Dissolved uranium was determined colorimetrically with Arsenazo-III at pH1 after separation and concentration with Dowex A1 in the presence of CyDTA as a masking agent. The yield was 100% and the reproducability about 0.3ppb. The average concentrations, range and number of observations were, in ppb:Rhine: April and June: 0,9 (0,6-1,7;11)IJsselmeer: August: 1,2 (1,2-1,3;3)North Sea, S. Bight: April and June: 3,5 (2,5-5,1; 25)Wadden Sea: July and September: 3,2 ( 2,9-3,5; 19)The values for the Rhine and the IJssel lake are relatively high, this is possibly related to the high use of phosphate fertilizers in the catchment area. The values for North Sea and Wadden Sea are not significantly different from the oceanic average of 3,3 ppb. There is no linear relationship between dissolved Ur and salinity in the Rhine estuary. On the shallow Balgzand tidal flats the water at low tide contained 0,6 ppb U less than in the adjacent tidal inlet. Possibly the anoxic sediments in this region concentrate a detectable amount of dissolved U from the overlying seawaterRhine |
