The amount of trihalomethanes (THM) in the drinking water of the city of Tabriz in 2016

Abstract

Introduction: Exploiting Surface Water resource as the main potable water supplies and the application of chlorine as the main disinfectant for drinking water have increased the rate of Disinfection by-products ( DBPS) formation. One main group of DBPS are Trihalomethane compounds (THMS) that their carcinogenic risks have been reported in humans and animals as well as adverse health effects in the liver , kidneys , and the central nervous system are the effects of these substances. Effective factors in the formation of trihalomethanes are temperature , pH , contact time with chlorine , concentration and characteristics of chlorine , residual chlorine , natural organic matter (NOMS) and bromine concentration. Objective of this survey is the determination of THMS concentration in Tabriz Water drinking Distribution system and the relation between THMS formation with temperature , pH , electrical conductivity , Total chlorine , free residual chlorine , calcium hardness , alkalinity and corrosion and sedimentation indexes as well as an estimate of the lifetime cancer risks and the risk of non-carcinogenic exposure to these compounds. as well as THMS concentration were determined using gas chromatography. Materials and Methods: In this descriptive cross-sectional study , considering that drinking water in Tabriz has been provided with various sources such as surface water (Nahand dam , norouzlo dam) and underground resources (2 active wells) , Therefore , 3 stations were considered. During spring and winter season, 66 water samples from 3 selected stations were collected according to standard method in 2016 . The reason for these two seasons been Variations in the concentration of organic substances in water resources and consequently the concentration of THMs precursors produced and the effect of temperature on the formation of THMs. Related parameters were measured by portable device in site. All statistical analyses were performed using the SPSS statistical package.

Result: According to the results , it was found that the mean total of trihalomethanes compounds in winter and spring was 9/59 μg / l and 256/9 μg / l, respectively. Therefore, the highest amount of terihalomethane during the measured period is in June in the spring. Among the three stations measured , the highest amount of trihalomethanes in both seasons is related to stations that use surface water (water of the nahand dam, water of the Noruzlou Dam) with a lot of organic matter. The total cancer risk for THMs exposure through ingestion found in winter and spring 3/19 × 10-4 , 3/48 × 10-4 and 8/56 × 10-3 , 9/34 × 10-3 for males and females, respectively. An average lifetime cancer risk for THMs exposure in the spring is greater than in winter , as the total concentration of trihalomethane compounds in the spring is greater than in winter. The total risk posed by exposure to trihalomethanes in drinking water for female is higher than that of male. The total Hazard index values are estimated to be males and females 23 × 10-3 , 25 × 10-3 and 46 × 10-2 , 5× 10-1 in winter and spring season, respectively. In both seasons, the average TOC in the first station is more than the other two stations. Based on the Pearson correlation coefficient , it was found that there is a correlation between the mean total of trihalomethanes and the concentration of temperature and pH. Estimation of Langelier saturation index (LSI), Ryznar stability index (RSI), aggressive index (AI) and Puckorius scaling index (PSI) that water is corrosive in Tabriz city. Conclusion: According to the T-test , a statistically significant difference was observed between mean winter wheat and spring (P <0.05). Therefore, seasonal changes were observed in this study. The mean total THMS concentration for the entire sample is 133.66 μg / L, which is higher than the US EPA. In both seasons, the concentration of trihalomethane compounds to cause carcinogenesis is higher than the acceptable level of USEPA (10-6). Hazard index values were found below unity for the cities implying that there would be no considerable non-cancer risk. Based on the Pearson correlation coefficient , there is a direct correlation between the increase in the average concentration of THMS compounds with increasing temperature and pH. According to the results of water, Tabriz city has corrosive properties.