Sediment organic carbon-water partition

The Kovi values are used to estimate BCFs (bioaccumulation after uptake from water), soil and sediment organic carbon-water partition coefficients, toxicities, and aqueous solubilities. Techniques for measuring... 

JSTdoc (DOC-water partition coefficient) = [Waterboundl/([Waterf,ee] /doc) Kocs (sediment organic carbon-water partition coefficient for water concentration with free PAH) = ([Sediment]//oc)/[Waterf,eg]... 

The BUSES model provides an estimate of the organic carbon/water partition coefficient (Koc) based on the octanol/water partition coefficient (Kow)- From these data, it is evident that the methyltins are less likely to partition onto organic carbon (in sediments, soils, biota) than are the butyl- and octyltin compormds due to then-lower partition coefficients and higher water solubilities. The 7/oc value can then be used to derive sohds/water partition coefficients in suspended matter, in sediment, and in soil using values of 10%, 5%, and 2% for organie carbon, representing typical organic carbon contents of suspended matter, sediment, and soil, respeetively. 

Dichlorobenzidine in solution has a strong tendency to be adsorbed onto soils and sediments. The extent of adsorption of hydrophobic (sparingly water soluble) compounds has been shown to be highly correlated with the organic carbon content of the adsorbents (Hassett et al. 1983). When adsorption is expressed as a function of organic carbon content, an organic carbon-water partition coefficient (K J is... 

The base set of partition coefficients needed for most multimedia models include the Henry s law constant (JCh) to describe partitioning between air and water, partition coefficients between water and various solid phases in soils, sediments, and particulate matter in the water coliunn (fCa), and a coefficient describing partitioning between air-borne particles and air (Kp). If not available from direct experimental measurements, soUd phase-water partition coefficients are often derived from the organic carbon-water partition coefficient, Kqc (Eq. 4), the underlying assumption being that sorption into organic matter dominates the overall sorption to bulk solid material. 

The other way of removing plasticizers from water is their adsorption at liquid-solid interface (i.e., soil or sediments) [11]. This process depends on hydrophobicity of the substance, i.e. is proportional to organic carbon-water partition coefficient Kqq - plasticizers with Kqq value greater than 1000 dm /kg are regarded as having relatively significant affinity for sediments and son. It means that it is of greater importance in the case of 2-ethylhexyl (hydrophobic alkyl chain) than in the case of dimethyl phthalate (see Table 3). 

KoC is an important parameter which describes the potential for movement or mobility of pesticides in soil, sediment and groundwater. Because of the structural complexity of these agrochemical molecules, the above simple relationship which considers only the chemical s hydrophobicity may fail for polar and ionic compounds. The effects of pH, soil properties, mineral surfaces and other factors influencing sorption become important. Other quantities, KD (sorption partition coefficient to the whole soil on a dry weight basis) and KqM (organic matter-water partition coefficient) are also commonly used to describe the extent of sorption. K0M is often estimated as 0.56 KoC, implying that organic matter is 56% carbon. 

By analogy to the case in the water column, we can define an equilibrium constant reflecting PCB partitioning between the organism lipid pool and the sediment organic carbon pool ... 

Not only the quantity but also the quality of organic matter has been shown to influence bioavailability (Karickhoff et al., 1979). Sediment organic carbon provides a primary food source for benthic organisms. DeWitt et al. (1992) found that sediment pore water partitioning and toxicity of fluoranthene to the amphipod, Rheopyxinius abronius, were affected by sediment organic matter quality. 

The suspended sediment/water partition coefficients have been measured for 19 chlorinated organics in 25 samples from the St. Clair, Detroit and Niagara Rivers. An excellent linear correlation (r = 0.87) between the organic-carbon corrected partition coefficient (Kqq) and the octanol/water partition coefficient (Kq, ) was found (log = 0.76 log + 1.66). Using this equation plus another equation developed in this paper it is shown that the percentage of chemical in the dissolved and particulate phases in the study rivers could be estimated from a chemical s to within a factor of two. The paper also discusses the time required for equilibrium to be achieved between the dissolved and particulate phases, and the potential importance of biota such as algae in the partitioning process. 

Partitioning, suspended sediment/water partition coefficient, Kp, organic-carbon corrected partition coefficient, Kq(, octanol/water partition coefficient, chlorinated hydrocarbons, Kq /Kq, correlations, St. Clair River, Detroit River, Niagara River. 

The Level I calculation suggests that if 100,000 kg (100 tonnes) of benzene are introduced into the 100,000 km2 environment, 99% will partition into air at a concentration of 9.9 x 10-7 g/m3 or about 1 pg/rn3. The water will contain nearly 1% at a low concentration of 4 pg/rn3 or equivalently 4 ng/L. Soils would contain 5 x 10-6 pg/g and sediments about 9.7 x 10 6 pg/g. These values would normally be undetectable as a result of the very low tendency of benzene to sorb to organic matter in these media. The fugacity is calculated to be 3.14 x 10-5 Pa. The dimensionless soil-water and sediment-water partition coefficients or ratios of Z values are 2.6 and 5.3 as a result of a Koc of about 55 and a few percent organic carbon in these media. There is little evidence of bioconcentration with a very low fish concentration of 3.0 x FT5 pg/g. The pie chart in Figure 1.7.6 clearly shows that air is the primary medium of accumulation. 

Kd is difficult to define when dealing with actual field conditions. Laboratory studies have demonstrated that an approximation of Kd can be made based on the more easily determined factors such as organic carbon content of the soil and the octanol-water partitioning coefficient of the compound. For sediment particles <50 pm ... 

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