Humic acid estuarine sediments

Humin varies widely in composition. Sediments derived from algal/microbial biomass have humin with paraffinic structures resembling those of corresponding humic acids. Estuarine or coastal marine sediments examined in this study have humin with highly aromatic structures which resemble coal-like materials rather than modern plant residues. In these latter sediments no structural correspondence exists between humin and humic acids which appear to more nearly reflect the nature of modern plant... 

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. 

Removal to sediments. Removal of surface-reactive trace elements from the oceans readily occurs by adsorption onto settling particles, and this process is most pronounced in the typically high-energy, particle-rich estuarine environment. Particles are supplied by rivers, augmented by additions of organic material generated within the estuary. Also, floes are created in estuaries from such components as humic acids and Fe. The interaction between dissolved and colloidal species is enhanced by the continuous resuspension of sediments in... 

Beller and Simoneit [20] studied the occurrence of hexachlorophene in extracts of estuarine sediments taken from the Hudson River. Hexachlorophene was detected only in the humic acid fractions of the samples, indicating that it could bind strongly to organic matter and was highly resistant to degradation in that form. 

Gundersen, J. L., W. G. Macintyre, and R. C. Hale, pH-dependent sorption of chlorinated guaiacols on estuarine sediments The effects of humic acids and TOC , Environ. Sci. Technol., 31, 188-193 (1997). 

Briichert, V. 1998. Early diagenesis of sulfur in estuarine sediments The role of sedimentary humic and fulvic acids. Geochimica et Cosmochimica Acta 62 1567-1586. 

Sea water contains a much lower concentration of dissolved organic matter than river water. More than half of this dissolved organic load is of a humic nature. These dissolved organic acids tend to flocculate as the salinity increases (10). Hair and Bassett (11) have observed an increase in the particulate humic acid load of an estuary as one approaches the sea. Although no studies of the distribution of humic materials throughout an estuarine system have been performed, it would appear that estuaries and their sediments in particular, act as a major sink for the dissolved and particulate humic materials. Nissenbaum and Kaplan (12) have observed that terrestrial humic materials are not deposited at great distances from shore in the marine system. A study of the flux of particulate carbon through the Chesapeake Bay comes to a similar conclusion (13). 

Fulvic acids. Marine sedimentary humic substances soluble in base and acid (fulvic acids) have previously been examined by and NMR (12). The dominant structural components were postulated to be polysaccharide - like substances, probably polyuronic acids. Solid-state NMR spectra of fulvic acids isolated from a number of marine and estuarine sediments are shown in Figure 1. Major peaks at 72 and 106 ppm betray the overwhelming presence of polysaccharide -like substances, and, as shown by Hatcher and others (12.), the moderate peak for carboxyl or amide carbon at 175 ppm suggests that these polysaccharides are more like polyuronides. Aromatic carbons (110 to 160 ppm) are decidedly minor components. Aliphatic carbons (0-50 ppm) are also minor components. H NMR spectra shown by Hatcher and others (12) indicate that these aliphatic structures are highly branched. 

Figure 2. Representative CPMAS NMR spectra of humic acid from marine and estuarine sediments.

The content of aromatic carbon varies considerably in marine and estuarine humic acids, but is, in all cases, greater than that of Mangrove Lake humic acids. This is probably a reflection of the greater contribution of vascular plant-derived material which can be expected to provide lignin-like components rich in aromatic structures. Note that the humic acids from fluvial sediments of the Potomac River are the most aromatic. Peaks at 150 and 55 ppm are characteristic of oxygen-substituted aromatic carbons typically associated with lignin of vascular plants. Humic acids from New York... 

Humic acids of marine and estuarine sediments are characterized by major amounts of paraffinic structures that previous studies have shown to be highly branched and to contain significant quantities of carboxyl/amide and alcohol/ether carbon. Some humic acids, namely those from well preserved sapropelic marine sediments show significant quantities of carbohydrate-like structures incorporated. This, no doubt, is a reflection of the solubility characteristics of polysaccharides which may have some carboxyl functionalities (uronic acid groups). 

Selective extraction was used to operationally determine the quantitative and qualitative distributions of PCB 8 and saturated hydrocarbons among free lipid (FL), humic acid (HA), and humin (HU) fractions of four contaminated estuarine sediments. In all samples, over 90% of the total sedimentary PCB s and hydrocarbons were extracted with FL fractions. Bound (HA and HD) and free assemblages of these compounds may have derived from different sources. Two polar, chlorinated pollutants also detected In this study, hexachlorophene (HCP) and pentachlorophenol (PCP), were proportionately more concentrated In bound fractions than the non-polar compounds HCP was detected only In HA fractions and was probably chemically hound to refractory organic matter. Selective extraction Is a promising technique for Investigating strongly bound polar pollutants, such as HCP, which apparently are not recovered by conventional solvent extraction. 

Table II lists two values for Kads at lOOZ SW. The bracketed value is that evaluated using a humic acid extracted from estuarine sediments. The sedimentary sample was obtained from the Chesapeake Bay near the town of Bivalve (BV). Because the values of Kads were so similar for the estuarine humic acid and the commercially prepared soil humic acid, use of the estuarine sample was discontinued and the soil humic acid was used consistently thoughout the study.

Strohal P, Huljev D (1971) Investigation of mercury-pollutant interaction with humic acids by means of radiotracers. Proc Symp Nucl Techn Environ Poll, IAEA, Vienna, p 349 Watling RL (1981) The identification and significance of mercury compounds in estuarine sediments. Int Conf Heavy Metals in the Enviroment, CEP Consultants Ltd., Amsterdam, p 591... 

The ratios of humic to fulvic acids in estuarine and coastal sediments range from 0.4 to 3.4, the higher values being associated with areas or sediments having a terrestrial influence (Palacas et al., 1968 Brown et al., 1972 Hue and Durand, 1973 Pelet and Debyser, 1977 MacFarlane, 1978). These values are also consistent with those from other marine and terrestrial environments (Ishiwatari, 1966 Kononova, 1975 Stuermer et al., 1978 Cronin and Morris, 1982). Other parameters measured on coastal humic substances, such as elemental composition, spectral properties, organic components, stable isotope ratios, or C ages (Pelet and Debyser, 1977 Stuermer et al., 1978 Benoit et al., 1979 Nissenbaum, 1979) are consistent with terrestrial or marine humic compounds, or a mixture of these two endmembers. 

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