Measuring and evaluating contamination in homes using geochemical analysis: sources, pathways, and health risks

<p dir="ltr">Residents spend significant time at home, aggravating concerns about their exposure to contaminants and the associated health risks, highlighting the critical importance of addressing home contamination. This thesis delves into the intricate relationship between outdoor and indoor environments and their contamination pathways. This study enhances our understanding of home environment contamination and human exposure by employing a multi-approach that includes analytical methods, comprehensive probabilistic health risk assessment, analysis of trace metal sources, quantification of particle infiltration, and identification of indoor particulate matter sizes. Unravelling these connections and pathways is essential for taking informed actions and implementing effective measures to minimize exposure risks.</p><p dir="ltr">The utility of pXRF as a practical and cost-effective method for analysing dust wipes in the mining and smelting areas of Noumea, and Thio, New Caledonia and Tsumeb, Namibia was carried out in Chapter 2. A comparison of pXRF and ICP-MS dust wipes analysis (n = 87) revealed strong agreement, with Spearman Rho correlations (0.489 - 0.956, p < 0.01) and coefficients of variation (r²: 0.432 - 0.989). Additionally, equations derived from ICP-MS results corrected pXRF data, improving mean recovery from 75-303% to 92-110%.</p><p dir="ltr">Chapter 3 focused on studying polycyclic aromatic hydrocarbons and trace metal levels, including chromium (Cr), nickel (Ni), copper (Cu), lead (Pb), and zinc (Zn), their sources, and health risks in homes across the industrialised Illawarra region and Australia. Elevated concentrations of these trace metals were found in home garden soils and indoor dust near industrial areas, showing how outdoor industrial contamination affects indoor trace metal levels. Associations between arsenic (As), lead (Pb), and zinc (Zn) concentrations in indoor dust and home age were noted in Illawarra homes, highlighting the combined effects of aging homes and outdoor industrial activities on trace metal levels, often surpassing outdoor levels. Low polycyclic aromatic hydrocarbons (PAHs) were found in 7 of 23 homes, remaining below carcinogenic thresholds. Using Monte Carlo probabilistic human health risk assessment, higher non-carcinogenic and carcinogenic risks among children than adults were revealed when exposed to indoor dust and garden soils in the Illawarra region and Australian homes (p<0.01).</p><p dir="ltr">Chapter 4 explored the pathways of trace metals from road dust and garden soils into indoor dust within homes. Higher Cu concentrations in road dust than in garden soils indicated an interaction between these environmental mediums. Similarly, correlations between garden soils and indoor dust for As and Zn showed their migration and interaction, with indoor dust having significantly higher concentrations of these trace metals. Conversely, Pb showed persistence and correlation between road dust, garden soils, and indoor dust, confirming its presence and resuspension across outdoor and indoor environments in Greater Sydney. Furthermore, a detailed analysis of individual dust particles using Scanning Electron Microscope (SEM) was used to estimate the proportion of indoor dust particles originating from outdoor sources. The study revealed that tracked-in outdoor particles represented an average of 57% of the total particle number in indoor dust samples.</p><p dir="ltr">Chapter 5 measured and evaluated particle size distribution, morphometry, and morphology in indoor dust, drawing from observations on migration patterns, heightened levels of trace metals indoors than outdoors (p < 0.05), and the fine texture of indoor dust (Chapter 3 and 4).</p><p dir="ltr">Analysis revealed that particles <250 μm comprised 45% of the bulk, with particles smaller than 20 μm making up 9% of the sample. PM2.5 (particles < 2.5 μm) constituted a substantial portion (76%) of suspended indoor 'settled dust' smaller than 20 μm from homes in Australia, Canada, China, Ghana, and Mexico, characterised by notably high circularity. These fine particles pose inhalation risks due to their size and shape, potentially penetrating deeply into the respiratory system.</p><p dir="ltr">Particles < 20 μm showed higher concentrations of arsenic (As), chromium (Cr), and nickel (Ni) compared to < 250 μm particles, raising concerns about potential health effects from inhalation or ingestion. On the other hand, consistent concentrations of lead (Pb) across particle sizes indicate potential health risks regardless of size or exposure route, particularly in Australian homes where mean Pb concentrations exceeded those in other homes studied. Furthermore, particles smaller than or equal to 2.5 μm corresponding to cerussite, a 'white' lead paint manufacturing component, were identified as capable of reaching deep into the alveolar region of the lungs. Cerussite's solubility under acidic conditions found in the alveolar region suggests potential health risks upon inhalation or ingestion.</p><p dir="ltr">By uncovering the link between outdoor and indoor contamination and potential health risks across its chapters, the findings in this thesis contributes invaluable insights to the existing literature on home environments and holds significant implications for policy development highlighting the urgency of addressing home contamination as a crucial step in safeguarding human health.</p>