Toxic metals mix it up in California air

UC DAVIS (US) — Very fine and ultrafine metal particles in the air are able to penetrate deep into the lungs and cardiovascular system, damaging arteries and the heart itself.

Published in the journal Aerosol Science and Technology, three studies focusing on aerosols and health note that risk-assessment of these particles is difficult because standard air samples don’t separate out the dangerous particles. Furthermore, there are few statistics available on the composition of the particles in the surrounding atmosphere.

“These studies yielded unique epidemiological data supporting a growing body of evidence from laboratory and medical studies, which strongly suggests that very fine and ultra-fine metal particles are damaging to human health,” says Thomas Cahill, professor emeritus of physics and atmospheric sciences at University of California, Davis.

In the three papers, Cahill and colleagues investigate the role that very fine and ultra-fine metal particles play in contributing to heart attacks, the reduction in heart attacks when ultra-fine particles were removed from the air in California’s San Joaquin Valley, and the increase in estimated cancer rates downwind of a rail yard in the northern California town of Roseville.

Metallic particles in the Central Valley

For the first study, researchers took air samples at five sites in California’s Central Valley, from Redding south to Bakersfield, and analyzed 42 elements, including very fine metals in eight size ranges, as well as integrated organic species. The samples were taken every three hours during a 17-day period in January 2009, when weather conditions caused valley air to stagnate.

The Central Valley runs the length of inland California from the Sacramento Valley in the north to the San Joaquin Valley in the south.

Researchers found a correlation between the levels of the particles in the air and the death rates due to ischemic heart disease, with the highest rates for both occurring in the southern San Joaquin Valley near Bakersfield. Ischemic heart disease is characterized by a reduction in blood supply, often due to the clogging of the arteries.

An analysis of local meteorology in that area revealed a nighttime flow of air off of nearby Interstate 5 and Highway 58, both steep stretches of road that require heavy breaking by large trucks traveling down into the valley, suggesting that fine and ultra-fine particles likely come from brake pads, brake drums, and metal additives in lubricating oils of trucks and cars passing through the valley.

The findings may also offer clues as to why children who grow up near freeways are more likely to suffer loss of lung function.

Heart attack decline

In the second study, researchers examined patterns in the atmospheric levels of very fine and ultra-fine aerosol particles of vanadium and nickel in the southern San Joaquin Valley.

Levels of these metal aerosols, as well as ammonium nitrate and sulfate, have historically been much higher in the southern end of the San Joaquin Valley than in the northern end, due to the burning of crude oil to generate steam used to recover heavy petroleum from oil wells in the area.

Furthermore, the southern San Joaquin Valley also historically has death rates due to strokes and ischemic heart disease that were roughly 60 percent greater than the rest of the Central Valley.

In 1990, new technologies were developed that made it possible to use natural gas, rather than crude oil, to fuel the petroleum extraction efforts.

Cahill and colleagues measured the ultra-fine vanadium and nickel aerosol particles in 2009 and compared those levels to pre-1990 levels, when crude oil was still being used for petroleum recovery. A sharp decrease in ischemic heart disease was seen in 2007 in the southern San Joaquin Valley that was mirrored by a dramatic decline in the levels of vanadium and nickel aerosols.

Those data support a growing body of evidence from laboratory and epidemiological studies, which suggest that the vanadium and nickel aerosols may play a role in causing ischemic heart disease.

The findings suggest that the rate of ischemic heart disease observed in communities downwind from the Port of Los Angeles in 2008 may be related to effluent from ocean-going ships that burn crude or residual oil.

Downwind from rail yard

In the third study, Cahill and colleagues monitored inorganic and organic aerosols downwind from the Roseville Rail Yard, northeast of Sacramento, in order to develop a profile of emissions from rail yard activities.

The rail yard is one of the largest such maintenance and service sites in the western United States, with more than 31,000 locomotives visiting annually.

Most of the aerosols monitored at the site are associated with exhaust from trains’ diesel-fueled engines. Most of the particles, especially the known carcinogen benzol[a]pyrene, are in the very fine and ultra-fine size-range, increasing the chances that they would be caught up in people’s lungs. Coarse-soil aerosols contaminated with metals and petroleum-derived particles were also present.

Findings identified very fine transition metals and contaminated soils that are potentially important to human health, and confirmed estimates of the health impacts of diesel exhaust downwind of the rail yard that were made earlier by the California Air Resources Board.

Funding was provided by the Sacramento Resources Legacy Fund, the Sacramento Metropolitan Air Quality Management District, the Yolo-Solano Air Quality Management District, and Breathe California of Sacramento-Emigrant Trails.

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