Life after treatment: detecting living microorganisms following exposure to UV light and chlorine dioxide

Abstract

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 (ClO 2 ). 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 ClO 2 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 ClO 2 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.

Alternative, indirect measures of ballast water treatment efficacy during a shipboard trial: a case study

“…Moreover, the large drop in ATP concentrations for UV-treated samples reported here (Figure 2) suggest that ATP serves as sensitive indicator of successful ballast water treatment under full-scale, shipboard UV treatment doses. These results contrast with those of First and Drake (2014) who showed inconsistent ATP response to UV under laboratory, bench-scale UV dosing levels.…”

Evaluation of ultraviolet disinfection of microalgae by growth modeling: application to ballast water treatment

“…The impact of sublethal effects on cells which recover their viability after the dark period depends on the applied dose. In summary, the dark period showed two extra impacts on cell viability, in addition to the lethal effects observed in samples directly exposed to light: the damage caused by stressful dark conditions independently of the UV dose applied (First and Drake 2014), and the inhibition of repairing mechanisms, in this case with direct dependence on the UV dose.…”

“…According to the BWMC-Guideline 8, the evaluation of the treatment efficacy is based on the determination of living organisms by widely accepted standard methods (Gollasch et al 2012;Cullen and MacIntyre 2016), such as vital fluorescence stains detected using flow cytometry or fluorescence microscopy, ATP content, photosynthetic activity, or motility assessment (Hessen et al 1997;Sato et al 2004;Gavand et al 2007;Gallo-Villanueva et al 2011;Steinberg et al 2011Steinberg et al , 2012Fan et al 2013;Martínez et al 2013;Stehouwer et al 2013;Adams et al 2014;First and Drake 2014;Tilney et al 2014;Feng et al 2015;Gollasch et al 2015;Olsen et al 2015;van Slooten et al 2015;Wright et al 2015). However, the application of UV treatment does not cause immediate changes in the concentration of living organisms, although their growth curves become different over the time, depending on the applied UV dose (Tao et al 2010;Gorokhova et al 2012;Martínez et al 2012).…”

Which Ballast Water Management System Will You Put Aboard? Remnant Anxieties: A Mini-Review

“…First and Drake have stressed the necessity for correct irradiation dosage versus uninterrupted irradiation to overcome cellular repair mechanisms in target organisms, indicating that UV radiation may be incapable of destroying some microorganisms, such as bacterial spores and microalgae [29,30].…”