A new study led by the University of California, Davis has found that infant monkeys conceived while their mothers were naturally exposed to wildfire smoke shown significant behavioral changes compared to those conceived a few days after the exposure. These findings prove the importance of timing in the effects of smoke exposure during pregnancy, and suggest that exposure to such pollutants could have similar impacts on human infants.
“I think this will have an effect on future studies of exposures in pregnancy, because we’ll know when to look,” said study senior author Bill Lasley, a professor emeritus of Population Health and Reproduction at UC Davis. According to Lasley, existing studies of environmental exposure to pollutants during pregnancy in humans are largely retrospective, since women may not even realize that they are pregnant until weeks into the first trimester.
The Camp Fire – one of the largest and deadliest wildfires in California’s history – began on November 8, 2018 and provided a natural experiment in the effects of smoke exposure. At the peak of the breeding season for rhesus macaques housed in outdoor corrals at the California National Primate Center in Davis, the smoke blanketed the area, exposing many of the pregnant monkeys.
The 89 macaques conceived around that time were born approximately six months later. The researchers divided them into 52 animals conceived on or before November 22 – which were considered to be exposed to wildfire smoke during the first trimester – and 37 that were conceived later.
According to the scientists, the smoke exposed monkey infants showed increases in markers of inflammation, reduced cortisol responses to stress, memory deficits, and more passive temperaments than those conceived later. These effects appear similar to those identified in studies of prenatal exposure to air pollution, and are probably caused by airborne hydrocarbons such as phthalates, which were found in the smoke from the Camp Fire.
Unlike in the case of other mammals, the placenta of primates such as monkeys or humans produces hormones supporting brain development through the adrenal system. “Since fetal adrenal glands are the source of cortisol and other steroids for neurologic development, which determines behaviors, a scenario of a placenta-adrenal-brain axis could be the causal pathway,” explained Professor Lasley.
Further research is needed to clarify whether smoke exposure in humans could cause similar effects. The scientists are now beginning a prospective study on women with implanted embryos as a result of in vitro fertilization, since the time of conception is exactly known if the women are incidentally exposed to wildfire smoke or other types of pollutants.
The study is published in the journal Nature Communications.