Ammonia-rich sediment: Practical issues about embryotoxicity as endpoint supporting challenges in dredging activities.

Regulations for dredging and sediment management often require the use of toxicity tests to support sediment classification, together with chemical characterization; among available bioassays, embryotoxicity tests (conducted on aqueous phase prepared from sediment) are commonly applied to evaluate sub-chronic toxicity, as in the case of Italian legislation. However, toxicity tests can be influenced by several confounding factors, such as ammonia that, in the context of sediment management, generally is not considered as a "traditional" contaminant of concern due to its low persistence. In order to better address and optimize sediment management, it is therefore essential to understand the influence of ammonia on the observed sediment toxicity. The scope of this work is to provide an overview of the toxic effects of ammonia focusing on embryotoxicity endpoints, enabling a proper evaluation of sediment toxicity, discussing the role of ammonia on sediment quality classification, and contributing to improve the management options. The paper presents the results of an experimental activity aimed at evaluating the role of ammonia on sediment toxicity, jointly to a literature review delineating the range of ammonia toxicity thresholds on larval development evaluated in embryotoxicity tests for oysters, mussels and sea urchins. Results from this study demonstrated the influence of ammonia on sediment toxicity from a case-study (Venice lagoon), testing methods for toxicity identification evaluation and providing recommendation to support scientific discussion to pursue the most sustainable sediment management, especially when just the embryotoxicity endpoint is responding concomitantly to high ammonia levels, considering that; impacts primarily due to nonpersistent contaminants should be managed differently than persistent ones.