Report No FR0399

D J Bowen, J K Fawell and H Horth

Sept 1993



Concern over the storage of chlorine gas is accelerating the move to safer means of generating chlorine for drinking water disinfection such as on-site electrolytically generated chlorine (OSEGC) and the use of commercial sodium hypochlorite solutions. In order that water suppliers can reassure themselves of the safety in use of these processes, they need to be aware of the potential risks and margins of safety associated with the by-products, chlorate and chlorite in the treated water.


To evaluate the risks to the health of the general population associated with the presence of chlorate and chlorite in drinking water.


If levels of chlorate and chlorite produced as a result of the use of the OSEGC process and commercial hypochlorite solutions were found to be hazardous to the health of the population, then their use in drinking water disinfection would have to be severely curtailed or even prohibited, unless by-product formation could be minimised. Water suppliers, therefore, need to be fully aware of the situation in order to make well-informed decisions concerning the implementation of alternative disinfection processes.


  1. There are limitations in the available toxicological data on chlorate and chlorite which make the derivation of guideline values or standards, with a specific margin of safety, difficult.

  2. A risk assessment based on currently available information indicates that there is probably an adequate margin of safety with present UK operational limits.

  3. Further toxicological or epidemiological data, as well as further information on chlorate and chlorite concentrations in treated water are necessary if these margins of safety are to be confirmed


This report reviews the toxicology of the disinfection by-products chlorate and chlorite and assesses the implications of the use of disinfection processes that produce these, in particular the OSEGC process and commercial hypochlorite solutions. The major toxicological effect of chlorate and chlorite following short-term exposure appears to be the oxidative damage seen in the red blood cells, effects which have been noted in several species. However, it is not wholly clear which of the red cell components is more susceptible to damage or which species is the most sensitive. It was thought that humans may be more susceptible than rodents to the acute effects of chlorate; however, on the basis of information currently available, there is no reason to suppose that this is the case. Human and other experimental data are limited and one of the major problems in trying to evaluate the data for chlorate and chlorite results from the numerous gaps in the database. In an attempt to help clarify some of the grey areas, recommendations are made for further work which could help fill the data gaps. Although the position is not wholly satisfactory with regard to the availability of suitable data, the evidence indicates that chlorate and chlorite in drinking water, at current UK operational limits, are unlikely to result in a significant risk to the health of consumers.

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