Time dependence of characteristic parameter for semi-volatile organic compounds (SVOCs) emitted from indoor materials

- Significant decrease of y0 of TCPP in polyurethane foam over three months.
- Much lower decrease of y0 of DEHP in PVC materials.
- y0 decrease rate is positively related to SVOC vapor pressure.
- Discussions about potential reasons for y0 decrease are presented.

Semi-volatile organic compounds (SVOCs) are widely used in various indoor materials and their adverse health effects have been increasingly recognized. The gas-phase SVOC concentration in equilibrium with the source material (y0), as a characteristic parameter for SVOC sources, is mostly assumed to be constant in previous studies. However, decreases in y0 with time have been observed in some studies. As a first step to reveal the mechanism behind the phenomenon, this study quantitatively investigated the variation of y0 over time under two conditions: natural exposure to outdoor ambient (Case 1), and storage in a controlled ventilated chamber (Case 2). Three phthalates (Di-iso-butyl Phthalate (DiBP), Di-n-butyl Phthalate (DnBP), and di-(2-ethylhexyl) phthalate (DEHP)) emitted from polyvinyl chloride (PVC) floorings and one flame retardant (tris(2-chloroisopropyl) phosphate, TCPP) emitted from polyurethane foam (PUF) were targeted. Experimental results indicated that, for SVOCs with higher volatility, i.e., DiBP, DnBP, and TCPP, y0 decreased 16%-49% after 60 days' exposure for Case 1; and 16%-36% for Case 2. For SVOCs with lower volatility, i.e., DEHP, no significant decrease in y0 was observed after 60 days in both cases; while if prolonging the time to about 1.5 years, a decrease of 38% was observed. Discussion about potential reasons for the decrease of y0 was presented. The results obtained here provide a further understanding about SVOC source characteristics and therefore help providing source strength for estimating indoor SVOC health exposure.