Effect of sulfate level on selenium uptake by Ruppia maritima

Ruppia maritima (wigeongrass), the dominant aquatic macrophyte in the agricultural drainage evaporation ponds of the Central Valley of California, is a food source for various waterfowl and shorebirds. Whole-plant uptake and accumulation of selenate (SeO4−2 or Se+6), selenite (SeO3−2 or Se+4), and seleno-methionine (Se−2) by R. maritima from artificial evaporation pond water was compared over a 21 day period, and the effect of sulfate, a known selenate antagonist, on Se uptake was investigated. Plants were treated with 10, 100, or 1000 ug/l as selenium. Under both high and low sulfate conditions, R. maritima was found to accumulate seleno-methionine to a much higher level than either selenite or selenate. However, under low sulfate conditions, selenate uptake was two orders of magnitude greater than under high sulfate conditions, indicating a sulfate/selenate antagonism. Bioconcentration factors for seleno-methionine under high and low sulfate conditions and for selenate under low sulfate conditions were very high (up to 21,800 for seleno-methionine and 1080 for selenate).