 house dust is a repository for environmental pollutants that may accumulate indoors from both internal and external sources over long periods of time . 
 dust and tracked - in soil accumulate most efficiently in carpets , and the pollutants associated with dust and soil may present an exposure risk to infants and toddlers , who spend significant portions of their time in contact with or in close proximity to the floor and who engage in frequent mouthing activities . 
 the availability of carpet dust for exposure by transfer to the skin or by suspension into the air depends on particle size . in this study 
 , a large sample of residential house dust was obtained from a commercial cleaning service whose clients were homeowners residing in the raleigh - durham - chapel hill ( research triangle ) area of north carolina . 
 the composite dust was separated into seven size fractions ranging from < 4 to 500 microm in diameter , and each fraction was analyzed for 28 pesticides and 10 polycyclic aromatic hydrocarbons ( pahs ) . over 20% of the fractionated dust sample consisted of particles < 25 microm in diameter . 
 fourteen pesticides and all 10 of the target pahs were detected in one or more of the seven size - fractionated samples . 
 sample concentrations reported range from 0.02 to 22 microg / g ; the synthetic pyrethroids cis- and trans - permethrin were the most abundant pesticide residue . 
 the concentrations of nearly all of the target analytes increased gradually with decreasing particle size for the larger particles , then increased dramatically for the two smallest particle sizes ( 4 - 25 microm and < 4 microm).imagesfigure 1figure 2figure 3figure 4 
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