Towards Sustainable maritime Management: a re-visit of ammonia criterion values in Southeast Asian tropical seas

The maritime industry's transition to ammonia as a low-carbon fuel calls for a reassessment of environmental criteria, particularly in Southeast Asia's biodiverse yet data-deficient seas. This study addresses the knowledge gap by proposing updated ammonia criterion values tailored to Southeast Asian region. Using species sensitivity distributions (SSDs) and toxicity data from over 50 regionally relevant species. The study estimates  thresholds of 1.0 μM, 2.4 μM, and 4.3 μM of total ammonia nitrogen, which corresponds to protecting 99%, 95%, and 90% of species based on 96hr no observed effect concentration. These proposed concentrations are lower than those for non-tropical regions due to the inclusion of tropical reef-building corals, which are highly sensitive to ammonia. The study also compares these criteria with ammonia release scenarios from bunkering activities, underscoring the importance of situating such operations away from sensitive marine habitats. By providing a region-specific framework, this study offers new insights to guide policy development, ensuring a balance between environmental conservation and the maritime industry's sustainability objectives.