The Marine Chemistry Working Group (MCWG) concentrates its work around the status and fate of pollutants (organic substances and trace metals) in marine ecosystems and chemical oceanography (nutrients and ocean acidification). The remit of the group includes analytical challenges encountered in determining, evaluating and reporting chemicals in marine compart-ments from sample preparation to the final result, as well as crucial steps to achieve satisfactory Quality Assurance.

Contaminants of emerging concern (CECs) are highlighted as a major topic in this report, in terms of their identification, the collection of information on their presence, concentrations in marine compartments across the ICES area, their ecotoxicological potential, and the exchange of information on how to monitor these compounds. The occurrence of microplastics in sediments, current limitations with collection methods and the potential for these to act as vectors for pol-lutants was reviewed.

During this reporting period, particular attention was given to human activities at sea (e.g. off-shore windfarms, shipping, fishing) as a source of chemical pollution and the rapidly evolving regulations associated with these activities in order to anticipate their impact. MCWG also un-dertook a comprehensive review of national assessments completed prior to disposal of dredge materials at sea, including the comparison of regulated substances and thresholds used in the management of dredging activities, as well as monitoring approaches at disposal sites.

MCWG was interested in discussing advances and application in passive sampling techniques, particularly with regards to compliance monitoring, and continues updating on developments on passive sampling by informing on on-going projects from ICES area.

MCWG reviewed techniques for the analysis of discrete water samples for nutrient analysis and outcomes are presented. Quality Assurance of Information on Marine Environmental Monitor-ing (QUASIMEME) assessments of chlorophyll data in relation to analytical methods was ana-lysed, which provided the rationale for an update of the existing ICES Techniques in Marine Environmental Science (TIMES) 30 guidelines on chlorophyll determination.

A spreadsheet-based database on the occurrence of CECs in European waters corresponding to selected contaminant families was developed and is being maintained. New ICES TIMES Guide-lines for the use of Diffusive Gradients in Thin Films for measuring metal fluxes in sediment were published, and MCWG members also contributed to an ICES Viewpoint with the Working Group on Shipping Impacts in the Marine Environment (WGSHIP) on scrubber discharge water from ships considering risks to the marine environment and recommendations to reduce im-pacts.

Further publication are being finalised, notably an update of the TIMES 30 guideline on Chloro-phyll determination, the review on national and regional legislation for contaminants in seafood. The review of data on CECs will also be developed into a publication.