THE PRODUCTION OF CHLOROPHENOLS DURING THE CHLORINATION OF NATURAL WATERS Final report to the Department of the Environment DoE 2285-M/1
Report No DWI0030

FEB 1990

SUMMARY

I OBJECTIVES

The aims of the research covered by this report were:

• to study the production of chlorophenols during chlorination of natural substances in water; and

• to establish the important factors that control the reaction.

II REASONS

The production of chlorophenolic tastes in water supplies due to reaction of phenol (contaminating the water source) with chlorine applied as a disinfectant, is a problem that has been known for many years. However, there have been occasions when chlorophenolic tastes in water supplies could not be related to contamination of the water sources by phenol or any of its common homologues. Work carried out by the WRc in the past has indicated that high quality upland waters (containing no known waste water or other contamination) may produce chlorophenolic tastes. This suggested that natural water constituents could, under some conditions, react with chlorine to produce chlorophenols at levels that tainted water supplies. It is important that the possibility of generating chlorophenols (which are covered in the EC Drinking Water Directive by an MAC of 0.5 ęg/l "total phenols") is better understood.

III CONCLUSIONS

In some treatment works chlorophenols are commonly produced at low levels by the action of chlorine on natural water constituents. Chlorophenols can cause tainting of water supplies but at the levels found there are no health implications according to the available toxicity data. However, the potential of the raw water to produce chlorophenols is considerably greater.

The chemical reaction involved is unusual and is affected by pH and chlorine dose and related to TOC and colour. p-Hydroxybenzoic acid (a naturally occurring water constituent) produces chlorophenols on chlorination by what appears to be a similar reaction. However, it is not entirely clear why the potential for chlorophenol production is not achieved during treatment but this is probably due to the combined effect of insufficient or excessive chlorine dose, removal of some of the natural organic matter and possibly degradation of chlorophenols.

At some treatment works the levels of chlorophenols probably exceed the current MAC for total phenols occasionally for short periods of time. These incidents probably do not lead to any tainting of supplies and subsequent consumer complaints. Although there is no clean-cut evidence it seems likely that very infrequently, some incidents of chlorophenolic tastes in supply occur and are due to the phenomenon uncovered by this work.

IV RECOMMENDATIONS

The following further work is recommended:

• Characterisation of the types and amounts of natural phenolic substances in raw waters, particularly upland waters and an investigation of their reaction with chlorine to produce chlorophenols and other substances should be carried out. This would identify the exact precursors of chlorophenols (or confirm the involvement of p-hydroxybenzoic acid) and enable these to be monitored in raw waters to detect unusually high levels that could lead to problem levels of chlorophenols in supply.

• It would be prudent to determine the chlorophenol production potential of raw waters which contain high levels of organic matter and/or colour. Where this potential is high, periodic monitoring of treated water for chlorophenols should be carried out. In addition more lowland river waters should be investigated to confirm their low potential for production of chlorophenols.

• The precise role of stratification/de-stratification in the sudden release of "chlorophenol precursors" in raw waters was not established and a short specific study on this is recommended.

• Further investigations of the analytical and sample stability problems encountered in the work are needed, particularly the stability of chlorophenol in treated water and methods of preserving samples prior to analysis. This could be discussed by the Standing Committee of Analysts.

• The available data on odour threshold levels for chlorophenols covers an enormous range which is difficult to use practically. Some systematic work to establish the true values is needed.

• The data in this report has implications for monitoring water supplies and the potential of natural waters to produce contamination and consequently the information needs to be considered by the Drinking Water Inspectorate and the National Rivers Authority.

V RESUME OF CONTENTS

The formation of chlorophenols from chlorination of raw waters in the laboratory was studied. Controlling factors were investigated as was the nature of the likely naturally occurring precursors. The chlorophenol production potential and the levels in treated water were determined monthly at two water works treating upland water.

Copies of this report may be available as an Acrobat pdf download under the 'Find Completed Research' heading on the DWI website.