Sorption of dissolved microcystin using lanthanum-modified bentonite clay

摘要

Microcystins (MCs) are a class of cyanobacterial toxins ubiquitous in fresh waters throughout the world (Codd et al. 2005). These toxins primarily accumulate in the liver and kidneys of exposed mammals and fish and can cause severe health risks to these organisms (Ueno et al. 1996, Briand et al. 2003). Acknowledging risks associated with MC exposures has spurred many agencies to set guidelines for drinking and recreational waters (WHO 2003, USEPA 2015, USEPA 2016). Guideline concentrations are basedon total toxin (i.e., in the cell and in the water). Toxins housed intracellularly can accumulate in nearshore areas subsequently concentrating the toxin and increasing risks to humans and wildlife. Specific concerns regarding dissolved MCs has garneredenhanced regulatory scrutiny on managing toxic blooms, and restricted applied management initiatives due to potential release of toxins (Kenefick et al. 1993, Greenfield et al. 2014, USEPA 2018). Though dermal toxin sorption of dissolved toxin is an insignificant route of exposure for humans (USEPA 2016), and released MC often dilutes and biodegrades (Jones and Orr 1994, Lahti et al. 1997, Edwards et al. 2008), there is still concern associated with MC release. Some reasons often include difficulty to treat in drinking water systems and increased exposure routes to aquatic biota. The release of intracellular MCs following some chemical treatments has been documented, which often restricts approval of these approaches (Iwinski et al. 2016). However, depending on the growth stage of cyanobacteria, MCs may also be found extracellularly without treatment (Lahti et al. 1997, White et al. 2005, Lehman et al. 2013). In toxic cyanobacterial blooms, the release of accumulated toxin is often an unavoidable concern as the bloom naturally senesces (Chorus and Bartram 1999) or if exposed to natural stressors (ultraviolet light, salinity, physical damage; Ross et al. 2006). This natural toxin release can be of greater intensity than if it was managed at an earliergrowth stage.Therefore, methods that mitigate dissolved toxin are important in managing risks associated with toxic cyanobacteria independent of, or in concert with, other management approaches.