Report No DWI0020

IDENTIFICATION OP MUTAGENS IN DRINKING WATER (EC 9105) Final report to the Department of the Environment DoE 2489-M/1


Dec 1990



To develop and apply methods for the identification of mutagens in drinking water, to determine the levels of the potent mutagens, MX and its brominated analogues, BMXs, in UK drinking water supplies, and to estimate their survival during storage, distribution and boiling.


Mutagens are consistently produced during water treatment chlorination. The presence of mutagens indicates the possible presence of carcinogens and thus a potential health risk to the consumer. Knowing the identity of these mutagens would permit specific assessment of their biological effects.


Chlorine used in drinking water treatment reacts with some of the naturally-occurring organic substances in water to form many byproducts, including bacterial mutagens as detected in concentrated extracts using bacterial test systems.

Several mutagenic compounds, usually present at low g/l concentrations in drinking water, explained less than 5% of the mutagenic activity detected. However, a potent bacterial mutagen, MX, was found in UK drinking waters at concentrations ranging from 1 to 60 ng/l. These low concentrations of MX accounted for between 30 and 60% of the mutagenicity, depending on the water.

The chlorination byproducts responsible for about 35 to 65% of the mutagenicity have not been identified.

In water sources where bromide is present, much of the unexplained drinking water mutagencity could be due to BMX compounds (brominated analogues of MX), which are potent bacterial mutagens. BMX compounds have proved more difficult to measure than MX and a routine method does not yet exist. However? some BMX compounds have been found in laboratory chlorination experiments and in one chlorinated drinking water derived from a lowland river source which produces other brominated chlorination byproducts (brominated haloforms).

MX was relatively stable in drinking water at room temperature and consequently it survives distribution and is present in consumers' tapwater. MX and other mutagens were destroyed when tap water was boiled.

The risk to consumers from these bacterial mutagens in drinking water is not known.


Toxicity studies of MX and BMXs are needed so that the risk to consumers can be estimated.

The compounds responsible for the unexplained 35-65% of the mutagenicity in drinking water need to be identified.

BMXs could be as important as MX in explaining the mutagenicity of many drinking waters. Further work is required to improve the analytical technique for BMXs so that their concentrations in UK drinking water supplies can be determined and their contribution to the mutagenicity of drinking waters estimated.

There is a tendency in some countries to avoid chlorination byproducts by using other disinfectants, such as ozone. However, it is essential that the byproducts and mutagenicity of alternative disinfectants are thoroughly investigated so that proper comparisons can be made and sound decisions taken.


The work covered in this report was funded by the Department of the Environment (DoE) and concerns the identification of chlorination derived mutagens in drinking water. The characteristics of the mutagens and the techniques used to extract and concentrate the mutagens prior to testing and analysis are discussed. The potential of organic compounds to react with chlorine to produce mutagens was studied and the relevance of these organic compounds as precursors of mutagenicity in drinking water was investigated. The amino acids phenylalanine and tyrosine were used as models with which to study chlorination-derived mutagens. Among other chlorination products, a highly potent bacterial mutagen, MX, was identified in chlorinated tyrosine and was subsequently detected in UK drinking water.

A survey of MX in drinking waters derived from upland and lowland surface water sources was conducted and the contribution of MX to the mutagenicity of extracts was estimated. The contribution of other, less potent mutagens identified in drinking waters was also estimated. The mutagenicity of brominated analogues of MX, their production as a result of chlorination of bromide-containing water, and their presence in drinking water was investigated. The effect of storage, distribution and boiling of drinking water on MX and other mutagens was examined.

The results are discussed and recommendations are made for further work.

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