Estimation of amorphous organic carbon/water partition coefficients, subcooled liquid aqueous solubilities, and n-octanol/water partition coefficients of nonpolar chlorinated aromatic compounds from chlorine fragment constants

This study aims to derive the relation between the number of chlorine atoms in chlorobenzenes, polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), and dibenzofurans (PCDFs) and log Koc for linear partitioning between water and average amorphous organic carbon in soils or sediments. Because reliable determinations of log Koc are relatively sparse for chlorobenzenes and PCBs, and are even absent for PCDDs and PCDFs, a work-around solution was developed: First, the relation of n-octanol/water partitioning (Kow) and (subcooled) liquid solubility (Sl) to the number of chlorines was investigated. Slopes for the linear correlation of log Kow with the number of chlorines (corrected for the number of ortho-chlorines in the case of PCBs) appeared identical for chlorobenzenes, PCBs, PCDDs, and PCDFs. Such was also the case for log Sl. Slopes for the linear relation of chlorobenzenes and PCB log Koc values with the number of chlorines were similar for the various soils and sediments, though intercepts were different. The ortho-chlorine correction factor for PCB log Koc was equal to the ortho-chlorine correction factor for PCB log Kow and log Sl. For PCDDs and PCDFs, a relation between log Koc and the number of chlorine atoms was derived by combining the chlorobenzenes/PCB log Koc − log Kow and log Koc − log Sl relationships with log Kow (or Sl)-chlorine number relations for PCDDs and PCDFs.