Seasonal variation and human health risk assessment of heavy metals in settled indoor dust from an informal e-waste recycling community in Thailand

This study investigated seasonal variation, screening ecological indices, and potential human health risks associated with lead (Pb), chromium (Cr), and cadmium (Cd) in settled residential indoor dust from an informal e-waste recycling community in northeastern Thailand. A total of 96 dust samples were collected from living rooms (n = 48) and bedrooms (n = 48) of 16 houses during the cool, dry, and wet seasons. Metal concentrations were quantified using inductively coupled plasma optical emission spectrometry. Relative metal enrichment and integrated screening indices were evaluated using the geoaccumulation index (Igeo) and Hakanson's ecological risk index (RI), respectively, while potential non-carcinogenic and carcinogenic risks were estimated following the United States Environmental Protection Agency framework. Median concentrations of Pb, Cr, and Cd across all seasons were 114, 37, and 0.64 mg/kg, respectively. Linear mixed-effects models accounting for repeated household measurements demonstrated significant seasonal effects for all three metals, with concentrations generally higher during the cool and dry seasons than during the wet season. Compared with non-e-waste-contaminated residential reference data from Thailand, the investigated households had higher median concentrations of all three metals, although these comparisons do not establish a specific contamination source. Screening Igeo and RI indicated substantial relative enrichment, with Cd contributing most to the calculated indices; however, these soil- and sediment-derived metrics were used only for comparative screening and do not represent direct ecological effects. Children generally had higher dust-ingestion exposure and associated risk estimates than adults. The highest Pb-related hazard quotient and hazard index values were both 1.4 under the 95th percentile exposure scenario among children during the cool and dry seasons, indicating potential non-carcinogenic concern under higher-end exposure conditions. Cr(VI)-related risks were estimated assuming that 25% of measured total Cr was Cr(VI). The highest total carcinogenic risk was 1.5 × 10-5 for children during the dry season under the 95th percentile scenario. This value falls within the commonly used US EPA risk-management range of 1.0 × 10-6 to < 1.0 × 10-4 and should not be interpreted as evidence of safety or acceptability. Overall, the findings indicate elevated metal concentrations in residential indoor dust and potential Pb-related non-carcinogenic concern among highly exposed children. Further studies incorporating direct Cr speciation measurements and concurrent environmental and biomonitoring assessments are warranted.