Researchers from the School of Public Health at the University of Texas Health Science Center (UTSPH) in Houston recently published a study in the journal Science of the Total Environment, that examined, for the first time, the impact of the fine particulate matter that is released throughout the city on the mortality rate among Houstonians. The study, entitled “Fine particulate matter components and mortality in Greater Houston: Did the risk reduce from 2000 to 2011?”, aimed to determine if this type of pollution was associated with changes in mortality over the ten-year period between 2001 and 2011.
The current definition of particulate matter, also known as particle pollution or PM, according to the U.S. Environmental Protection Agency is a complex mixture of extremely small particles and liquid droplets, made up of a number of components including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles. PMs that are 2.5 micrometers in diameter or smaller are known as fine particles. Fine particles, such as those found in smoke and haze, are most often attributed to sources like forest fires, or they can form when gases emitted from power plants, industries and automobiles react in the air.
In assessing the public health impact from the levels of fine particulate matter throughout Houston, senior study author Dr. Kai Zhang, Professor, Division of Epidemiology, Human Genetics and Environmental Sciences at UTSPH, and doctoral student Suyang Liu, analyzed both the city’s death records and 17 selected PM2.5 components from the U.S. Environmental Protection Agency’s Chemical Speciation Network over the 10 year period selected. Researchers used a special statistical model to compare the differences over time.
Their findings showed that there was a seasonal difference in death rates with the strongest association in mortality and level of fine particulate matter occurring in the winter months. Another important finding was the association between increased ammonium (0.881 μg/m3), nitrate (0.487 μg/m3), sulfate (2.245 μg/m3), and vanadium (0.004 μg/m3) levels with an increased risk in mortality.
In a University press release about the study’s findings, Dr. Zhang explained, “Particles this small could easily enter our bodies and cause health problems, especially for children, the elderly and those with respiratory and cardiovascular issues. Within PM2.5, some components are more harmful than others, but our understanding on health effects of each component is limited. Even when PM2.5 concentrations are generally below the national standard limit for short-term PM2.5 exposure, they are still likely to cause adverse health effects. Although this risk is not as high as other risk factors like smoke and hypertension, PM2.5 air pollution affects everyone, everywhere.”
“We think this association is the highest in winter because wind is blowing inland, outland and across long distances. This could lead to particles being blown in from regional sources. Air pollution regulations implemented in Houston since 2000 succeeded to some extent. Further control measures to reduce air pollution should not only focus on mass, but the specific sources of PM2.5 components that are most associated with mortality.” concluded Dr. Zhang.