PERSPECTIVE pubs.acs.org/est
Shredding Light on Cyanobacteria Toxins: ES&T’s Best Technology Paper 2010 Thanh Wang*
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ncreased input of nutrients from both anthropogenic and natural sources often leads to severe problems with eutrophication in rivers, lakes, and reservoirs. Certain strains of cyanobacteria that thrive during these algal bloom events produce toxins that can be released in substantial amounts and cause practical problems for drinking water treatment. In the 2010 top technology paper of ES&T, Yingping Huang and his colleagues (pictured in photo by Zhu Kui) at the China Three Gorges University and the Chinese Academy of Sciences introduced a new efficient method to eliminate one of the most commonly found cyanotoxin in water, microcystin-LR (MC-LR), by using a relatively new semiconductor material, bismuth oxybromide (BiOBr) as photocatalyst (Environ. Sci. Technol. DOI 10.1021/ es103422j). Microcystins are cyclic peptides that are acute toxic to animals and human, acting mainly through interactions with protein phosphatase PP1 and PP2A. Exposure to high levels of these environmentally persistent microcystins can lead to liver damage and even result in death. Also, chronic exposure to low levels of microcystins has been suspected of causing cancer. As a result, the World Health Organization has established a provisional safe guideline value of 1 μg/L of MC-LR in drinking water. However, one problem is that traditional water treatments, such as chlorination, active carbon filtration, or ozonation are not able to completely remove MC-LR in drinking water. Recent research has focused on eliminating MC-LR by use of so-called advanced oxidation processes with semiconducting materials. One such commonly used method is the photocatalytic destruction by titanium dioxide (TiO2) under the irradiation of UV light. However, these processes also cannot completely degrade MCLR in water. This is mainly due to the difficulties in fully removing the chemically stable active carboxylic and guanidino groups, which are the primary functional groups that bind with r 2011 American Chemical Society
PP1 and PP2, says Yingping Huang, a professor and the vice director of his university’s Engineering Research Center for EcoEnvironment in the Three Gorges Reservoir Region. Having the drawbacks in mind, Huang and his group set out to find more efficient materials to photodegrade MC-LR. He noted that “as a new type catalyst, the synthesis and characteristics of BiOBr have been previously studied and [show] good catalytic activity under visible light”. Using BiOBr to photodegrade MCLR for the first time, they found some unique features of this method. The “photocatalytic mechanism of BiOBr/Vis system is different from TiO2/UV system, and we are currently conducting experiments to verify our premise”, says Huang. By using liquid chromatography coupled with mass spectrometry together with water enriched in the heavier 18O isotope as solvent, the researchers were able to identify new degradation products of MC-LR specific to the BiOBr system. An important discovery was that BiOBr could selectively decarboxylate the stable free carboxyl groups which were previously found difficult to degrade by other methods. Since these key functional groups are effectively eliminated, it could mean that the toxicity can be reduced even if the macrostructure of MC-LR is not completely destroyed. This study could therefore provide a promising strategy in dealing with a globally prevalent problem. Further benefits are that this method can work under visible light at neutral pH, and “because BiOBr could be recycled by simple filtration for at least up to ten times without loss of catalytic activity, it also has a good future in water treatment under sunlight”, Huang says. They are currently working on further elucidating detailed MC-LR degradation pathways by this method and also validating its practical feasibility in drinking water treatment.
’ AUTHOR INFORMATION Corresponding Author
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[email protected].
Published: March 30, 2011 2521
dx.doi.org/10.1021/es200500a | Environ. Sci. Technol. 2011, 45, 2521–2521
