Central Park Sediment Cores Contradict Current Scientific Thinking
Examining sediment cores from New York's Central Park Lake dating back 100 years, a group of scientists conclude that incineration of solid waste, rather than leaded gasoline, has been the dominant source of atmospheric lead to the New York City metropolitan area, and possibly many other urban areas during the 20th century. The findings are in sharp contrast to current mainstream thinking in the scientific community and provide a new perspective on the environmental impact of burning solid waste, according to the researchers.
The study, reported in the Jan. 20 web edition of the scientific journal Environmental Science & Technology, published by the American Chemical Society, the world's largest scientific society, involved researchers from Columbia University, Rensselaer Polytechnic Institute and the New York State Department of Environmental Conservation. The article is scheduled to appear in the March 1 print issue of the journal.
Lead deposition rates to the atmosphere reached a peak "from the late 1930s to early 1960s, decades before maximum emissions from combustion of leaded gasoline," according to the article. This time frame corresponds to major incinerator construction and operation programs in the New York area, the article notes.
Even when the use of leaded gasoline was at its "period of maximum use" in the late 1960s to early 1970s, the sediments clearly indicate "that these additional inputs of lead contributed a relatively small fraction of the total lead deposits to the site," the article claims. Other potential lead-contributing activities, including coal burning, smelting and metal refining, also were found not to be likely dominant sources.
The finding brings into question the common assumption that declines in human blood lead levels and atmospheric lead levels in urban centers during the 1970s and 1980s were primarily due to the introduction of unleaded gasoline, says the study's lead author Steven Chillrud, Ph.D., of Columbia's Lamont-Doherty Earth Observatory in Palisades, N.Y.
"Solid waste combustion has been underestimated as a source of atmospheric lead and other contaminants," Chillrud says. "Furthermore," he adds, "current growth of incinerator use in urban centers in China and the common practice of residential garbage burning in Pakistan and many other developing nations make this work relevant to present day and future atmospheric contaminant fluxes and related human exposures."
The burning of municipal solid waste also "dominated the inputs of several other atmospheric metals, including zinc, tin, cadmium, antimony and possibly silver," Chillrud adds.
The researchers are now investigating the importance of solid waste incineration as a source of mercury, dioxins, PCBs (polycyclic biphenyls) and PAHs (polyaromatic hydrocarbons) to the New York City atmosphere.
The study was funded by the National Institute of Environmental Health Science's Superfund Basic Research Program and the Hudson River Foundation of New York City.
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