The World Health Organization (WHO) reports that air pollution is a major environmental risk to health. Those health effects directly related to air pollution include lung cancer, stroke, heart disease, and respiratory diseases. And, globally, these account for approximately 4.2 million—air pollution-related—premature deaths every year. But researchers are also discovering other—surprising—health effects that may be related to the amount of air pollution we’re exposed to, including effects on our brain. A large California study discovered that older women who live in areas with high air pollution rates were at 81 percent greater risk of cognitive decline and 92 percent more likely to develop dementia, including Alzheimer’s. The same study also looked at the brains of female mice that were exposed to similar levels of air pollution and found damaged neurons in the hippocampus, the memory centre vulnerable to both brain aging and Alzheimer’s disease. A large UK retrospective study also found a strong correlation between the amount of air pollution people are exposed to and their risk of developing dementia. Other research has discovered that particulates from air pollution can travel through a pregnant woman’s bloodstream and into the placenta of her growing fetus, raising concerns that air pollution can have a long and damaging effect on growing brains. UK researchers are investigating the benefits of planting smaller trees with “hairy, rough leaves” in the formation of hedges (“tredges”), near busy roadsides close to schools. Because of their smaller size (closer to pollution-emitting tailpipes), the tredges have demonstrated they are better able than trees to capture dangerous particulates and, thus, reduce the level of exposure for children in those settings.