Data are submitted to the MERMAN database by relevant UK 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. These timeseries were then assessed for status and trends using the methods described 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. (Note that if the extraction date at the top of the assessment application is later than 30 April 2020, the assessment has been updated.)

The National Performance Framework Clean Seas Indicator is constructed by selecting the timeseries in Scottish waters and making regional assessments of the concentrations of cadmium, lead, mercury, PAHs and PCBs in biota and sediment in three regions: the Northern North Sea, Minches and Western Scotland and Irish Sea (Clyde & Solway). For each contaminant or contaminant group, region, and biota / sediment, the mean concentration is compared to the EAC (or an equivalent threshold when the EAC has not been established). The Indicator is the percentage of these comparisons in which the mean concentration is significantly below the threshold. The results and the methods behind them can be found at http://marine.gov.scot/datafiles/npf/clean_seas/2019/Clean_Seas_Indicato... and the links within. Regional assessments for selected contaminant groups, biological effects, and a fourth region (Scottish Continental Shelf) that are not used in the Clean Seas Indicator can also be found at the same location.

The data archived here are the raw data for the timeseries in Scottish waters of selected metals, PAHs, PCBs, polybrominated diphenyl ethers, imposex (VDS), ethoxyresorufin-O-deethylase (EROD) activity and bile metabolites. The summary measures of trend and status from each timeseries that form the input to the regional assessments are also archived.

The data and regional assessments are also the basis of the assessments of these contaminants and biological effects in Scotland's Marine Assessment 2020.