Dissolved organic carbon humic materials

Wallis (1979) and Telang et al. (1981) measured dissolved organic carbon and humic substances in groundwater of the Marmot Creek system in Canada and found that humic substances were the dominant fraction of the dissolved organic carbon. Humic substances contributed approximately 900 Lig C/L and 90% of the dissolved organic carbon. No characterization of the humic material was done. 

There is more current literature which speaks to exactly this point. Hassett -0 has found that the sorption of organic compounds from water to suspended particles is altered in the presence of dissolved organic carbon. Griffin Chian - - and Diachenko have found that the volatility of organic compounds in water decreases when humic materials are present. Perdue -2 has found that the rate of hydrolysis of the octyl ester of 2,4-D is decreased in the presence of humic materials. 

Landrum P.F., M.D. Reinhold, S.R. Nihart, and B.J. Eadie. 1985. Predicting the bioavailability of organic xenobiotics to Pontoporeia hoyi in the presence of humic and fulvic materials and natural dissolved organic carbon. Environ. Toxicol. Chem. 4, 459-467. 

A number of UV-vis absorption ratios have been measured to provide information about the state of humification and content of humic material in the dissolved organic carbon (DOC). For example, the ratio of the ultraviolet absorbance at 254 nm (UV254) with the DOC content provides an estimate of the abundance of ultraviolet absorbing species and may also be used for comparison of the aromaticity of various humic materials (McDonald et al., 2004). 

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). 

Dissolved organic carbon (DOC) measurements were obtained on the size-fraction ated concentrates with a PHOTOchem Organic Carbon Analyzer (Sybron, Model E3500) as an indication of the concentration of humic materials in each fraction. DOC values are reported as ppmC (mgL" ) The major cations in each fraction were determined by inductively coupled plasma spectroscopy (Instruments SA, Model JY 86). 

Size exclusion chromatography (SEC) has been used to measure molecular weight (MW) distribution of humic substances (3, 6-9). Coupled with detection methods such as molecular fluorescence spectroscopy and dissolved organic carbon analysis (7), electrochemical detection (9), and atomic emission spectroscopy (5), SEC has been used extensively to study humic-metal complexes. A major disadvantage of SEC is that it does not provide adequate resolution for separating humic materials as they do not appear to be made up of distinct fractions with large differences in MW. 

In natural waters, Tl is not precipitated as a carbonate nor as an hydroxide, and is also hardly bound to soluble humic material. Therefore, toxicity is largely independent of water characteristics, such as hardness, dissolved organic carbon, or suspended matter (Nehr-ing, 1962 Zitko et al., 1975). 

The immunoassay also was examined for interference by naturally occurring humic and fulvic acids (14), which account for the majority of dissolved organic carbon in natural waters (15). Atrazine was measured in water samples that contained from 5 to 100 mg/L of humic and fulvic acid from the Suwannee River (standard-reference surface-water sample) (16) and humic and fulvic acids from Biscayne aquifer near Miami, Florida (17). For all samples, there was no difference between the immunoassay response in the presence and absence of the humic material. These data indicate... 

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