The drinking water quality standards and guidelines in developed countries are subject to periodical reviews and revisions. To be consistent with the trends of international drinking water quality management systems, the Environmental Protection Administration (EPA) launched a three-year project entitled “Screening and monitoring of candidate contaminants for source water and drinking water standards”. The purposes of this project were to assess the current drinking water quality regulatory systems and to review the water quality standards in Taiwan. The results and recommendations for third year study were:
Seventy-six water samples taken from four water treatment plants were analyzed for 13 water quality items. The results showed that most of the volatile organic matters (1,2- dichloropropane, cis-1,2-dichloroethene, trans-1,2- dichloroethene, 1,2- dichlorobenzene, 1,4- dichlorobenzene, xylenes and styrene) were not detected from raw water, from sediment tank water and finished water. Dichloromethane was detected only in one sample (1.19%). There were 40.48%, 44.05%, and 63.10% of formaldehyde, bisphenol A and nonylphenol detected, respectively. However, the formaldehyde concentrations were lower than the maximum contaminant levels of other countries and there are no standards for bisphenol A and nonylphenol currently. The results of health risk assessment of bisphenol A and nonylphenol showed that the hazard quotient (HQ) values were less than 1, which indicated that they were not beyond the tolerance amount of human body. On the contrary, because of the use of aluminum slat in coagulation processes, the residual total/dissolved aluminum levels in some clean water samples exceeded foreign standard/guideline values of 0.2 mg/L. However, the result of health risk assessment showed that the HQ value was less than 1, which indicated that it was not beyond the tolerance amount of human body.
The procedures of risk assessment of 28 (Contaminant Candidate List) CCL1 have been conducted using data gathered from this three-year project, the Environmental Analysis Laboratory, and water supply enterprise. The analysis results of the health risk assessment of 28 candidate contaminants (chlorite and haloacetic acids were not included) showed that the hazard quotient (HQ) were less than 1, which indicated that they were not beyond the tolerance amount of human body. In the cancer risk (CR), the risks of 28 candidate contaminants were ranged from 5.3×10-5 ~10-7. Therefore, the concentrations of these 28 candidate contaminants were almost acceptable from the aspect of health risk assessment.
Based on the screening process and evaluation criteria developed by the USEPA, the CCLs, the priority list of contaminants which are not regulated, were proposed in this project. The suggested first CCL (CCL1) and second CCL (CCL2) contain 30 and 20 chemicals, respectively. In order to regulate the emerging contaminants from high-tech industries, the newly added third CCL (CCL3) includes 19 chemicals. In addition, 28 items on CCL1 were provided to the EPA for the next phase of regulatory determinations.
The evaluations of advanced water treatment processes and cost benefit analysis for the removal of 30 CCL1 contaminants were achieved. Advanced treatment processes, including ozone oxidation, activated carbon adsorption and low-pressure membrane, were evaluated. Results of a cost/benefit analysis showed that the processes of ozone oxidation and activated carbon adsorption were more practical than others.
It is suggested that EPA could set up the “Guidelines for the unregulated contaminant monitoring rule in drinking water” and “the Guidelines for multiple sampling and analysis of drinking water”. The water supply enterprise should enforce the drinking water management plan, and then conduct multiple analyses of samples. In addition, EPA, Ministry of Economic Affairs and water supply enterprise should jointly discuss related issues and set up regulations (such as number of drinking water standards, items and frequencies of monitoring programs, monitoring of contaminants in CCLs, drinking water management plan, etc.) in response to global trends in drinking water management.
Key words: drinking water quality standards, Contaminant Candidate List, water quality analysis, health risk assessment