Environmental and health risk assessment of trihalomethanes in drinking water : a case study

Abstract

A comprehensive research related with chlorination by products in drinking water was conducted to assess health-associated risks. Three communities, namely St. John's, Clarenville, and Shoal Harbour were chosen in Newfoundland. Gas Chromatography/ Mass Spectrophotometer (GC/MS) was used for the analysis of the samples at Environmental Quality Laboratory in Newfoundland. Four trihalomethanes (THMs) species, namely chloroform, dichloro-bromomethane, chloro-dibromomethane, and bromoform were analysed. Chloroform was found to be in maximum concentration in comparison to other species. To analyse seasonal variation of the data, both Student's t- test and Mann-Whitney test were conducted. As a result of hypothesis testing, the null hypothesis, which was that the mean chloroform concentrations (for Student's t-test) and median chloroform concentrations (for Mann-Whitney test) respectively for the two seasons were equal, was not rejected for Clarenville and St. John's, whereas rejected for Shoal Harbour. Due to significant presence and known behaviour of chloroform, risk was estimated based on chloroform concentration only. For St. John's the chloroform concentration varied from non detectable level (<1) to 73 μg/L in summer and 3 to 60 μg/L in winter, respectively. For Clarenville the concentration varied from 375 to 512 μg/L in summer and 361 to 557 μg/L in winter. Similarly, for Shoal Harbour, it varied from 203 to 330 μg/L in summer and 155 to 235 μg/L in winter respectively. The lower concentration of chloroform in winter can be attributed to the fact that lesser chlorination practices are performed. The risk associated with chloroform was evaluated through different exposure pathways: ingestion, inhalation and dermal contact through showers. Lifetime risk from water ingestion ranged from 0.08 x 10⁻⁴ to 0.82 x 10⁻⁴ (summer) and 0.07 x 10⁻⁴ to 0.78 x 10⁻⁴ (winter). Lifetime risk from normal shower as a result of 10 minutes shower ranged from 0.48 x 10⁻⁴ to 6.33 x 10⁻⁴ (summer) and 0.40 x 10⁻⁴ to 6.07 x 10⁻⁴ (winter). To address issues pertaining to limited number of samples, probabilistic risk analysis was also conducted on the original set of data. The software @R1SK was used to perform the risk analysis and simulation. Latin Hypercube Simulations was performed to estimate the risk and the results were plotted. The risk values estimated using @RISK were compared with those estimated using deterministic approach.