Model development to predict environmental concentrations of chemical substances in marine sediment when the substance is applied via feed in marine aquaculture: Task 1.2. Conceptual Model

The European Food Safety Authority (EFSA) assesses the safety of fish feed additives used in aquaculture. To evaluate their potential environmental risks, it is essential to calculate the predicted environmental concentrations (PEC) in advance and compare them to known exposure thresholds (first step) or to predict no effect concentrations (second step). This report outlines a conceptual framework for developing a model designed to calculate PEC in sediment for additives introduced into marine aquaculture through fish feed.

The model represents the processes that influence the concentration of an additive in marine sediment after its introduction via fish feed. Additives can enter the water column in particulate form directly from feed spillage, and/or through excretion in faeces, or in dissolved form. In the water column, additives in particulate form are transported to the seabed, where sediment processes—such as chemical transformation, resuspension, and mixing—govern their long-term accumulation. Additives excreted in dissolved form can also contribute to sediment concentrations through adsorption onto particles or directly onto the sediment.

The model is divided into four main components: feed to water, water to sediment, sediment to PEC, and site PEC to general assessment. Each component includes sub-processes that are individually discussed, incorporating current scientific understanding from laboratory experiments, field studies, and existing models where available.

Recommendations are provided for formulating the equations of the conceptual model, detailing which processes to include, their functional forms, and the flexibility needed to address different modelling demands. Some processes are unique to specific additives, reflecting their distinct characteristics and behaviours. In a first step (step I) of the environmental risk assessment, these processes will either be assigned default conservative values or excluded altogether. This approach ensures that the model remains widely applicable.