On the basis of earlier reports on high selenium levels in organs of m
arine waders from the Dutch Wadden Sea, adverse effects in wader repro
duction were anticipated. A local breeding population of the wader Hae
matopus ostralegus, oystercatcher, was examined for embryotoxicity and
selenium levels in eggs and parental blood. Egg and/or blood samples
from breeding oystercatchers were obtained also from two reference sit
es, a Dutch meadow nature reserve and a Norwegian Atlantic island. The
blood selenium levels were high in the Dutch marine birds (red blood
cells contained 21 mg/kg vs 0.1-1.2 mg/kg dry weight in man), but the
highest red blood cell levels were recorded in the red cells of birds
sampled at the Norwegian reference site (maximal value 42 mg/kg dry we
ight). Both the concentrations in eggs from the Wadden Sea and in eggs
from inland pastures (about 2 mg/kg dry weight), were at background l
evel and embryotoxicity was not observed. Considering the results, it
was concluded that selenium is not a potential threat to the reproduct
ion of waders from the Dutch Wadden Sea, despite the high selenium con
centrations in the tissues of the waders foraging in this area. Seleni
um in egg white was about 1.6 times higher than in yolk. The first egg
had a 10% higher egg white and a 19% higher yolk concentration compar
ed to the subsequent eggs in the coastal clutches. Red blood cell leve
ls were about 3.5 times higher in marine feeding birds than in inland
feeding birds. Selenium concentrations in the plasma and red blood cel
ls were positively correlated.