Life after treatment: detecting living microorganisms following exposure to UV light and chlorine dioxide
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Rapid analytical methods are needed to quantify living microorganisms to determine if ships’ discharged ballast water is in compliance with national and international standards. Traditionally, regrowth assays and microscope counts of stained organisms—which are time-consuming, require expensive equipment, and require extensive staff training—are used to assess microorganisms. The goal of this study was to evaluate other approaches. Both ambient microorganisms from an oligotrophic marine environment and laboratory cultures of marine algae were evaluated following exposure to two types of ballast water treatment: ultraviolet (UV) light and chlorine dioxide (ClO2). Microorganisms in two size classes (<10 and ≥10 to <50 μm) were quantified using regrowth assays and vital staining, and samples were evaluated using two rapid approaches: (1) chlorophyll a fluorescence and photochemical yield were measured using a pulse amplitude modulated fluorometer and (2) the concentration of adenosine triphosphate (ATP) was measured with a handheld luminometer. The response of microorganisms to UV and ClO2 was evident in measurements of photochemical yield, as photochemical yield decreased at high doses. However, initial values of photochemical yield were variable and species-specific. Oddly, in some trials, initial fluorescence increased at intermediate UV doses; this phenomenon could lead to overestimation of total biomass. In samples treated with UV light, ATP was not significantly different among any of the doses used; however, concentrations of ATP were significantly lower at the highest dose of ClO2 than control samples. These results demonstrate that approaches used for ballast water testing can be treatment-specific, and compliance approaches should be validated to determine their utility with the appropriate treatments.
KeywordsBallast water Ultraviolet radiation Invasive species Disinfection Protists Ballast water management systems
This work was supported by the USCG Environmental Standards Division (CG-OES-3; MIPR HSCG23-11-X-MMS154, Tasks 5.2 and 5.3) and does not represent official USCG policy. We are grateful to Richard Everett (USCG) for advice and guidance with this work. We appreciate the comments and suggestions of two anonymous reviewers, which helped to improve and clarify an earlier draft of this manuscript. We very much appreciate the contributions of Stephanie Robbins-Wamsley and Scott Riley (SAIC, Inc., Key West, FL). The research, which was conducted at the Naval Research Laboratory in Key West, was supported by Diane Lysogorski (Section Head of NRL Code 6136 and Director of the Center for Corrosion Science and Engineering, Key West, Florida). Finally, this manuscript was improved by reviews from Ms. Lysogorski, Gina Bergner (USCG), and Richard Colton (Superintendent, Chemistry Division, Naval Research Laboratory)—we thank you.
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