Disinfection and toxicological assessments of pulsed UV and pulsed-plasma gas-discharge treated-water containing the waterborne protozoan enteroparasite Cryptosporidium parvum

We report for the first time on the comparative use of pulsed-plasma gas-discharge (PPGD) and pulsed UV light (PUV) for the novel destruction of the waterborne enteroparasite Cryptosporidium parvum. It also describes the first cyto-, geno- and ecotoxicological assays undertaken to assess the safety of water decontaminated using PPGD and PUV. During PPGD treatments, the application of high voltage pulses (16kV, 10pps) to gas-injected water (N₂ or O₂, flow rate 2.5L/min) resulted in the formation of a plasma that generated free radicals, ultraviolet light, acoustic shock waves and electric fields that killed ca. 4 log C. parvum oocysts in 32min exposure. Findings showed that PPGD-treated water produced significant cytotoxic properties (as determined by MTT and neutral red assays), genotoxic properties (as determined by comet and Ames assays), and ecotoxic properties (as determined by Microtox™, Thamnotox™ and Daphnotox™ assays) that are representative of different trophic levels in aquatic environment (p<0.05). Depending in part on the type of injected gas used, PPGD-treated water became either alkaline (pH≤8.58, using O₂) or acidic (pH≥3.21, using N₂) and contained varying levels of reactive free radicals such as ozone (0.8mg/L) and/or dissociated nitric and nitrous acid that contributed to the observed disinfection and toxicity. Chemical analysis of PPGD-treated water revealed increasing levels of electrode metals that were present at ≤30 times the tolerated respective values for EU drinking water. PUV-treated water did not exhibit any toxicity and was shown to be far superior to that of PPGD for killing C. parvum oocysts taking only 90s of pulsing [UV dose of 6.29μJ/cm²] to produce a 4-log reduction compared to a similar reduction level achieved after 32min PPGD treatment as determined by combined in vitro CaCo-2 cell culture-qPCR.