Data are submitted to the MERMAN database from relevant Competent Monitoring Authorities. A series of templates are populated by submitting officers and submitted to the database which has in-built data restrictions and a data filter to ensure high quality, accurate data are submitted. The data filter has formulae in-built which use Accredited Quality Control information from known standards, limits, standard deviations and/or inter laboratory calibration exercises to calculate a score. Only data that pass a threshold agreed with the national advisory bodies are used for assessments.

The data for 1999 - 2018 were extracted from MERMAN on 30 April 2020. Further data checks were made and records with obvious errors were deleted or corrected. The concentration and biological effects data were standardised to agreed units and bases and, in the case of sediment, were normalised to 5% aluminium (metals) and 2.5% organic carbon (organics). The data were grouped into time series, typically of a single contaminant in a single species at a single monitoring station. Time series with no data for the period 2013 - 2018 were excluded. The data archived here are those for selected metals, polycyclic aromatic hyrdocarbons, polychlorobiphenyls, polybrominated diphenyl ethers, tributyltin and its derivatives, imposex (VDS), ethoxyresorufin-O-deethylase (EROD), bile metabolites and other biological effects measurements.

The methods used to assess the individual time series and synthesise the results at a regional level can be found at https://www.bodc.ac.uk/projects/data_management/uk/merman/assessments_an.... The results for the most recent CSEMP assessment can be found at the same location (if the extraction date at the top of the assessment application is later than 30 April 2020, the assessment has been updated).