Elevated arsenic concentrations were found in ground water near Canal Fulton, Ohio. The hydrologie and chemical properties of the area were studied to determine the source of the arsenic and evaluate the possibility of a similar problem occurring elsewhere. Two major aquifer systems exist within the study area: the Sharon Sandstone of the upland areas; and the outwash sand and gravel deposits of the buried valleys. Ground‐water flow is generally from the north, but local variations are caused by the Tuscarawas River valley on the south and west of the study area. Within the study area, there is no evidence for an anthropogenic source of arsenic to the ground water. Agricultural soils, abandoned underground coal mines, industrial impoundments to the north, and an abandoned industrial dump site within the study area were all eliminated as possible sources for the arsenic. The arsenic in Canal Fulton ground water is entirely inorganic, consisting of about equal parts of arsenate and arsenite. Reduction‐oxidation (redox) considerations suggest that arsenic is controlled by an adsorption equilibrium with ferric hydroxides, and that the reduction of the ferric hydroxides by a recent lowering of Eh and/or pH in the aquifer has liberated both iron and arsenic to solution. A high correlation between ferrous iron and total dissolved arsenic supports this model. It is hypothesized that Eh conditions have been lowered in the aquifer by either the recent introduction of methane gas or the deposition of a thick layer of till during the last glacial retreat. The methane gas could be leaking from deep underground storage at the site and reducing oxidized compounds. The deposition of till would have eliminated local recharge of oxygenated waters.
A method has been developed for precise measurement of 234U/238U activity ratios in natural waters and carbonates using quadrupole inductively coupled plasma mass spectrometry. A recovery of 80–85% of seawater U is achieved by Fe(III) coprecipitation followed by extraction chromatography with a supported dipentyl pentane phosphonate material; 90–95% of U is recovered from carbonates, which are are dissolved in HNO3 and subjected to the same extraction Chromatographic preparation. Isotopic measurements are made via recirculating pneumatic nebulization of small volumes of solutions containing 0.5–5 mg/L U. 234U/235U measured as a proxy for determination of 234U/238U; iridium is added to sample solutions and the ion ratio 191Ir40Ar+/193Ir40Ar+is measured for internal mass discrimination correction. 234U/238U activity ratios in the range 1.143–1.154 are observed for 13 seawater and contemporary corals, in agreement with the established marine 234U/238U activity ratio. For sample sizes of 5–25 μg U, ICPMS uncertainties of +/- 0.2–0.5 % relative, 2σ standard error, approach those obtained for < 0.1 μg U by thermal ionization mass spectrometry. Measurements of 234U/238U activity ratios in bottled waters, Lake Erie surface waters, mollusk fossils, and fertilizers are also demonstrated.
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