Title:
Calculating the retention of volatile organic compounds in the lung on the basis of their physicochemical properties.

Abstract:
In the workplace, deliberate or accidental exposure to volatile organic compounds (VOCs) may occur by ingestion, but more usually through inhalation or dermal contact. The basic model of occupational exposure assumes repeated inhalation exposure during long periods of time, such as 8-h daily, 40-h per working week. Evaluation of the systemic health effects of industrial chemicals can be based on biological levels or internal doses absorbed in dermal or inhalation exposures. The lungs are the primary route of absorption in exposure to gases, vapors, and aerosols. In inhalation exposure, the dose absorbed can be calculated using the following equation: [formula in text] where C, concentration in the air; T, duration of exposure; V, lung ventilation; R, lung retention expressed as % of intake. As lung retention of VOCs has been studied on human volunteers in costly and time-consuming chamber-type experiments, available data are limited. To calculate dosage for the purpose of risk assessment, the default value of 100% is used. As the lung retention of VOCs in lungs can vary from less than 20 to more than 90%, a possibility of predicting the retention values on the basis of blood/air partition coefficients (K(B)) has been investigated. Lung retention data for 36 compounds were obtained from the existing scientific literature. These values derive from human volunteer studies lasting at least 2h. The K(B) values were either the already published experimental data or were calculated based on their physicochemical properties using a published solvation equation. The compounds under study were divided arbitrarily into two groups: water soluble (>10 g/l) and slightly soluble in water (<10 g/l) compounds. For water soluble compounds, the correlation between K(B) and lung retention was high (r=0.75 and 0.73 respectively); this referred both to K(B) values obtained experimentally or calculated in this report. For the compounds slightly soluble in water, the respective values amounted to 0.79 and 0.82. The obtained results indicate that VOC retention in the lung can be calculated solely on the basis of the partition coefficient K(B). As the descriptors used in the solvation equation can be predicted from chemical structure, this finding indicates that it is possible to assess lung retention for any chemical structure of VOC. The model described in the present report can be a practical alternative to the necessity costly and long-lasting chamber-type experiments which are also questionable on ethical grounds.