(Beyond Pesticides, July 27, 2009)
A mother’s exposure to urban air pollutants known as polycyclic aromatic hydrocarbons (PAHs) can adversely affect a child’s intelligence quotient or IQ, according to the new study “Prenatal Airborne Polycyclic Aromatic Hydrocarbon Exposure and Child IQ at Age 5 Years.” PAHs are widespread in urban environments and throughout the world as they have many sources, several of which are related to pesticides, including creosote used for wood preservation, burning pesticide-laden grass seed fields, and exposure to organochlorine pesticides whether banned, yet ubiquitous DDT or the still used insecticide dicofol. Other sources include synthetic turf fields and the burning of coal, diesel, oil and gas, or other organic substances such as tobacco. PAHs have been known to be bioaccumulative, carcinogenic and disrupt the endocrine system.
The new study, funded by the National Institute of Environmental Health Sciences (NIEHS), a branch of the National Institutes of Health, the U.S. Environmental Protection Agency and several private foundations, found that children exposed to high levels of PAHs in New York City had full scale and verbal IQ scores that were 4.31 and 4.67 points lower than those of less exposed children. High PAH levels were defined as above the median of 2.26 nanograms per cubic meter (ng/m3). A difference of four points, which was the average seen in this study, could be educationally meaningful in terms of school success, as reflected, for example, in standardized testing and other measures of academic performance. However, the researchers point out that the effects may vary among individual children.
“This research clearly shows that environmental PAHs at levels encountered in an urban setting can adversely affect a child’s IQ,” said Linda Birnbaum, Ph.D., director of NIEHS. “This is the first study to report an association between PAH exposure and IQ, and it should serve as a warning bell to us all. We need to do more to prevent environmental exposures from harming our children.”
The study was conducted by scientists from the Columbia University Center for Children’s Environmental Health. It included children who were born to non-smoking black and Dominican-American women age 18 to 35 who resided in Washington Heights, Harlem or the South Bronx in New York. The children were followed from utero to 5 years of age. The mothers wore personal air monitors during pregnancy to measure exposure to PAHs and they responded to questionnaires.
At 5 years of age, 249 children were given an intelligence test known as the Wechsler Preschool and Primary Scale of the Intelligence, which provides verbal, performance and full-scale IQ scores. The test is regarded as a validated, reliable and sensitive instrument for assessing intelligence. The researchers developed models to calculate the associations between prenatal PAH exposure and IQ. They accounted for other factors such as second-hand smoke exposure, lead, mother’s education and the quality of the home caretaking environment. Study participants exposed to air pollution levels below the average were designated as having low exposure, while those exposed to pollution levels above the median were identified as high exposure.
“The decrease in full-scale IQ score among the more exposed children is similar to that seen with low-level lead exposure,” said lead author Frederica P. Perera, Dr.P.H., professor at Columbia’s Mailman School of Public Health and director of the Columbia Center for Children’s Environmental Health.
A 1999 study found that PAHs that are abundant in house dusts increase the toxicity of chlorpyrifos in vitro, particularly at low levels (i.e., 2-50 FM PAHs with 1-180 nM chlorpyrifos-oxon, a metabolite of chlorpyrifos that inhibits acetyl cholinesterase.
According to Beyond Pesticides’ wood preservatives campaign research, PAHs are one of the three classes of chemicals found in coal-tar creosote that are known to cause harmful health effects. Many of the components of the creosote mixture, such as PAHs, are rapidly absorbed through the lungs, stomach and intestines. Creosote is made up of about 75-85 percent PAHs. PAHs can attach to soil particles and may move with sediments into streams or remain part of a tarlike mass, but they may also move into groundwater in sandy soils low in organic matter. The remaining PAHs are bioaccumulative and carcinogenic. According to ATSDR’s Toxicological Profile on PAHs, “Studies of people show that individuals exposed by breathing or skin contact for long periods to mixtures that contain PAHs and other compounds can also develop cancer.” Creosote contains several carcinogenic PAHs, including benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene. The Department of Health and Human Services has determined that these three PAHs are known animal carcinogens. The EPA and the International Agency for Research on Cancer (IARC) have determined they are probable human carcinogens.
“IQ is an important predictor of future academic performance,” said Dr. Perera. “Fortunately, airborne PAH concentrations can be reduced through currently available controls, alternative energy sources and policy interventions.”
This study adds to the body of scientific literature that links toxic chemical exposure to intellectual impairment in children. Joseph L. Jacobson, Ph.D., and Sandra W. Jacobson, Ph.D., in “Intellectual Impairment in Children Exposed to Polychlorinated Biphenyls in Utero” (1996), conclude that infants and young children whose mothers had eaten a diet of Great Lakes fish contaminated with polychlorinated biphenyls (PCBs) suffer adverse neurologic and intellectual function.