Occurrence and human exposure assessment of amine-based rubber additives in indoor environments

Previous studies have primarily focused on the environmental occurrence of amine-based rubber additives, whereas their non-dietary exposure pathways in residential settings remain poorly characterized. This study investigated residential exposure to amine-based rubber additives using indoor dust, polydimethylsiloxane (PDMS) passive air samplers, handwipes, and silicone wristbands collected from 109 residents in Shenzhen, China. Fifteen target compounds, including p -phenylenediamine derivatives (PPDs) and their quinone oxidation products (PPDQs), were analyzed. Indoor dust was the major reservoir, with a median total concentration of 489 ng/g, and was dominated by hexa(methoxymethyl)melamine (HMMM; 121 ng/g) and 1,3-diphenylguanidine (DPG; 91.7 ng/g). Handwipe samples were enriched with diphenylamine (DPhA; 2.13 ng for two hands) and 1,3-diphenylguanidine (DPG; 1.09 ng for two hands), while N-(1,3-dimethylbutyl)- N ′-phenyl- p- quinonediimine (6PPDQ) was more frequently detected than its precursor N-(1,3-dimethylbutyl)- N ′-phenyl- p -phenylenediamine (6PPD). Silicone wristbands, used as integrated personal samplers, mainly accumulated HMMM and DPhA, with median concentrations of 3.62 and 1.71 ng/g, respectively. A positive correlation between 6PPD and 6PPDQ in dust ( r = 0.48, p < 0.001) suggested common sources and/or oxidative transformation, while the significant dust–handwipe correlation of 6PPDQ indicated transfer from dust to hands. Exposure assessment showed that dust ingestion was the dominant pathway, with the median estimated daily intakes via this route of 0.275 and 1.64 ng/kg bw/day for adults and young children, respectively; the median total intake across all four assessed pathways was 0.366 ng/kg bw/day for adults. Although current exposure levels were below available toxicological reference values, uncertainties remain regarding long-term chronic exposure.