Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2005
Publication Date: 1/3/2006
Citation: Chow, A.T., Guo, F., Gao, S., Breuer, R.S. 2006. Trihalomethane Reactivity of Water- and Sodium Hydroxide-Extractable Organic Carbon Fractions from Peat Soils. Journal of Environmental Quality, 35: 114-121. Interpretive Summary: Agricultural peat soils in the Sacramento - San Joaquin Delta contribute organic carbon to Delta waters that serve as a source of drinking water for 22 million people. Due to the complexity of natural organic matter, identification of reactive organic carbons or fractions to form health hazardous compounds as disinfection by-products (DBPs) during chlorination process has been presenting great challenges. This study used an integrated approach to determine reactivity of organic carbon fractions well defined in soil science and those isolated with procedures commonly used in the water industry for direct evaluation of DBP reactivity. The largest and the most reactive organic carbon fractions associated with these isolations from Delta soils are identified from this research. The knowledge assists in better understanding and interpretation of organic carbon from soil origin in affecting Delta water quality.
Technical Abstract: Certain organic carbon moieties in drinking source waters of the Sacramento–San Joaquin Delta can react with chlorine during disinfection to form potentially carcinogenic and mutagenic trihalomethanes. The properties of reactive organic carbon in Delta waters, particularly those of soil origin, have been poorly understood. This study attempts to characterize trihalomethane reactivity of soil organic carbon from three representative Delta peat soils. Soil organic carbon was extracted from all three soils with either deionized H2O or 0.1 M NaOH and sequentially separated into humic acids, fulvic acids, and nonhumic substances for quantitation of trihalomethane formation potential. Water-extractable organic carbon represented only 0.4 to 0.7% of total soil organic carbon, whereas NaOH extracted 38 to 51% of total soil organic carbon. The sizes and specific trihalomethane formation potential (STHMFP) of individual organic carbon fractions differed with extractants. Fulvic acids were the largest fraction in H2O-extractable organic carbon, whereas humic acids were the largest fraction in NaOH-extractable organic carbon. Among the fractions derived from H2O-extractable carbon, fulvic acids had the greatest specific ultraviolet absorbance and STHMFP and had the majority of reactive organic carbon. Among the fractions from NaOH-extractable organic carbon, humic acids and fulvic acids had similar STHMFP and, thus, were equally reactive. Humic acids were associated with the majority of trihalomethane reactivity of NaOH-extractable organic carbon. The nonhumic substances were less reactive than either humic acids or fulvic acids regardless of extractants. Specific ultraviolet absorbance was not a good predictor of trihalomethane reactivity of organic carbon fractions separated from the soils.