Organic contaminants in marine sediments and seawater: A review for drawing environmental diagnostics and searching for informative predictors.

Marine ecosystems represent major sinks for persistent organic pollutants (POPs). Yet, while their regulations fit localized activity and emissions, POPs are mobile and can persist away from their source. The present review draws an environmental diagnostic of the organic substances studied over the past forty months, which ones accumulated the most, and where. Maximum reported concentration was used as a proxy for the accumulation of contaminants. POPs occurrences studied in the Jan 2018-April 2021 period were recorded into a database, along with (i) the geographical location of the sample and its coastal or offshore origin, (ii) the type of compartment analyzed (water vs sediment), as well as (iii) the POPs and the sample physical-chemical parameters reported. In the articles reviewed, maximum reported concentrations of POPs were in the ng/L range in seawater and in the μg/kg range in sediments. Some hotspots presented concentrations high enough to represent a hazard for sea organisms in the water columns (μg/L range) or in surficial sediments (mg/kg range). On a global scale, offshore (>1 km from the coast) maximum reported concentrations were, for the majority of the POPs, equivalent or higher than coastal ones. Finally, a POP solubility threshold (900 mg/L) was observed above which POPs would not be found in offshore waters, but only in sediments. This review highlights that studying POP accumulation away from their sources is fundamental for the diagnostic of long-lasting marine POPs contaminations. Further, POPs lipophilicity is a good predictor for offshore transport, and an indicator of interest for predicting sediment accumulation. Although POPs fate and transport in oceans is complex and require a finer analysis that this review could provide, the present work is a step forward identifying the hotspots in which POPs could be of particular concern, along with chemical indicators to predict for POPs accumulation in marine reservoirs.