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Temporal trends in contaminants in Herring in the Baltic Sea in the period 1980-2008
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Key message
The temporal trend analyses of heavy metals showed 19 significant trends (8 upwards and 11 downwards) out of 50 tests. The remarkable upward trends were cadmium (2), zinc (5), and copper (1). The downward trends were lead (5), mercury (5), and zinc (1).
The temporal trend analyses of PCB’s (Poly Chlorinated Biphenyls) and Lindane showed 54 significant trends (all downwards) out of 78 tests.
Results and assessment
The temporal trend analyses of heavy metals showed 19 significant trends (8 upwards and 11 downwards) out of 50 tests. For cadmium 2 areas (Hanöbukt, and Gävlebukt) had strong significant upward trends. For lead 5 areas showed a downward trend (Kattegat N, Hanöbukt, Stockholm area, Gävlebukt, and Luleå area). Mercury showed significant downward trends in 5 areas (Hanöbukt, Stockholm area, Gävlebukt, Bothnian Sea, and Luleå area). Zinc showed increasing trends in 5 areas (Kattegat N, Hanöbukt, Outer Gulf of Finland, Gävlebukt, and Luleå area) and a decreasing trend in one area (Bothnian Sea). Copper showed an increasing trend in one area (Gävlebukt). One upwards trend was found for copper (Gävlebukt).
Compared with the last update of the indicator in 2007, no general improvement can be found in relation to the heavy metals. The number of significant trends has increased from 14 to 19. This increase constitutes of 3 increasing trends and 2 decreasing trends. It should be emphasized that the increasing number of years in a time series in general increase the chance of getting a significant result (the type II error (no significant results, despite the fact there is actual a trend) decreases with the number of years). At the same time lack of data in more recent years from some areas impairs the comparison and the fact that the length of some time series are rather limited makes significant test results less likely. The two significant upwards trends for cadmium and on upward trend for zinc is starting to be reversed by decreasing concentrations during the last years.
The temporal trend analyses of PCB’s (Poly Chlorinated Biphenyls) and lindane showed 54 significant trends (all downwards) out of 78 tests. Compared with the last update of the indicator in 2007 the number of significant trends has increased from 41 to 54.
The trends documented in Table 1 are summarised in the Figures 1-13.
The observed upward trend in the concentration of cadmium in herring is comparable to observations in other biotic matrices. The temporal trend of cadmium in seawater shows in general a downward trend. This remarkable difference between matrices has so far no clear explanation.
The downward trends of lead in the majority of the areas are probably caused by the reduced atmospheric input of anthropogenic lead due to the removal of lead from the petrol. The causes of the two upward trends in zinc are not clear.
Both copper and zinc are involved in many metabolic processes and carry out specific physiological roles which means that the observed changes can be related to natural variability as well as anthropogenic activities.
The very pronounced reduction in the concentration of PCB’s in many areas is probably a result of the regulations and bans in the countries around the Baltic Sea.
The downward trend in the concentration of lindane in herring in five areas is probably a result of regulations and bans in countries around Baltic Sea leading to a reduced emission of lindane.
Table 1: The results of the time trend analysis using a non-parametric Mann-Kendall test. For each area and substances the results of the test are given. All the chemical analyses for Heavy metals are done on liver tissue except for Mercury where the analyses are done on muscle tissue. All the chemical analyses for PCB’s and Lindane are done on muscle tissue. Upper row (r): the Kendall tau correlation coefficient. Middle row (P): significance level. Lower row (n); number of observations (years) in the time series. The last year in the time series are indicated italic in parentheses. The significant upward trends are indicated by P-values shown in bold while significant downward trends are indicated by P-values in italics. The significance level of P<0.05 are used.
| Area | Cadmium (liver) | Lead (liver) | Mercury (muscle) | Copper (liver) | Zinc (liver) | |
| Kattegat N | r | 0.022 | -0.56 | -0.225 | -0.261 | 0.398 |
| P | 0.888 | 0.0003 | 0.107 | 0.1013 | 0.0128 | |
| n | 22 (2003) | 22 (2003) | 26 (2006) | 22 (2003) | 21 (2003) | |
| Hanöbukt | r | 0.561 | -0.499 | -0.437 | 0.27 | 0.459 |
| P | 0.0003 | 0.0013 | 0.0014 | 0.084 | 0.003 | |
| n | 22 (2003) | 22 (2003) | 27 (2006) | 22 (2003) | 22 (2003) | |
| Stockholm area | r | 0.294 | -0.619 | -0.458 | -0.106 | -0.249 |
| P | 0.065 | <0.0001 | 0.0008 | 0.505 | 0.127 | |
| n | 21 (2003) | 21 (2003) | 27 (2006) | 21 (2003) | 20 (2003) | |
| Åland | r | 0.195 | 0.356 | -0.031 | 0.429 | -0.619 |
| P | 0.543 | 0.317 | 0.89 | 0.176 | 0.0509 | |
| n | 7 (2004) | 7 (2004) | 12 (2004) | 7 (2004) | 7 (2004) | |
| Outer Gulf of Finland | r | -0.333 | -0.577 | 0.126 | -0.333 | 0.733 |
| P | 0.348 | 0.143 | 0.499 | 0.348 | 0.0388 | |
| n | 6 (2004) | 6 (2004) | 16 (2004) | 6 (2004) | 6 (2004) | |
| Inner Gulf of Finland | r | -0.111 | 0.471 | -0.324 | 0.056 | -0.444 |
| P | 0.677 | 0.121 | 0.054 | 0.835 | 0.095 | |
| n | 9 (2006) | 9 (2006) | 19 (2006) | 9 (2006) | 9 (2006) | |
| Gävlebukt | r | 0.537 | -0.454 | -0.633 | 0.414 | 0.445 |
| P | 0.0005 | 0.0036 | <0.0001 | 0.0083 | 0.0053 | |
| n | 22 (2003) | 22 (2003) | 27 (2006) | 22 (2003) | 21 (2003) | |
| Bothnian Sea | r | 0.333 | 0.447 | -0.415 | -0.156 | -0.511 |
| P | 0.18 | 0.117 | 0.0381 | 0.531 | 0.0397 | |
| n | 10 (2007) | 10 (2007) | 15 (2007) | 10 (2007) | 10 (2007) | |
| Bothnian Bay | r | -0.222 | 0.471 | -0.128 | 0.167 | 0.167 |
| P | 0.404 | 0.121 | 0.397 | 0.532 | 0.531 | |
| n | 9 (2007) | 9 (2007) | 23 (2007) | 9 (2007) | 9 (2007) | |
| Luleå | r | 0.096 | -0.604 | -0.345 | -0.004 | 0.396 |
| P | 525 | <0.0001 | 0.011 | 0.979 | 0.011 | |
| n | 23 (2003) | 23 (2003) | 28 (2006) | 23 (2003) | 22 (2003) |
Table 1 Continued
| Area | CB28 | CB52 | CB101 | CB118 | CB138 | CB153 | CB180 | HCHG Lindane | |
| Kattegat N | r | -0.331 | -0.45 | -0.842 | -0.832 | -0.832 | -0.681 | -0.554 | -0.779 |
| P | 0.055 | 0.0066 | <0.0001 | <0.0001 | <0.0001 | <0.0001 | 0.0007 | <0.0001 | |
| n | 20 (2008) | 20 (2008) | 20 (2008) | 20 (2008) | 20 (2008) | 20 (2008) | 20 (2008) | 17 (2007) | |
| Hanöbukt | r | 0.071 | -0.45 | -0.38 | -0.368 | -0.189 | 0.0421 | 0.116 | -0.738 |
| P | 0.674 | 0.0071 | 0.023 | 0.0231 | 0.243 | 0.795 | 0.475 | <0.0001 | |
| n | 19 (2008) | 19 (2008) | 19 (2008) | 20 (2008) | 20 (2008) | 20 (2008) | 20 (2008) | 18 (2004) | |
| Stockholm area | r | -0.56 | -0.547 | -0.558 | -0.567 | 0.602 | -0.394 | -0.498 | -0.895 |
| P | 0.0003 | 0.0004 | 0.0003 | 0.0002 | <0.0001 | 0.0103 | 0.0012 | <0.0001 | |
| n | 22 (2008) | 22 (2008) | 22 (2008) | 22 (2008) | 22 (2008) | 22 (2008) | 22 (2008) | 19 (2007) | |
| Åland | r | 0.195 | -0.786 | -0.571 | -0.786 | -0.714 | -0.929 | -0.143 | |
| P | 0.543 | 0.0065 | 0.0478 | 0.0065 | 0.0133 | 0.0013 | 0.652 | ||
| n | 5 (2002) | 7 (2002) | 8 (2002) | 8 (2002) | 8 (2002) | 8 (2002) | 8 (2002) | 7 (2002) | |
| Outer Gulf of Finland | r | -0.182 | -0.429 | -0.429 | -0.571 | -0.429 | -0.5 | 0.238 | |
| P | 0.533 | 0.138 | 0.138 | 0.0478 | 0.138 | 0.0833 | 0.453 | ||
| n | 4 (2002) | 8 (2002) | 8 (2002) | 8 (2002) | 8 (2002) | 8 (2002) | 8 (2002) | 7 (2002) | |
| Inner Gulf of Finland | r | -0.366 | -0.022 | -0.429 | -0.429 | -0.657 | -0.593 | -0.695 | -0.462 |
| P | 0.173 | 0.913 | 0.026 | 0.026 | 0.0006 | 0.0021 | 0.0003 | 0.0281 | |
| n | 9 (2006) | 14 (2006) | 15 (2006) | 15 (2006) | 15 (2006) | 15 (2006) | 15 (2006) | 13 (2006) | |
| Gävlebukt | r | 0.048 | -0.458 | -0.4 | -0.2 | -0.4 | -0.263 | -0.368 | -0.912 |
| P | 0.778 | 0.791 | 0.0137 | 0.218 | 0.0137 | 0.105 | 0.023 | <0.0001 | |
| n | 19 (2008) | 18 (2008) | 20 (2008) | 20 (2008) | 20 (2008) | 20 (2008) | 20 (2008) | 17 (2006) | |
| Bothnian Sea | r | -0.197 | -0.184 | -515 | -0.606 | -0.748 | -0.727 | -0.788 | -0.477 |
| P | 0.463 | 0.435 | 0.0197 | 0.0061 | 0.0008 | 0.001 | 0.0004 | 0.0423 | |
| n | 9 (2007) | 11 (2007) | 12 (2007) | 12 (2007) | 12 (2007) | 12 (2007) | 12 (2007) | 12 (2007) | |
| Bothnian Bay | r | -0.114 | -0.211 | -0.44 | -0.421 | -0.517 | -0.524 | -0.448 | -0.323 |
| P | 0.673 | 0.297 | 0.0227 | 0.0292 | 0.0075 | 0.0065 | 0.02 | 0.127 | |
| n | 9 (2007) | 14 (2007) | 15 (2007) | 15 (2007) | 15 (2007) | 15 (2007) | 15 (2007) | 13 (2007) | |
| Luleå | r | -0.377 | -0.428 | -0.552 | -0.524 | -0.61 | -0.419 | -0.486 | -0.935 |
| P | 0.0479 | 0.0146 | 0.0005 | 0.0009 | 0.0001 | 0.0079 | 0.0021 | <0.0001 | |
| n | 19 (2008) | 18 (2008) | 21 (2008) | 21 (2008) | 21 (2008) | 21 (2008) | 21 (2008) | 18 (2007) |
Fig.1. Temporal trends of cadmium in herring livers. Red arrows indicate a significant upward trend. Green arrows indicate a significant downwards trend. Blue dots indicate no significant trend.
Fig.2. Temporal trends of lead in herring livers. Red arrows indicate a significant upward trend. Green arrows indicate a significant downwards trend. Blue dots indicate no significant trend.
Fig.3. Temporal trends of mercury in herring livers. Red arrows indicate a significant upward trend. Green arrows indicate a significant downwards trend. Blue dots indicate no significant trend.
Fig.4. Temporal trends of cupper in herring livers. Red arrows indicate a significant upward trend. Green arrows indicate a significant downwards trend. Blue dots indicate no significant trend.
Fig.5. Temporal trends of zinc in herring livers. Red arrows indicate a significant upward trend. Green arrows indicate a significant downwards trend. Blue dots indicate no significant trend.
Fig.6. Temporal trends of CB28 in herring livers. Red arrows indicate a significant upward trend. Green arrows indicate a significant downwards trend. Blue dots indicate no significant trend.
Fig.7. Temporal trends of CB52 in herring livers. Red arrows indicate a significant upward trend. Green arrows indicate a significant downwards trend. Blue dots indicate no significant trend.
Fig.8. Temporal trends of CB101 in herring livers. Red arrows indicate a significant upward trend. Green arrows indicate a significant downwards trend. Blue dots indicate no significant trend.
Fig.9. Temporal trends of CB118 in herring livers. Red arrows indicate a significant upward trend. Green arrows indicate a significant downwards trend. Blue dots indicate no significant trend.
Fig.10. Temporal trends of lead CB138 in herring livers. Red arrows indicate a significant upward trend. Green arrows indicate a significant downwards trend. Blue dots indicate no significant trend.
Fig.11. Temporal trends of CB153 in herring livers. Red arrows indicate a significant upward trend. Green arrows indicate a significant downwards trend. Blue dots indicate no significant trend.
Fig.12. Temporal trends of CB180 in herring livers. Red arrows indicate a significant upward trend. Green arrows indicate a significant downwards trend. Blue dots indicate no significant trend.
Fig.13. Temporal trends of Lindane in herring livers. Red arrows indicate a significant upward trend. Green arrows indicate a significant downwards trend. Blue dots indicate no significant trend.
Metadata
Data on various contaminants (cadmium, lead, mercury, copper, zinc, PCB’s and Lindane) in Herring exists from several areas of the Baltic Sea. Based on extractions from the ICES Database on contaminants in biota 10 areas with sufficient temporal coverage were identified. The areas are listed in Table 1 and 2. The length of the time series is rather variable. Some of them extend back to 1980 while others cover only the very recent years. Only time series of more than 5 years are considered in this analysis, and the number of years covered are indicated in the tables. Time series that ended before 2003 are not treated in this analysis.
Time trend analyses were made using the non-parametric Mann-Kendall test using a two-sided test with a significance level of 5%. The analyses revealed some significant trends in various contaminants. The yearly median concentration is uses as a basis for the test. The detailed results of the analyses can be found in Table 1 and 2. In total, 73 (57%) of the 128 trend-tests showed a significant trend. Even though repetitive testing increases the risk of making a Type I error (getting a significant trend when there actually are no trend) the number of significant trends is well over what would be expected (~6-7) from this error. The time frame for this analysis is the period 1980-2008. Data from some years (especially 2003) are lacking in some areas.
For reference purposes, please cite this Baltic Sea Environment Fact Sheets as follows:
[Author’s name(s)], [Year]. [Baltic Sea Environment Fact Sheets title]. HELCOM Baltic Sea Environment Fact Sheets 2010. Online. [Date Viewed], http://www.helcom.fi/environment2/ifs/en_GB/cover/.
Last updated 14 January 2011