Ecotoxicity of marine sediments: Sampling and laboratory artifacts and their impacts on risk classification

Assessing the ecotoxicological risk of marine sediments is now a critical factor in deciding how to treat dredged material in harbor and coastal areas. Although ecotoxicological analyses are routinely required by some regulatory agencies in Europe, laboratory skills necessary to perform them are often underestimated. According to the Italian Ministerial decree No. 173/2016, ecotoxicological tests are performed on the solid phase and elutriates, and the classification of sediment quality is defined using the "Weight of Evidence" (WOE) approach. However, the decree does not provide adequate information regarding the preparation techniques and laboratory skills. As result, a wide variability among laboratories occurs. An error in the classification of ecotoxicological risk has a negative impact on the whole environmental quality and/or the economy and management of the interested area. Thus, the main aim of this study was to determine if such variability can affect the ecotoxicological outcomes of tested species and WOE associated classification, producing different options for the management of dredged sediments. Four different sediment types were selected to assess the ecotoxicological responses and their changes as a function of variability of the following factors: a) the storage time laps (STL) for both the solid phase and the elutriates; b) the methods used to prepare the elutriates (centrifugation vs. filtration), and the conservation method used for the elutriates (freshly prepared vs. freezing). Results suggest a wide variability of ecotoxicological responses among the four sediment samples here considered, differentiated according to chemical pollution, grain-size texture, and macronutrient contents. The storage time laps significantly affect the physicochemical parameters and the ecotoxicity of both the solid phase test and elutriates. For the elutriates preparation, centrifugation is preferred to filtration to preserve a better representation of sediment heterogeneity. Freezing of elutriates does not seem to show any significant effects on the toxicity. Findings allow to define a weighted schedule of the storage time of sediments and elutriates useful for laboratories to scale analytical priority and strategies related to different sediment types.