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 - 2014 were extracted from MERMAN on 6 July 2016. 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 2009 - 2014 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 2015 CSEMP assessment are no longer available online, but the results for the most recent assessment can be found at https://www.bodc.ac.uk/projects/data_management/uk/merman/assessments_an....

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 proportion 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/2015/Clean_Seas_Indicato... and the links within.

The data archived here are the raw data for the timeseries in Scottish waters of selected metals, PAHs and PCBs. The summary measures of trend and status from each timeseries that form the input to the regional assessments are also archived.

Note that the Clean Seas Indicator originally included assessments from a fourth region, the Scottish Continental Shelf. However, it was difficult to get adequate spatial coverage in this region so it was dropped from the Indicator in 2018. At the same time, the 2015 Indicator was recalculated using just the Northern North Sea, Minches and Western Scotland, and Irish Sea (Clyde & Solway).