5. RESULTS OF SUBSYSTEM 2: HEALTH EFFECTS AND RISKS RELATED TO DRINKING WATER |
5.1 Organization of monitoring activities
In 2000, the subsystem activities were being carried out in all 30 selected localities. The Public Health Centres of Litoměřice and Pardubice continued their volunteer cooperation (Table 3.1). Within this subsystem, drinking water quality is also monitored in other important cities or water supply systems of the districts, the administrative centres of which participate in the Monitoring System.
Each of the participating Public Health Centres had to carry out a minimum number of complex analyses of drinking water, ranging from 8 to 20 according to the population supplied with drinking water from the public water mains network, and to maintain a set of uniform drinking water quality indicators.
Drinking water quality has been monitored both in the water supply network and at the outlet from the water treatment plant. Results of the analyses performed by the drinking water producers (distributors) were also included among the Monitoring System data. Until 2000, the binding basis for drinking water quality assessment was the Czech national standard ČSN 757111 “Drinking Water”. Since January 1st, 2001, the public health requirements for drinking water quality have been set by Regulation No. 376/2000 of the Ministry of Health of the Czech Republic. The basis for evaluating radiological indicators is Ordinance No. 184/1997 of the State Office for Nuclear Safety on the requirements for ensuring protection from radiation.
Immediate reporting of water quality emergencies, possibly putting at hazard the population health, and of changes in water quality requiring principal measures to be taken by the public health authorities, including water supply outage, is also part of the Monitoring System.
5.2 Monitoring of impaired health indicators
The Monitoring System is focused on the notification of selected infectious diseases potentially transmissible through contaminated water and intoxications due to chemical contamination of drinking water. Information is obtained from the epidemiological information system EPIDAT and through direct notification by collaborating Public Health Centres. Based on data analysis, it can be stated that no case of infection or intoxication was revealed to be attributable to the consumption of water fromthe public water supply systems monitored. Water was confirmed to be the vector of infection in only 17 cases out of 34 350 cases of potentially water-borne infectious diseases reported within the system EPIDAT from the districts monitored. Nevertheless, laboratory and epidemiological investigations showed that none of these infections had been caused by drinking water from the water supply systems monitored. In most cases, the infection was acquired from private well water or during outdoor bathing, several cases were acquired abroad. Likewise, reports by collaborating Public Health Centres did not indicate in the district level any case of infection attributable to drinking water from the water supply systems monitored in the year 2000.
5.3 Drinking water quality
Analyses of 6671 drinking water samples taken from water supply systems of all districts monitored in the year 2000 provided 176 129 results concerning drinking water quality indicators. The limits of indicators with significance for health, i.e., the maximum limit value (MLV) and the limit value of reference risk (LVRR), were exceeded in 557 cases (0.32 %). The limit values (LV) of indicators primarily characterizing the sensory qualities of drinking water were not met for 3363 findings (1.95 %). In all, 9041 cases of non-compliance with the limit values for quality indicators were recorded (5.4 %). Comparison of the data obtained in 1994 to 2000 evidenced a slightly decreasing trend in the MLV and LVRR exceedance rates (from 0.80 % to 0.30 %), no marked changes occurring in the other indicators.
The evaluation of drinking water quality according to its source is presented in Fig. 5.1. As in previous years, the recommended values of quality indicators are best met in waters produced from underground sources. In drinking water produced from mixed sources, the limit values were exceeded with the lowest frequency while the indicators with significance for health with the MLV and LVRR were exceeded with the highest frequency.
The evaluation of drinking water quality in the public water supply systems monitored is documented in Fig. 5.2. As for the biological and microbiological indicators, the limit values for coliform bacteria were still most frequently exceeded (Fig. 5.2a). The downward trend in their exceedance frequency observed in 1996 to 1999 stopped in 2000. For indicators, the limits of which are given by the recommended value (RV) or indicative value (IV), the results obtained in the year 2000 are comparable with those of previous years (Fig. 5.2b). As regards the indicators influencing the sensory characteristics of water (Fig. 5.2c), the downward tendency in exceedance of the limits for aluminium, manganese and iron contents was confirmed in 2000. The values of the indicators with significance for health in the water supply systems monitored are shown in Fig. 5.2d. The downward tendency in exceedance of limit values for chloroform continued, the frequency of the MLV exceedance fell below 2 % in 2000. An increase in the limit value exceedance was found for dichlorobenzenes as compared to 1999.
As in previous years, a high frequency of non-compliance with the limit values for active chlorine content was recorded (Fig. 5.2e). For this indicator, both the failure to meet the limit value for the minimum content of 0.05 mg Cl/L and the exceedance of the recommended maximum chlorine content, i.e. 0.3 mg Cl/L, have been monitored (Fig. 5.2e). The proportion of overchlorinated water samples at the outlets of water treatment plants reached 65 % in 2000 and the frequency of failure to meet the minimum chlorine content in the water supply systems increased again and reached more than 30 %.
Evaluation of drinking water quality in the water supply systems monitored related to the total number of analyses according to the MLV and LVRR limit values exceedance is given in Fig. 5.3. The MLVs and LVRRs of the indicators with highest significance for health were exceeded most frequently in Kolín, Znojmo and Šumperk. In contrast, no exceedance of these limits was recorded in 12 cities (Benešov, Brno, Havlíčkův Brod, Hodonín, Karviná, Kladno, Klatovy, Kroměříž, Mělník, Olomouc, Pardubice and Sokolov). As many as 2546 samples of drinking water from the water supply systems of the cities monitored were analysed. Non-compliance with the MLV and LVRR for at least one indicator was recorded in 69 samples.
Table 5.1 shows the trends in non-compliance with different limit values in the public water supply systems for the period of routine monitoring (1994 to 2000). For the MLVs and LVRRs, indicators with the highest significance for health, no statistically significant increase was found and a decrease was recorded in ten cities. A statistically significant decrease in the indicators with the LV was found in Mělník, no increase was recorded in any of the cities monitored. The proportion of non-compliance with the recommended or indicative values showed a statistically significant increase in České Budějovice and a decrease in Plzeň.
Table 5.1 | Drinking water quality in public water supplies of cities under Monitoring System, 1994-2000 |
In 2000 the study of the National Institute of Public Health focused on the monitoring of selected disinfection products in the water supply systems continued. The chemicals monitored were those recommended by the WHO (Guidelines for drinking water quality, second edition, volume 1, World Health Organization, Geneva 1993) and included in the EU Council Directive 98/83/EC and Regulation No. 376/2000 of the Ministry of Health of the Czech Republic that sets the requirements for drinking water quality and extent and frequency of its monitoring. To be analysed for the presence of trihalogenmethanes (trichloromethane - chloroform, dibromochloromethane, bromodichloromethane and tribromomethane - bromoform), bromites and chlorites, drinking water was sampled as planned, i.e., three times per year (in February, May and October) by Public Health Service workers. The samples obtained were analysed in the specialized laboratory of the National Institute of Public Health. A total of 97 results on the each chemical monitored in drinking water were obtained. The requirements of the World Health Organization, EU and Regulation No. 376/2000 of the Ministry of Health of the Czech Republic were met for 100 % of the drinking water samples. Since these contaminants are included in the set of drinking water quality indicators, their further monitoring is justified (Fig. 5.5).
5.4 Assessment of exposure to selected contaminants
For selected contaminants with the exposure limits established (barium, chloroform, nitrites, nitrates, hexachlorobenzene, aluminium, cadmium, manganese, copper, nickel, lead, mercury, selenium, tetrachloromethane, zinc and iron), the population exposure from the intake of drinking water was assessed, based on the assumption that a human drinks one litre of drinking water daily from the public water supply on average (Summary Report 1995). The acceptable daily intake (ADI) was applied as the exposure limit. Only if the ADI had not been established (manganese, selenium), the US EPA limit (RfD) was applied. The results are presented in Fig. 5.4 as the total population exposure for the median and 90th percentile of the content of contaminants in the public water supply systems monitored. Just as in the whole previous period, exposure to nitrates is clearly predominant, however reaching 7 % of the ADI only (Fig. 5.4a). Exposure to barium follows, amounting to 1.4 % of the ADI. Exposure determined from 90th percentile values also exceeded 1 % of the ADIs for chloroform, nickel and lead (Fig. 5.4b). The concentrations of the other contaminants in drinking water often do not reach the detection limit of the analytical method employed (in more than 50 % of cases). Exposure to such contaminants cannot be assessed with accuracy, nevertheless, it can be positively stated that it is lower than 1 % of the exposure limit.
The evaluation of exposure in relation to the population supplied by each of the systems is documented in Fig. 5.4c. As for the intake of nitrates with drinking water, it was between 10 % and 20 % of the ADI for less than 14 % of the population of the cities monitored and reached over 20 % for 0.5 % of this population. The mean exposure did not exceed 10 % of the exposure limit in any of the localities monitored. The results remain without substantial changes as compared to previous years.
Table 5.2 shows trends in the population exposure to selected contaminants from drinking water intake in 1994 to 2000. Important contaminants were assessed, for which the exposure limits had been set and aggregated exposure to which for all the cities monitored had exceeded 1 % of the exposure limit for at least one year. From the data in the table, it is apparent that any correlation for the majority of the data was not found and that the hypothesis of random distribution was not disproved. A statistically significant decrease in exposure to barium was recorded in Havlíčkův Brod. As regards nitrates, exposure increased significantly in Brno, Havlíčkův Brod, and Hodonín, and, in contrast, decreased significantly in Děčín, Jindřichův Hradec, Klatovy, Most, Ostrava, Praha, Sokolov and Šumperk (repeatedly). Exposure to other contaminants assessed (manganese, nickel, lead, selenium and chloroform) showed slight variation, never exceeding 1 % of the ADI.
Owing to the presence of natural radionuclides in drinking water, the population was exposed to a dose of 0.02 mSv per year on average, which accounts for about 1 % of the total irradiation from natural sources.
Table 5.2 |
Trends of exposure to selected significant contaminants
from drinking water, 1994-2000 (Evaluation of contaminants with exposure higher than 1 % exposure limit) |
5.5 Carcinogenic risk assessment
To predict probable increase in risk of cancer resulting from chronic exposure to chemicals from drinking water, a linear no-threshold dose-effect model was applied. The calculation was made for the following chemicals: 1,1,2,2-tetrachloroethene, 1,1,2-trichloroethene, 1,1-dichloroethene, 1,2-dichloroethane, 2,4,6-trichlorophenol, arsenic, benzene, benzo(a)pyrene, hexachlorobenzene, chloroethene, chloroform, lindane, p,p-dichlorodiphenyltrichloroethane, pentachlorophenol, polychlorinated biphenyls and tetrachloromethane. Based on the median concentrations established in the cities monitored, contribution to the increased risk of developing cancer was estimated for each chemical separately. If for some contaminant most results were below the detection limit of the analytical method used, its contribution to the risk was not taken into account. The overall estimate of increased risk of cancer for each of the localities was then expressed as a sum of the contributions of all contaminants assessed. The risk estimates for each of the cities monitored are given in Fig. 5.6. Consumption of drinking water could contribute to the increased risk of cancer in the cities monitored in the range of one case per year per one million to one thousand million population. Altogether, less than one additional case of cancer resulting from consumption of drinking water from the public water supply system could be expected in all cities monitored, i.e. among 3.5 million population.
5.6 Partial conclusions
In 2000, no case of either infection or intoxication was reported, which could be attributed to the consumption of drinking water from the public water supply networks of the cities monitored.
As regards the presence of chemicals with significance for health in drinking water, most frequently exceeded were the limits for chloroform, just as in the previous year, and newly also for dichlorobenzenes. Of biological and microbiological indicators of drinking water quality, the count of coliform bacteria most frequently failed to be observed. In 2000, as in previous years, the frequency of non-compliance with the limit for the active chlorine content in the water supply networks was high.
Population exposure to selected inorganic and organic substances does not pose any significant risk. The intake of nitrates with drinking water reaches 7.3 % of the exposure limit, that of barium amounts to 1.4 % of the exposure limit. The intake of other contaminants with drinking water does not exceed 1 % of the respective exposure limits. The estimate of the probability of increased incidence of cancer resulting from chronic exposure to 15 organic substances and arsenic compounds from drinking water has shown that less than one additional case of cancer attributable to consumption of drinking water from the public water supply networks is to be expected in 2000 for all of the cities monitored.
Statistical analysis of the trends in the selected indicators monitored in 1994 to 2000 has shown that the hypothesis of random distribution of the findings is not disproved for the vast majority of cases. From this fact it can be stated that any significant linear trends in drinking water quality have not occurred in the water supply systems of the cities monitored.