Degradation of cyanotoxin microcystin-LR in synthetic and natural waters by chemical-free UV/VUV radiation

This study investigated the capability of ultraviolet radiation at 254 nm and 185 nm (UV/VUV) to degrade cyanotoxin microcystin-LR (MC-LR). Results showed 70% toxin reduction solely by 254 nm direct photolysis (epsilon (254) = 13,225 +/- 814 M(-1)cm(-1); Phi(254) = 0.29 +/- 0.03 mol/Einstein). The addition of 185 nm increased MC-LR degradation through advanced oxidation by (OH)-O-center dot (k(center dot OH,MC-LR) = 2.25 +/- 0.39 x 10(10) M(-1)s(-1)). Alkalinity and organics (DOC) reduced MC-LR degradation by scavenging (OH)-O-center dot (k(obs,MilliQ) = 0.117 cm(2)/mJ; k(obs,50ppmAlk) = 0.0497 cm(2)/mJ; k(obs,6ppmDOC) = 0.019 cm(2)/mJ). Chloride absorbed 185 nm, impacting +OH formation and generating cr, while also scavenging (OH)-O-center dot. However, Cl-center dot is reactive and (OH)-O-center dot scavenging is reversible, resulting in relatively low impact on MC-LR degradation (k(obs,50ppmCl) = 0.0939 cm(2)/mJ). In natural water, MC-LR could be degraded from a typical concentration ((similar to)15 mu g/L) to below detection (< 0.5 mu g/L) with a UV254 fluence of 200 mJ/cm(2) using UV/VUV. The presence of cyanobacterial cells impeded MC-LR degradation; however, 90% MC-LR degradation could still be achieved. UV/VUV is a promising chemical-free technology capable of MC-LR degradation in a variety of water conditions, and a potentially suitable treatment option for small, remote communities.