Think about how much time you spend indoors… In general, people spend over 70% of their time inside (Health Canada, 1989). With all that time spent inside, think about all the dust you’re inevitably breathing in…It’s a lot! Dust is something we can’t evade when indoors. Unfortunately, it’s a repository for contaminants, mainly semi-volatile organic compounds such as pesticides, and particle bound matter which can include heavy metals (Butte & Heinzow, 2002; Charlesworth et al., 2011). Constant exposure to these kinds of contaminants, and just dust in general, can lead to a lot of adverse health effects, such as respiratory disease, heart disease and metal exposure which provides a host of other health risks (e.g. Health Canada, 1989; Yoshinaga et al., 2014; Hogervorst et al., 2007). House dust can even contain carcinogenic substances (Maertens et al., 2004). Children are especially at risk since they have a more frequent opportunity to ingest dust as a result of crawling on the ground or placing dusty objects in their mouth (Lewis et al., 1994; Maertens et al., 2008).
Settled house dust is derived from a variety of things, this includes materials from humans (hair, skin flakes, textile fibers), or materials that are brought inside from the outdoor environment (soil and road dust). About 20-30% of house dust originates from outdoor soil (Rutz et al., 1997). Studying dust, also referred to as particulate matter, provides insight on contaminant exposure and contaminant source. Depending on where it’s from, it will have different health implications. It’s important for us to know where it originates from so that health assessments can incorporate this knowledge and be improved.
In the second year of my Bachelor of Science degree, I had the opportunity to work with the late Dr. Jack Cornett on a research project about dust in Vancouver homes and their adjacent roads and soil. My project was linked to a wider study on dust that also looked at homes in Winnipeg and Ottawa, in addition to Vancouver. We wanted to know how much of the house dust was composed of road dust and soil. In order to trace the sources, we measured radionuclides in the samples.
You might be wondering, what on Earth are radionuclides?? Well, they are unstable chemical elements. Everything around us is made of chemical elements, also known as atoms, such as the proteins in our body, the glass in our windows, etc. Each of these atoms have protons, electrons, and neutrons, in other words: positive, negative, and neutral components. When there is an uneven number of protons and neutrons, the atom is considered unstable, which makes it radioactive. So, in order to become stable, it emits a lot of energy in the form of gamma rays, which are small energy waves that are more energetic than UV rays or X-rays. (e.g. Gilmore, 2008). To simplify this, think of a kid that’s had a lot of sugar, so they run around to get rid of the excess energy. Radioactive decay is the term used for the process of releasing energy.
These radionuclides may sound dangerous, and they are in high concentrations, but in fact they’re all around us. Certain materials will have certain kinds of these radionuclides, therefore by measuring them, we can trace where certain materials come from.
In the research project I was involved in, we measured radionuclides in the different samples of dust (house, road, soil) to figure out the different compositions of house dust. Source materials can be traced using radionuclides. For example, Uranium(U-238), Thallium (Th-232), and Radium (Ra-226) are most often associated with outdoor soil, whereas Cesium (Cs-137), and Beryllium (Be-7) are associated with outdoor fine-grained aerosol particles, such as road dust.
Since these radionuclides are indicative of certain materials, we can analyze samples using gamma spectrometry in order to determine which radionuclides are in a sample and how much. That will tell us what portion of that house dust comes from outdoor soil, outdoor road dust, or from inside the home.
For this project, I got to work at the University of Ottawa’s Advanced Research Complex, in the AE Lalonde AMS Laboratory. It was a stunning research building with various sophisticated new labs. It was really cool, especially since it was my first time working in a “real” lab. I remember I was super nervous to meet with my supervisor, Dr. Jack Cornett. It was my first time working closely with a professor and I didn’t want him to think I wasn’t worthy of the position. Of course, it turns out I had nothing to worry about, he was kind and very helpful, all the attributes of a great teacher and mentor.
In order to find out which radionuclides my samples contain, we needed to measure the gamma rays with a gamma spectrometer. The way it works is: the sample is placed into the gamma spectrometer, the gamma rays emitted by the radionuclides in the sample are detected by a germanium crystal inside the machine where it then turns that energy into something that can be recorded on the computer. The different energy levels that are recorded, shown as peaks on the computer, tell us which radionuclides are present and how much of them are present.
After measurements were taken, I did some calculations and then prepared and presented a research poster of my work at the University’s annual poster symposium. It was my first time making a poster, so it’s not great, but I guess everyone has to start somewhere!
The main radionuclides found in our analyses, were: Cesium (Cs-137), Radium (Ra-226), Potassium (K-40), and Lead (Pb-210). Cesium was being brought indoors via soil dust, Radium and Potassium via soil and road dust, and Lead via road dust. Further calculations would have needed to be done to determine the proportions of soil and road dust in the house dust samples, but since my role in the project was minor, I didn’t proceed any further.
As harmless as dust may seem, it contains a conglomerate of things that can cause adverse health effects. With the amount of time we generally spend indoors, it’s important to keep your indoor environment clean. For me, this research experience was eye-opening and was my first time doing something significant. If there are any students reading this, I advise you to get out of your comfort zone and try new things, especially if it’s career related. Getting outside of student teaching labs and being in a real lab surrounded by professionals is definitely daunting, but the sooner you get exposed to it, the sooner you’ll feel comfortable in that environment and be inspired. I was so nervous when I initially emailed to ask whether I could do this project with my supervisor, but I did it anyways and since then, the experience has fostered many other great opportunities!
References
Butte & Heinzow. 2002. Pollutants in house dust as indicators of indoor contamination. Reviews of Environmental Contamination and Toxicology, 175: 1-46. https://pubmed.ncbi.nlm.nih.gov/12206053/
Charlesworth et al. 2011.A review of the distribution of particulate trace elements in urban terrestrial environments and its application to considerations of risk. Environnmental Geochemistry and Health, 33: 103-123. https://link.springer.com/article/10.1007/s10653-010-9325-7?null
Gilmore, Gordon. 2008. Practical Gamma-ray Spectrometry, 2nd Edition. John Wiley & Sons Ltd. West Sussex, England. https://onlinelibrary.wiley.com/doi/book/10.1002/9780470861981
Health Canada. 1989. Exposure Guidelines for Residential Indoor Air Quality: A Report of the Federal-Provincial Advisory Committee on Environmental and Occupational Health. Health Canada: Ottawa, Canada. https://www.toalltech.com/wp-content/themes/alltech/images/air_quality.pdf
Hogervorst et al. 2007. House dust as possible route of environmental exposure to cadmium and lead in the adult general population. Environmental Research, 103(1): 30-37. https://www.sciencedirect.com/science/article/pii/S0013935106001289?casa_token=qqrCSejF82kAAAAA:sHFU-Pwx-ni0xXcOnr9gchtoRTM4Y_mJJPMtf5PtMxCa9ThatotFUmiVsEjZuZq3sRwhSzUnZMex
Lewis et al. 1994. Evaluation of methods for monitoring the potential exposure of small children to pesticides in the residential environment. Archives of Environmental Contamination and Toxicology, 26: 37-46. https://link.springer.com/article/10.1007/BF00212792
Maertens et al. 2004. The mutagenic hazards of settled house dust: a review. Reviews in Mutation Research, 567(2-3): 401-425. https://www.sciencedirect.com/science/article/pii/S1383574204000614?casa_token=b39gSPU8T78AAAAA:bG1yELwGM2x0ErKuup5Wtp9-iG3h4M2Uf5azd8AHuVGqE-j9qL68BNnLvJlD0LNolVeeMjauD-1w
Maertens et al. 2008. Mutagenic and Carcinogenic Hazards of Settled House Dust I: Polycyclic Aromatic Hydrocarbon Content and Excess Lifetime Cancer Risk from Preschool Exposure. Environmental Science & Technology, 42(5): 1747-1753. https://pubs.acs.org/doi/10.1021/es702449c
Rutz et al. 1997. Pilot study to determine levels of contamination in indoor dust resulting from contamination of soils. Journal of Soil Contamination, 6(5): 525-536. https://www.tandfonline.com/doi/abs/10.1080/15320389709383584
Yoshinaga et al. 2014. Lead and other elements in house dust of Japanese residences – Source of lead and health risks due to metal exposure. Environmental Pollution, 189: 223-228. https://www.sciencedirect.com/science/article/pii/S0269749114000943?casa_token=x6YPE5_jX1QAAAAA:QJLv-xvYdSSo7JByEVZA3L_QLbG091xarx_wbsMXHKxhc3sMeIRpcgplr3Gc44cv17NB9NO4j34o