determination of trihalomethanes concentration in ahvaz water distribution network in 2011

background trihalomethanes (thms) are major group of chlorinated by products, potentially hazardous and carcinogenicity of these compounds was recognized. the purpose of this study was survey on thms concentration in ahvaz drinking water. material and methods a descriptive cross-sectional study was based on 36-week sampling program during the winter, spring and summer of 2011 in water distribution network of the no. 1 and no. 2 water treatment plants (wtp1 and wtp2) in ahvaz city was conducted. sampling in the distribution networks was taken from finished water and three points of distribution networks. thm species analyses carried out by gas chromatograph system (gc/µecd) with head space technique. spss software was used for data analysis. one-way anova test was used for thms average comparison between seasons and sampling point and t-test was used for comparison between two distribution networks. results in this study, the total thms determined in winter, spring and summer ranged from 20.5-86µg/l, 18.92-66.06µg/l and 17.35-174.75µg/l respectively. conclusion according to this study, only in 6 samples the total thms concentration exceed the u.s.epa mcl (80 µg/l) and only in 3 samples exceed from the iran standard and who guideline (∑thm/who guideline≤1). average values of the total thms in summer were 1.4 and 1.6 times higher than winter and spring respectively. furthermore, brominated thms were dominant species.