Purpose: The present study evaluated the effects of Superdispersant-25 (SD25), a commercial dispersant stockpiled in the United Kingdom for oil spill response, on the sorption dynamics of two polyaromatic hydrocarbons, naphthalene (NAP) and phenanthrene (PHE), in sediment-seawater systems using three sediments near hydrocarbon exploration areas in the Faroe-Shetland Channel and North Sea. Materials and methods: Batch experiments were conducted to evaluate the effects of SD25 on the solubility (analysed by gas chromatography), distribution coefficients and desorption hysteresis of NAP and PHE separately as well as SD25 in the three sediments (analysed by UV-vis spectroscopy and surface tension measurements, respectively). Results and discussion: The results revealed that SD25 readily adsorbed to all sediment types but did not desorb from silty loam. SD25 application increased the solubility in seawater of PHE but not of NAP. Adsorbed SD25 increased the distribution coefficients of both polyaromatic hydrocarbons in sand but not silty loam and the solubilising effect of SD25 appeared to drive increased adsorption of PHE rather than sediment-adsorbed SD25 concentration. Conclusions: The findings highlight the influence of SD25 application on the sorption dynamics of NAP and PHE in marine sediments from areas near hydrocarbon exploration and production regions. An understanding of these interactions may aid responders in the decision-making process of dispersant application in the event of a spill as seabed characteristics affect oil-dispersant-sediment interactions. Response to Reviewers: Thank you for the comments on the latest version of the manuscript. As in the first revision, I've enclosed replies in a separate file for ease of visualisation. Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation Ref.: Ms. No. JSSS-D-18-00190R1 Replies to reviewers' and editors' comments Comments by reviewers and editors are shown in italics and responses in bold.
