Description:
The indicator measures the extent to which levels of metals, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) are sufficiently low that they are unlikely to harm marine organisms in Scottish waters.
Source of Data:
Contaminant data are collected as part of the UK Clean Seas Environmental Monitoring Programme (CSEMP) to:
a) cover five contaminant groups – cadmium, lead, mercury, PAHs and PCBs;
b) in biota (fish and shellfish) and sediments; and,
c) for four biogeographic regions around Scotland – Northern North Sea, Scottish Continental Shelf, Minches and Western Scotland, and Irish Sea (Clyde & Solway).
The data are submitted to the UK Marine Environment Monitoring and Assessment National (MERMAN) database.
Annual assessments of the data are made by the UK Clean Safe Seas Evidence Group (CSSEG). The assessments consist of the analysis of a large number of time series, each of the concentration of a single contaminant in a single species (for biota) at a single monitoring station.
The Clean Seas Indicator for e.g. the year 2020 is constructing by synthesising the results of the 2020 CSEMP assessment at the biogeographic regional level. For biota and sediment in turn, the mean concentration of each contaminant group in each region is compared to the OSPAR Environmental Assessment Criterion (EAC), or an equivalent threshold when the EAC has not been established. If the mean concentration is statistically significantly below the EAC, then it is unlikely to cause harm to marine life and is acceptably low.
There are currently accepted EACs (or equivalent) for mercury, PAHs, and PCBs in both biota and sediment, and for cadmium and lead in sediment. Combining these with the four regions gives 32 possible comparisons of mean concentrations against EACs. However, it has proved difficult to make regional assessments in the Scottish Continental Shelf due to inadequate spatial coverage. Therefore, only three regions – Northern North Sea, Minches and Western Scotland, and Irish Sea (Clyde & Solway) – are used in the Clean Seas Indicator. With these three regions, there are 24 possible comparisons of mean concentrations against EACs. The Indicator is the proportion of these comparisons in which concentrations are acceptably low.
Note that there are two sets of Indicator values that have been superseded:
- The Indicator for 2015-2020 was previously calculated using a different threshold for mercury in biota and with thresholds for cadmium and lead in biota. However, these thresholds were for assessing food safety rather than environmental health and are now not considered appropriate for making environmental assessments.
The Indicator for 2015 – 2017 was originally calculated using all four regions (i.e. including the Scottish Continental Shelf).
Definitions:
Biogeographic region Scottish waters are divided into four biogeographic regions for contaminant assessments: Northern North Sea, Scottish Continental Shelf, Minches and Western Scotland, and Irish Sea (Clyde & Solway). Of these, only assessments in the Northern North Sea, Minches and Western Scotland, and Irish Sea (Clyde & Solway) are used in the Clean Seas Indicator. (A fifth region, the Atlantic North West Approaches, is rarely sampled because of its remoteness and depth.)
Polycyclic aromatic hydrocarbons occur naturally, but also arise from incomplete combustion and crude oil and refinery products. There are many PAHs but the Indicator only uses data for nine of them.
Polychlorinated biphenyls are man-made and have been used as coolants, lubricants, plasticizers and sealing agents. They were banned over 30 years ago but are extremely persistent in the environment and can still be found in old electrical equipment. There are many PCBs but the Indicator only used data for seven of them.
Environment Assessment Criterion are thresholds developed by the Oslo and Paris Commission for assessing the status of chemical concentrations. If concentrations are below the EAC then they are unlikely to cause adverse effects in marine organisms. EAC are only available for some of the contaminant groups (PAHs and PCBs in biota and PCBs in sediment). Other thresholds are used when EACs are unavailable: these are the Effects Range Low, which is used for cadmium, lead, mercury and PAHs in sediment, and the Quality Standard secondary poisoning, which is used for mercury in biota.
Criteria for Change:
This evaluation is based on: any difference in the Indicator of 4% or more over last year's figure suggests that the position has changed. An increase of 4% or more suggests the position is improving; whereas a decrease of 4% or more suggests the position is worsening.
Future issues or reviews:
The Indicator is currently paused. This is because of the loss of chemical analysis facilities following Storm Arwen. Samples have continued to be collected and will be analysed when chemical facilities are operational once more. Some chemical analysis has been possible, but insufficient to provide the data required for the Indicator. Those data that are available have been submitted to MERMAN and then to the International Council for the Exploration of the Sea, where they are used in annual contaminant assessments for OSPAR. These assessments (and the raw data) can be accessed here.