Have high selenium concentrations in wading birds their origin in mercury?

The relationship between selenium and mercury in marine waders from the Wadden Sea (known to have high tissue selenium concentrations), was investigated in the framework of the possibility that high mercury concentrations may have induced parallel selenium accumulation to detoxify the mercury. The selenium and mercury concentrations are shown to be negatively correlated in both the liver and kidneys of these birds. In the tissues and red blood cells of oystercatchers, positive correlations between the two elements are found. The atom increment Se/Hg ratio in the pooled oystercatcher tissue and red cell data is 32:1. This ratio greatly exceeds the 1:1 ratio found when selenium is accumulated to detoxify mercury. Furthermore, breeding females are able to excrete mercury independently of selenium from the red blood cells, probably into the eggs; the whole egg mercury concentrations of the local breeding populations are low. From these results it is concluded that the high selenium concentrations in waders do not have their origin in elevated levels of mercury.