The goal of this work is the modeling and calculation of volatilization factors (VFs) from water to air for volatile organic compounds (VOCs) in order to perform human health risk - base d reference levels (RLs) for the safe use of water. The VF models have been developed starting from the overall mass - transfer coefficients ( K overall ) concept from air to water for two interaction geometries (flat surface and spherical droplets) in indoor a nd outdoor scenarios . For a case study with five groups of risk scenarios and thirty VOCs , theoretical VFs have been calculated by using the developed models. Results showed that K overall values for flat and spherical surface geometries were close to the m ass transfer coefficient for water ( K L ) when Henry ’s law constant ( K H ) was high. I n the case of s pherical drop geometry , the fraction of volatilization ( f V ) was asymptotical when increasing K H with f V values also limited due to K overall . VFs for flat surfa ces were calculated from the emission flux of VOCs , and results showed values close to 1000 K H for the most conservative indoor scenarios and almost constant values for outdoor scenarios. VFs for spherical geometry in indoor scenarios followed also constant VFs and were far from 1000 K H . The highest calculated VF values corresponded to the E2A, E2B, E3A and E5A scenarios and were compared with experimental and real results in order to check the goodness of flat and sphere geometry models. Results showed an ov erestimation of OPEN ACCESS Toxics 2014 , 2 277 calculated values for the E2A and E2B scenarios and an underestimation for the E3A and E5A scenarios. In both cases , most of the calculated VFs were from 0.1 - to 10 - times higher than experimental /real values

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