Chemicals in drinking water

Stability of the test chemical in drinking water under study conditions should be determined prior to study initiation. Consideration should be given to conducting stability tests on test chemical-drinking water admixtures presented to some test animals. Besides difficulties of inherent stability, changes in chemical concentrations may result from other influences. Chemicals with low vapor pressure can volatilize from the water into the air space located above the water of an inverted water bottle thus, a majority of the chemical may be found in the dead space, not in the water. 

TABLE 1 WHO Guideline Values for Chemicals in Drinking Water and EPA National Drinking Water Standards [2,3] ... 

THMs are generally found at the highest concentration of any synthetic organic chemical in drinking water. 

Table IV lists the results of risk calculations provided in the preliminary proposal for the substances that were proposed as potential carcinogens in the regulatory context at that time (44). 1,1-Dichloroethylene was later converted to a listing of equivocal evidence of carcinogenicity. The table includes calculations made by the USEPA CAG and the NAS Safe Drinking Water Committee. These calculations attempt to project concentrations of each chemical in drinking water that, if consumed for a lifetime (70 years) at the rate of 2 L of water per day would contribute an excess lifetime cancer risk of up to 1 in 100,000 and up to 1 in 1,000,000. The quality of evidence of carcinogenicity ranging from sufficient in humans to limited in animals is also included for each chemical. Provisional ADI values calculated from chronic toxicity data only are included for the sake of comparison.

Concentrate Approach. The advantages and disadvantages of using concentrates to estimate health hazards due to organic chemicals in drinking water include the following ... 

Howd RA, Brown JP, Morry DW, et al. 2000. Development of California public health goals (PHGs) for chemicals in drinking water. J Appl Toxicol 20 365-380... 

The objective of this publication is to help users at national or local level to establish which chemicals in a particular setting should be given priority in developing strategies for risk management and monitoring of chemicals in drinking-water, The document will be useful to public... 

Limiting the number of chemicals to be managed on the basis of available resources for monitoring or control, without consideration of the potential for health effects associated with particular chemicals, could result in unacceptably high levels of hazardous chemicals in drinking-water. A more rational way to set priorities is needed. The present document is intended to meet this need by providing a simple, rapid and rational basis for assigning priority to specific chemicals, which can complement administrative practices at local or national level. 

Table 1.1 Categorization of sources of chemicals in drinking-water...

The presence of a particular chemical in drinking-water does not necessarily result in human exposure to a concentration that may cause concern for example, the concentration of the chemical may be well below the guideline value. Part B of this publication provides guidance on assessing the likely occurrence of chemicals associated with the main sources of chemicals in drinking-water. 

Unless there is strong evidence that particular chemicals are currently found or will be found in the near future, at levels that may compromise the health of a significant proportion of the population, the inclusion of those chemicals in drinking-water monitoring programmes is not justified, particularly where resources are limited. It is often more effective to maintain an ongoing programme of pollution control and risk assessment in the catchment,... 

The facilities and resources available may be sufficient to allow a comprehensive analytical assessment of the inorganic constituents in a source.1 However, such an assessment is often not possible in which case, the following sections and Table 4.1 indicate the naturally occurring chemicals that should be considered in setting priorities for chemicals in drinking-water sources. 

Fluoride, arsenic, selenium and, in certain circumstances, nitrate should be given high priority. As noted in Chapter 2, the presence of these chemicals in drinking-water has been shown to cause health effects. The natural occurrence of these chemicals is relatively common in water supplies around the world in both developing and developed countries therefore, they should be assumed to be potentially present, and consideration should be given as to whether they are actually present in concentrations of concern. 

Manufacturing and processing industries are also a potential source of chemicals in drinking-water. Assessment of the types and amounts of chemicals in the effluent discharged from industrial sources should be used to make judgements on the possible chemicals that could be present in receiving water used as a drinking-water source. 

X Potential source of chemical in drinking water, To be taken into consideration as part of the assessment of priority chemicals,... 

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