Towards sustainable maritime management: A re-visit of ammonia criterion values in Southeast Asian tropical seas.

The maritime industry's shift towards ammonia as a low-carbon fuel demands a re-evaluation of environmental criteria, especially in biodiverse and yet data-sparse Southeast Asian tropical seas. To fill the knowledge gap, this study proposes an updated set of ammonia criterion values for these marine environments, detailing the development process, assumptions, and limitations. Utilizing the widely used species sensitivity distributions with over 50 regionally relevant species, the study estimates criterion values for ammonia in Southeast Asian tropical seas. These values, calculated at 29°C and pH 8, are estimated to be 1.0 μM, 2.4 μM, and 4.3 μM of total ammonia nitrogen, protecting 99 %, 95 %, and 90 % of species, respectively. The estimated concentrations are notably lower than in non-tropical regions due to the inclusion of tropical reef-building corals that are highly sensitive to ammonia. Comparing ammonia accidental releases during bunkering operation scenarios with suggested concentrations highlights the need to locate ammonia bunkering operations away from sensitive marine species. Furthermore, the study discusses the limitations of the current method, emphasizing the need to consider ecosystem connectivity and biogeochemical cycling when assessing the environmental impact of ammonia release. Overall, this study lays a crucial foundation for informing policies that strike a balance between environmental protection and the sustainability goals of the maritime industry.