Chemical Papers 67 (2) 173–185 (2013) DOI: 10.2478/s11696-012-0257-9 ORIGINAL PAPER Improvement of aquatic pollutant partition coefficient correlations using 1D molecular descriptors – chlorobenzene case study a Cristina Maria, a Carmen Tociu, b Gheorghe Maria* a National Institute for Research and Development in Environmental Protection, Spl. Independentei 294, 060031 Bucharest, Romania b Department of Chemical & Biochemical Engineering, University Politehnica of Bucharest, Polizu 1, 011061 Bucharest, Romania Received 18 May 2012; Revised 1 July 2012; Accepted 11 July 2012 Partition coefficients between environmental compartments are essential parameters in any pre- dictive models on pollutants’ fate in various emission scenarios. When sufficient experimental data are not available, empirical algebraic models are capable of predicting the pollutant partitioning characteristics based on bulk physico–chemical properties or various molecular structural features. When the use of sophisticated rules based on detailed 2D–3D molecular descriptors is not avail- able as a quick option, inexpensive, simple correlations based solely on octanol-1-ol (octanol)–water partition coefficients (Kow) are extensively employed. The present study investigates enhancing the adequacy of such hydrophobicity-based models by adding simple 1D descriptors, readily identifiable by inspecting the substance structure (i.e. the number of chlorine atoms bound to aromatic rings, or the number of aromatic 5- or 6-atom rings, etc.), in addition to the pollutant’s solubility in water. Exemplification is made for predicting the water–biota (fish)–sediment partition coefficients for chlorobenzenes (CBz). c  2012 Institute of Chemistry, Slovak Academy of Sciences Keywords: water–biota partition coefficients, water–sediment partition coefficients, empirical cor- relations, chlorobenzenes, 1D molecular descriptors Introduction Pollution of the aquatic environment with toxic substances, particularly with persistent organic pol- lutants (POP) resulting from industrial processes, re- mains a major concern for modern society, represented by the difficulty of removing them from wastew- aters by conventional means. Even when present only in traces in the aquatic environment, their bio- concentration potential is high, due to their high hy- drophobicity and affinity to organisms’ lipids. The long-term presence even in small concentrations (be- low the regulation thresholds) results in continuous accumulation of POP in organisms and sediments by different mechanisms (Mackay & Fraser, 2000; van Leeuwen & Vermeire, 2007). When a pollutant is discharged into surface wa- ters, the model-based (in silico) methods for evalu- ating the risk potential and pollutant transport takes into account the thermodynamic partitioning between environmental phases, transport terms (dispersive– advective), and abiotic (chemical) and biotic (by microorganisms) degradation terms (Mackay, 2001; Maria & Maria, 2006, 2008, 2009). Various levels of model complexity are available for predicting pol- lutant distribution among the phases, defined for a closed/open steady-state/dynamic system including thermodynamic relationships and chemical reactions (Mackay, 2001). Models are based on mass balances relating the pollution source and water body charac- teristics to the transport, phase transfer and accumu- lation (in suspended solids, sediments, or living organ- *Corresponding author, e-mail: gmaria99m@hotmail.com Author copy