Two recent studies looking at regions in North Carolina and Pennsylvania have added to the growing evidence linking increased rates of autism spectrum disorders to the presence of air pollutants.
ASDs, which affect interpersonal relations and work achievement and typically are diagnosed in early childhood, affect 1 in 68 children in the U.S. According to the CDC, both environmental and genetic factors can influence whether a child develops ASD.
Two recent studies examined exposure to air pollution one looked at exposure to coarse and fine particulate matter, and the other at exposure to chromium and styrene.
Exposure to PM10
The first study, by University of Wisconsin-Milwaukee researcher Amy Kalkbrenner, published Oct. 15 on the website of the journal Epidemiology, showed pollutions impact on autism rates in North Carolina is similar to results of pollution-autism studies in California despite weather and climate differences.
Building on previous studies, Kalkbrenner and her colleagues also showed women in the third trimester of pregnancy were more susceptible to the damaging effects of air pollution on their unborn child.
It adds another piece supporting the hypothesis that environmental chemicals are part of the autism puzzle, Kalkbrenner, an assistant professor in UWMs Joseph J. Zilber School of Public Health, said in a UWM news release.
Kalkbrenners research team focused on exposure to coarse and fine particulate matter, known as PM10, which partly comes from traffic-related air pollution. For the study, they evaluated records covering preconception through the first birthday for 87,000 children in North Carolina and 77,500 children in California born in the mid-to-late 1990s. Investigators selected key regions in each state based on their ability to simultaneously measure the level of particulate matter present, and know which children had autism in these regions.
Researchers used a new, more exact tool to measure the levels of particulate matter in smaller slices of time, based on pollution at the familys address during pregnancy. This allowed them to compare exposures during specific weeks of pregnancy. The 645 North Carolina children and 334 California children who later developed some form of ASDs then were compared with all other children. Researchers adjusted for state, race and ethnicity, maternal age and education, median income and urbanization of neighborhoods.
It was important to look at eastern states because of differences in climate, seasonal weather patterns and the chemical make-up of the particulate matter that could affect brain development, Kalkbrenner said in the release.
Evidence for a link between a chemical exposure and a health impact like autism is stronger when it can be shown in more than one region, she said in the release.
The team found the concentration of particulate matter was highest among children born in summer months in North Carolina and those born in fall and winter months in California.
Reasons for increased susceptibility in the third trimester of pregnancy are not known. However, Kalkbrenner said this finding is consistent with theories showing links between autism and altered brain network development, specifically synaptic connections developing during the final months of pregnancy.
Weve now had three solid studies saying the same thing, Kalkbrenner said in the release. The evidence is pretty compelling that something is going on with air pollution and autism.
She added further study is needed to determine the neurodevelopmental effects of specific chemical pollutants during precise developmental windows. The study can be found online at http://journals.lww.com/epidem/Abstract/publishahead/Particulate_Matter_Exposure,_Prenatal_and.99266.aspx.
Research looks at chromium, styrene
Children with ASD were more likely to have been exposed to higher levels of certain air toxics during their mothers pregnancies and the first two years of life compared with children without ASD, according to the preliminary findings of a University of Pittsburgh Graduate School of Public Health study.
This research, funded by The Heinz Endowments, was presented Oct. 22 at the American Association for Aerosol Researchs annual meeting in Orlando, Fla. The abstract can be found at http://aaarabstracts.com/2014/viewabstract.php?pid=599.
Despite its serious social impact, the causes of autism are poorly understood, principal investigator Evelyn Talbott, DrPH, a professor of epidemiology at Pitt Public Health, said in a Pitt news release. Very few studies of autism have included environmental exposures while taking into account other personal and behavioral risk factors. Our analysis is an addition to the small but growing body of research that considers air toxics as one of the risk factors for ASD.
Talbott and her colleagues performed a population-based study of families with and without ASD living in six southwestern Pennsylvania counties. Their findings showed links between increased levels of chromium and styrene and childhood ASD.
For the study, the investigators interviewed 217 families of children with ASD and compared these findings with information from two separate sets of comparison families of children without ASD born during the same time period within the six-county area. The families lived in Allegheny, Armstrong, Beaver, Butler, Washington and Westmoreland counties, and the children were born between 2005 and 2009.
One of the strengths of the study was the ability to have two types of controls, which provided a comparison of representative air toxics in neighborhoods of those children with and without ASD, Talbott said in the release.
For each family, the team used the National Air Toxics Assessment to estimate the exposure to 30 pollutants known to cause endocrine disruption or neurodevelopmental issues. NATA is the Environmental Protection Agencys ongoing comprehensive evaluation of air toxics in the U.S., most recently conducted in 2005.
Based on the childs exposure to concentrations of air toxics during the mothers pregnancy and the first two years of life, the researchers found children with higher exposure to styrene and chromium were at a 1.4- to 2-fold greater risk of ASD, after accounting for the age of the mother, maternal cigarette smoking, race and education. Other NATA compounds associated with increased risk included cyanide, methylene chloride, methanol and arsenic. As these compounds often are found in combination with each other, further study is needed.
Styrene is used in the production of plastics and paints and also is one of the products of combustion when burning gasoline in vehicles. Chromium is a heavy metal, and air pollution containing it typically is the result of industrial processes and the hardening of steel. It also can come from the ash created from the burning of coal at power plants. Cyanide, methylene chloride, methanol and arsenic all are used in a number of industries and can be found in vehicle exhaust.
Our results add to the growing body of evidence linking environmental exposures, such as air pollution, to ASD, Talbott said in the release. The next step will be confirming our findings with studies that measure the specific exposure to air pollutants at an individual level to verify these EPA-modeled estimates.