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Harmful algal blooms (HABs) in coastal areas similarly impact both ecosystems and human health. The translocation of phytoplankton species via maritime transport can potentially promote the growth of HABs in coastal systems. Accordingly, ballast water must be disinfected. The main goal of this study is to assess the effectiveness of different emerging biocides, including H2O2, peracetic acid (PAA), peroxymonosulfate (PMS), and peroxydisulfate (PDS). The effectiveness of these biocides is compared with that of conventional chlorination methods. Their effects on two ichthyotoxic microalgae with worldwide distribution, i.e., Prymnesium parvum and Heterosigma akashiwo, are examined. To ensure the prolonged effectiveness of the different reagents, their concentration–response curves for 14 days are constructed and examined. The results suggest a strong but shorter effect by PMS (EC50 = 0.40–1.99 mg·L-1) and PAA (EC50 = 0.32–2.70 mg·L-1), a maintained effect by H2O2 (EC50 = 6.67–7.08 mg·L-1), and a negligible effect by PDS. H. akashiwo indicates higher resistance than P. parvum, except when H2O2 is used. Based on the growth inhibition performance and consumption of the reagents as well as a review of important aspects regarding their application, using H2O2, PAA, or PMS can be a feasible alternative to chlorine-based reagents for inhibiting the growth of harmful phytoplankton. This work has been co-funded by the 2014–2020 ERDF Operational Programme and by the Department of Economy, Knowledge, Business and University of the Regional Government of Andalusia (Spain). Project Ref.: FEDER-UCA18–108023. This work is part of the project TED2021–130994B-C31; TED2021–130994B-C33 and Grant IJC2020–042741-I funded by MCIN/AEI/10.13039/501100011033 and by the European Union NextGenerationEU/PRTR.

Meeting the recent biological standards established by the Ballast Water Management Convention requires the application of ballast water treatment systems; ultraviolet irradiation is a frequently used option. However, organisms can repair the damage caused by ultraviolet irradiation primarily with photo-repair mechanisms that are dependent on the availability of light. The objective of this study is to quantify the impact of dark storage following ultraviolet irradiation on the viability of the microalgae Tetraselmis suecica. Results showed that one day of dark storage after ultraviolet irradiation enhanced the inactivation rate by 50% with respect to the absence of dark storage and increased up to the 84% with five days of dark storage. These results are consistent with photorepair, mostly in the first two days, prevented in the dark. The dose required to inactivate a determined ratio of organisms was correlated with the length of the dark post-treatment according to an inverse proportional function. This correlation may help to optimize the operation of ultraviolet ballast water treatment systems. Further, the results show that growth assays can detect organisms that are capable of repair after treatment with UV., This work was supported by the Spanish Ministry of Economy and Competitiveness-FEDER through the R+D AVANTE Project [CTM2014-52116-R].

10 pages, 4 figures, 3 tables, The sublethal effects of two antifoulants currently used in power plant cooling systems were assessed in the common mussel Mytilus galloprovincialis. The concentrations of sodium hypochlorite (NaClO) and an alkyl amine surfactant (Mexel®432) assayed, were within the range of those currently discharged by power plants into receiving waters. Enzymatic activities and oxidative stress responses were measured in digestive gland and gill of mussels after 1, 3, 7 and 14 days of exposure, as well as histopathology in gill tissue. Both antifoulants caused a pathological response in gills and the activities of the enzymes glutathione S-transferase, catalase, acetylcholinesterase and the lipid peroxidation levels were also affected. Exposure to NaClO caused a greater toxicological response than Mexel®432. In both treatments, gills appeared to be the most affected tissue, although Mexel®432 also significantly affected digestive gland parameters, This work was funded by grants: CTM2005-02658 to E.N. and AGL2007-61211/ACU (Ministerio Educación y Ciencia of Spain) and Proyecto de Excelencia PO7-RNM-02843 (Consejería de Innovación, Ciencia y Empresa. Junta de Andalucía) to J.M.M.