The development of renewable energy is an indispensable step toward a sustainable society. Liquid Organic Hydrogen Carriers (LOHCs) are very promising vectors for hydrogen storage and transportation. LOHC systems consist of a pair of H2-lean, typically (poly)cyclic aromatic compounds, and H2-rich form, (poly)cyclic heteroaromatic compounds. The scale of LOHC implementation can reach that of liquid fossil fuels if full replacement shall occur – in this scenario there is a high likelihood of release of LOHC chemicals into the environment. Until now, the LOHC systems based on dibenzyltoluene and benzyltoluene are technically mature but there are some technological hurdles Thus, it is of high interest for LOHC developers to find potential LOHC, which allow similar hydrogen capacity but also similar or better hazard profile. To avoid regrettable substitution (of fossil fuels or one LOHC system by another) a comprehensive hazard profile is crucial before widespread use. This study aims to understand the harmful effects of novel LOHC compounds by conducting ecotoxicity tests with Raphidocelis subcapitata, Daphnia magna and Vibrio fischeri, and biodegradation test to determine their persistence. Additionally, the octanol-water partition coefficient (log Kow) is used to build Quantitative Structure Activity Relationship (QSAR) to determine the mode of toxic action of novel LOHC compounds. The exposure concentration of test solutions in ecotoxicity tests was measured using LC/MS-MS. The comparative hazard assessment was conducted including comparisons between different forms of the same carrier (H2-lean vs H2-rich forms) and between LOHCs and conventional energy sources (fossil fuels). All tested LOHC compounds seem to be baseline toxicants (i.e. toxicity is driven by hydrophobicity of compounds). H2-lean form of novel LOHC is readily biodegradable. On the other hand, H2-rich and partially hydrogenated forms are rather less biodegradable. Overall, tested LOHC compounds seem to have similar level of environmental hazard to that of diesel oil based system. The research outcome will be of the highest interest to environmental scientists, LOHC developers (in academia and industry), regulatory agencies, governments, and the general public. Keywords: Acute