Factors associated with metal constituents in indoor particulate matter in different communities in South Africa

Metal constituents in indoor particulate matter (PM) emitted by household materials and indoor activities present an environmental challenge globally. This study investigated the variation of metal constituent concentrations in indoor PM collected from different communities and the association of metals with household characteristics and indoor occupant activities. PM_2.5 and PM₁₀ samples collected on Teflon filters during the field studies in the south and north Durban and Highveld region of South Africa were analysed for metal constituents by digesting in nitric acid and hydrochloric acid solution (aqua regia). These samples were analysed for metals using inductively coupled plasma-optical emission spectrometry (ICP-OES). Standardised interviews and structured household walkthrough assessments that were conducted provided additional covariates. Multivariate linear regression models were developed using factors from the factor analysis, and variables identified in the bivariate analysis. The decreasing order of metal content in PM_2.5 was as follows: Fe > Cr > Cu > Mn > Al > Hg > Zn > As > Cd > Pb, whereas in PM₁₀ the metal content had the following decreasing order: Fe > Al > As > Cu > Cr > Hg > Zn > Cd > Mn > Pb. Metal concentrations (Cd, Fe, Mn, and Pb) in PM_2.5 varied significantly in different geographical locations. Household characteristics including higher household age, presence of a ceiling, and cemented floor type were significantly associated with increased Cr, Fe, and Hg in indoor PM_2.5, respectively (p < 0.05). The association of metallic components in indoor PM with household characteristics provides an opportunity to raise issues of deteriorated old households to local authorities and policymakers who need to implement strategies to replace old building materials releasing metal-rich particles.