Air-water partition coefficients for a suite of polycyclic aromatic and other C10 through C20 unsaturated hydrocarbons

The air-water partition coefficients (Kaw) for 86 large polycyclic aromatic hydrocarbons and their unsaturated relatives were estimated using high-level G4(MP2) gas and aqueous phase calculations with the SMD, IEFPCM-UFF, and CPCM solvation models. An extensive method validation effort was undertaken which involved confirming that, via comparisons to experimental enthalpies of formation, gas-phase energies at the G4(MP2) level for the compounds of interest were at or near thermochemical accuracy. Investigations of the three solvation models using a range of neutral and ionic compounds suggested that while no clear preferential solvation model could be chosen in advance for accurate Kaw estimates of the target compounds, the employment of increasingly higher levels of theory would result in lower Kaw errors. Subsequent calculations on the polycyclic aromatic and unsaturated hydrocarbons at the G4(MP2) level revealed excellent agreement for the IEFPCM-UFF and CPCM models against limited available experimental data. The IEFPCM-UFF-G4(MP2) and CPCM-G4(MP2) solvation energy calculation approaches are anticipated to give Kaw estimates within typical experimental ranges, each having general Kaw errors of less than 0.5 log10 units. When applied to other large organic compounds, the method should allow development of a broad and reliable Kaw database for multimedia environmental modeling efforts on various contaminants.

Estimation of physicochemical properties of 52 non-PBDE brominated flame retardants and evaluation of their overall persistence and long-range transport potential

Non-PBDE (polybromodiphenyl ether) brominated flame retardants (BFRs) used as alternatives to PBDEs should be evaluated in terms of their environmental contamination potential. We first used two well-known estimation tools, EPI Suite and SPARC, to estimate the physicochemical properties of 52 non-PBDE BFRs. We assessed the dependence of the properties on the molecular weight and chemical structure of the compounds. The accuracy of the estimates was evaluated by comparing results with previous experimental data. In the case of EPI Suite, we have recommended an appropriate calculation method for the air-water partition coefficient. Half-lives in each environmental medium were also estimated with EPI Suite. Based on the estimated properties and half-lives, the overall persistence (Pov) and long-range transport potential (LRTP) of the BFRs were calculated using the Organization for Economic Cooperation and Development Pov and LRTP Screening Tool. We selected some POP-like chemicals from among the non-PBDE BFRs on the basis of their Pov and LRTP. From a Monte Carlo analysis of the calculated results for the selected BFRs, we suggest physicochemical properties to be measured in the future.