Humic substances river water

An extraction method for isolating humic substances from water by using XAD-8 has been proposed by Thurman and Malcolm (9) (see box). Humic substances in natural waters represent almost the entire hydrophobic acid fraction. This method has been used to isolate 4.25 g of humic substances from 24,500 L of ground water from the Fox-hills-Laramie aquifer and to obtain 500 g of humic material from 10,400 L of the Suwannee River (Table II). The sample from the Suwannee River was collected as a reference sample of aquatic humic substances by the International Humic Substances Society. In both of the examples cited, a fc cutoff of 100 was used. 

Apparent first-order rate constant phototransformation al X > 285 nm, k = (1.38 0.12) x 102 h 1 in purified water, and k = (1.68 0.12) x 10 2 h 1 in Capot river water with t,/2 40 h (Zamy et al. 2004) Oxidation half-life ranged from t,/2 5 h of midday sunlight during summer to t,/2 = 12 h during winter estimated from kinetic data for oxygenation reactions photosensitized by humic substances in water exposed to sunlight (Zepp et al. 1981) ... 

In some systems, such as lake and river waters, the suspended inorganic particles may be coated by biological polymers, termed humic substances, which prevent flocculation by either steric or electrostatic mechanisms. These can also interact with added inorganic salts (31) that can neutralize charged functional groups on these polymers. 

Currently available CRMs for Cr(lll)/(VI) species There exist a lyophilized water certified for Cr(III)/Cr(VI) and a binder-free glass fiber filter loaded with welding dust certified for Cr(VI) and total Cr (Vercoutere et al. 1998 Christensen et al. 1999) issued by the BCR. They consist of a set of specimens for single use. There is a need for more CRMs, such as a Cr(VI) in industrial effluents and in river water containing, e.g. humic substances. 

Calculated equilibrium speciation of (a) mercury and (b) copper during estuarine mixing of hypothetical river water with seawater. Hum, humic substance. Note logarithmic scale on y-axis. Source. From Mantoura, R. F. C., et al. (1978). Estuarine and Coastal Marine Science 6, 387 08. 

FLUORESCENCE Spectra. Fluorescence data are presented in Table V. All samples derived from drinking water gave an emission maximum between 417 and 430 nm, whereas the excitation maximum ranged between 346 and 365 nm. Miami IB showed an excitation maximum similar to the CFH samples, but the maximum was quite different from the one exhibited by the aquatic humic substances from the Satilla River. The emission maximum of these samples (Table V), however, was very similar. 

Data in this and other reports indicate three sources for dissolved organic substances in rivers, lakes, and reservoirs lignins, carbohydrates, and lipids. This study and others using degradative approaches (24) clearly established lignin as a precursor for dissolved humic substances. Similarly, carbohydrates are known to be a component of dissolved organic substances in natural waters (I). 

Black C, produced by wild fires and humic substances (HS), the natural by products of SOM decomposition in soil and water systems, are certainly the classes of organic compounds that most closely approximate this recalcitrant behavior. HS occur widely, being found in large amounts not only in the soil and sediments but also in lakes, rivers, ground waters, and even the open ocean (Stevenson, 1994). Besides these relatively refractory substances, more labile compounds can persist in soil for a much longer time than would be predicted from their inherent recalcitrance to decomposition. SOM stabilization (Figure 5.2) is generally considered to occur by three main mechanisms (i) physical protection, (ii) chemical stabilization, and (iii) biochemical stabilization (Six et al., 2002). 

Gel filtration chromatography using Sephadex G100 as column packing and ultraviolet detectors, have been used in studies carried out on the elution of humic acid [8] and in characterisation studies on secondary sewage effluents [9] and in organic substances in river waters [10],... 

Photolysis first-order rate constants for photosensitized reactions in water with various humic substances as sensitizers k = 0.17 h-1 with aquatic humus from Aucilla River, k = 0.12 Ir1 with Aldrich humic acid, k = 0.091 Ir1 with Fluka humic acid and k = 0.11 Ir1 with Contech fulvic acid in sunlight, corresponding to half-lives of 4 to 8 h (Zepp et al. 1981) photolysis t,/2 = > 50 yr at 15°C and a pH 5-9 (Torang et al. 2002). Oxidation rate constant k for gas-phase second order rate constants, koH for reaction with OH radical, kN03 with N03 radical and kQ3 with 03 or as indicated, data at other temperatures and/or the Arrhenius expression see reference ... 

According to their acidity, humic substances are hydrophobic and are split into two groups humic and fulvic acids. Humic acids are stable molecules originating from the ageing of organic matter. They are responsible for water coloration and represent 40-60% of natural organic matter in rivers and lakes. Fulvic acids are smaller than the humic acids and are generally less aromatic than humic acids extracted from the same pool of DOM. 

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