Review of QSAR Models for Bioconcentration

New laws resulting from enactment of the United Nations Stockholm Convention in May 2004 together with the new REACH legislation, have led to significant new activity in the assessment of Persistent, Bioaccumulative, Toxic substances (PBT). Bioconcentration is the process of accumulation of chemicals by organisms through non-dietary routes. The tendency of a substance to bioconcentrate in aquatic organisms is usually expressed as its bioconcentration factor (BCF). Typically, fish are the target organisms of BCF assessments due to their importance as a human food source and the availability of standardized testing protocols. Experimental determination of the BCF is generally expensive and technically demanding to perform. For this reason, measuring the BCFs of many thousands of chemicals that are of potential regulatory interest is not feasible. The limited availability of empirical data, the high test costs together with the regulatory constraints and the international push for reduced animal testing is resulting in a greater reliance on QSAR models in PBT assessment. In this review several QSAR approaches to estimate BCF are described. Linear relationships that correlate BCF with octanol/water partition coefficient available in the literature and currently used in regulatory applications are compared and re-examined. Other approaches based on experimentally derived descriptors, such as water solubility and surface tension, are also considered. In addition, new QSAR approaches aimed to evaluate the potential of other descriptors to model BCF values are described and examined. Finally, recent QSAR approaches proposed to model the B-profile, and food web bioaccumulation are illustrated.