Melamine derivatives in indoor dust from China: Temporal trends and human exposure before and during COVID-19 pandemic.

Melamine-based compounds (MELs) are emerging indoor contaminants with potential health risks, yet their temporal variations and exposure implications remain poorly characterized. In this study, we analyzed MELs in 66 paired indoor dust samples from residential households in Tianjin, China, comparing pre- and during-COVID-19 periods. Four traditional MELs, i.e., MEL, ammeline, ammelide, and cyanuric acid (CYA), were detected in all samples, with total MEL concentrations (∑MELs) ranging from 61.2 to 5.83 × 104 ng/g (median: 6.73 ×103 ng/g). During the pandemic, ∑MEL concentrations increased 1.73-fold (8.25 ×103 vs. 4.76 ×103 ng/g, p < 0.01), with CYA emerging as the predominant compound (median: 2.82 ×103 ng/g), likely due to its extensive use in disinfectants (up to 0.4 % and 20 % in liquid and tablet formulations, respectively). Human exposure assessment revealed that infants had the highest estimated daily intakes (EDIs, 40.1-69.6 ng/kg bw/day), about an order of magnitude higher than adults (3.31-5.74 ng/kg bw/day), primarily through dust ingestion. Non-carcinogenic risks (HQs<1) and lifetime cancer risks (maximum median from teenagers: 7.98 ×10-8) remained within negligible limits. Monte Carlo simulations identified indoor dust concentration and body weight as key risk determinants. These findings underscore the environmental consequences of pandemic-driven disinfection practices and the urgent need for regulatory oversight of MEL-containing materials.