Effect of molecular weight on retention of polycyclic aromatic hydrocarbons in the lung

The objective of this study was to test the hypothesis that a molecular weight of 300 daltons is a determining factor for greater retention of non-polar organic molecules in the lung. Previous work in our laboratory using anthraquinone dyes has shown that compounds having a molecular weight greater than 300 daltons are retained in the lung with halftimes similar to those found for insoluble inorganic particles. We wished to determine if this finding also pertained to another class of chemicals. In the present study, polycyclic aromatic hydrocarbons having varying molecular weights between 202 to 432 daltons were instilled into rat lungs and the percentage of the compound retained after 24 h, 1 wk and 6 wk was determined. Increased lung retention of nonpolar organic compounds of 300 daltons and higher was observed. The results showed that, in general, as the molecular weight increased the percentage of compound that remained in the lung at 24 h also increased up to a molecular weight of 300, where the retention tended to plateau. (author)