“No Evidence of a Safe Threshold” of Air Pollution

Air pollution has wide-ranging and deleterious effects on human health and is a major issue for the global community. Ambient air pollution resulting from fine particulate matter (PM2.5) are considered a major modifiable contributor to cardiovascular disease, suggested by previous studies to cause inflammation of the lungs and blood vessels, provoking clots and causing heart rhythm disturbances. Joel D. Schwartz, from the Harvard School of Public Health (Massachusetts, USA), and colleagues used satellite data to determine particle levels and temperatures in every zip code in New England. This allowed them to examine the effects of PM2.5 on locations far from monitoring stations, and to look at the effects of short-term exposures and annual average exposures simultaneously. They analyzed health data from everyone covered by Medicare in New England -- 2.4 million people -- between 2003 and 2008 and followed them each year until they died. Data analysis revealed that both short- and long-term PM2.5 exposure was significantly associated with higher death rates, even when restricted to zip codes and times with annual exposures below EPA standards. Short-term (two-day) exposure led to a 2.14% increase in mortality per 10 microgram per cubic meter increase in PM2.5 concentration, and long-term (one-year) exposure led to a 7.52% increase in mortality for each 10 microgram per cubic meter increase. Writing that: “we estimated significant acute and chronic effects of PM2.5 exposures below current EPA standards,” the lead investigator comments that: “there is no evidence of a safe threshold even at levels far below current standards.”