Safety evaluation of physical plasma for water treatment in recirculating aquaculture systems

Cold atmospheric plasma (CAP) is a promising technology for wastewater remediation, particularly for recirculating aquaculture systems (RAS) with persistent microbial residues. In our previous studies, CAP already demonstrated a high inactivation efficacy against fish-pathogenic microorganisms (up to 5 orders of magnitude) in model aquaculture water, which was composed according to the cultivation of Baltic sturgeon at the Research Centre for Agriculture and Fisheries (Born, Germany). However, in addition to the antimicrobial efficacy fish welfare and product safety, as in particular described by toxicity and mutagenicity, are crucial requirements for the future implementation of this technology in RAS. Therefore, internationally accepted toxicity tests were conducted in the present studies. The potential toxicity of a plasma treatment was analyzed using a fish cell line (RTgill-W1) following OECD Test Guideline No. 249. A possible water toxicity was evaluated in accordance to the DIN EN ISO 11348-1 by a bioluminescence assay using Aliivibrio fischeri as a water borne microorganism resulting in a IC 50 of 21%. No poisoning of fish cells could be identified for CAP admixtures of up to 30%. Additionally, a mutagenicity assay with Escherichia coli WP2 uvrA revealed no changes. Moreover, analyses by ion-chromatography of CAP-treated water showed neither a formation nor a degradation of the toxic agent bromate in RAS water. In conclusion, CAP is a promising, adjustable and safe technology for the treatment of water in aquaculture systems although further research towards optimization, scaling, and associated economic considerations for an implementation of the technology is needed.