​​​​​​​​​​​​Results and confidence

Good status was achieved in terms of concentrations of hexabromocyclododecane (HBCDD) in fish in all evaluated assessment units during the period 2011-2016 as the upper confidence concentrations were below the threshold value of 167µg/kg wet weight (ww) (or 167ng/g ww) (Results figure 1).

The results are based on HBCDD concentrations in different fish species, but also different matrixes, i.e. muscle and liver (Results figure 1). This brings extra variability in the results due to species differences and matrix specific properties.

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Results figure 1. Concentrations of HBCDD 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 is below the threshold value and red colour that the assessed area is above.


Mean concentration of HBCDD in fish from all monitored stations were well below the threshold value (Results figure 2). The lowest values of HBCDD are observed in assessment unit SEA-001 (Kattegat open sea subbasin) with the upper 95% confidence interval of 0.35 ng/g ww in fish and the highest concentrations in assessment unit in SEA-017  (Bothnian Bay open sea subbasin) with upper confidence values of 3.4 ng/g ww in fish. These values are adjusted to a mean lipid content of 5%. The threshold value is about 50 times higher than the maximum upper confidence value detected.


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Results figure 2: Spatial variation of the HBCDD sampling stations in biota (herring, cod, perch, eelpout and European flounder) (left) and status assessment by assessment unit in biota (right). Green colour indicates that the upper 95 % confidence interval for HBCDD concentrations are 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: HBCDD.


Evaluation of temporal trends

Long term data from biota monitoring stations show increasing HBCDD concentrations from the 1970s and 1980s to the 2000s (Bignert et al. 2017). Cod from south-eastern Gotland show a high increase with concentration values four times higher in the 2000s than in the 1980s.

Since the end of the 1990s, decreasing levels are seen at the Swedish west coast station Fladen for both herring and cod, and the same trend is also detected for herring from Utlängan in the southern Baltic Proper, and in herring from two stations in the Bothnian Sea (Results figure 3 and Bignert et al. 2017).


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Results figure 3: Temporal trend of HBCDD concentration (ng/g wet weight) in herring muscle from the Bothnian Sea, the south Baltic Proper and in Kattegat (HQS – threshold level, grey colour- confidence level 95% range (see Assessment protocol).


Evaluation of secondary matrices

Concentrations of HBCDD have also been monitored in sediments by some countries (Sweden, Lithuania, and open sea subbasins of the Bothnian Bay, Bothnian Sea, Åland Sea and Northern Baltic Proper). When these results are assessed against the QS for sediment all assessment units with data show a status below the threshold, except for LIT-002 and LIT-006 where short time series data (initial data) contribute to the assessment (Results figure 4).


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Results figure 4: Status assessment results based on secondary threshold evaluation of HBCDD in sediment. 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: HBCDD.


Confidence of indicator status evaluation

The overall confidence of the assessment is high.

The geographical resolution of the current biota dataset for the whole Baltic Sea is moderate, though low or absent in some assessment units. Monitoring in sediments generally has low spatial and temporal coverage. No detailed geographical studies to investigate the variability in HBCDD concentrations across the region have yet been carried out. However, good status is widely achieved and the distance from the measured concentrations in fish to the current threshold value is large, with the smallest distance observed in SEA-017 (Bothnian Bay open sea subbasin) where the threshold value is 50 times higher than the reported mean value. Therefore the confidence that the observed levels do not exceed the current threshold value is high.

It should also be noted that the majority of the monitoring stations are selected as reference stations and potential local problems with HBCDD may occur in areas not included in the current monitoring programmes.