Sørensen P.B., Vorkamp K., Thomsen M., Falk K., Møller S. 2004. Technical Report from NERI no. 509, 126 p.

 

Summary

 

The problem and purpose

 

Peregrine falcons (Falco peregrinus) are top predators and thus subject to biomagnification leading to accumulation of Persistent Organic Pollutants (POPs). Furthermore, the route of migration leads the birds through relatively contaminated areas in both the north and central parts of the continental America. It is well known that some organochlorine chemicals can induce indirect or direct toxicological effects, including a thinning of eggshells. Several studies over the past decades have addressed the effects of chlorinated compounds such as DDT (and breakdown products) and PCBs, although long term trends in the occurrence in the arctic have seldom been conducted. Recently, unexpectedly high contamination levels of brominated flame retardants were observed in Swedish peregrine falcon eggs. The contamination by some xenobiotic chemicals may decrease temporally due to regulation in usage, while the contamination level may increase for others. This induces a profile of contamination level that may change with time and influence the eggshell thickness.

 

The purpose of this project is to study the contamination by xenobiotics and shell thickness of peregrine falcon eggs from Southern Greenland. The xenobiotics include both the classic chlorinated compounds, some pesticides and the more newly identified brominated flame retardants. Time trends and possible correlation profiles are investigated.

 

Frame of investigation

 

The contamination by xenobiotics is measured for Peregrine falcon (Falco peregrinus) eggs collected in South Greenland between 1981 and 2003. Egg samples are taken from 28 different clutches and includes 41 single eggs. The egg tissue concentration level is identified for a broad suite of 55 single chemicals including Polychlorinated biphenyls (PCBs), DDT (including DDD, DDE), HCH, HCB, toxaphene congeners and chlordane-related compounds and the newly identified contaminants brominated flame-retardants PBDES, HBCD and TBBPA. The eggshell thickness is measured for the same eggs as used in the chemical analysis and also for shell fractions collected in other 47 clutches during the period of investigation.

 

Results

 

Contamination level

 

The concentration range between the different substances is large, covering 5 orders of magnitude. So, the variability in concentration level for the same substance but between eggs is much smaller than the variability between compounds in the same egg.

 

On average, the sum of PCBs and DDT dominates the contamination by accounting for 95 % of the total contaminant load analysed in the eggs. Median summed concentrations were 55 µg/g lipid weight for PCBs and 40 µg/g on lipid weight basis for DDT (and its degradation products). The highest concentration level for a single component was measured for p,p’-DDE in the range for single eggs of respectively 0.7-9.1 m g/g wet weight and 9-170 m g/g lipid weight. Taking into account the high variability in contamination levels and the actual uncertainty inherent in the effect assessment, this range seems close to the reported limit of 20 m g/g wet weight above which population declines are reported to occur. Furthermore, 42 % of the eggs analysed exceeded the NOAEL level of 3 µg/g wet weight for p,p’-DDE. This seriously indicates a problematic contamination of the eggs.

 

PBDEs were detected in all eggs, with a medium summed concentration of 1.9 µg/g lipid weight. This is among the highest PBDE concentration ever detected in wildlife. The main congener was BDE-153. Relatively low but measurable concentration levels were detected for BDE-209, which indicates some degree of bioavailability and accumulation potential in biota. HBCD was likewise detected in the eggs, however, the concentrations were low, while TBBPA was only detected in terms of the degradation product dimethyl-TBBPA. PCB concentrations were lower than in Norwegian peregrine falcon eggs, but higher than in samples from Alaska. DDT concentrations were similar in Greenland, Norway and Alaska. Summed PBDE concentrations were similar to the results for wild peregrine falcons in Sweden.

 

The correlation between substances is positive, showing the strongest correlation within the same class of substances.

 

Correlation between contamination level and eggshell thickness

 

A higher contaminant level is seen to induce a thinner eggshell. Also the molecular flexibility is shown to have negative influence on the eggshell thickness as suggested by several investigators. This indicates a clear reduction in eggshell thickness due to an eco-toxicological effect. The observed intercorrelation between the single substances does not allow the identification of particular chemicals with the strongest effect on eggshell thickness. However, both the PLS-regression and single chemical correlation analysis with the eggshells, indicate that the PBDEs seem to have a negative influence on eggshell thickness.

 

Temporal development in contamination level and eggshell thickness

 

The concentration level for several PCBs shows a decreasing tendency while the majority of the PBDEs was seen to increase in contamination level during the period of investigation. This coincides with the fact that the PCBs are not in usage any more, while the PBDEs are used in increasing quantities during the period of investigation. This is in contrast to results for guillemot eggs from the Baltic Sea, but in agreement with studies on biota from North America. The discrepancy between the European and North American study areas might be caused by regulatory measures only taken in Europe to regulate the PBDEs. DDT and the degradation products remain constant in time. The time trend for the sum of all measured contaminants shows a constant level during the period of investigation. As p,p’-DDE dominates the level of contamination the constant temporal level of this single substance was the single factor most responsible for the constant contamination level in general. Both eggshell measurements and multivariate statistics show a positive time trend for the eggshell thickness, which, however, is only relatively weak and not statistically significant.

 

General conclusion

 

The Peregrine falcon eggs are contaminated to a relatively high degree with xenobiotics and the temporal development of the contamination seems to be status quo. The eggshells seem influenced by this contamination and it has not been possible to identify remarkable improvement in the ecotoxicological pressure on the Peregrine falcons during the period of investigation.

 

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