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Stumper #49.






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Mite-y Dust

Where does our house dust come from and what is it made of? Well, it comes from everywhere! Dust particles are blown about by the wind, even carried from country to country all over the world. The soil in Bermuda, for example, contains dust from Africa. Also, it may surprise you to know that thousands of tons of space dust fall on Earth every year, and some of it eventually makes its way into our houses. So, one exotic component of dust &ndash mixed in with cloth fibers, dust mite droppings, pollen, human and pet dead skin flakes, mold spores, insect parts, plant debris, chemical pollutants, and bacteria &ndash is millions-of-years-old extraterrestrial detritus.

Science researchers as well as forensic experts study the microscopic stuff of dust found in our homes, at crime scenes and on victims. In one research project when particle detectors were placed in a house and the researchers folded clothes, dusted, made beds, vacuumed and did other everyday activities they found that dusting stirred up significant amounts of particles, but more dust resulted from two people just walking around and sitting on furniture. It seems that each of us walks around constantly enveloped in our personal dust cloud, dispersing it as we move and picking up more along the way. One study estimates that about two-thirds of house dust is tracked in from outdoors.

Bacteria lurking in household dust produce chemicals called endotoxins, which are now thought to trigger asthma-related wheezing and other allergy symptoms as does the protein in dust mite droppings. The obvious response to this and other information about the health problems caused by dust might be to try to eliminate it from the household environment &ndash but this may not be the right thing to do. There is evidence that limited exposure to such irritants is actually advantageous. Early exposure to bacteria and allergens can develop a child's immune system while children growing up in a 'cleaner' environment tend not to develop such vigorous protection. So, simply reducing dust and the numbers of the tiny, eight-legged, dust mites is probably best. Dealing with more noxious chemical pollutants in dust is another matter however.

Stumper Questions:
1. To what does the phrase, 'take-home exposure pathway' refer?
2. Are dust mites insects?
3. If we estimate that a single, tiny, dust mite takes up an area of 0.12 sq. mm, about how many do you think might fit packed closely together in a single layer on the flat, circular head of a pin that is 2 mm across: 25, 75, or 125?

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