Mercury pore waters

Benoit JM, Gilmour CC, Mason RP, Heyes A (1999) Sulfide controls on mercury speciation and bioavailability to methylating bacteria in sediment pore waters. Environ Sci Technol 33 951-957... 

At the end of this section focused on analytical problems, it should be mentioned that Thoming et al. [199] have evidenced that electrodialysis allows one to remove heavy metals from soils. During this process, the metals, including mercury, are transferred under the applied electric field to the pore water in either dissolved form or attached to colloids. This method is especially appropriate for the purification of fine-grained soils. 

The assembly of functionalized nanostructured silica with uniform pore channels using neutral alkylamine surfactants (S°I° -> HMS) and non-ionic alkylpolyethyleneoxide surfactants (N°I° —> MSU-X) provides many advantages over conventional electrostatic assembly pathways (S+f, etc.). In contrast with electrostatically assembled MCM-41-type materials, mesostructured adsorbents produced by non-electrostatic assembly methods typically possess pore channel structures and particle morphologies which improve their ability to interact with targeted adsorbate species. Moreover, non-electrostatic assembly pathways are well-suited for the direct synthesis of functionalized mesostructured silica by one-step preparation processes under ambient temperature, neutral pH conditions. The environmental application of such materials for the treatment of mercury-contaminated water is also demonstrated. 

The distribution of Hg within seepage lakes is a net result of the processes that control Hg transport between the atmosphere, water column, seston, sediments, and groundwater. This discussion focuses on the processes that control the exchange of Hg between the sediments and lake water. We first present data on spatial and temporal concentrations in the water column, sediments, pore water, and groundwater. These data set the context for a subsequent discussion of the chemical and physical processes responsible for the transport of mercury across the sediment-water interface and are necessary for assessing transport rates. 

Figure 4. Mercury concentrations in littoral zone pore waters in Pallette Lake...

The subsurface maximum in pore-water HgT (Figure 3) suggested that diffusion from the profundal sediments to the overlying water column could be important. Fickian diffusive flux calculations (eq 2) were used to estimate Hg loading from pore waters. Diffusion coefficients for mercury in pore waters were not available. However, free-water diffusion coefficients for monovalent anions (see Table I) averaged about 5 X 10"6 cm2/s (53, 55) and... 

Figure 9 Dissolved mercury speciation in sediment pore waters as a function of sulfide concentration. Note that the most bioavailable form, HgS°, is the dominant chemical form at log S <, (—4.7) (source Benoit et al., 1999a).

Benoit J. M., Mason R. P., and Gilmour C. C. (1999b) Estimation of mercury-sulfide speciation in sediment pore waters using octanol-water partitioning and implications for availabihty to methylating bacteria. Environ. Toxicol. Chem. 18, 2138-2141. 

Branfireun B. A., Bishop K., Roulet N. T., Granberg G., and Nilsson M. (2001) Mercury cycling in boreal ecosystems the long-term effect of acid rain constituents on peatland pore water methylmercury concentrations. Geophys. Res. Lett. 28(7), 1227-1230. 

Gobeil C. and Cossa D. (1993) Mercury in sediments and sediment pore water in the Laurentian Trough. Can. J. Fish. Aquat. Sci. 50, 1794-1800. 

CovELLi S, Faganeli j, Horvat M and Brambati A (1999) Pore water distribution and benthic fluxes measurements of mercury and methylmercury in the Gulf of Trieste (northern Adriatic Sea). Estuar Coast Shelf Sci 48 415 —428. 

Mercury and water porosimetry measurements have shown that the GDL pore structure changes during lifetime tests. Large pore (30-60 um diameter) volume has decreased, while small-pore volume increases. The loss in large-pore volume is likely due to irreversible fuel cell compression [118]. 

Sulphate concentrations may also be determined accurately by potentiometric back-titration of excess Ba + with a mercury electrode following the precipitation of BaS04 Mucci, 1991). The seawater sample is freed from most seasalt cations with an ion-exchange-column. Then the eluate is reacted with an excess of barium, and after filtration of precipitated BaS04, the solution is titrated potentiometrically with an EGTA solution (see also Section 11.2) to the endpoint. The method applies over a wide range of salinities and sulphate concentrations in 1 mL or less of seawater and marine pore water samples, however, it is somewhat less precise (c.v. of about 0.6 %) than the simple gravimetric procedure described. 

One practical method is to use the same method as described for measuring particle density using mercury, except that mercury is replaced by a liquid which penetrates pores. Water and organic solvents are often used. The same equation can be used by replacing ph with the density of the liquid employed. 

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