daily bus commutes would be highly significant,” says Zhu, whose team now hopes to continue with a long-term study measuring exposure levels in buses with children aboard. “The EPA has said that school buses are by far the safest way to transport children between school and home. Our goal is to make it also the cleanest way.”

Zhu’s solutions to dangerous environmental exposures have global implications. Outside of her school bus work, she has collaborated with researchers at Peking University in China – bringing lessons learned from Los Angeles’ successful air-pollution reduction effort to Beijing as Chinese policy makers grapple with smog levels that have reached 20 times the limit recommended by the World Health Organization. And Zhu isn’t alone. In disparate settings including FSPH laboratories and Central Valley farms, Fielding School researchers are identifying the risks we face through our daily chemical exposures and developing solutions so that we can breathe more easily.

Yifang Zhu in front of buses
For the 25 million U.S. children who commute on school buses nearly every day, an on-board air filtration system tested by Dr. Yifang Zhu and her Fielding School team could reduce exposure to vehicular pollutants by up to 88 percent.

THE RISING PREVALENCE OF AUTISM spectrum disorder in the U.S. can’t be entirely explained by diagnostic changes or genetic factors. That leaves room for the possibility that environmental exposures are playing a role, notes Dr. Ondine von Ehrenstein, assistant professor in the Department of Community Health Sciences.

In a 2014 study published in the journal Epidemiology, von Ehrenstein, who collaborates with Dr. Beate Ritz, professor and chair of the Fielding School’s Department of Epidemiology, examined the potential association between exposure to California Air Resources Board-monitored air toxics during specific periods of pregnancy and increased risk of autism. Von Ehrenstein, Ritz and their collaborators found 30-70 percent risk increases for autism in children exposed in utero to several traffic- and industry-related toxics. Now, the FSPH team is part of the first large-scale systematic investigation of the potential effects of prenatal pesticide exposure on autism risk.

“Exposures involving the developing brain and nervous system may cause substantial public health impacts – as illustrated, for example, by the case of lead,” von Ehrenstein notes. “Identifying adverse environmental factors that are amenable to prevention during early-life development should be a public health policy priority.”

POLLUTION LEVELS in greater Los Angeles have improved in the last several decades, thanks in part to stricter state and local regulations and the use of cleaner fuels. But air pollutants are still a cause for considerable concern – particularly during childhood and earlier.

Aware of the evidence that the developing fetus is particularly vulnerable to environmental influences, Dr. Julia Heck, an assistant professor of epidemiology at the Fielding School, set out to explore a potential link between prenatal exposures to air pollutants and rare childhood cancers. Heck used a sophisticated dispersion model for the State of California, along with data from the California Air Resources Board’s community-based air pollution monitors, to determine levels of exposure to traffic pollution and air toxics during pregnancy. Heck and colleagues then overlaid data from the California Cancer Registry, as well as state birth records, to provide evidence suggesting a potential link between maternal exposure to specific pollutants and the risk of neuroblastoma, retinoblastoma, germ cell tumors, and the two major types of leukemia in children.

“It would have been hard to do this study anywhere else,” Heck says. “California has been at the forefront of environmental monitoring, so we have many years of air pollution data for dozens of air toxics.” Among other resources, Heck has also had access to the geographic information system (GIS) land-use model and exposure assessment methodologies developed by Ritz and her team.

PERFLUORINATED CHEMICALS (PFCS) have been used broadly in industry and commercial products for decades. But in the last decade, concerns have been raised by reports that these ubiquitous compounds persist in the environment, potentially accumulating to exposure levels that can be harmful. PFCs are classified as endocrine-destructing compounds for their ability to disrupt the hormone system of mammals; there are also hints of their ability to cross the placental barrier and expose the fetus during the most vulnerable period of development. “We all have measurable amounts of PFCs in our blood,” says Zeyan Liew (PhD ’14), a postdoctoral scholar in the Fielding School’s Department of Epidemiology who is working with Ritz. “But very little is known about the reproductive and developmental effects, in part because it’s been so hard to study.”

For his doctoral dissertation at the Fielding School, Liew made use of a singular resource. The Danish National Birth Cohort recruited 100,000 pregnant women in Denmark from 1996 to 2002, collecting and storing prenatal blood samples and then following their children to learn more about early determinants of health. Liew received funding to study the impact of prenatal exposure to several types of PFCs on the risk of autism, attention deficit hyperactivity disorder, and cerebral palsy. The funding came via a grant awarded to Dr. Jørn Olsen, former chair of the Department of Epidemiology and founder of the Danish National Birth Cohort, and to Ritz, who was Liew’s PhD mentor.

Liew found prenatal PFC exposure to be associated with increased risk of cerebral palsy (CP) in children. He is continuing to study the Danish cohort to learn whether PFC exposures affect children’s cognitive functions and intellectual development.

Beate Ritz photo and aerial shot of farmland
Through maps of land use and a sophisticated geographic information system approach incorporating state pesticide records, Dr. Beate Ritz and her colleagues have conducted pioneering studies in California’s Central Valley showing the impact of specific pesticides and of the genetic variations that render exposed individuals susceptible to Parkinson’s disease.

PESTICIDE USE has increased dramatically over the last 50 years, to the point that an estimated 5.2 billion pounds of active ingredients were employed in 2007 – or nearly one pound for each person on the globe. But the distribution is far from equal. About 40 percent of the overall use is in agriculture, which is why, when concerns began to grow in the early 2000s about an association between pesticide exposure and Parkinson’s disease, some neurologists began to refer to the farm towns in California’s Central Valley as “Parkinson’s Alley.”

Much of what is now known about increased susceptibility to the neurodegenerative brain disease among Central Valley farmworkers – as well as others who live or work near fields and come into contact with the agricultural chemicals through dust, air, or well water – comes from the work of Dr. Beate Ritz, professor and chair of the Fielding School’s Department of Epidemiology, and her colleagues at the UCLA Center for Gene-Environment Studies of Parkinson’s Disease, which Ritz co-directs. Their studies over the last 15 years of approximately 1,600 Central Valley residents have built a compelling case for the ways in which genetic and environmental influences conspire to increase the Parkinson’s disease risk through an interplay between neurotoxic pesticides and biologic mechanisms that increase susceptibility of the aging brain.

Ritz was a junior Fielding School faculty member in 1996 when she became intrigued with the idea of investigating the potential Parkinson’s/pesticides link. “We have this large Central Valley with so much agricultural activity and high-intensity chemical use through four growing seasons,” she explains. In the 1980s, a neurologist in the San Francisco Bay Area, William Langston, had linked the compound MPTP, found in synthetic heroin, to early-onset Parkinson’s in a cluster of heroin addicts. Since MPTP’s chemical structure closely resembled paraquat, a widely used herbicide, that reignited the debate over whether something in the environment – specifically pesticides – might trigger Parkinson’s. Ritz also knew she had a rich data source: Since the early 1970s, California law had required detailed reports on pesticide use. “This resource was now electronically available, and had never been systematically used for human studies,” Ritz says.

Exposure to pesticides had long been suspected as a risk factor for Parkinson’s disease, but previous studies had been limited by their reliance on people’s recollection of chemical usage, which made accurate exposure assessment difficult. Ritz and her colleagues overcame that hurdle by using maps of land use and a sophisticated geographic information system approach incorporating the pesticide application records. In doing so, they have been able to provide a high-resolution view of the impact of specific pesticides and of the genetic variations that render exposed individuals susceptible to the disease.

Fifteen years of research have told a powerful story. Among the many findings reported by Ritz’s team:

  • Central Valley residents living near fields where the pesticides paraquat and maneb were used between 1974 and 1999 were nearly twice as likely to develop Parkinson’s as others living in the region.
  • Further studies have also implicated ziram, benomyl, and other commonly used neurotoxic pesticides such as the insecticides organophosphates and pyrethoids.
  • Simply living or working near fields on which pesticides are applied can increase risk in non-farmers.
  • Those consuming private well water and living within 500 feet of farms with long-term pesticide use were nearly twice as likely to end up with the disease.
  • The level of risk from being exposed to the harmful pesticides depends on an individual’s genetic makeup, which in the most-exposed groups can increase the chances of developing Parkinson’s by up to six-fold.

ALONG THE WAY, Ritz has mentored numerous doctoral students and junior faculty. “The methods she has developed can be used for studying many different diseases, including others that pesticides may be influencing,” says Kimberly Paul, a current PhD student who has worked on the Parkinson’s studies with Ritz since 2012. “Unfortunately, there are many negative health outcomes that can be found in the Central Valley at a much higher rate than one would expect.”

While her studies continue to build a case for the problem, Ritz has also been active in efforts to address it. She has discussed her findings with community-based groups seeking to promote protective measures, and has shared her views with federal legislators seeking to revise the 1976 Toxic Substances Control Act – including accepting an invitation to meet with California Sen. Dianne Feinstein to discuss her work and its implications on the need to strengthen the law.

“We should encourage these Central Valley communities to build a ring of greenery around the neighborhoods to separate them from the agriculture,” Ritz says. “But we also have to think about the workplaces, and promote integrated pest management that avoids pesticide use to the greatest extent possible – especially use of many neurotoxic pesticides.” •