Pore waters concentration

POi that is incorporated into the authigenic apatite is thought to be supplied primarily via the decomposition of organic materials at the sea floor. A variety of additional processes, such as cycling at redox boundaries or incorporation by microbial communities, may act to elevate pore water concentrations, promoting... 

Table 2. DTMF tailings average pore water concentrations for 2008 boreholes.

Table 4 Observed sediment toxicity values for H. azteca and C. dilutus and pore water concentrations predicted by equilibrium partitioning [25]...

Sedimentation rates range from centimeters per year in coastal sediments down to millimeters per thousand years on the deep-sea floor. Thus, the effects of molecular diffusion are generally greater than that of advection in shaping pore-water concentration profiles. 

If the pore water concentration profile of the solute does not change over time, d [S]/dt = 0 (which implies that k, D, and s are constants), Eq. 12.5 becomes an ordinary differential equation. For a nonconservative solute whose concentration decreases (exponentially) with depth such that [5] —> 0 as z —> oo, the solution to this equation is given by... 

These solutions to the one-dimensional advection-diffusion model can be used to estimate reaction rate constants Ck) from the pore-water concentrations of S, if and s are known. More sophisticated approaches have been used to define the reaction rate term as the sum of multiple removals and additions whose functionalities are not necessarily first-order. Information on the reaction kinetics is empirically obtained by determining which algorithmic representation of the rate law best fits the vertical depth concentration data. The best-fit rate law can then be used to provide some insight into potential... 

Most commonly observed pore-water concentration profiles, (a) A nonreactive substance, such as chloride (b) a chemical, such as O2, which undergoes removal in the surface sediment as a result of aerobic respiration (c) a chemical that is consumed by a reaction that occurs in a subsurface layer, such as Fe2+(aq) precipitating with S2-(aq) to form FeS2(s) (d) a chemical released in surface sediments, such as silica via dissolution of siliceous hard parts (e) a chemical released into pore waters from a subsurface layer, such as Mn +(aq) by the reduction of Mn02(s) and (f) a chemical released at one depth (reactive layer 1), such as Fe2+(aq) by reduction of FeOOFI(s), and removal at another depth (reactive layer 2), such as Fe +(aq) precipitating as FeS2(s). Source From Schulz,... 

This assumption is reasonable because the toxicity of pyrethroids to benthic organisms is predictable from the equilibrium partitioning-derived pore water concentration (8), and the pyrethroids in this study have values comparable to those of cypermethrin (10). 

Sediments in the Mississippi River were accidentally contaminated with a low-level radioactive waste material that leaked from a nuclear power plant on the river. Pore water concentrations of radioactive compounds were measured following the spill and found to be 10 g/m over a 2-mm depth. The water contamination was 30% radioactive cesium ( Cs), with a half-life of 30 years, and 70% radioactive cobalt ( °Co), with a half-life of 6 years. Objections by the local residents are preventing clean-up efforts because some professor at the local state university convinced them that dredging the sediments and placing them in a disposal facility downstream would expose the residents to still more radioactivity. The state has decided that the sediments should be capped with 10 cm of clay and needs a quick estimate of the diffusion of radioactive material through the clay cap (Figure E2.8.1). If the drinking water limit (10 g/m ) is reached at mid-depth in the cap, the state will increase its thickness. Will this occur ... 

Figure 4 illustrates the effect of different binding mechanisms on the porewater concentrations of metals and metalloid species in relation to the solid-phase concentrations. First, if a certain component were very soluble and not bound to the solid in any way, the pore water concentration at equilibrium would equal the total concentration in the system. However,... 

Illustrative Example 9.2 Evaluating the Concentration Dependence of Sorption of Phenanthrene to Soil and Sediment POM Illustrative Example 9.3 Estimating Pore Water Concentrations in a Polluted Sediment... 

Estimating Pore Water Concentrations in a Polluted Sediment... 

Commonly, we are interested in estimating the concentration of a chemical in the pore water of a sediment bed. For example, we may be concerned that a pollutant is diffusing out of a contaminated sediment bed into the overlying waters the rate of this exchange will be proportional to the difference in dissolved concentrations in the pore water and the overlying water (see Chapter 19). Or we may be interested in the biouptake of the pollutants by invertebrates living in the bed (see Chapter 10). Such uptake may be proportional to the pore water concentrations, which themselves are proportional to the concentrations in the solids. 

For PCB101, the pore water concentration at equilibrium is estimated to be ... 

In order to describe the equilibrium situation with respect to the sediment, we assume that the PCBs are sorbed primarily by the natural organic matter. That is, we express the sediment pore water concentration (subscript pw) as a function of the corresponding measured sediment concentration by using Kid = fK Kmc (see Chapter 9) ... 

For t —> the pore water concentration is everywhere equal to the external solute... 

Exchange was measured at typical pore-water concentrations of Ca2+ and NH4 +. For the Ca2+-saturated and NH4+-saturated sediments, KG was calculated by mass balance from measurements of initial and final calcium and ammonium concentrations in solution the total concentration of exchange sites was known. On the untreated sediment, KG could be determined only after these simplifying assumptions were made ... 

Hg Concentrations in Pore Waters. Profundal sediment pore-water concentrations varied from 10 to 30 ng/L throughout the profile (Figure 3). 

Despite the limitations, EP is still the reference theory for discussing the accumulation of organic chemicals in soil organisms and for extrapolation between media and matrices. The use of EP requires that body residues and effects observed in biota first have to be related to pore water concentrations. 

The extrapolation from total soil concentration to bioavailable pore water concentration of heavy metals makes use of the model illustrated in equation 2.1 (above). 

In many references that describe the relationship between the concentration of a contaminant in the pore water and the total concentration in soil, the kind of pore water concentration assessed (inclusive or exclusive of organic and inorganic metal complexes) is not mentioned. 

Equilibrium partitioning for calculating the pore water concentration of hydrophobic organic substances in sediments for comparison with the safe value in water (Di Toro et al. 1991). 

---