The adsorption of cyanobacterial hepatoxins as a function of soil properties

Abstract

Cyanobacterial hepatotoxins present a risk to public health when present in drinking water supplies. Existing removal strategies, although efficient, are not economically viable or practical for remote Australian communities and developing nations. Bank filtration is a natural process and a potential low cost, toxin removal strategy. Batch studies were conducted in 12 texturally diverse soils to examine the soil properties influencing the adsorption of the cyanobacterial hepatotoxins, microcystin-LR and nodularin. Sorption isotherms were measured. Freundlich and linear isotherms were observed for both toxins with adsorption coefficients not exceeding 2.75 l kg 21 for nodularin and 3.8 l kg 21 for microcystin. Significant positive correlations were identified between hepatotoxin sorption and clay and silt contents of the soils. Desorption of toxins was also measured in three different soils. Pure nodularin and microcystin-LR readily desorbed from all soils.

Analysis of intracellular and extracellular microcystin variants in sediments and pore waters by accelerated solvent extraction and high performance liquid chromatography-tandem mass spectrometry

“…Microcystins with higher recovery predominantly distributed into pore waters while those with lower recovery tended to adsorb to sediment particles. Our findings are consistent with experimentally-derived octanol-water and soil-water distribution coefficients for microcystins [6,33,34]. Furthermore, Harada and Tsuji [30] observed that more hydrophilic microcystins such as MC-RR absorbed strongly to sediments.…”

Adsorption characteristics of multiple microcystins and cylindrospermopsin on sediment: Implications for toxin monitoring and drinking water treatment

“…The adsorption behavior of cyanotoxins onto sediment has been interpreted by the most commonly used adsorption equations including Linear, Freundlich and Langmuir sorption isotherms (Grüzmacher et al, 2009;Miller et al, 2005;Wu et al, 2011). To determine the amount of adsorbed MCs onto the sediment, the differences between the initial concentrations of cyanotoxins from their equilibrium concentrations were calculated.…”

“…Our results contradict the only published study in peer-reviewed journals that has investigated the desorption of MCLR from natural sediments. Miller et al (2005) reported that the majority of the pure MCLR and nodularin at two initial concentrations of 1.0 mg L À1 and 2.0 mg L À1 were desorbed after 24 h from sandy sediment samples. The authors stated that after 120 h all the adsorbed MCLR has been desorbed and sediments had reversible bonding with cyanotoxins.…”

“…However, our results demonstrated that cyanotoxins bonded tightly with sandy sediment with almost irreversible reactions. The observed reactions of cyanotoxins with sediment could be related to: (1) hydrophobic interactions with the OC content of sediment, or (2) ligand exchange of hydroxyl groups on clay particles with functional groups (such as carboxylic acid groups) on the cyanotoxins (Miller et al, 2005). However, to determine the exact reactions, thermodynamic studies of bonding sites need to be conducted.…”

“…All of the studies that have investigated the adsorption of cyanotoxins onto sediment focused on bulk soil behavior (Grützmacher et al, 2009;Klitzke et al, 2011;Miller et al, 2005;Wu et al, 2011). However, separation of bulk sediments into different size fractions enhances understanding with regards to sorption capacity and mobility of sediment particles and transport of sorbed contaminants over a large area in aquatic systems (de Jonge et al, 2000;Qi et al, 2014) and in drinking water treatment.…”