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Mercury concentrations in fish muscle
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Key message
The results concerning the development of mercury concentration in the investigated matrices are not consistent. The concentration in herring from the northern Baltic Proper seems to increase during the investigated time period until the mid 90ies but with a decreasing trend the recent 15 years. The concentrations in spring caught herring from the southern Bothnian Sea and the southern Baltic Proper are at lower levels today compared to the beginning of the investigated time period. The annual mean concentrations in herring muscle during the investigated time period are all below 100 ng/g except for a few years at Ängskärsklubb.
Figure 1. Spatial variation in mean concentration of mercury in herring muscle (2007-2009 in ng/g fresh weight). The highest concentration around (65 ng/g ) was found in the northern part of the Baltic Proper (Lagnö), the lowest around (8 ng/g) in the Gulf of Riga. Some of the sampling sites have only been analysed for two years this far. The Swedish data originates from the Swedish national monitoring programme and are analysed at the Department of Applied Environmental Science, University of Stockholm. Additional data is obtained from ICES database.
Results and assessments
Relevance of the indicator for describing developments in the environment
Analyses of contaminants in biotic samples, in contrast to abiotic matrices, exhibit the bioavaliable part of the contaminants. Herring are commonly used for human consumption.
Policy relevance and policy references
The North Sea Conference (1984, 1987, 1990) that covers all routes of pollution to the North Sea, states that the mercury discharges are to be reduced by 70% between 1985 and 1995, using 1985 as a base year.The Minister Declaration from 1988, within HELCOM, calls for a reduction of the discharges of mercury to air and water by 50% by 1995 with 1987 as a base year.
The use of mercury in the paper pulp industries has been banned in Sweden since 1966.
According to a governmental proposition (1993/94:163) the aim is that all mercury usage should have ceased the year 2000 in Sweden.
Assessment
There is no common general trend for mercury in herring muscle for the investigated time series.Mercury was monitored in spring caught herring from Ängskärsklubb and Karlskrona for four years in the beginning of the seventies, and these series were taken up again in 1996. Both series show significantly lower concentrations during the recent time period compared to the concentrations in the early seventies, at Ängskärsklubb this decrease is about 60%.
The time series for autumn caught herring from Ängskärsklubb in the Bothnian Sea shows a very large between-year variation. Although the sampling site at Ängskärsklubb is located rather far off the coast, the mercury concentration in our herring samples could be influenced by local discharges. Ängskärsklubb may thus not be representative of the Bothnian Sea.
Figure 2. Temporal trends of mercury concentration (ng/g fresh weight) in herring muscle from four different sampling sites in the Baltic Sea (1980-2009). Harufjärden (Bothnian Bay), Ängskärsklubb (S. Bothnian Sea), Landsort (N. Baltic Proper), Utlängan (S. Baltic Proper). The magenta coloured line represents a decreasing trend during the last ten years at Landsort and the blue line is a simple 3-point running mean smoother fitted to the annual geometric mean values. The horizontal line is the mean concentration of the analysed period. A red cross represents a suspected outlier.
Figure 3. Temporal trends of mercury concentration (ng/g fresh weight) in spring caught herring muscle from southern Bothnian Sea (Ängskärsklubb) and the southern part of Baltic Proper (Karlskrona) (1971-2009). The red lines presented are based on a log-linear regression analyses and show decreasing trends of about 2.5 and 0.92 % per year respectively. The linear dotted line is the mean concentration of the analysed period. A red cross represent a suspected outlier.
References
Bignert, A., Berger, U., Boalt, E., Borg, H., Danielsson S., Eriksson, U., Haglund, P., Hedman, J., Holm, K., Johansson, A-K., Miller, A., Nyberg, E., Nylund, K..2011. Comments Concerning the National Swedish Contaminant Monitoring Programme in Marine Biota. Report to the Swedish Environmental Protection Agency, 2011. 224 pp.Data
Trend (in %) assessed from the annual geometric mean of concentrations of mercury (ng/g fresh weight) in various matrices and sites during the time period 1971/80-2009 and the estimated mean concentration for the last year (2009). The trend is reported, if p<0.1. The age interval, the total number of analyses and the number of years are also presented. The numbers presented in brackets are the 95% confidence intervals.
| Matrix | age | n analyses | n yrs | year | trend(95% ci) | mean concentration of last year (95% ci) |
| Herring muscle | ||||||
| Harufjärden | 3-5 | 467 | 29 | 80-09 | 38 (31-46) | |
| Ängskärsklubb | 3-5 | 449 | 29 | 80-09 | 39 (26-60) | |
| Ängskärsklubb, spring | 232 | 18 | 72-09 | -2.5 (-3.5,-1.6)* | 23 (19-27) | |
| Landsort | 3-5 | 439 | 30 | 80-09 | 27 (21-37) | |
| Utlängan | 2-4 | 454 | 30 | 80-09 | 20 (15-27) | |
| Utlängan, spring | 232 | 18 | 72-09 | -.92 (-1.7,-.16)* | 18 (16-20) |
* significant trend, p < 0.05
Metadata
Technical information
Data source: The ICES database and results from the National Swedish Monitoring Programme of Contaminants in Biota.For the Swedish data, sampling, sample preparation, storage in specimen bank and evaluation of results are carried out by the Department of Contaminant Research at the Swedish Museum of Natural History, Stockholm. Chemical Analysis is carried out at the Department of Applied Environmental Science at Stockholm University.
Geographical coverage: see data table and map.
Temporal coverage: see data table and figures.
Methodology and frequency of data collection, see Bignert et al, 2011
Methodology of data manipulation. For a detailed description of statistical methods use, see Bignert et al. 2011.
Quality information
The number of years required to detect an annual change of 10 % varied between 9 and 16 years for the herring time series.
For reference purposes, please cite this indicator fact sheet as follows:
[Author’s name(s)], [Year]. [Baltic Sea Environment Fact Sheets title]. HELCOM Baltic Sea Environment Fact Sheets 2011. Online. [Date Viewed], http://www.helcom.fi/environment2/ifs/en_GB/cover/.
Last updated: 19.9.2011