QSARs versus BLM

In Chapter 1 it was noted that the biotic ligand model (BLM) estimates equilibrium concentrations or activities of dissolved metals species that can compete for and adsorb to ligands on biological surfaces. Chapter 5 provided detailed information about quantitative structure-activity relationships (QSARs) for metal ions. The purpose of this chapter is to distinguish between QSARs and the BLM for metals. 

The technical basis for the BLM was described by DiToro et al. (2001). Its application to acute aquatic copper toxicity was described by Santore et al. (2001). Paquin et al. (2002) provided a historical overview of the BLM, while the final section of this chapter provides a list of 175 references describing BLM studies published from 2001 to 2011. 

The BLM concept is a permutation of the free ion activity model (FIAM) (e.g., see Campbell 1995). As a primary distinction, the FIAM predicts metal uptake by aquatic organisms by assuming that metal internalization is related to the free metal ion activity in the bulk solution however, the BLM assumes that the association of metals with biotic ligands of the organism determines the toxic effects (Zeng et al., 2009). Additional differences between the FIAM and BLM were discussed by Hassler et al. (2004). 

In QSARs, the biological activity is also produced by the interaction between the ligand and the biological receptor of an organism. The only difference is that the ligand in QSARs is a chemical species, and the biological receptor is the biotic ligand. 

The BLM is very similar to QSARs, in that they both use a series of physicochemical and biological parameters that would characterize and describe  

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