Chemicals in homes and gardens: understanding sources, exposure and risk

Chemicals are ubiquitous in our homes and gardens. However, the properties that make some chemicals favourable, like medicinal benefits or water repellence, can also make them harmful to human health. This study examined over 100 chemicals in indoor dust, vegetable patch soil and backyard soil (132 samples), and over 900 additional chemicals in a subset of indoor dust samples (6 samples), to explore chemical presence and risk to human health in residential settings. Trace metals, per and poly-fluoroalkyl substances (PFAS) and polycyclic aromatic hydrocarbons (PAHs) were frequently present in dust, while pesticides were infrequently detected. For PFAS, soil primarily contained carboxylic acids (PFCAs) and sulfonic acids (PFSAs), while dust contained a range of PFAS precursors. Anomalously elevated total recoverable hydrocarbons (TRH) in dust were found to be from natural human oils, rather than crude oil that health-based guidelines are protective of. Presence of pharmaceuticals and personal care products (PPCPs) and their metabolites suggests indoor dust is a reservoir of both chemical presence, and past human exposure. Flooring (e.g., carpets), soil concentrations, and traffic density had the greatest influence on chemical presence in dust. Health risk screening found that the ingestion of 99.5% (183/184) of chemicals in dust assessed was below the Threshold of Toxicological Concern (TTC). The exception was lead (Pb), which was only above the TTC in one home, shown to be impacted by legacy Pb paint contamination. From the broad analysis undertaken, we suggest that future work prioritise reducing exposure to key risk drivers, like Pb in urban environments, while continuing to monitor PFAS as knowledge of toxicity evolves. We further recommend ongoing exploration of the utility of tools like the TTC to improve risk assessment efficiency for environmental exposures.