Seasonal Variation of Disinfection By-products in Drinking Water in Central Chile

The formation of trihalomethanes (THMs) during water disinfection is related to several parameters such as water temperature, free chlorine and availability of dissolved organic matter. This paper compares and quantifies the THMs in drinking water from Concepcion city in the Bio Bio Region of central Chile, during summer of 2007 and autumn-winter 2008. THM concentrations in the source water were low (0.001-0.023 mu g L-1). The concentration ranges in summer sampling period for the drinking water were 9.7-111.6, 0.1-1.0 and 0.9-25.5 mu g L-1 for chloroform (CHCl3), and dibromochloromethane (CHClBr2) and bromodichloromethane (CHCl2Br), respectively; and 5.4-182.0, 0.1-0.9, 0.9-35.2 mu g L-1 respectively for the autumn-winter sampling period. Bromoform was not detected in any sample. There were significant correlations between the THMs concentration and residence time of the water into the network, distance from the treatment plant and an inverse correlation to free chlorine and UV absorbance. In this system, temperature was not a major factor in the THM concentrations at the point of use although lower overall concentrations were measured in summer. The Additive Toxicity Index Value (0.07-1.4) for winter samples indicated that the Chilean Norm was exceeded at the more distant water utilisation points, where the residence time in the system was >600 minutes. This was not the case in summer as utilisation rates were greater reducing the residence times. Dichloromethane (DCM) was also detected at elevated concentrations in the water supply and exceeded the Chilean Norm (20 mu g L-1) at all points in the system, up to 12 times, and may pose more of a health risk than the THMs.