Treatment options for microcystin toxins: Similarities and differences between variants

Abstract

Over sixty variants of the blue-green algal toxin microcystin have been identified. The two microcystin variants LR and LA vary in only one amino group ie. arginine for microcystin LR and alanine for microcystin LA. In the literature to date, the general consensus has been that m-LR and m-LA should respond similarly to a range of water treatment processes. This is the case for ozonation and biodegradation by organisms colonising granular activated carbon filters; there is negligible difference in the response to these processes between the two variants. However, the adsorption of m-LR onto activated carbon is significantly higher than that of m-LA. This result is surprising as m-LA has a lower molecular weight, and is more hydrophobic, factors that would be expected to favour the adsorption of this compound over m-LR. This trend is also seen for the variants RR and YR. The effect is seen on both negatively and positively charged carbons, indicating that the difference between the variants is not caused by electrostatic interactions with the carbon surface. Electrostatic shielding experiments suggest that electrostatic repulsion between the adsorbed m-LA molecules, with a net charge of -2, may be responsible for the low adsorption. The other variants tested have a lower net charge and therefor experience lower intermolecular repulsion in the adsorbed state.

Spatial and temporal patterns in microcystin toxins in Lake of the Woods surface waters

“…MC-LA, with a mammalian toxicity as high as MC-LR (Chorus and Bartram 2001), appears to be more persistent in aquatic systems (e.g. Newcombe et al 2003, Zastepa et al 2014 and can lead to wildlife fatalities through food web bioaccumulation (Miller et al 2010). Although concentrations of MCs were generally low in samples at offshore sites (<1 µg/L), blooms accumulating along shorelines and beaches frequently had high concentrations (up to ∼600 µg MC-LR equivalents/L, Table 3), posing potential risk to drinking and recreational water in these areas and pointing to a need to sample shorelines at multiple sites to understand the range of toxins along an area.…”

Development of an mlrA Gene-Directed TaqMan PCR Assay for Quantitative Assessment of Microcystin-Degrading Bacteria within Water Treatment Plant Sand Filter Biofilms

“…In dissolved (extracellular) form, microcystins are not efficiently removed by conventional water treatment processes (6), and more advanced treatment options, such as activated carbon application or ozonation, are usually employed. However, these are expensive alternatives, and removal efficiencies are often compromised by the presence of natural organic matter (15). Biological filtration of microcystins is now recognized as an alternative treatment barrier (1,7,8,14) and is favored by water utilities, as the process is generally low technology, chemical free, and requires little maintenance, where retrofitting of the process into existing water treatment plant (WTP) infrastructure is often feasible.…”

Genetically Engineered Bacteria Immobilized in Alginate as an Option of Cyanotoxins Removal

“…Several experiments indicated that biologically active filters (granular activated carbon and sand) may be an attractive water treatment option [17]- [19]. It has been documented that MC removal in this system is not only due to physical processes but mainly to biological degradation.…”