​​​​​​​​Results and confidence

Current status in the Baltic Sea

All scale 4 assessment units evaluated for the primary matrix biota achieved good status during the period 2011-2016, except for unit FIN-006 (Merenkurkun sisäsaaristo). It should be noted that those assessment units failing the threshold were generally dominated by few and short data series (i.e. 'initial' data, see assessment protocol) for this current assessment. This means that the upper confidence concentration of PFOS in sampled fish were below the threshold value (Key message figure 1 and Results figure 1). The primary threshold value is set to 9.1 µg/kg wet weight in fish muscle (or 9.1 ng/g ww) with the protection goal of human health.

There are currently areas in the Baltic Sea that are not covered by any PFOS monitoring (Results figure 2). The Estonian coastline of Gulf of Finland and the Gulf of Riga lack reported PFOS concentrations. There are also areas where the results are only based on measurements of 1-2 years ('initial' data: open circles in Results figure 2.). Thus increased monitoring is needed to enable a status evaluation for the entire Baltic Sea. The lowest mean concentration in the aggregated assessment (0.32 ng/g ww muscle) is observed in area SEA-001 (the Kattegat open sea subbasin) and the highest concentration in area FIN-006 (Merenkurkun sisäsaaristo) with estimated upper confidence interval of 13 ng/g ww muscle (1.4 times the threshold value) (Results figure 1).

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Results figure 1: Concentrations of PFOS in fish relative to the threshold value. Filled circles represent a mean value for each assessment unit and the bar represents the upper 95% confidence limit. Green colour indicates that the assessed area achieves the threshold value and red colour that the assessed area fails the threshold.



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Results figure 2: Spatial distribution of PFOS monitoring stations for biota (herring, cod, perch, eelpout and European flounder are represented) (left) and status assessment by assessment unit in biota (right). Green colour indicates that the upper 95 % confidence interval for PFOS concentration is below the threshold value (i.e. good status). Small open circles indicate a status assessment based on only 1-2 years of data (initial data), small filled circles indicate that data is not suitable to assess a trend (treated with initial methodology), large filled circles that no detectable concentration trends can be identified during the whole monitoring period (full data), and the filled arrow indicate that there is a statistically defined upward or downward trend during the monitoring period. Click here to access interactive maps at the HELCOM Map and Data Service: PFOS.

It is important to be aware that the results used for this core indicator are mainly (but not completely) based on fish from stations considered as reference stations with no local pollution. There are most likely local areas within the Baltic Sea where the pollution load of PFOS is higher than presented in the evaluation outcome of this indicator. 


Evaluation of temporal trends

Increasing PFOS concentrations have been shown in biota time series starting in the 1970s and 1980s (Bignert et al. 2017). However, some downward trends are seen in herring from the Bothnian Sea, the offshore station in the Northern Baltic Proper and in Kattegat in the more recent time period (Results figures 2 and 3) in the current assessment.


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Results figure 3: Temporal trend of PFOS concentration (µg/kg wet weight) in herring liver from the Bothnian Sea, the off shore station in the Northern Baltic Proper and in Kattegat (HQS – threshold level, grey colour- confidence level 95% range (see Assessment protocol).


Evaluation of secondary matrices

Concentrations of PFOS have also been monitored in surface water by some countries (Denmark, Germany and Lithuania). When these results are assessed for the QS(secondary poisoning) set in water, all assessment units fail the threshold value (Results figure 4 and 5). The water QS is derived from biota QS and the difference in PFOS status between biota and water are most likely due to uncertainties in translation of biota QS into water QS. The translation involves assumptions of bioconcentration factors and biomagnification factors with a precautionary approach and may lead to a stricter QS value in water. 


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Results figure 4: Spatial distribution of PFOS monitoring stations for the secondary threshold evaluation in seawater (left) and status assessment by assessment unit in seawater (right). Green colour indicates that the upper 95 % confidence interval for PFOS concentration is below the threshold value (i.e. good status). Small open circles indicate a status assessment based on only 1-2 years of data (initial data), small filled circles indicate that data is not suitable to assess a trend (treated with initial methodology), large filled circles that no detectable concentration trends can be identified during the whole monitoring period (full data), and the filled arrow indicate that there is a statistically defined upward or downward trend during the monitoring period. The assessment is carried out using scale 4 HELCOM assessment units (defined in the HELCOM Monitoring and Assessment Strategy Annex 4). Click here to access interactive maps at the HELCOM Map and Data Service: PFOS.


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Results figure 5: Concentrations of PFOS in water relative to the threshold value. Filled circles represent a mean value for each assessment unit and the bar represents the upper 95% confidence limit. Green colour indicates that the assessed area achieves the threshold value and red colour that the assessed area fails the threshold.


Confidence of the indicator status evaluation

The geographical resolution for the coverage of the whole Baltic Sea is low. No detailed geographical studies to investigate the variability have yet been carried out. The conversion of PFOS concentrations in liver to muscle values introduces uncertainties into the status evaluation. In addition, the trophic level of the fish used for monitoring (predominantly herring, which has a trophic level of approximately 3 in the Baltic Sea) is lower than recommended for the threshold value, thus leading to possible underestimations in relation to the threshold value.

With the uncertainties and low geographical coverage taken into account, but with values considerably lower than the threshold value, the confidence in the evaluation of the aggregated assessment units is considered to be high.