TIME-RELATED FACTORS INFLUENCE THE CONCENTRATIONS OF SDDT, PCBS AND SHELL PARAMETERS IN EGGS OF BALTIC GUILLEMOT (URIA-AALGE), 1861-1989

Three hundred and nine eggs of guillemot (Uria aalge) have been used t o study the time trends in DDT and PCB pollution of the Baltic during the period 1969-1989. As a comparison, herring (Clupea harengus) from the Baltic have been used. Eggshell thickness has been studied in 370 eggs collected between 1861-1989. The inter-relationships between vari ous morphological chemical parameters were studied with respect to the date of egglaying (first-laid eggs and replacement eggs) and year of collection. The following morphological and chemical parameters have b een studied: weight, length and breadth of eggs; weight, thickness, th ickness index and density index of eggshells; fat content and concentr ations of sDDT and PCBs in the eggs. sDDT and PCBs concentrations have decreased in the Baltic since the 1970s. Eggshell thickness is signif icantly lower in recent material compared to historical material colle cted before 1946; it has increased since the 1970s but is still lower than before 1946. Compared to the first-laid eggs, replacement eggs ha d significantly lower values for morphological data. The concentration s of sDDT and PCBs were significantly higher in replacement eggs. Fat content was similar in the two groups. The results show that date of e gglaying has to be considered in monitoring studies and that such cons iderations will improve the interpretation of data and reduce the numb er of samples needed.