The Biological Basis for Ballast Water Performance Standards: “Viable/Non-Viable” or “Live/Dead”?

Abstract

The shipping industry is critical to international commerce; however, contemporary shipping practices involve uptake and discharge of ballast water, which introduces the potential for transfer of nonindigenous, invasive species among geographically distinct habitats. To counteract this hazard, regulations for ballast water management have been implemented by the International Maritime Organization (IMO) and by regulatory agencies such as the United States Coast Guard (USCG). IMO and USCG discharge standards are numerically identical, but involve different definitions of treatment end points, which are based on fundamentally different biological assays for quantification of ballast water treatment effectiveness. Available assays for quantification of the responses of organisms in the 10-50 μm size range include vital stains based on fluorescein diacetate (FDA), sometimes used in combination with 5-chloromethylfluorescein diacetate (CMFDA), observations of motility, and the most probable number dilution culture method (MPN). The mechanisms and implications of these assays are discussed relative to the Type Approval process, which quantitatively evaluates compliance with ballast water discharge standards (BWDSs) under controlled shipboard and land-based tests. For antimicrobial processes that accomplish treatment by preventing subsequent replication of the target species, the FDA/CMFDA and MPN methods can yield dramatically different results. An important example of a treatment process that is affected by the choice of assay is ultraviolet (UV) irradiation. Results of laboratory and field experiments have demonstrated UV-based technologies to be effective for accomplishing the objectives of ballast water treatment (inactivation of cellular reproduction), when the MPN assay is used as the basis for evaluation. The FDA, CMFDA, motility, and MPN methods are subject to well recognized sources of error; however, the MPN method is based on a response that is consistent with the objectives of ballast water management as well as the mechanism of action of UV-based inactivation. Complementary assays are available for use in compliance testing; however, the development of relevant indicative tests remains as a research priority. Historical lessons learned from applications of vital stains (and other indirect methods) for quantification of microbial responses to UV irradiation in other settings also support the use of assays that provide a direct measure of growth and reproduction, such as MPN. Collectively, these observations point to the use of MPN assays as the standard for type testing, especially when UV-based treatment is employed.

Effects on inactivation of Tetraselmis suecica following treatment by KBAL: a UV-based ballast water treatment system with an in-line vacuum drop

“…This is consistent with previous studies of UV-irradiated T. suecica [27,34,35], but also to bacteria, and yeast [42]. For samples irradiated at low UV doses, no immediate shutdown of the cellular functions occur even when the reproductive capacity is lost (i.e., live but non-viable cells) [29,38,42,43]. Non-viable cells may suffer from UV-induced DNA damages, which can be counteracted by DNA repair mechanisms [44].…”

“…However, the same samples did not meet the discharge standards of IMO and the USCG when assessing metabolism, not even after the second treatment. The different results for metabolic (living) and reproductive (viable) T. suecica cells after KBAL treatments, clearly highlights a challenge UV-based BWTS can encounter when meeting different testing regimes, which previously has been highlighted by several authors [38,39].…”

Technical Considerations for Development of Policy and Approvals for In-Water Cleaning of Ship Biofouling

“…However, because no technology (especially new and complex technologies) is perfect, interest in requiring the release of only dead, non-viable or local/native organisms would appear reasonable. The problem remains that methods for appropriate levels of species identification, and for definitive determination of live vs. dead and/or viable vs. non-viable (including propagules and tissue fragments but excluding residual baseplates or basal shell material remaining after reactive IWC) are in dispute and often challenging and error-prone (e.g., Zaiko et al, 2016;Blatchley et al, 2018). However, where IWC systems are required to minimize discharges of the dissolved and particulate components of biocidal coatings to appropriate levels, or to treat/disinfect debris to prevent the release of possible pathogens, this secondary processing of debris will likely have a similar effect on macrofouling organisms and their propagules (Scianni and Georgiades, 2019;Georgiades et al, 2021).…”

Systems of environmental innovation: sectoral and technological perspectives on ballast water treatment systems

“…According to Cullen (2018Cullen ( : p. 1634), there are "two fundamentally different methodologies that have been employed for enumerating potentially invasive organisms" for BWTS type approval testing: (1) stain-motility (S-M) and (2) most probable number (MPN). Research has shown evidence that the efficacy of MPN method is as efficient as S-M for verifying that BWTS meet the standards for type approval (Blatchley et al 2018; 6 Excluding ships operating in territorial waters of their flag states, ships with permanent or sealed ballast, warships and ships that discharge their ballast water to approved onshore reception facilities (Čampara et al 2019). 7 BWE is not accepted by USCG beyond 2021.…”