Sorption processes sediments

The presence of suspended solid materials increases the extent of LAS biodegradation [13,28], but the rate of the process remains invariable. The influence of the particulate material is due specifically to the increased density of the microbiota associated with sediments. However, suspended solids may also reduce the bioavailability of IAS as a result of its sorption onto preferential sites (e.g. clays, humic acids), although this is a secondary effect due to the reversibility of the sorption process. Salinity does not affect IAS degradation directly, but could also reduce LAS bioavailability by reducing the solubility of this molecule [5], Another relevant factor to be taken into account is that biodegradation processes in the marine environment could be limited by the concentration of nutrients, especially of phosphorus and nitrogen [34],... 

Despite these reservations, environmental distribution values may be considered valid for the sorption process, to a first approximation. On this basis, it can be concluded that detected environmental partition coefficients show the clear affinity of surfactants to particulate material. The affinity is higher for cationic surfactants than for other surfactants, as shown by the high partition coefficient values (Table 5.4.1). Partition coefficients are also higher for the water column than for sediments (Table 5.4.1), and it is difficult to offer an explanation for this, bearing in mind the many factors affecting the partition coefficient in both natural water and sediment. 

Based on these monitoring results and some estimations of volatilisation and sediment burial rates, Ferguson et al. concluded that the estuarine fate of APEO metabolites in Jamaica Bay is determined mainly by sorption processes, degradation in the water, and advective transport out of the estuary [15]. 

The description of the sorption process is largely based on empirical correlations, without knowledge of the detailed structure of the sediments. No doubt, in the future a greater effort will have to be made to understand sorption behavior in terms of sediment constituents. It will not suffice to consider sorption onto sediments simply in terms of partitioning into a uniform, thermodynamically ideal, stationary organic phase. 

The extraction of aromatic chlorophenols (e.g., chloroguaiacols, chloro-catechols) is complicated by the different sorption processes that control their binding within the soil-sediment structure [411-413]. The free, physically adsorbed chlorophenolics can be extracted with solvent, but this may only account for 1-5% of the total concentration of these pollutants in the sediment. Martinsen et al. [414] found that -hexane or cyclohexane and iso-propanol... 

An example of first-order plots is shown in Fig. 1 for benzo[a]pyrene (i.e., B[a]P) sorption on three different soils (in terms of organic matter content) and two sediment samples (marine and fresh water) at two different concentrations [1]. It can be noted that the plots are linear at both concentrations, which would indicate that the sorption process is first order. The findings that the rate constants are not significantly changed with concentration is a good indication that the reaction is first order under the experimental conditions that were imposed. 

Another important consideration in investigation of the reaction of sorbed pesticides is the nature of the sorption process itself. Sorption/desorption kinetics and the physicochemical characteristics of the pesticide molecules in the sediment-sorbed state can be expected to influence the kinetic observations made in experimental systems. 

Several investigations have, however, verified the inadequacy of this representation of the sorption process. Variations of with sediment concentration ( 19, M) have... 

Environmental Protection Agency (22). Figure 1 is a plot of the sediment/aqueous concentration ratio versus time for this system. It is characterized by a rapid sorption process and a much slower sorption process which does not reach equilibrium until about 10 days after initial mixing of the sediment and chlorpyrifos solution. 

Here, kj represents a pseudo first-order rate constant (linear in sediment concentration) for the sorption process, k the... 

Gao, S., Goldberg, S., Herbel, M.J. et al. (2006) Sorption processes affecting arsenic solubility in oxidized surface sediments from Tulare Lake bed, California. Chemical Geology, 228(1-3 Special Issue), 33-43. 

Karickhoff (1980) and Karickhoff et al. (1979) have studied sorption and desorption kinetics of hydrophobic pollutants on sediments. Sorption kinetics of pyrene, phenanthrene, and naphthalene on sediments showed an initial rapid increase in sorption with time (5-15 min) followed by a slow approach to equilibrium (Fig. 6.7). This same type of behavior was observed for pesticide sorption on soils and soil constituents and suggests rapid sorption on readily available sites followed by tortuous diffusion-controlled reactions. Karickhoff et al. (1979) modeled sorption of the hydrophobic aromatic hydrocarbons on the sediments using a two-stage kinetic process. The chemicals were fractionated into a labile state (equilibrium occurring in 1 h) and a nonlabile state. 

Steen, W.C., Paris, D.F., Baughman, G.L. (1979) Effects of sediment sorption on microbial degradation of toxic substances, pp. 168-173. In Proceedings of the Symposium on Processes Involving Comaminants and Sediments. Baker, R., Editor, American Chemical Society, Washington, DC. 

Many adsorbates and/or adsorbents are redox sensitive. The specific adsorption in such systems depends on the redox potential, which is very difficult to measure or control, thus, systematic studies in this direction are rare. On the other hand some practical implications are well known, e.g. the uptake of chromates by soils and sediments in enhanced on addition of Fe(II) salts [27] as an effect of a redox reaction, in which Cr(VI) is reduced to Cr(III). A few examples of redox reactions accompanying sorption processes are reported in the column results". The changes of oxidation state in the sorption process are probably more common than it is apparent from literature reports, but they are often overlooked, namely, analytical methods must be specially tailored to observe these changes. 

Root, R.A. et al., Arsenic sequestration by sorption processes in high-iron sediments, Geochim. Cosmochim. Acta, 71, 5782, 2007. 

PROBABLE FATE photolysis . C-Cl bond photolysis can occur, not important in aquatic organisms, photooxidation half-life in air 9,24-92.4 hrs, reported to photodegrade in water in spite of the lack of a photoreactive center oxidation-, not an important process hydrolysis . very slow, not important, first-order hydrolytic half-life 207 days, reaction with hydroxyl radicals in atmosphere has a half-life of 2.3 days volatilization may be an important process, however, information is contradictory, volatilization half-life from a model river 6 days, half-life from a model pond considering effects of adsorption 500 days, slow volatilization from water is expected with a rate dependent upon the rate of diffusion through air sorption important for transport to anaerobic sediments biological processes biodegradation is important occurs slowly in aerobic conditions, occurs quickly and extensively in anaerobic conditions... 

PROBABLE FATE photolysis C-CI photolysis can occur, not important in aquatic systems, photooxidation half-life in air 9.24 hrs-3.85 days oxidation not an important process hydrolysis very slow, not important, first-order hydrolytic half-life 207 days volatilization information is contradictory as to how important process is sorption important for transport to anaerobic sediments biological processes biodegradation could be important... 

PROBABLE FATE photolysis, no information is available, may not be an important fate process based on the stability of thin films exposed to light >300 nm, if released to the atmosphere, it will react with hydroxyl radicals, with a half-life of 1.23 hr oxidation probably not important hydrolysis probably an important process, hydrolysis half-lives of endosulfan isomers 35.4-37.5 days at pH 7 and 150.6-187.3 days at pH 5.5 volatilization no information available, evaporation from water is probably an important fate process based on an estimated half-life of 43 hr from a river Im deep, flowing 1 m/s and a wind velocity of 3 m/s, evaporation from lakes and deeper streams and rivers will be slower sorption no information available, if released to soil, it will be expected to bind to the soil, if released to water, it will be expected to bind to the sediment biological processes no information available... 

PROBABLE FATE photolysis , possible dechlorination of C=C bond, photooxidation half-life in air 6 hrs-2.5 days, vapor phase reactions with photochemically produced hydroxyl radicals have a half-life of 1.5 days oxidation not expected to be important hydrolysis very slow, not expected to be important volatilization not an important process, evaporates slowly to air, volatilization from a model river 60 hr sorption occurs to a moderate degree, sticks strongly to soil particles, if released to water, will adsorb strongly to suspended and bottom sediment biological processes biotransformation occurs very slowly, but could be important... 

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