Title: Chlorate in Drinking Water
Funder: Department for Environment, Food and Rural Affairs

Abstract: Description The aim of this project is to establish what current concentrations of chlorate are in drinking water supplied in England and Wales and any implications should a new health based value be established. Chlorate is a disinfection by product that can arise during the water treatment process where sodium hypochlorite, chlorine dioxide or onsite electrolytic chlorination (OSEC) is used for disinfection purposes. Water companies have a regulatory duty to minimise disinfection by-products, however currently there is no prescribed concentration or value (PCV) for chlorate in drinking water. Consequently there is no routine regulatory monitoring for this species and as such limited data is held by the Drinking Water Inspectorate (DWI) on the concentrations found in public supplies. DWI has identified this as a gap in its knowledge. Controls on chlorate are in place through national conditions of use for OSEC and chlorine dioxide and purity requirement under the BSEN for sodium hypochlorite. These should ensure that the World Health Organisation (WHO) provisional guideline value for chlorate (0.7mg/L)1,2 is not exceeded. Water companies will gather data to comply with these requirements but it is not centrally reported.A recent Joint FAO/WHO Expert Committee on Food Additives (JECFA) committee has proposed an a acceptable daily intake (ADI) of 10 µg/kg bw for chlorate, and using standard assumptions, this would correspond to a health-based value of about 0.2 mg/L, which is below the current WHO provisional guideline of 0.7 mg/l. In addition, by extrapolation from perchlorate, EFSA has used a TDI of 3 µg/kg bw. This would correspond to an even more stringent value for drinking water. The project will provide evidence of the current levels of chlorate arising from hypochlorite, chlorine dioxide and OSEC in England and Wales. It will also provide an understanding of the possible impact on disinfection practices, should a tighter health based value be adopted. Objective The objectives are to:1) Contact water companies in England and Wales and obtain information to determine the number of treatment work sites which operate using calcium hypochlorite, sodium hypochlorite, chlorine dioxide or OSEC compared to traditional chlorine gas. 2) Contact and obtain from water companies in England and Wales operational data sets for chlorate in treated waters and other relevant supplementary information such as source water type being treated, type of disinfection used and dose. 3) Devise and conduct a monitoring programme, working with water companies in England and Wales, to enable the determination of chlorate in final waters at treatment works using calcium hypochlorite, sodium hypochlorite, chlorine dioxide and OSEC as the disinfection type. The contractor should consider and recommend the most appropriate sampling type, whether this is the final water or in the case of calcium and sodium hypochlorite or OSEC, determining the chlorate concentration of the hypochlorite solution being used and calculating what the concentration in the water would be based on dosing volumes. Additional information such as the age, concentration and temperature of the stored disinfectant should be collected, along with any other water quality parameters deemed appropriate, so that relationships between these factors and the chlorate concentration can be determined. The contractor should also consider the benefit of determining the concentrations of other by-products such as bromate, perchlorate and chlorite as a consequence of the disinfection method employed, however, this should only be considered if the cost of analysis is such it does not detrimentally impact on the size of the sampling programme. The contractor should consider inclusion of a small number of chlorine gas sites effectively as “control” sites.4) As part of the sampling programme the contractor should also consider the use of chlorine dioxide as a disinfectant in large buildings and the potential for the formation of chlorate to occur where it is used. The contractor should consider obtaining data from manufacturers of WRAS approved fitting for generation of chlorine dioxide to determine the level of chlorate and chlorite produced by their systems. As a minimum 10 buildings where this practice is adopted should be identified and included in the sampling programme and the concentrations of chlorate that is produced by this equipment, must be investigated. A desktop review of the available current best practice for the operation of chlorine dioxide disinfection plants for use within large buildings must be undertaken. Consideration should be given to whether best practice can be improved to minimise the potential for chlorate formation.5) Report the findings of the study including the impact should new health based value be established and advise on any possible future areas of research. The report must be submitted electronically in Microsoft Word format, with the main body of text using Arial 11pt font, the report should be no more than one hundred pages, excluding appendices.


Research activity codes: 2.2 FACTORS RELATING TO PHYSICAL ENVIRONMENT;3.2 INTERVENTIONS TO ALTER PHYSICAL AND BIOLOGICAL ENVIRONMENTAL RISKS
Health categories: GENERIC HEALTH RELEVANCE;ORAL AND GASTROINTESTINAL