How to Determine Aquatic Humic Substances

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Aquatic Humic Substances (AHS) result from the decomposition of plant and animal residues and are found in soil, sediment, and water. They are widespread in nature and are mostly comprised from naturally occurring dissolved organic matter in water.

AHSs are an important component in water systems, particularly as they relate to the potential fate of chemicals in the aquatic environment. For example, upon chlorination, AHS may form trihalomethanes (THMs). THMs formation is a concern in drinking water systems and thus a determination for the presence of AHS is useful to evaluate potential sources of THMs. AHS can change the toxicity or the benefits of materials by making them more available or less available to organisms. These are just two examples of the impact AHS has on the fate and transport of analytes and environmental contaminates.

The procedure followed by Columbia Analytical for the determination of AHS is described in Standard Methods for the Examination of Water and Wastewater SM 5510B and SM 5310C. Samples collected for this procedure should be collected in organic free glass containers and should be stored in the dark at 4°C.

The amount of AHS present is determined by concentrating the water sample, at a pH of six, on an anion exchange column of diethylaminoethyl (DEAE) cellulose. The testing is performed in duplicate to evaluate precision in each matrix. The AHSs are removed from the DEAE cellulose under basic conditions and the eluent is acidified to minimize carbon dioxide contamination from the air. Any carbon dioxide that may be present is removed via purging with nitrogen. The concentration of dissolved organic carbon is then determined via persulfate oxidation and infrared spectroscopy. The AHS present is calculated as two times the dissolved organic carbon concentration.

Determining the level of AHS in an aquatic system provides information that may be useful in understanding the potential formation of biotoxic components and the impact to organisms present in the ecosystem.

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