Interim report of the HELCOM CORESET project

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ing national data sets. Note: the values given here are provisional and require further validation when new
data becomes available.
The 90% percentile (P90) separates the upper 10% of all values in the group from the lower 90%. The
rationale for this decision was that elevated MN frequency would lie above the P90 percentile, whereas the
majority of values below P90 belong to unexposed, weakly-medium exposed or non-responding adapted
individuals. P90 values were calculated for those stations/areas which were considered being reference
stations (i.e. no known local sources of contamination or those areas which were not considered unequivocally
as reference sites but as those less infl uenced from human and industrial activity).
ACs in bivalves Mytilus edulis, Mytilus trossulus, Macoma balthica (data from MN analysis in 2370 specimens),
in fi sh Limanda limanda, Zoarces viviparus, Platichthys fl esus, Gadus morhua and Clupea harengus
(data from MN analysis in 3239 specimens) from Baltic Sea have been calculated using NRC (Lithuania)
databases (Table 3.22).
Table 3.22. Assessment criteria of MN frequency levels in bivalve mollusc and fi sh. BR =Background
response; ER = Elevated response; n = number of specimens analysed.
Species Size (cm) T (ºC) Region Tissue BR ER n
Mytilus edulis 1.5-3 8-18 Baltic Sea Gills 2.50 1810
Mytilus trossulus 2-3 3-15 Baltic Sea Gills 4.50 230
Macoma balthica 1-3 13-18 Baltic Sea Gills 2.90 330
Zoarces viviparus 15-32 7-17 Baltic Sea Erythrocytes 0.38 824
Limanda limanda 18-25 8-17 Baltic Sea Erythrocytes 0.49 117
Platichthys fl esus 17-39 10-17 Baltic Sea
coastal
Erythrocytes 0.29 828
Platichthys fl esus 18-40 6-18 Baltic Sea
offshore
Erythrocytes 0.23 970
Gadus morhua 20-48 13-15 Baltic Sea Erythrocytes 0.38 50
Clupea harengus 16-29 6-18 Baltic Sea Erythrocytes 0.39 450
Distribution of indicator species in Baltic Sea subregions
MN test has generally been applied to organisms where other biological-effects techniques and contaminant
levels are well documented. That is the case for mussels and for certain demersal fi sh species (as
European fl ounder, dab or Atlantic cod), which are routinely used in biomonitoring programs and assess
contamination along western European marine. However, the MN assay may be adapted for alternative
sentinel species using site-specifi c monitoring criteria.
When selecting an indicator fi sh species, consideration must be given to its karyotype as many teleosts are
characterised by an elevated number of small chromosomes (Udroiu et al. 2006). Thus, in certain cases MN
formed after exposure to clastogenic contaminants will be very small and hard to detect by light microscopy.
This can be addressed to a certain extent by using fl uorescent staining. After selecting target/suitable
species, researchers should also ensure that other factors including age, sex, temperature and diet are
similar between the sample groups. If conducting transplantation studies, consideration needs to be given
to the cellular turnover rate of the tissue being examined to ensure suffi cient cells have gone through cell
division. For example, if using blood the regularities of erythropoiesis should be known prior to sampling.
Large-scale and long-term studies took place from 2001 to 2010 at the Nature Research Centre (NRC,
Lithuania) on MN and other abnormal nuclear formations in different fi sh and bivalve species inhabiting
various sites of the Baltic Sea. These studies revealed the relevance of environmental genotoxicity levels