The Science of House Dust



Let’s venture into the science of house dust so that, at the very least, we will make the act of dusting seem far less prosaic. Since 40 000 tons of space dust falls on our planet’s surface, some of it makes up the dust in our homes along with Earth’s own stony fragments and soil minerals. The powdery residue on forgotten books and collectibles, along with the dust bunnies hiding under the bed, also contain a heterogeneous assortment of construction materials, synthetic fibers, skin flakes, hair, insect and plant debris, dust mites, fungi, bacteria and fragments of household items.

The bacteria and fungi are present because of dust’s organic matter. The type of fungi in dust is largely determined by where one lives. In contrast, the variety of bacteria depends on who lives inside the house of dust.  Nondiphtheiroid Corynebacterium prefer the skin of men over that of women, so the amount of that bacteria reflects the ratio of men to women in a home.

Households with more men have dust with higher concentrations of Corynebacterium bacteria.
Lactobacillus sp 01.png
Lactobacillus, mostly from vaginal walls, is found in higher concentrations in dust from households that have more women.

Thanks to their saliva and feces, pets in the home also influence what bacterial species thrive in the dust. We are all too aware of a city’s compromised variety of animals. Similarly, microorganisms in dust from urban areas shows less biodiversity than those from rural environments. Of interest to housekeepers is that bacteria can make cleaning more difficult, especially after weeks or months of neglect. With time, bacteria in dust secrete sticky exopolymers, causing the dust to stick to the surface. Exopolymers are part of the biofilm that help bacteria survive by anchoring them, and the thicker the film becomes, the more difficult it is to scrub off.  Humidity and evaporation in the home also lead to cycles of expansion, contraction and crystallization. These processes help dust particles penetrate into imperfections of wood and other receptacles.

Fungi in dust can concentrate metals. The metallic elements can originate from outdoor minerals, or from within the home itself. Paint, for example, especially if old layers from less regulated eras are exposed during renovations, can make significant contributions. One study of 50 residences located in 10 neighborhoods across the city of Ottawa, Canada revealed that the multi-element profiles of indoor dust differs from dust of surrounding streets and yards. For example home dust had an average of 222  ppm of lead versus 33 and 34 ppm for street and soil dust, respectively.  The contents of vacuum cleaner bags had 1.6 ppm of mercury versus 0.018  and 0.048 ppm in street and soil dust. There was 4 ppm of arsenic in house dust versus an average of 1.7 ppm for outdoor sources.

Tris(2,3-dibromopropyl) phosphate.svg
tris(2,3-dibromopropyl) phosphate

In general, dust receives a variety of compounds from consumer goods brought into homes. These substances come from multiple classes of chemicals: phthalates which occur in the highest concentrations, followed by phenols, resorcinol-formaldehyde resins , fragrances, and polyfluoroalkyl substances (PFAS). In the dust of 75% of the homes in California, there was TDBPP (tris(2,3-dibromopropyl) phosphate), a compound once widely used as a flame retardant in plastics and textiles. The use of this group 2A carcinogen was banned from children’s sleepwear in 1977.

di-isononyl phthalate. Compared to that of  adults, children’s urine has a concentration that is 5 times higher.

Critics of such studies invariably point out that many compounds are detected only because of extremely sensitive instrumentation which picks up concentrations of 1 to 100 parts per billion, the upper range being that of the phtalates. They also point out that even though di-isononyl phthalate can lead to male genital birth defects, the effect is very concentration-dependent. What the non-precautionary attitude overlooks is that the phtalates are only one small part of the environmental soup. In addition to dealing with natural plant secondary metabolites and geological minerals (some of which we have evolved protective defenses against), our bodies must now cope with a host of other compounds from work and home environments, from air, food, pharmaceuticals, drinks and water. We can’t look at each contaminant in isolation and comfort ourselves with the small concentration each one contributes. Nor can we forget that all of the compounds have appeared in under 20 seconds relative to the total time of mammalian evolution. It is more sensible to be concerned about the likely significant sum of seemingly small effects. It is advisable to stop synthesizing the more pernicious compounds entirely and to reduce exposure to the other necessary evils.

Meanwhile let’s make an effort to keep the chemistry in our homes simpler and to dust frequently.


From the abstract of an interesting investigation into the relationship between compounds lie triclosan (an antibacterial compound added to cleaning products) and antibiotic resistance in house dust-bacteria

The ubiquitous use of antimicrobial chemicals may have undesired consequences, particularly on microbes in buildings. This study shows that the taxonomy and function of microbes in indoor dust are strongly associated with antimicrobial chemicals—more so than any other feature of the buildings. Moreover, we identified links between antimicrobial chemical concentrations in dust and culturable bacteria that are cross-resistant to three clinically relevant antibiotics. These findings suggest that humans may be influencing the microbial species and genes that are found indoors through the addition and removal of particular antimicrobial chemicals.




Poisonous Neighborhoods of the Periodic Table

Painting by author, but castle-outline is from the cover of a forgotten book.

In describing the periodic table’s regions of related elements in Periodic Kingdoms,  P.W. Atkins drops the dry tone of textbooks and reaches for a little imagery.

The kingdom is not an amorphous jumble of regions, but a closely organized state in which the character of one region is close to that of its neighbour. There are few sharp boundaries. Rather the landscape is largely characterized by transitions: savannah blends into gentle valleys which deepen into almost fathomless gorges.

But as imaginative as he gets, the regions are the same ones we normally encounter. It would have been preferable if he had discussed the realm of gold, mercury, thallium and lead whose unique color, liquid state, poisonous nature and role in car batteries, respectively, can only be explained with relativistic effects. (In lead, the effect is explained here.)

Today I noticed some regions that are rarely, if ever, mentioned elsewhere—the periodic table’s poisonous neighborhoods. In the graphic below, I included either poisonous compounds or the ions responsible for the toxic nature of the substance. If the element does not appear by itself, as in the case of elemental sulfur, then it is not poisonous. Thallium is another example. The neutral version of the element is not found naturally. If synthesized artificially, the neutral form quickly reacts to form its poisonous version. The list is not meant to be exhaustive, but I tried to stick to the nastiest examples.

graphic created by author

Ingestion of aqueous HCl or hydrochloric acid is rare. But there is a detailed documented case of a 61 year old woman who in  a suicide attempt drank 200 ml of a 30-33% solution. By the time she had reached the hospital, the acid had killed tissue from the mouth to the base of her stomach, and ten hours later, she died of multi-organ failure. The gaseous form of HCl is also highly poisonous. A half hour exposure  to only 500 mg per liter of air (ppm) is fatal.

Much smaller concentrations of the related hydrogen fluoride gas can irritate the eyes, nose, and respiratory tract. A concentration of as little as 50 ppm will be fatal as it will cause the heart to beat erratically and fluid to accumulate in the lungs.

The protection we have against hydrogen sulfide poisoning is that our noses are extremely sensitive to its rotten egg stench. Most people can detect only 0.00047 ppm, a level that is 850 000 smaller than the approximately 400 ppm lethal level. H2S kills like cyanide by taking oxygen’s place and binding to iron cytochromes of the mitochondria.

Phosphine, PH3, smells like a blend of garlic on top of decaying fish. In 2010 in Utah, a freak accident  involving phosphine killed two children. Aluminum phosphide (AlP) was applied too close to the house by a pest control company. The phosphine gas formed by the reaction between the compound and water and what was intended for rodents seeped through a crack in the foundation and found its way into the home. It also killed two French-Canadian tourists in Thailand in 2010, and they were not the only victims. Phosphine poisonings are not uncommon in Southeast Asia.


One of the most bizarre cases of arsenic poisoning may have occurred in 2007 in Peru where the Carancas meteorite possibly produced arsenic-containing gases such as arsine, AsH3. It could have been formed when the meteorite’s hot surface met an underground water supply tainted with arsenic ions. More than 600 villagers presumably became ill. But the reports may have been exaggerated, and the gases emanating from the groundwater may have been sulfurous in nature and not arsine.

In 2010, in Zamfara, Nigeria, as many as 400 children died from lead poisoning. The villagers had ignored the dying of ducks a year earlier. For Pb (lead), ducks are sentinels like canaries in a coal mine. In this case, a nearby gold mine was the source of the lead contamination. Lead poisons by interfering with gene-regulating proteins, molecules that turn on and shut off the expression of DNA. The metal achieves this by displacing other metals from the protein complexes.


Prussian blue is the antidote to thallium poisoning, which was carried out routinely by Saddam Hussein. In a cruel case after Hussein’s death, still in Iraq, someone  with an axe to grind placed the tasteless, odorless poison in a large cake. Two children were killed. Thirty others were saved but suffered hair loss and dermatitis, two classic symptoms of the poisoning.

Mercury is another problem associated with gold extraction and Hg-contamination has become an issue in places like Segovia, Columbia. All forms of the metal wreck cellular function by changing the 3D (tertiary and quaternary) structure of proteins and by binding with sulfhydryl and selenohydryl groups.

Finally, cadmium poisoning or the itai-itai disease(translates to “it hurts- it hurts”) softens the bones and causes kidney failure. Cadmium is known to increase oxidative stress by being a catalyst in the formation of reactive oxygen species. In 2010, 12 million Shrek glasses sold by McDonald’s were recalled due to contamination by cadmium. There was not enough of the metal to cause poisoning, but the glasses were recalled because long term exposure to small amounts of cadmium can lead to cancer.

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