Sediment Menominee River

Adsorption processes may be particularly important in influencing species concentrations, since the arsenic present in the pore waters will probably be in equilibrium with arsenic adsorbed on solid surfaces. Arsenic in any species measured in pore waters may be only a fraction of the total amount of that species present in the sediments, the rest being adsorbed to or incorporated into particulate matter. Thus, it is important to study the sorptive characteristics of each of the arsenic species in the sediments. In the Menominee River sediments studied, the four oxygenated arsenic species (arsenate, arsenite, monomethyl arsonic acid and cacodylic acid) are often present together and competing among themselves and with phosphate for the same sorption sites. The competitive adsorptive characteristics of the species could greatly influence... 

In order to obtain a general overview of the sorptive characteristics of the various arsenic species and phosphate on Menominee River sediments a short-term experiment was performed. A Menominee River sediment slurry was spiked with arsenic or phosphate and the loss from solution was measured. 

The sorption of phosphate and the arsenic species on the twelve soils used in Wauchope s experiment correlated well with both the clay content and the iron content of the soils. The Menominee River sediments, however, were anaerobic, so iron should have been present as Fe(0H)2 rather than the Fe(0H)3 which was, presumably, present in Wauchope s alluvial soils. 

An example of each case was calculated using the adsorption constants for anaerobic Menominee River sediments listed in Table IV. The first order rate constant used was 0.04 day, corresponding to a half life of 17 days. Initial reactant concentrations of 0.001 M were chosen to approximate conditions in moderately contaminated sediments (16). A sediment solids concentration of 60 g (corresponding to 95% water) was used. 

Experimental. An uncontaminated sediment sample was collected from the Menominee River. The sediment had no distinctive odor, appeared to be a mixture of sand and clay, and was anaerobic (i.e., the pore waters had a redox potential of approximately -115 mV). The sample was stored in a plastic bag at 4°C until use. 

Experimental. Anaerobic sediments were obtained from an uncontaminated area of the Menominee River (site 55c,... 

Sorption of monomethyl arsonic acid (MMAA), dimethyl arsinic acid (DMAA), and arsenate on anaerobic bottom sediments from the Menominee River, Wisconsin are described by Langmuir Isotherms. These results were Incorporated Into a kinetic model of arsenic species transforamtlon which takes sorption Into account. Model predictions were found to be sensitive to the sediment water content and r, the adsorptive capacity of the sediment. Demethylatlon of MMAA and DMAA was observed In sediment Incubation experiments. The predictions of the sorption/kinetic model were In good agreement with the results of the Incubation experiments. 

Interstitial water from sediment sampled at the mouth of the Menominee River near Marinette, WI, was also analyzed for each arsenic species. The water was contaminated with arsenic MMAA and had considerable air exposure. The results of this analysis are presented in Table 19. 

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