Trihalomethane formation potential of aquatic and terrestrial fulvic and humic acids: examining correlation between specific trihalomethane formation potential and specific ultraviolet absorbance Mohamed Y. Z. Abouleish A and Martha J. M. Wells B,C,D A Department of Biology, Chemistry, and Environmental Sciences, American University of Sharjah, PO Box 26666, Sharjah, United Arab Emirates. B Center for the Management, Utilisation, and Protection of Water Resources and Department of Chemistry, Tennessee Technological University, Cookeville, TN 38505, USA. C Present address: EnviroChem Services, 224 Windsor Drive, Cookeville, TN 38506, USA. D Corresponding author. Email: mjmwells@tntech.edu; info@envirochemservices.net Environmental context. When surface water is disinfected to produce potable drinking water, toxic by-products are generated by reaction with naturally occurring organic matter. The production of trihalomethane disinfection by-products was investigated for different types of well-characterised organic matter from various geographic locations. Increased understanding of the character of organic matter dissolved in water is needed for improving the ability to provide safe water and protect public health. Abstract. Trihalomethanes (THMs) – a class of disinfection by-products (DBPs) including chloroform – are produced when natural water is chlorinated. Many THMs are believed to result from the reaction of chlorine with the aromatic structures in humic substances, which can be represented by ultraviolet absorbance at 254 nm (UVA). However, in the literature, plots of the specific, or carbon-normalised, UVA (SUVA) compared with the specific, or carbon-normalised, trihalomethane formation potential, THMFP (STHMFP) are poorly correlated. Therefore, well characterised samples of organic matter were obtained from the International Humic Substances Society (IHSS) to study the effect of type (fulvic acid, FA; humic acid, HA), origin (aquatic, terrestrial), geographical source (Nordic, Suwannee River, peat, soil) and pH (6, 9) on the formation of trihalomethanes. In this research, parameters expressed on a weight-average moles-of-humic substance basis were compared with those on a mass-of-carbon basis. Using factorial analysis, SUVA was statistically described by the main effect type (P ¼ 0.0044), whereas STHMFP was statistically described by the main effects type (P ¼ 0.0078) and origin (P ¼ 0.0210). Separate relationships between SUVA and STHMFP normalised to moles of humic substance were defined for aquatic substances (R 2 ¼ 0.9948) and for terrestrial substances (R 2 ¼ 0.9512). The occurrence of aquatically derived fulvic-like humic acid (Suwannee River humic acid) and aquatically derived terrestrial-like humic acid (Nordic humic acid) were observed. Some aquatic substances were capable of generating levels of THMs per mole of humic substance that were greater than or equal to the most reactive terrestrial humic acid. Additional keywords: disinfection by-products, drinking water treatment, factorial analysis, STHMFP, SUVA. Received 19 March 2012, accepted 10 August 2012, published online 5 October 2012 Introduction The water treatment industry strives to maintain simultaneous control of microbial quality and disinfectant by-product (DBP) formation. Evaluating risk is a trade-off between inactivating disease-causing pathogens in water and generating potentially toxic by-products formed during disinfection of water. Current regulations in the United States require water treatment plants to monitor drinking water for certain DBPs. Trihalomethanes (THMs) – the most commonly observed DBPs – are a family of chemicals that include chloroform, bromodichloromethane (BDCM), dibromochloromethane (DBCM) and bromoform. [1–3] Chloroform is usually the preva- lent by-product, yet brominated THMs exist when high levels of inorganic bromide are present. [4,5] THMs are probable carcino- gens in laboratory animals [4,6–8] and have been linked to adverse reproductive outcomes and spontaneous abortions in humans. [5,9] Toxicologically important DBPs were recently discussed. [10] The formation of THMs is believed to result from the reaction of chlorine with the aromatic structures in humic substances (HSs). [11–13] Other studies suggest that non-aromatic dissolved organic carbon (DOC) also participates in the forma- tion of THMs. [3,14] Natural organic matter (NOM) is composed of many different types of compounds that do not necessarily all behave similarly. [15] The concentration of THMs produced during disinfection depends on the characteristics of NOM CSIRO PUBLISHING Environ. Chem. 2012, 9, 450–461 http://dx.doi.org/10.1071/EN12041 Journal compilation Ó CSIRO 2012 www.publish.csiro.au/journals/env 450