Adsorption of Microcystin LR and LW on Suspended Particulate Matter (SPM) at Different pH

Abstract

The occurrence of microcystins (MC) during aquatic blooms of cyanobacteria in eutrophicated freshwater body has increasingly become an environmental and health concern worldwide. An experimental study was conducted to investigate the adsorption of two common variants of microcystins, MCLR and MCLW, onto SPM at different pH values. The results showed that most microcystins spiked into an SPM solution with the concentration of 0.25g/l was adsorbed onto solids at pH3 (>95%) and 7 (>85%).At pH13, the proportion of adsorbed microcystin decreased to 8-29% for MCLR and 38-47% for MCLW. The adsorption of MCLR and MCLW onto SPM fitted well with S type of Freundlich isotherm except for pH3 at which L type of Freundlich isotherm was suitable for MCLW. At pH3 and 7, linear isotherm was also able to describe the adsorption of MCLR and MCLW. The adsorption of MCLR and MCLW decreased significantly with the elevated pH, which is consistent with the pH-dependent hydrophobicity.

Microcystis toxigenic strains in urban lakes: a case of study in Mexico City

“…On the other hand, it is known that some cyanotoxins, such as microcystins, can be adsorbed by suspended particles in the water-such as organic detritus- (Morris et al 2000;Liu et al 2008), becoming an additional exposure or immobilization pathway. In the present study, the collected water was filtered, evaluating thereby only the toxicity of water-soluble substances.…”

“…The toxicity assessment of purified cyanotoxins might not reflect at all the events occurring in the environment, as it has been demonstrated that their toxicity is susceptible to be modified when they are associated to other molecules (Liu et al 2008). Hence, a better option would be to make assessments with crude extracts, evaluating the toxic effects of the different cellular components after blooms have occurred in natural environments (Sotero-Santos et al 2006).…”

Cyanobacterial and microcystins dynamics following the application of hydrogen peroxide to waste stabilisation ponds

“…In the full-scale trial, there would also have been a significantly higher loading of sediment than in the laboratory trials, where wastewater was collected from the surface of ponds. Adsorption by sediments, and subsequent biodegradation, may have accelerated the reduction of microcystins in the full-scale trial compared to the laboratory trials (Harada and Tsuji, 1998;Liu et al, 2008). Biodegradation, UV radiation and adsorption may all have played a role in the longer term reduction of microcystins from the dissolved phase, and may have accelerated their reduction compared to the smaller scale trials under controlled laboratory conditions.…”

Mechanisms and Factors Influencing Adsorption of Microcystin-LR on Biochars

“…The ionizable groups (two carboxyls and one guanidino) of MCLR can be deprotonated or protonated to make MCLR positive or negative at different pH values, respectively. According to the pKa values of MCLR (pKa 1 , 2.09; pKa 2 , 2.19; pKa 3 , 12.48) (Liu et al 2008), the mass fractions of MCLR species can be calculated as follows:…”