Sedimentation ratio

It appears that pesticides with solubiHties greater than 10 mg/L are mainly transported in the aqueous phase (48) as a result of the interaction of solution/sediment ratio in the mnoff and the pesticide sorption coefficient. For instance, on a silt loam soil with a steep slope (>12%), >80% of atra2ine transport occurs in the aqueous phase (49). In contrast, it has been found that total metolachlor losses in mnoff from plots with medium ground slopes (2—9%) were <1% of appHed chemical (50). Of the metolachlor in the mnoff, sediment carried 20 to 46% of the total transported pesticide over the monitoring period. 

The reactants are then mixed in various proportions, and the sedimentation ratio (scompiex/smucin)—the ratio of the sedimentation coefficient of the complex to that of the pure mucin itself—is used as the measure for mucoad-hesion. The ultra-violet absorption optics on the XL-A or XL-1 ultracentrifuge have been used as the main optical detection system. Although the polysaccharide is generally invisible in the near UV ( 280 nm), at the concentrations normally employed the mucin—in uncomplexed and complexed form—is detectable. 

The fact that HBCD is found in fish indicates that it is also bioavailable. However, the low fish to sediment ratio (below 1) does not agree with the high ratios reported by Sellstrom et al. [29] for pikes from a Swedish River. Pike is a predator at the top of the food chain and the higher fish to sediment ratio in this specie could indicate the biomagnification of this compound through the aquatic trophic chain. 

The first contaminated area, along the Cinca River and downstream of Monzon, reveals the covariant nature of PBDE and HBCD concentrations in the fish examined here. The amount of each contaminant is highly correlated within each fish. A likely explanation of this correlation is that the contaminants are being acquired from the same source (Cinca River). Moreover, PBDEs and HBCD are bioavailable as indicated by large fish to sediment ratios. Some correlations were found between the concentration levels of BFRs and the length and weight of specimen fishes,... 

Altabet, M. A., Francois, R., Mnrray, D. W., and Prell, W. L. (1995). CHmate-related variations in denitrification in the Arabian Sea from sediment ratios. Nature 373, 506—509. 

Sedimentation ratio is often used to assess suspension stability. Byron reported the sedimentation ratios for a 1% sodium fluoresein suspension formulation with different amounts of surfactant (sorbitan trioleate) after standing for 20 days at room temperature. The suspension formulation with the lowest sedimentation ratio had thebest-flocculated system. However, all formulations were easily redispersible one complete revolution of the container was sufficient to produce a homogeneous dispersion. There was no clear difference in the times taken to reach apparent sedimentation equilibrium. Physical stability of the formulation was determined according to ... 

For example. Great Lakes sediments containing elevated levels of PAHs were reported by Eadie et al. (1983) to be the source of the body burdens of the compounds in bottom-dwelling invertebrates. Varanasi et al. (1985) found that benzo[a]pyrene was accumulated in fish, amphipod crustaceans, shrimp, and clams when estuarine sediment was the source of the compound. Approximate tissue to sediment ratios were 0.6-1.2 for amphipods, 0.1 for clams, and 0.05 for fish and shrimp. 

These results indicated that BDE-209 is bioavailable, but the bioavailability potential is lower than that observed for other BDE congeners, with fish-to-sediment values much lower (0.0 013 and 0.0 Oil for the 2004 and 2005 sampling campaigns, respectively). It should be pointed out that an important factor affecting the ratios may be that the system is not in equilibrium because PBDEs are released directly to the river in industrial park effluents, and new inputs are ongoing. The low fish-to-sediment ratios obtained could be an indication of a recent release of BDE-209 from the industrial park that has contaminated the sediment but not yet been taken up by barbels or carps. 

To optimize our tumbler method, we tested various ratios of dichloromethane to methanol at various solvent-to-sediment ratios. Replicate... 

Evidence from 6 C studies (Sackett, 1964 Nissenbaum and Kaplan, 1972) and studies of the offshore decrease of terrestrially derived lignin material (Gardner and Menzel, 1974 Hedges and Parker, 1976) have led investigators to conclude that only a minor fraction of terrestrial humic substances are transported beyond the estuaries. The approach these investigators took was to compare sediment ratios with lignin oxidation... 

Naturally occurring radionuclides such as radium isotopes and radon-222 have gained popularity as tracers of SGD due to their enrichment in ground-water relative to other sources and their built-in radioactive clocks . The enrichment of these tracers is owed to the fact that the water-sediment ratio in aquifers is usually quite small and that aquifer sediments (and sediments in general) are enriched in many U and Th series isotopes while many of these isotopes are particle reactive and remain bound to the sediments, some like Ra can easily partition into the aqueous phase. Radon-222 (tia = 3.82 days) is the daughter product of Ra (G/2= 1600 years) and a noble gas therefore, it is even more enriched in groundwater than radium. 

Cesium-137 is a fallout radioisotope from nuclear weapons tests and does not occur naturally. The first significant appearance of Cs-137 in the atmosphere was in the early 1950s, and it was present in peak quantities in 1963-1964. Like Pb-210, Cs-137 is carried down by rainwater and accumulates in the sediment, where it decays radioactively with a half-life of 30 years. Thus, a profile of Cs-137 concentration with depth (Figure 14.28) shows a maximum activity at a depth corresponding to 1963 and a tail , where cesium-137 is first detectable associated with deposition in the 1950s. The early 1980s peak is associated with the fallout from the 1986 accident at Chernobyl. This peak is also used to determine sediment accumulation rates in selected Northern European wetlands. In these wetlands, the Chernobyl peaks can be used to measure sedimentation ratios from 1963 to 1986 and 1986 to present. 

Comparisons of depth plots of Ti-normalized values for a series of parameters in HIN.2 to the same ratio in local surface soils (Fig. 9) reveal important information about sources of elements. The soil value is a composite mean of all the soil analyses. The Fe/Ti ratios of the top 10 cm of the core (approximately 1980 onward) are very similar to soil values. Deeper in the core, Fe/Ti values peak at approximately 15 cm (1970) and exceed the ratio in sods. Below this peak, the sediment ratios decrease and fall substantially below values in modem surface soil. 

Figure 14.1 Lead isotopic signatures (displayed as Pb/ Pb versus Pb/ ° Pb) of 24 sediments collected from the Wilkes area (Antarctica). The ellipse shows background sediment ratios. Isotopic signatures of major Australian (Broken Hill and Mount Isa) and US (Idaho, Missouri, and Utah) deposits are included. Error bars representing instrumental precision (1 SD) are comparable in size to the symbols used.

Figure 12 Sedimentation ratio (Fucar liquid k wiai) vs. yield stress at a field...

Figure 13 Sedimentation ratio (Fdcar liquid/Fi ,ai) vs. yield stress at a field strength of 2000 V/mm for samples containing 0.05g/ml of hydrophobically modified saponite (adsorbed surfactant (Ci6)2f>MABr) and different additives in 7-hex.adecanc. The type and concentration of additives are listed in the legend. All samples stood 1 day at rest before the sedimentation ratio was measured. Reproduced with permission from T. Diirrschmidt, and H. Hoffmann, Colloids and Surfaces A, 156(1999)257.

Correlations between PAHs in the environmental matrix and tissue can be useful in assessment of environmental exposure. One study found a strong gradient of PAH concentration both in sediment and in mussel Mytilus edulis and Modiolus modiolus) tissue up to several kilometers away from a ferro-alloy smelter (Bjorseth et al. 1979). Near the smelter, the sediments produced a tissue to sediment ratio of about 2 (dry/dry wt) for total PAH. Interestingly, benzo[b]fluoranthene was the dominant PAH in mussels at all stations however, in sediment it was only the fifth most abundant PAH (although the four most abundant PAHs were less water soluble). In another study, Dunn (1980) found a high correlation (r = 0.78) between mussels Mytilus edulis) and sediment benzo[a]pyrene concentrations. 

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