TRANSFORMATION PRODUCTS IN GROUNDWATERS
Report No FR0332
C J Cable
A review of the potential problems of contamination of groundwaters by substances derived from commercial chemicals used in domestic, industrial and agricultural situations will enable any necessary analytical development and monitoring to be identified. This should lead to characterisation and quantification of any contamination, and ultimately to better protection of groundwaters.
To review the potential problem of transformation products in groundwater in relation to analysis and monitoring requirements.
It is well known that some chemicals used, transported or disposed of in the environment can enter water sources, survive conventional water treatment, and hence contaminate water supplies; for example, pesticides, petroleum products and chlorinated solvents. However, some chemicals can be transformed into new substances, i.e. transformation products (TPs), by a variety of processes - including reaction with water treatment oxidants such as chlorine. Such TPs may be derived from chemicals of little environmental concern, i.e., those presenting no risk of significant environmental contamination per se, or, at the other extreme, they may be derived from chemicals which are themselves potentially important contaminants of water sources and supplies.
There is direct evidence of the contamination of groundwater sources by vinyl chloride and other chloroethene derivatives of tetrachloroethene, trichloroethene and other anthropogenic volatile halogenated hydrocarbon solvents. There is also direct evidence for contamination from complex mixtures of polar TPs of petrochemicals.
Indirect evidence, drawn from reports of contamination of surface waters in the UK and ground and surface waters elsewhere, indicates that a number of other anthropogenic environmental contaminants could give rise to TPs with the potential to contaminate UK groundwaters. These TPs include additional chlorinated hydrocarbons plus volatile organosulphur compounds derived from volatile halogenated hydrocarbons. Also, there are TPs of bulk-usage pesticides, carboxylic acid derivatives of anionic and nonionic surfactants and a range of partially-oxidised derivatives of coal-based substances such as polycyclic aromatic hydrocarbons.
A need was identified for a more methodical assessment of groundwater contamination. Important factors to be considered include the level of usage of the anthropogenic substances that are potential precursors of TPs in groundwaters, the vulnerability of groundwater sites, the physical properties of substances that may be transported into groundwaters (whether TPs or TP precursors), and the significance as groundwater contaminants (in terms of toxicity, aesthetics and persistence) of the TPs themselves.
More extensive monitoring of significant TPs which have already been found in some groundwaters, such as vinyl chloride and other chloroethenes, should be considered. It is important to get some idea of the relationship between the concentrations of these and their presumed precursors, TCE and PCE which are also significant groundwater contaminants since this will enable some estimate of the formation and long-term fate of the TPs. Further investigation of other chlorinated hydrocarbon solvents that may contaminate UK groundwaters, e.g. 1,1-dichloroethane, chlorobenzene and various dichlorobenzenes is also recommended. The TPs of certain pesticides may need to be monitored, particularly ethylenethiourea and methyl isothiocyanate.
In this report an assessment of the possibility of groundwater contamination by transformation products from some other classes of chemicals that may be released into the UK environment is considered. This suggests that there may well be a potential problem with TPs in groundwater but is is recommended that a more methodical approach, reflecting the basic considerations mentioned above, should be developed and applied so that analytical development and monitoring can be undertaken if this proves necessary.
VI RESUME OF CONTENTS
In order to assess the potential problem of TPs in groundwater, direct evidence, i.e. information on their presence their groundwater, is reviewed. Indirect evidence, i.e. information on the presence of TPs in waters other than groundwaters (e.g. surface waters), is also reviewed. The general potential of commercial chemicals to produce TPs that may threaten groundwater is discussed.
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