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The Biotic Ligand Model (BLM) is a tool used in aquatic toxicology that examines the bioavailability of metals in the aquatic environment and the affinity of these metals to accumulate on gill surfaces of organisms. BLM depends on the site-specific water quality including such parameters as pH, hardness, and dissolved organic carbon. In this model, lethal accumulation values (accumulation of metal on the gill surface, in the case of fish, that cause mortality in 50% of the population) are used to be predictive of lethal concentration values that are more universal for aquatic toxicology and the development of standards. Collection of water chemistry parameters for a given site, incorporation of the data into the BLM computer model and analysis of the output data is used to accomplish BLM analysis. Comparison of these values derived from the model, have repeatedly been found to be comparable to the results of lethal tissue concentrations from acute toxicity tests (Arnold et al. 2005). The BLM was developed from the gill surface interaction model (GSIM) and the free ion activity model (FIAM).〔 Both of these models also address how metals interact with organisms and aquatic environments. Currently, the (Environmental Protection Agency ) (EPA) uses the BLM as a tool to outline (Ambient Water Quality Criteria ) (AWQC) for surface water. Because BLM is so useful for investigation of metals in surface water, there are developmental plans to expand BLM for use in marine and estuarine environments. ==History== Current knowledge of how specific water quality parameters alter the toxicity of metals to aquatic life is still growing. In 1973, Zitko ''et al''. provided evidence that the free metal ion played a stronger role in determining toxicity than did the metals overall concentration.〔 Shortly after, in 1976, Zitko ''et al''. established that Ca2+ and Mg2+ (hardness cations) were in competition with metal ions at the binding sites of the metals.〔 This competition at the binding site resulted in lower toxicity of metals as the hardness of the water they were in increased. Pagenkopf ''et al.'' used a chemical equilibrium model to explain how water chemistry will control which form of a metal is present and how that was related to the metal’s toxicity.〔 Both of these findings helped establish that metal toxicity and availability is directly related to the free ion activity of the metal.〔 This led to the development of what is now called (the free-ion activity model ) (FIAM).〔 The FIAM describes effects of metals based on metal speciation and their subsequent interactions with organisms.〔 The free ion activity model was created to explain original observations about behaviors of metals in aquatic organisms and to examine the “universal importance of free metal ion activities in determining the uptake, nutrition and toxicity cationic trace metals”. It is now known that aqueous concentrations of metals are poor predictors of the bioavailability of a particular metal. Further, as the biotic ligand model addresses, the binding of trace metal to a site is not only dependent on the concentration of the metal in question.〔 Parent ''et al.'' describe cell surface interactions according to the FIAM by saying that the biological response that is elicited is the result of the concentration of cell surface complexes, either metal or metal ligand.〔 The original FIAM did not address other roles that ligands play besides complexing metals and how these other roles could affect the biological response of an organism.〔 Around the same time that the free ion activity model was proposed, the gill surface interaction model (GSIM) was introduced by Pagenkopf in 1983.〔 The model was put into use in order to evaluate toxicity test results of metals as well as metals in mixtures.〔 Pagennkopf outlined that the compilation of previous studies on metals necessitated further examination of how metal toxicity changes as a function of pH, hardness and complexation capacity for the toxicity of metals to fishes.〔 In the gill surface interaction model both metal hardness and complexation are included. Pagenkopf lays out several major concepts that are the basis of the GSIM.〔 # 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Biotic Ligand Model」の詳細全文を読む スポンサード リンク
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