The possible role of selenium in antioxidation in marine waders; a preliminary study.

In a marine wader, the oystercatcher (Haematopus ostralegus), the activity of the selenium-dependent enzyme glutathione peroxidase (GSH-Px) in the red blood cells (RBC) was measured. The average activity, 97 +/- 19 units/g Hb, is within the range reported for mammals. No correlation was observed between the selenium concentration and GSH-Px activity in the erythrocytes and it is calculated that only a small percentage of the selenium present in the RBC is bound to the enzyme. Therefore, it is concluded that the high selenium concentrations in the avian red cells cannot be ascribed to GSH-Px. It is argued that a function of selenium in antioxidation is still possible. The positive relationship found between selenium and iron concentrations in the tissues of the oystercatcher directs to such a role. A pitfall in the measurement of GSH-Px activity is outlined.

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.

The bioavailability of various selenium compounds to a marine wading bird.

The uptake of dietary selenium (about 3.5 mg/kg AF dry wt) as selenomethionine, selenocystine, selenite, selenate, and fish selenium in the plasma and red blood cells (RBC) of the oystercatcher has been investigated. The birds received the various selenium compounds subsequently, for at least 9 wk. After dietary supplementation of selenocystine, selenite, and selenate, plasma selenium was about 350 micrograms/L and RBC selenium 2.1 mg/kg dry wt. After supplementation of selenomethionine, the plasma concentration increased to 630 micrograms/L, and the RBC concentration to 4.1 mg/kg dry wt. When the fodder contained 3.1 mg/kg fish Se, an average plasma and RBC concentration of 415 micrograms/L and 14.4 mg/kg dry wt, respectively, was measured. The maximal increase of the selenium concentration in the plasma was attained at first sampling, 14 d after a change in dietary selenium (selenomethionine or fish Se); the uptake seemed to be a concentration-regulated process. RBC concentrations (Y in mg/kg drug wt) increased with time (X in d) according to Y = a - b e-cX. Fifty percent of the total increase was attained within 17 d, suggesting that diffusion into the RBC played a role. The selenium concentration in the plasma was positively correlated with the (fish)Se concentration in the fodder; the RBC concentration (60 d after the change in diet) was positively correlated with the plasma concentration. When the diet contained fish Se, the blood selenium concentrations of the captive birds were similar to the concentrations measured in field birds. Fish Se is a yet undetermined selenium compound. The present experiment showed that fish Se differed from selenomethionine, selenocystine, selenite, or selenate in uptake from the food and uptake in the RBC.

Selenium status in Charadriiformes. Tissue distribution and seasonal, geographical, and species variation.

The distribution of selenium in a marine wader, the Oystercatcher (Haematopus ostralegus) is given by the levels in 15 tissues and plasma. Red blood cells (RBC) contain the highest level (23 mg/kg dry wt) followed by liver, lung, and kidney (17-19 mg/kg). Most other tissues range from 3-10 mg/kg. The average kidney and liver concentrations of the Oystercatcher belong to the concentrations characteristic in birds. However, the Oystercatcher's tissue selenium concentrations are in general four- to fivefold mammalian levels, but in liver and lung, 11- to 13-fold and in the RBC, 12- to 33-fold. The selenium plasma and RBC levels of the Oystercatcher vary during the year from 280 to 410 micrograms/L and 13 to 30 mg/kg dry wt, respectively; the plasma concentrations are positively correlated with the RBC selenium concentrations. An overview of literature data shows that the selenium kidney and liver concentrations of birds do not vary with geographical latitude and size (length) of the birds. In species of the orders Charadriiformes and Procellariiformes, high selenium kidney, and to a lesser extent liver, concentrations may occur. A function of selenium in antioxidation is suggested.

The variability and significance of selenium concentrations in Shorebird feathers.

The selenium distribution in the flight feathers of a marine wader, the Oystercatcher (Heamatopus ostralegus), is investigated. In the wing the highest concentrations are found in the outer primaries, notably primary 8. The inner tail feather exceeds the primary 8 concentration. Whithin the vane of a single feather, the highest concentrations are found in the tip, the lowest at the basis of the feather. The results are discussed in relation to the use of the feather as an indicator of selenium exposure.In comparing marine wader species shortly after completion of the feather growth, a negative relation is found between the fresh primary 8 vane concentration and body weight of the species. A functional role of selenium in respect to the metabolic rate is suggested.

Selenium, mercury, arsenic and cadmium in the lifecycle of the dunlin, Calidris alpina, a migrant wader.

Migrant waders accumulate pollutants from their marine moulting and wintering grounds in Western Europe. In examining the possible consequences on the reproduction of the Dunlin (Calidris alpina), it was found that no adverse effects are to be expected from selenium, mercury, arsenic or cadmium. Though selenium is accumulated in very high concentrations in the kidney, after the bird's departure from the marine environment for the freshwater breeding areas, levels decline rapidly. Mercury exposure in Western Europe is not excessive, as shown by the relatively low levels in the summer plumage. Feather element concentrations proved to be a useful indicator of the different moulting and wintering areas used by the birds.

The use of bird feathers for indicating heavy metal pollution.

Feather material has been investigated as suitable indicating tissue for heavy metal pollution. At least three different routes are described through which trace metal content in the feathers can increase: internal deposition during growth, contamination by the bird's secretion and outside contamination.As mercury is only deposited during feather growth, the feather burden reflects the internal contamination of the bird. Internal deposition of zinc appears to be well regulated in the shaft but concentrations differ widely in the vanes. No external contamination of the vanes could be demonstrated, so these levels reflect contamination from inside. Selenium and lead contamination can be deposited by the birds secretion. When the time elapsed after feather formation is accounted for, the feather can give indirectly an indication of the birds exposure to these elements.