EFFECT OF DISTRIBUTION ON ORGANIC CONTAMINANTS IN POTABLE WATER (HET
9155) Final report to the Department of the Environment DoE 2215-M/1
Report No DWI0032
The objectives of the contract were:
Most studies to date on the nature of organic contamination of water supplies have focussed on raw and finished water samples. Little information is available on the fate of organic contaminants during distribution or on the introduction of new contaminants before water reaches the consumer's tap, eg by leaching from pipe materials or following application of mains renovation processes. The exposure of consumers to organic contaminants introduced during distribution either from materials of construction or by processes such as renovation needs to be assessed since such substances go directly to the consumer.
Epoxy resin relining of cast iron water mains
Four hour cure process
The laboratory and field trials on the original process involving 4 hour cure prior to return to service showed that relatively high levels of organic contaminants leached into water during the first 24 hours after relining. A full report on the laboratory and field investigations was submitted to the DoE Committee on Chemicals and Materials of Construction for use in Public Water Supply and Swimming Pools (CCM), who were considering applications for approval of epoxy resin formulations for in-situ relining of water mains. The Committee concluded that the high levels of organic contaminants leached from the resins were unacceptable on health grounds.
Sixteen hour cure process
Extending the curing period substantially reduced the degree of leaching of organic contaminants from the resin into the water. Results from leaching tests were submitted to the CCM who concluded that a resin system could be used by the Water Industry, on a limited basis, in order that the process could be further developed.
Consideration of new toxicity data and additional leachate data has enabled full approval to be given for an epoxy resin formulation for the in-situ relining of water mains. One requirement was that the epoxy resin must be applied in accordance with various stipulations.
Organic compounds introduced into drinking water by plastic pipes
Leaching of organic contaminants from PE pipe
Laboratory studies showed that a variety of organic chemicals leach from blue MDPE pipe to give low concentrations in drinking water. These were generally substances used in the manufacture of the pipe such as antioxidants, W stabilisers and their degradation products. The same substances were detected at very low levels in several field studies particularly from recently installed blue MDPE mains. In particular, Irganox 1010 and 1076 were found to leach from MDPE pipe and their degradation product, 2,6-di-tert-butyl-p-benzoquinone, was found to be a common contaminant in water distributed by MDPE pipe. This degree and type of leaching is not believed to be significant in relation to possible risks to health but some alkylated-p-benzoquinones have a strong tendency to cause tastes and further investigations would be prudent. Phthalimide was also found to leach from blue MDPE and this proved to be due to its presence as an impurity related to the blue pigment copper phthalocyanine. Results shoved that while phthalimide could leach from new HDPE pipe its presence in water distributed through MDPE systems was very sporadic. Evidence for the formation of chlorophthalimide was obtained, but accurate quantitative analysis of this compound proved difficult due to its instability. There is little toxicological data for phthalimide and none for chlorophthalimide.
Leaching of organic contaminants from u-PVC pipe
Studies showed that a range of organic chemicals leached from new u-PVC pipe into water. However, the levels were very low and do not appear to pose any risks to health based on available toxicity data.
Leaching of organic contaminants from GRP pipe
A wide range of contaminants were found to leach into drinking water from GRP pipe including a range of phthalates and styrene. The leaching rates were appreciable although depletion with time would be expected.
Permeation of PE pipes by organic chemicals
Permeation by natural gas odorants
A contact time of at least 40 days was required for natural gas odorants to permeate blue MDPE and produce a discernible taste/odour in a water sample. Once breakthrough had occurred it appeared that at least two days were required for a sufficient amount of odorants to permeate the pipe and cause a slight off-taste. For a strong taste to be transmitted to the water a 7 day exposure to the pipe was required.
With the use of PE gas pipes, which are much less likely to leak than iron gas pipes, the likelihood of PE water pipes being exposed to natural gas for long periods seems remote.
Permeation of PE by potential soil contaminants
The laboratory experiments demonstrated that blue MDPE was readily permeated by non-polar chemicals such as toluene, slowly permeated by phenol, a more polar substance, but not permeated by more complex polar molecules such as the pesticides paraquat, malathion and atrazine. In additional experiments significant penetration of MDPE occurred with m-cresol, nitrobenzene, chlorobenzoic acid and cyclohexane. Although attempts were made, accurate prediction of the rate of permeation by chemicals from physical/chemical data could not be made. PE pipe is clearly vulnerable to permeation by certain chemicals which could lead to significant contamination of supplies, at least on a local basis.
Permeation of PE pipe laid in contaminated ground
No significant permeation of a MDPE service pipe (and a u-PVC fire main) installed in a contaminated land site was encountered. In view of the known susceptibility of MDPE to permeation by certain organic compounds, the experimental results appear surprising. However, the site was contaminated mainly with compounds thought not to readily permeate MDPE or u-PVC. In addition, it is possible that compounds bound onto soil particles may not be 'available' for permeation. The results from this investigation indicate that the effect of soil particles on permeation behaviour may be significant. Since the soil contaminants were specific to this particular site it was not possible to draw broad conclusions covering other sites, with different contaminants.
The effect of the distribution system on organic compounds in drinking water
The work carried out to determine the changes, during distribution, in the nature of organic contaminants present in finished water and also to identify any contaminants arising from the distribution system itself showed that few changes took place. However only one treatment works/distribution system was studied and it is possible that other systems may give different results.
A wide range of organic contaminants was always present in the finished water and virtually all of these were found in distributed samples, even at the extremities. Contaminants such as phthalates, atrazine, simazine and organic phosphates showed no marked changed in levels during distribution. THM levels increased through the distribution system, due to further chlorination reaction or breakdown of chlorinated THM precursors but TOC and AOX did not show any significant changes.
A small number of organic contaminants were found only in distribution samples. However, the source of these is difficult to explain in terms of our knowledge of distribution materials and other potential sources. The information gathered suggests that monitoring for the Water Supply (Water Quality) Regulations 1989 could be undertaken for some substances at supply points (treatment works, service reservoirs etc.) rather than consumers taps. For example, this should be the case for atrazine and simazine.
Effect of mains renovation techniques on water quality
All the techniques studied led to levels of PAH in drinking water exceeding for a substantial period of time maximum values specified in the Water Supply (Water Quality) Regulations 1989. These techniques remove corrosion products from the inside of the mains which may uncover fresh coal-tar pitch surfaces from which leaching can take place. Subsequent work carried out by WRc Engineering, indicated that relining with epoxy resin reduced the PAH to acceptable levels. Clearly, use of the cleaning/renovation techniques described in the report without relining the pipe cannot be recommended at the present time.
Leaching of organic compounds into water from reservoir/tank linings
Only a limited amount of experimental work was possible on the leaching of organic contaminants from tank or reservoir linings. However the one product examined tan epoxy-resin based coating) did demonstrate that a relatively high concentration of one of the ingredients used in the formulation could leach into water in the short term, although this level did rapidly reduce with time. Although it is difficult to use the results from the epoxy resin coating studied to predict the behaviour of other coatings, it does appear likely that some ingredients in any product will leach into water, particularly in the first few hours after application and following the first contact with water.
The work has shown that the distribution system is a potential source of organic contamination of drinking water. This is important bearing in mind that distributed water goes directly to the consumer. Thus it is vital to ensure that distribution materials and processes do not lead to significant organic contamination of supplies. Currently this is covered mainly by the Committee on Chemicals and Materials of Construction for use in Public Water Supply and Swimming Pools (CCM) and to some extent the Water Byelaws Advisory Scheme.
Organic substances can enter supplies in several ways, ie leaching from plastic materials, application of renovation processes and permeation of certain plastic pipes. Some introduction of organic chemicals from such sources is inevitable at some level, particularly in the early stages ie with a newly laid pipe or after a recent renovation. This is not significant in itself. However, it is important to fully evaluate materials and processes prior to use with respect to any potential to introduce, or cause, significant levels of organic contamination. Such evaluation inevitably requires complex trace organic analysis for known substances (formulation components) and unsuspected components (formulation impurities, byproducts etc) - the latter needing techniques such as gas chromatography - mass spectrometry (GC-MS). An assessment of the possible effect of chlorine (or any other disinfectant in supply) is essential in many cases. This is because new chemicals could be formed .
An outcome of this work has been that the CCM has largely incorporated several of the methods or approaches developed into their approval scheme for materials and chemicals for use in contact with potable water.
At the present time the testing of materials is being considered by several EEC Committees with a view to establishing standard methods for EEC countries. In many ways the UK systems for evaluating materials is more stringent than the schemes operated in other countries. Such schemes rarely include any evaluation of unsuspected chemicals. Consequently the strength of the UK approach needs to be included in any future EC protocol.
It is recommended that materials, chemicals and processes connected with the distribution system are rigorously evaluated before use for any potential to cause significant levels of organic contamination. This assessment requires complex trace organic analysis, not only for the known formulation constituents but also for unsuspected impurities and byproducts using techniques based on mass spectrometry. In addition, the effect of chlorine (or any other disinfectant in supply) needs to be evaluated. Such evaluations need to be carried out where appropriate under realistic conditions. It should be noted that during the duration of this project these recommendations have been largely incorporated into the approval scheme operated by CCM. The Water Bill has added mandatory power to the UK approval scheme and the CCM is under revision. It is recommended that the vigorous approach of CCH is maintained and that the new revised scheme is made more 'visible' to industry.
The more stringent UK approach should be incorporated in any new scheme developed by the EEC Committees. Possibly the data in this report could help in assuring this.
V RESUME OF CONTENTS
The report covers studies aimed at assessing the potential for organic chemical contamination of water supplies in the distribution system and includes, pipe renovation techniques, especially in situ epoxy resin relining, leaching from plastic materials and their permeation by chemicals from contaminated soil. In addition a detailed investigation was carried out on the effect of distribution on the range of organic chemicals in finished water.
Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.