The Carbon Isotopic Composition of Trihalomethanes Formed from Chemically Distinct Dissolved Organic Carbon Isolates from the Sacramento-San Joaquin River Delta, California, USA.

Abstract

Dissolved hydrophobic and hydrophilic acids were isolated from samples collected at five channel sites within the Sacramento-San Joaquin Rivers and Delta, California, USA, and from a peat island agricultural drain to examine the relationship between the chemical composition of dissolved organic carbon and the formation of trihalomethane, and to test whether peat island-derived dissolved organic carbon contributed substantially to reactivity. The chemical composition of the isolates was quite variable, as indicated by significant differences in carbon-13 nuclear magnetic resonance spectra and carbon to nitrogen concentrations ratios, though the variability was not consistent with simple mixing of river- and peat-derived dissolved organic carbon. The lowest propensity to form trihalomethane observed was in the peat island agricultural drain sample, suggesting the addition of peat island waters into Delta channels did not increase the amount of trihalomethane formed from channel water dissolved organic carbon. Changes in the chemical and isotopic composition of the isolates suggest the source of the trihalomethane precursors was different among samples and between isolates. The carbon isotopic composition of the trihalomethane formed from the isolates generally tracked the carbon isotopic composition of the isolates themselves, but variability in the carbon isotopic composition of the trihalomethane was higher.

Keywords: Carbon Isotopic, Trihalomethanes, Carbon Isolates

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