Beyond phthalates: gas phase concentrations and modeled gas/particle distribution of modern plasticizers

The ongoing health debate about polymer plasticizers based on the esters of phthalic acid, especially di(2-ethylhexyl) phthalate (DEHP), has caused a trend towards using phthalates of lower volatility such as diisononyl phthalate (DINP) and towards other acid esters, such as adipates, terephthalates, citrates, etc. Probably the most important of these so-called "alternative" plasticizers is diisononyl cyclohexane-1,2-dicarboxylate (DINCH). In the indoor environment, the continuously growing market share of this compound since its launch in 2002 is inter alia apparent from the increasing concentration of DINCH in settled house dust. From the epidemiological point of view there is considerable interest in identifying how semi-volatile organic compounds (SVOCs) distribute in the indoor environment, especially in air, airborne particles and sedimented house dust. This, however, requires reliable experimental concentration data for the different media and good measurements or estimates of their physical and chemical properties. This paper reports on air concentrations for DINP, DINCH, diisobutyl phthalate (DIBP), diisobutyl adipate (DIBA), diisobutyl succinate (DIBS) and diisobutyl glutarate (DIBG) from emission studies in the Field and Laboratory Emission Cell (FLEC). For DINP and DINCH it took about 50 days to reach the steady-state value: for four months no decay in the concentration could be observed. Moreover, vapor pressures p(0) and octanol-air partitioning coefficients K(OA) were obtained for 37 phthalate and non-phthalate plasticizers from two different algorithms: EPI Suite and SPARC. It is shown that calculated gas/particle partition coefficients K(p) and fractions can widely differ due to the uncertainty in the predicted p(0) and K(OA) values. For most of the investigated compounds reliable experimental vapor pressures are not available. Rough estimates can be obtained from the measured emission rate of the pure compound in a microchamber as is shown for di-n-butyl phthalate (DnBP), di(2-ethylhexyl) adipate(DEHA), tri(octyl) trimellitate (TOTM) and DEHP.