Microcystins adsorption

Studies since, on four microcystin variants, have shown large differences in the adsorption of the variants [71, 77, 78]. Surprisingly, the largest and the most hydrophihc of the toxins studied, mRR with two arginine groups in the variable positions, showed the highest adsorption on a range of PACs, contrary... 

The adsorption of microcystins has been shown to be strongly affected by NOM [78]. In this work the effect, for four microcystin variants, was shown to be a function of the DOC concentration. This is prohahly a result of the direct competitive effect, where the competitive NOM, those compounds approximately the same molecular weight as the microcystins, makes up the hulk of the NOM. Therefore the bulk characterization parameter, DOC, gives an indication of the concentration of competing compounds, where for MIB and geosmin it could not [27, 63, 69]. 

Figure 26.10 Adsorption of microcystins LR and LA as a fimction of time, showing HSDM fits and predictions. (Reprodnced with permission fi om Ref. [71].)...

Predictive tools have been used in an attempt to predict breakthrough of microcystins, but in these cases the results were not accurate due to biological degradation occurring, as well as adsorption [83, 84]. Figure 26.11 illustrates both forms of removal on a laboratory-scale GAC column. Initially the GAC,... 

Cook, D. and Newcombe, G. (2002). Effect of natural organic matter concentration and character on the adsorption of microcystin analogues onto PAC. Proceedings of the American Water Works Association Water Quality Technology Conference, November 11-13, 2002, Seatde, USA. CD ROM. 

High Performance Liquid Chromatography was used to determine microcystin-LR concentrations in both adsorption and photodegradation studies. The presence of possible breakdown products of photodegraded MLR toxin was investigated by GC-MS analysis. Details of these techniques are given elsewhere (Feitz, A.J. Waite, T.D. Jones, G.J. Boyden, B.H. Orr, P.T. Environ. ScL TechnoL, submitted). 

Figure 4. Percentage of 85 nM microcystin-LR removed at various pH after one hour contact time with 1 g/L Ti02 in the dark. The solid line represents the percentage of 85 nM MLR adsorption to 1 g/L Ti02 as a function of pH predicted using a surface complexation model. The initial removal rate of microcystin-LR from solution in the light is also shown as a function of pH. (Reproduced from Feitz et al.. Environ. Sci. TechnoL submitted).

While not always justified (7), it has been common under conditions where adsorption is the (rapid) precursor to a rate controlling surface-mediated degradative step, to assume that the initial rate of contaminant removal is dependent upon both an equilibrium adsorbed contaminant concentration and the concentration of surface-located oxidizing species (7, 5). Under these conditions, an expression for the initial rate of removal of microcystin-LR may be written as ... 

Hyenstrand, R Metcalf, J.S. Beattie, K.A. Codd, G.A. Effects of adsorption to plastic and solvent conditions in the analysis of the cyanobacterial toxin microcystin-LR by high performance liquid chromatography. Wat. Res. 2001, 35, 3508-3511. 

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