Early detection of chloroform hot spots in the Montevideo drinking water network

Abstract

The use of chlorine to disinfect water produces a series of by-products, particularly trihalomethanes. This is important given that there is a recognized association with different types of cancer after prolonged exposure, as well as with probable adverse effects on reproduction, especially in relation to offspring. The concentrations of these organic compounds vary greatly depending on the season and the conditions involved in providing water for consumption. This study was aimed at determining the geographic distribution pattern of chloroform in the city of Montevideo, and correlating that with the characteristics of the water distribution network. A total of 400 samples were taken from a sampling network between 2009 and 2015. Chloroform was identified by analyzing these samples using the headspace gas chromatography/mass spectrometry method. Data regarding piping length, diameter, and type of material were obtained. A geographic information system was constructed and hot spots were analyzed using the Getis–Ord G_i* statistic. A neighborhood piping density index was also proposed. The analysis found two zones in the city: hot and cold spots. The proposed index showed an increase in the G_i* statistic as the neighborhoods’ piping density increased, with a strong correlation. In addition, the highest G_i* statistic values corresponded to larger amounts of iron piping in neighborhoods. This work was able to determine that the hot spots were associated with the piping density in the neighborhoods as well as with the type of piping material, particularly iron.

Keywords:

• Trihalomethanes
• chloroform
• disinfection by-products
• geostatistic
• water distribution network

PUBLIC INTEREST STATEMENT

Providing people with water that is suitable for consumption is increasingly challenging for all societies due to larger populations as well as a gradual deterioration in the sources of the raw water that is extracted for the treatment process. Compounding this are growing urban centers that have aging supply networks alongside networks with new characteristics, creating a complex maze that needs to be characterized. In the case of Uruguay, the disinfection process is performed by chlorinating water. Trihalomethanes are some of the known by-products from this process, which must be properly monitored in order to be maintained at acceptable levels, thereby reducing the risk of health disorders. This work contributes to understanding the formation of trihalomethanes in the network and to determining the geographic zones that show a capability of reaching higher levels of these compounds over time. Mitigation and control plans can be developed based on this data, which will have an impact on population health.

Acknowledgements

The authors thank the water supplier in Uruguay (Obras Sanitarias del Estado [OSE, Spanish acronym] and Dr. Jose Carlos Guerrero Antunez for his thorough reading of the manuscript and his suggestions.

Cover Image

Source: The cover photos were taken by the authors at the Santa Lucia River and the Aguas Corrientes dam in the department of Canelones.

Additional information

Funding

The authors received no direct funding for this research.

Notes on contributors

Mariana Gomez-Camponovo

An interdisciplinary group was formed of professionals with extensive research experience, consisting of chemists, geographers, epidemiologists, and engineers. From the perspective of their disciplines, each has contributed to addressing the complex issue of the quality of water for human consumption. Specifically, the working group has been researching organic byproducts formed by the chlorination process used to disinfect water, and possible effects on health. To understand how THMs behave in a drinking water system, a dense monitoring network was developed in the city of Montevideo, the capital of Uruguay. Advances in the development of geostatistical models have made it possible to delimit zones in the city according to the presence of organic byproducts in water for consumption. In order to address the problem, this working group aims to use this methodology in other cities in the country where the sources of raw water and the management of the supply networks vary.