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Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 703 records · Page 39Linked to original sources
USGS2002

Determination of phosphate in natural waters by activation analysis of tungstophosphoric acid

Activation analysis may be used to determine quantitatively traces of phosphate in natural waters. Methods based on the reaction 31 P( n,γ ) 32 P are subject to interference by sulfur and chlorine which give rise to 32 P through n,p and n,α reactions. If the ratio of phosphorus to sulfur or chlorine is small, as it is in most natural waters, accurate analyses by these methods are difficult to achieve. In the activation analysis method, molybdate and tungstate ions are added to samples containing phosphate ion to form tungstomolybdophosphoric acid. The complex is extracted with 2,6-dimethyl-4-heptanone. After activation of an aliquot of the organic phase for 1 hour at a flux of 10 13 neutrons per cm 2 , per second, the gamma spectrum is essentially that of tungsten-187. The induced activity is proportional to the concentration of phosphate in the sample. A test of the method showed it to give accurate results at concentrations of 4 to at least 200 p.p.b. of phosphorus when an aliquot of 100 μl. was activated. By suitable reagent purification, counting for longer times, and activation of larger aliquots, the detection limit could be lowered several hundredfold.

Environmental Science & Technology↗
USGS2002

Migration and redistribution of zinc and cadmium in marine estuarine system

A survey of trace-element levels in the estuarine sediments of Texas shows that Corpus Christi Bay has anomalously high concentrations of zinc and cadmium. Maps of elemental abundance within the bay indicate large concentration gradients, the highest values being near the harbor entrance. Seasonal determinations of metal levels in the harbor and bay waters also revealed variations with time. During summer, stagnation of the harbor water increases the concentration of metals so that significant quantities precipitate in the reducing environment of the bottom water. In winter, the exchange of water between the bay and the harbor increases, and metals are redissolved from harbor deposits, washed into the bay, and adsorbed by particles settling to the bottom.

Environmental Science & Technology↗