Comparative effectiveness of UV wavelengths for the inactivation of Cryptosporidium parvum oocysts in water K.G. Linden*, G. Shin** and M.D. Sobsey** *Duke University, Dept of Civil and Environmental Engineering, Durham, NC, 27708, USA **University of North Carolina, Chapel Hill, NC, USA (E-mail: kglinden@duke.edu) Abstract Cryptosporidium parvum oocysts in water were exposed to distinct wavelength bands of collimated beam ultraviolet (UV) radiation across the germicidal UV wavelength range (210–295 nm) that were emitted from a medium pressure (MP) mercury vapour lamp. The dose of UV radiation transmitted though each narrow bandpass filter was measured utilising potassium ferrioxalate actinometry. Oocyst infectivity was determined using a cell culture assay and titre was expressed as an MPN. The log 10 inactivation for each band of radiation was determined for a dose of 2 mJ/cm 2 . Doses from all wavelengths between 250–275 nm resulted in approximately 2 log 10 inactivation of Cryptosporidium parvum oocyst infectivity while doses with wavelengths higher and lower than this range were less effective. Because polychromatic radiation from MP UV lamps had about the same germicidal activity between the wavelengths of 250–275 nm for inactivation of oocyst infectivity, there was no unique advantage of MP UV over low pressure (LP) UV except for the simultaneous delivery of a wide range of germicidal wavelengths. Keywords Ultraviolet disinfection; Cryptosporidium parvum inactivation; polychromatic UV radiation Introduction Cryptosporidium parvum continues to be one of the most important waterborne pathogens because of its presence in wastewater and some drinking water sources as well as resistance to treatment processes including chemical disinfection. Previous studies suggested that oocysts were very resistant to UV radiation based on excystation and “vital dye” staining assays (Ransome et al., 1993; Campbell et al., 1995). However, recent studies (Clancy et al., 1998; Bukhari et al., 1999) indicated that UV radiation from medium pressure UV lamps extensively inactivated C. parvum infectivity for mice at relatively low doses (<19 mJ/cm 2 ). Low pressure (LP) quasi-monochromatic UV lamps emitting germicidal 254 nm radiation are the standard for performing microbiocidal research and for disinfect- ing microbes in water and wastewater because they are readily available, inexpensive, easy to use and simple to measure for UV radiation output. However, upon examination of the microbiocidal effects of different wavelengths in the germicidal range, it is apparent that other wavelengths are effective and some are as effec- tive or more effective against bacteria than the UV 254 emitted from LP lamps (Gates, 1929). The increasing use of MP mercury vapour lamps emitting polychromatic radiation encompassing the germicidal wavelengths through the visible and into the near infrared range prompted an evaluation of the relative efficacy of different UV wavelengths for the inactivation of C. parvum in water. Development of information on which wavelengths are most effective for inactivation of specific pathogens provides a basis for engineers to devel- op lamps with specific output spectra to target selected pathogen groups or lamps that are effective against a wide array of health-related microorganisms. The purpose of this study was to quantify the inactivation of C. parvum oocysts by specific bands of UV radiation emitted from MP UV lamps and to determine which wavelengths were most effective for oocyst inactivation as determined by cell culture infectivity assay. Water Science and Technology Vol 43 No 12 pp 171–174 © IWA Publishing 2001 171 Downloaded from http://iwaponline.com/wst/article-pdf/43/12/171/429037/171.pdf by guest on 25 April 2021