Report No DWI0312

Sept 1985


Since 1977, the Water Research Centre, under contract to the Department of the Environment, has been involved in a programme of work to investigate whether carcinogenic substances are present in drinking water and, if so, whether their presence represents a significant risk to human health. Methods have been developed for concentrating the organic compounds in water samples and for testing these complex extracts in bacterial mutagenicity assays which are predictive of carcinogenic activity.

Results have indicated that concentrated drinking water extracts derived from surface sources are invariably mutagenic in bacterial test systems. The compounds responsible for the observed activity have not yet been identified, but it has been shown that they are formed when the water is chlorinated for disinfection purposes. The precursors of the mutagenic compounds are probably common, naturally-occurring organics in water, such as humic acids.

More recently, genotoxicity tests using cultured mammalian cells have been carried out on concentrated drinking water extracts. These too are giving positive results, indicating that the mutagens are capable of inducing genetic damage in mammalian cells. Although this work in higher cell systems is still at an intermediate stage, it is likely that the conclusions from these studies will be that the chlorination of surface waters results in the production of compounds which may represent a qualitative risk to human health. Before a quantitative evaluation of the risk can be made information on the identify of the mutagens is required. Even then it will be very difficult to accurately quantify this risk.

Future research which will be required to produce a risk/benefit evaluation on this use of chlorine for the disinfection of water is outlined. This will include increasing our efforts to identify the mutagenic agents and investigations into possible ways of removing these compounds from drinking water or preventing their formation.

Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.