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Shigella
There are more than 30 types of Shigella.
USDA
By David W. Layton, Paloma I. Beamer
Most indoor household dust that collects on furniture and floors actually comes from outdoors, a new study finds.
Where does it come from? Scientists in Arizona are reporting a surprising answer to that question, which has puzzled and perplexed generations of men and women confronted with layers of dust on furniture and floors. Most of indoor dust comes from outdoors. Their report was published in the Nov. 1, 2009 issue of ACS' Environmental Science & Technology, a semi-monthly journal.
In the study, David Layton and Paloma Beamer point out that household dust consists of a potpourri that includes dead skin shed by people, fibers from carpets and upholstered furniture, and tracked-in soil and airborne particles blown in from outdoors. It can include lead, arsenic and other potentially harmful substances that migrate indoors from outside air and soil. That can be a special concern for children, who consume those substances by putting dust-contaminated toys and other objects into their mouths.
The scientists describe development and use on homes in the Midwest of a computer model that can track distribution of contaminated soil and airborne particulates into residences from outdoors. They found that over 60 percent of house dust originates outdoors. They estimated that nearly 60 percent of the arsenic in floor dust could come from arsenic in the surrounding air, with the remainder derived from tracked-in soil. The researchers point out the model could be used to evaluate methods for reducing contaminants in dust and associated human exposures.
Abstract
Migration of Contaminated Soil and Airborne Particulates to Indoor Dust
We have developed a modeling and measurement framework for assessing transport of contaminated soils and airborne particulates into a residence, their subsequent distribution indoors via resuspension and deposition processes, and removal by cleaning and building exhalation of suspended particles. The model explicitly accounts for the formation of house dust as a mixture of organic matter (OM) such as shed skin cells and organic fibers, soil tracked-in on footwear, and particulate matter (PM) derived from the infiltration of outdoor air. We derived formulas for use with measurements of inorganic contaminants, crustal tracers, OM, and PM to quantify selected transport parameters. Application of the model to residences in the U.S. Midwest indicates that arsenic (As) in ambient air can account for nearly 60% of the As input to floor dust, with soil track-in representing the remainder. Historic data on lead (Pb) contamination in Sacramento, CA, were used to reconstruct sources of Pb in indoor dust, showing that airborne Pb was likely the dominant source in the early 1980s. However, as airborne Pb levels declined due to the phase-out of leaded gasoline, soil resuspension and track-in eventually became the primary sources of Pb in house dust.
Full article: http://pubs.acs.org/stoken/presspac/presspac/full/10.1021/es9003735
Authors: David W. Layton and Paloma I. Beamer*
Community, Environment and Policy Division, Mel and Enid Zuckerman College of Public Health, University of Arizona Tucson, Arizona
Environ. Sci. Technol., 2009, 43 (21), pp 8199–8205
Copyright © 2009 American Chemical Society
*Corresponding author e-mail: pbeamer@email.arizona.edu; phone: (520) 626-0006; fax: (520) 626-8009; mailing address: 1295 N. Martin Ave, P.O. Box 245210, Tucson, AZ 85724.
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