National Performance Framework - Clean Seas Indicator 2020

The Clean Seas Indicator for 2020 is 93%. This means that 93% of assessments of metals, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in biota and sediment in Scottish marine waters show concentrations that are unlikely to harm marine organisms. The Indicator is unchanged from its 2019 value.

The Indicator is calculated by assessing the concentrations of cadmium, lead, mercury, PAHs and PCBs in biota (fish and shellfish) and sediment in three1 regions: the Northern North Sea, Minches and Western Scotland and Irish Sea (Clyde & Solway). Of the 30 possible assessments, 28 (93%) show acceptable concentrations and 2 show unacceptable concentrations. These are tabulated below with a ✓ indicating acceptable and a ✕ indicating unacceptable.


compartment region cadmium lead mercury PAHs PCBs
biota Northern North Sea ✓ ✓ ✓ ✓ ✓
biota Minches and Western Scotland ✓ ✓ ✓ ✓ ✓
biota Irish Sea (Clyde & Solway) ✓ ✓ ✓ ✓ ✓
sediment Northern North Sea ✓ ✓ ✓ ✓ ✓
sediment Minches and Western Scotland ✓ ✓ ✓ ✓ ✓
sediment Irish Sea (Clyde & Solway) ✓ ✕ ✕ ✓ ✓


The thresholds used to assess whether levels are acceptable differ between contaminants and biota / sediment. Environmental Assessment Criteria (EAC) are used for PCBs in biota and sediment and for PAHs in biota; Effects Range Low (ERL) are used for metals and PAHs in sediment; and Maximum Permissible Concentrations2 (MPC) are used for metals in biota. More information can be found here for biota and sediment.

The raw data used in the assessments can be downloaded here.

Full details of the assessments are available as follows:

These describe the statistical methodology used, and present regional assessments of trends, status with respect to the EAC, ERL or MPC, and status with respect to the Background Assessment Concentration, a more stringent threshold used to assess whether concentrations are at background levels.

They also link to assessments where a more appropriate threshold has been used for mercury in biota and where the PCBs have been separated into groups with different toxicities. These changes reflect developments in international contaminant assessments such as the OSPAR assessment for the North Sea and north-east Atlantic. The 2021 Indicator will be updated to reflect these developments (and the Indicator for previous years will be recalculated for consistency).

Regional assessments of other contaminants and biological effects that do not contribute to the Indicator are also available:


1 Until 2017 the Indicator also included contaminant assessments from a fourth region, the Scottish Continental Shelf. However, difficulties in ensuring adequate spatial coverage in this region resulted in it being dropped from the Indicator in 2018. At the same time, the Indicator for 2015‑2017 was recalculated using just the three regions currently considered. ↩︎

2 The Indicator reports for 2015‑2019 refer to the MPC as the European Commission food standard (EC), but MPC is the preferred terminology. ↩︎