Health Stream Literature Summary - Issue 50 - June 2008

Disinfection by-product formation and mitigation strategies in point-of-use chlorination of turbid and non-turbid waters in western Kenya.
Lantagne, D.S., Blount, B.C., Cardinali, F. and Quick, R. (2008) Journal of Water & Health, 6(1); 67-82.

The Safe Water System (SWS) developed by the US Centers for Disease Control and Prevention and the Pan American Health organisation has resulted in reductions in diarrheal disease in users in developing countries. The SWS includes three elements: water treatment with dilute sodium hypochlorite at the point-of-use, storage of water in a safe container and behaviour change communication to improve hygiene and water and food handling practices. There has been some concern expressed about the formation of disinfection by-products in water treated with sodium hypochlorite and the risk to SWS users. This study was conducted in September 2003 in rural Western Kenya where an SWS program began in 1999. An investigation was conducted of the formation of disinfection by-products (trihalomethanes (THMs)) resulting from the chlorination of stored water from a variety of sources with varying turbidity levels and the effectiveness of several mitigation strategies.

Six different water sources used for drinking by local communities were analysed for THM concentrations after chlorination: lake, river, earth pond, protected well, open well and a rainwater catchment system. To assess whether using different types of water storage containers led to different THM exposure risk, water treatment procedures were conducted in water stored in both 20-litre HDPE plastic jerry cans and locally purchased ceramic pots. THM concentrations were measured for each of the six water sources after three different treatment procedures were used in plastic jerry cans and in ceramic pots. The three treatments included: the addition of sodium hypochlorite solution; filtration of sample water through a local cloth before adding sodium hypochlorite, and settling of the water for 24 hours and decanting supernatant water before adding sodium hypochlorite. Also samples in plastic jerry cans were treated with PuR, an alternative point-of-use water treatment product and samples in ceramic pots were pre-treated with the natural flocculant moringa seeds. The PuR system comprises sachets of ferrous sulphate flocculant and calcium hypochlorite. Water from each of the six sources was collected in eight 20 litre plastic jerry cans and transported to the lab for analysis for chemical and bacteriological water quality parameters before treatment began. Turbidity, temperature, pH and conductivity were also measured. For each of the six water sources at 1 hour, 8 hours and 24 hours after each treatment procedure was completed, three water quality testing procedures were undertaken: free chlorine and total chlorine were measured; total coliform and E. coli samples were collected and analysed; and a THM sample was collected and stored on ice for later analysis.

Turbidity values ranging from 4.2 to 305 NTU were found in source water from the six sources. There were 143 water samples analysed for four different THMs including chloroform, bromodichloromethane, dibromochloromethane and bromoform. None of these samples exceed the World Health Organization (WHO) guideline values for any of these individual THMs or for the additive total THM (TTHM) ratio guideline values irrespective of the water source or storage container. There were 16 of the 48 samples taken at 24 hours after chlorine addition that exceeded the USEPA maximum contaminant level (MCL) for TTHM. There were no significant differences in THM concentrations seen between water stored in ceramic and plastic storage containers, showing that TTHMs were not absorbed into the ceramic and that organic material with TTHMs formation potential did not leach from the ceramic containers into the stored water. Most of the TTHMs were formed within 8 hours after chlorine addition. Pretreatment of water by filtration through a cloth or settling for 24 hours and decanting supernatant water before chlorination did not appear to significantly reduce THM formation. The use of PuR resulted in significantly lower TTHM concentrations at 24 hours after treatment than the use of chlorination only and was therefore an effective TTHM mitigation strategy. The use of ground moringa seeds was found to increase TTHM concentrations as compared to chlorination alone, particularly at 24 hours after the addition of sodium hypochlorite solution. Turbidity was significantly related to TTHM concentration at 24 hours after chlorine addition in both plastic and ceramic containers.

This study provides clear evidence that the use of the Safe Water System in both turbid and non-turbid waters does not cause the formation of trihalomethanes in excess of the WHO drinking water guideline values. It is suggested that when the microbiological quality of water can not be assured that households adopt or continue to use the Safe Water System or PuR in both turbid and non-turbid waters in western Kenya.