Thresholds and Status evaluation

The threshold values for sediment and imposex in this core indicator are not yet commonly agreed.

The threshold values are included as test threshold values for the purposes of the 2018 'State of the Baltic Sea' report, and the results are to be considered as intermediate.


Good Status is achieved if the concentrations of TBT are below the specified threshold values (Thresholds figure 1).

threshold figure 1.png

Thresholds figure 1. Good status is achieved if the concentrations of TBT are below the threshold values listed in Good environmental status table 1.


The good status threshold for TBT are based on Environmental Quality Standards (EQS) for water and biota (Good environmental status table 1) which have been defined at EU level for substances included in the priority list under the Water Framework Directive, WFD (European Commission 2000, 2013).

The threshold value is applicable if concentrations are measured in the appropriate matrix. For historical reasons, the countries around the Baltic Sea have differing monitoring strategies. As a pragmatic approach, a threshold value is defined for primary matrix (sediment). However, if suitable monitoring data is not available in a region the secondary threshold value can be used for the evaluation of alternative matrixes (biota, water) (Thresholds table 1). Under the WFD, Member States may establish other values than EQS for alternative matrixes if specific criteria are met (see Art 3.3. in European Commission 2008a, revised in European Commission 2013).


Thresholds table 1. Threshold value for TBT and imposex (EQS – Environmental Quality Standard, AA- Annual Average Concentration, QS – Quality Standard, BAC = Background assessment criteria). Note that the threshold values for sediment (*), biota (*) and imposex (*) are not yet commonly agreed and included as test threshold value.

Threshold values
TBTSediment*1.6 μg /kg dw sediment (5% TOC)
QSsediment[1]Water0.2 ng/l waterEQS water[2]
Mussel*12 μg/kg dw musselEAC[3]



(ISI for Littorina littorea)

GastropodsPeringia ulvae: 0.1 Nucella lapillus: 2.0 Neptunea antiqua: 2.0 Hinia reticulata: 0.3 Buccinum undatum: 0.3 Littorina littorea: <0.3 Gercken & Sordyl 2009;
Magnusson et al. 2016;
OSPAR (2010a) EcoQO

[1] Threshold derived from Swedish legislation (HVMFS 2013:19, and incorporated into HELCOM processes during CORSET II (

[2] European Commission (2013) Directive 2013/39/EU of the European Parliament and of the Council of 12 August 2013 amending Directives 2000/60/EC and 2008/105/EC as regards priority substances in the field of water policy. Off. J. Eur. Union L 226: 1-17.

[3] OSPAR 2010b