Suspended humic acid concentration

Acid as a Function of Suspended Humic Acid Concentration... 

Conclusions. Diphenyl mercury, a neutral organometallic compound, which does not contain any markedly acidic or basic functional groups was found to adsorb only onto humic acid. No sorptive behavior could be detected with respect to bentonite, MnO or Fe(OH)-. The rather low value of Kads indicates a simple molecular attraction. However, the decrease in Kads with an increase in ionic strength Indicates that DPM is competing with the metal ions in seawater for adsorption sites. The increasing nonlinearity of adsorption isotherms with increasing suspended humic acid concentration is also similar to results obtained for metal ion adsorption. 

Adsorption isotherms and conditional adsorption constants (Kads) were determined for the adsorption of diphenyl mercury and phenylmercurie ion (introduced as phenylmercuric acetate) from a seawater matrix onto several solid phases. Diphenyl mercury was found to adsorb onto humic acid, but no adsorption was detected onto bentonite, amorphous FeCOH) or hydrous MnO,. The value of Kads was found to decrease with increasing ionic strength for the diphenyl mercury - humic acid system in seawater. As the concentraction of suspended humic acid increased, the nonlinearity of the diphenyl mercury - humic acid system became more pronounced at an increasingly lower diphenyl mercury concentration. Phenylmercuric ion adsorbed most strongly onto humic acid although adsorption onto FeCOH) and MnO was detected and Kads values were determined. Kads values for PMA with humic acid, MnO and Fe(OH) were found to decrease with decreasing salinity. 

Figure 3. Adsorption isotherms for DPM and various concentrations of suspended humic acid in seawater.

In our work we concentrate on the interactions between di- and tri-valent metal radionuclides which enter estuarine and seawater in ionic forms and humic and fulvic acids of different origins. However, as humic substances react with metals, not only in dissolved but also in undissolved states, we report some data on the adsorption of trace metal radionuclides on suspended humic acids. 

Figure 9. Concentration factors (log for the adsorption of Cd on different suspended humic acids in the river water. Concentration of humic acids 35 mg dm . Particle size between 0.45 and 32 um.

This removal may also include diffusion of soluble U(VI) from seawater into the sediment via pore water. Uranium-organic matter complexes are also prevalent in the marine environment. Organically bound uranium was found to make up to 20% of the dissolved U concentration in the open ocean." ° Uranium may also be enriched in estuarine colloids and in suspended organic matter within the surface ocean. " Scott" and Maeda and Windom" have suggested the possibility that humic acids can efficiently scavenge uranium in low salinity regions of some estuaries. Finally, sedimentary organic matter can also efficiently complex or adsorb uranium and other radionuclides. 

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],... 

Not only are accurate data for trace metals in rivers sparse, there are complications that exist at the river-sea interface. The increase in salinity occurring at the river-sea water interface, with its concomitant increase in the concentrations of the major seawater cations, can lead to flocculation and sedimentation of trace metals such as iron (Boyle et al., 1978 Sholkovitz and Copeland, 1983) or to desorption from suspended riverine particles of trace metals such as barium (Edmond et al., 1978). In organic-rich rivers a major fraction of dissolved trace metals can exist in physiochemical association with colloidal humic acids. Sholkovitz and Copeland (1983) used product-mode mixing experiments on filtered Scottish river water, and observed that iron removal was almost complete due to the flocculation of strongly associated iron-humic acid colloids in the presence of the increased... 

Amino Acids. Kemp and Mudrochova (1973) determined amino acids and amino sugars by ion-exchange chromatography in 6N HCl hydrolysates of humic and fulvic acids from Lake Ontario sediments. They obtained total amino acids of 21.5% for humic acid and 12.6% for fulvic acid. Total amino sugars accounted for only 1.9 and 1.3% for humic acid and fulvic acid, respectively. They found the amino acid distribution in the humic acid resembled that of zooplankton and suspended sediment samples, with the exception of glycine which was higher in the sediments. This lends support for the assumed autochthonous nature of lake sediment organic matter. On the other hand, basic amino acid concentrations were low in the fulvic acid and its amino acid distribution resembled the combined form in the interstitial waters. 

Suspended and bottom sediments are widely regarded as a sink for PCB s and other hydrophobic organic pollutants released Into aquatic systems. The mechanism commonly proposed to explain the affinity of PCB s for sediments Is equilibrium sorption or partitioning, which Is a function of the aqueous solubility of PCB Isomers and the attractiveness of the sedimentary matrix to PCB s (1-4). Field and laboratory studies Indicate that sedimentary organic matter plays a fundamental role In PCB-sedlment associations (5-12) and that humic substances are Important components of the sedimentary organic matrix for such associations (6,13-16). For example, Choi and Chen (O found that sedimentary PCB and DDT concentrations were linearly related to the humic acid content of sediments from Los Angeles Harbor. Fierce et al. (15) determined that humic acid could account... 

The adsorption of diphenylmercury (DPM) and phenylmercuric ion (PM) was studied on the solid phases described above (hydrous manganese oxides, amorphous iron oxides, humic acid and bentonite clay). The solid phase (5-15 mg) was added to 25-50 ml of filtered seawater yielding solid phase concentrations of approximately 100 to 400 ppm suspended matter. The concentration of seawater was also varied in order to study the variation of adsorptive behavior with changes in ionic strength. The suspension was then spiked with either DPM or PMA to yield concentrations of organometallic which varied from 0.10 to 3.5 ppm. The range in organometallic concentration used for this study was determined by the sensitivity of the detection method and the solubility of DPM and PMA in seawater. 

The effect of concentration of suspended adsorbent on sorptive behavior in a seawater matrix was studied by determining adsorption isotherms for DPM and 94, 150, 200,400, and 1000 ppm humic acid. The corresponding values of Kads (Table III) show no definite trend with respect to Increased adsorbent concentration. This is not totally unexpected in view of O Connor and Connolly s observation that systems with low Kads values do not show dramatic changes of Kads with changes in suspended matter concentrations 9). Only systems with high Kads values typically show definite decreases in Kads with increases in adsorbent concentration. 

Phenylmercuric ion was introduced to the various solid phase-seawater suspensions as an aqueous solution of phenylmercuric acetate (PMA). Adsorption of phenylmercuric ion onto all solid phases studied, except bentonite clay, was noted at solid concentrations of 150 ppm (suspended). Adsorption isotherms for humic acid, hydrous MnO and amorphous Fe(OH)2 are shown in Figure A. Values of Kads for phenylmercuric ion and these solid phases are listed in Table IV. 

As a whole, this process has profound implications for metal cycling in rivers which drain highly leached and low relief podsolitic terrains. The interaction between dissolved organics and dissolved solutes may, however, be limited in other Amazonian river systems. In the Rio Negro, where suspended solids are found in extremely low concentrations, the humic substances behave rather conservatively with a HA FA of 0.64. However, in the Amazon mainstream, the hydrophobic humic acids become selectively adsorbed onto fine suspended particles fi-om the Rio Solimoes (6), such that the HA FA drops to only 0.31 (7). Although the fiilvic acids are compositionally hydrophilic, and therefore, are not readily adsorbed onto detrital material, the drastic loss of humic acids could result in a decrease in available reactive sites for organo-metallic interactions. 

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