5. HEALTH EFFECTS AND RISKS RELATED TO DRINKING WATER POLLUTION |
5.1 Organisation of monitoring activities
In 2003, subsystem II activities were carried out in all 30 selected towns (Tab. 3.1). The District Public Health Centres Litoměřice and Pardubice continued their volunteer participation.
Each of the participating Public Health Centres was required to carry out a minimum quota of complete drinking water analyses (ranging from 8 to 20 depending on the size of the population supplied by each of the public systems) and to analyze the same set of water quality indicators.
Drinking water quality is monitored both within the water supply system and at the outlet of water treatment plants. Data from analyses performed by drinking water producers (distributors) are also entered in the Monitoring System.
Since 2001 till 2004, the public health requirements for drinking water quality have been set by Regulation No. 376/2000 of the Ministry of Health, Czech Republic, compliant with WHO guidelines of 1993 and partially harmonized with Directive 98/83/EC on the quality of water intended for human consumption. This regulation was used as a basis for evaluation of the results obtained in 2003. Evaluation of radiological indicators, based on Regulation No. 307/2002 of the State Office for Nuclear Safety on Requirements for Assurance of Radiation Protection, focused on compliance with guiding levels of volume activity.
Immediate reporting of water quality emergencies that may pose a threat to population health and reporting of changes in water quality requiring intervention by Public Health Authorities (water supply outage, for example) are also parts of the Monitoring System.
5.2 Monitoring health indicators
The monitoring of health indicators is based on reporting of selected infectious diseases potentially transmissible through contaminated water and cases of poisoning due to chemical contamination of drinking water. Information is obtained from the EPIDAT epidemiological information system and through direct reports from the participating Public Health Centres. No case of either infection or poisoning attributable to drinking water consumption from any of the monitored public water supply systems was identified; water was confirmed as a vector in only 109 out of 30,291 reported cases of infections, but none of these 109 cases was associated with drinking water from the water supplies monitored, as revealed by laboratory and epidemiological analyses. Likewise, reports by participating Public Health Centres did not indicate a single case of infection or chemical poisoning by drinking water from any of the public water systems in the monitored districts.
5.3 Drinking water quality
In 2003, analyses of 2,200 drinking water samples collected either at the consumer’s tap in the monitored cities or at the outlet of a water treatment plant yielded 48,553 units of data on drinking water quality indicators. In all, 1,020 instances of failure to comply with the limit values for drinking water quality indicators were recorded.
From the total of 2,068 analyses of water quality indicators in tap water, the limit values – the maximum limit value (MLV) and limit value of reference risk (LVRR) – were exceeded in 27 instances. Limit values (LV) for indicators of sensory qualities of drinking water were not met in 980 instances. Comparison of the data obtained in 1994–2002 reveals a slightly downward trend in the MLV and LVRR exceedance rates (from 0.8 % to 0.1 %) with no marked changes in the other indicators in 2003.
The highest frequency of exceeded limits irrespective of limit value type was found in drinking water produced from surface sources.
Drinking water quality in monitored public water supplies is evaluated in Fig. 5.1a–d and Fig. 5.2. As for biological and microbiological quality indicators, the limit values for coliform bacteria were once again the most frequently exceeded (Fig. 5.1a), at a rate of 2.8 % of above-limit samples. In terms of the indicators associated with the sensory characteristics of water (5.1b), limit values were most frequently exceeded for free chlorine (36.8 %), chlorites (11.6 %) and iron (7 %). Nitrate content, limited by the highest limit value to date, was exceeded in 0.7 % (12 out of a total 1,704 samples). The frequency of exceeding the values of indicators limited by the highest limit value and the limit value of reference risk, including mostly substances significant healthwise, was the highest in extractable non-polar substances (indicator of pollution of drinking water with mineral oil), however, in only 2.3 % of the total number of determinations. In the other indicators, the limit values have been exceeded in sporadic findings (e.g. mercury – in 2 above-limit findings out of 359). The exceeding in indicators limited by MLV and LVRR in water supply networks of the cities under follow-up is documented in Fig. 5.1c.
As in previous years, a high rate of non-compliance with limit values for chlorine was recorded in 2003 (Fig. 5.1d). For this indicator, both failure to meet the limit value for a minimum content of 0.05 mg Cl/L and exceedance of the maximum recommended chlorine content of 0.3 mg Cl/L are monitored. The proportion of under-chlorinated water samples collected at the outlets of water treatment plants exceeded 40 % in 2002, while the upward rising trend observed since 1998 stopped in 2003. However, non-compliance with chlorine limit values should not be considered separately without taking into account other related indicators: if the microbial quality, content of chlorination by-products and sensory qualities of the resulting water are satisfactory, no negative conclusions should be drawn from non-compliance with the chlorine limits. In fact, the number of over-chlorinated samples has risen slightly, comprising 7 % in 2003. The recorded maximum chlorine values (about 2 mg/L) do not represent a direct health hazard according to latest knowledge.
The greatest frequency of above-limit findings in indicators having a limit value, in 2003 has been found in Ústí nad Orlicí (5 %), the lowest in Jihlava, Havlíčkův Brod and in Prague (see Tab. 5.1, Fig. 5.2). The exceeding of limits in healthwise important indicators having the highest MLV or LVRR was the same in 2003 as in previous years, i.e. only sporadically, 0.5 % at the most in Pardubice. The limits in these indicators have not been exceeded in 15 cities.
In the course of 10 years of monitoring, the mean annual nitrate concentrations in drinking water from the water supply network were in a wide range of from 0.05 mg/L (Jablonec nad Nisou, 2002) to 50 mg/L (Svitavy, 1999, 2000), i.e. up to the limit value set in Decree No. 376/2000 (Fig. 5.3). In the year 2003 nitrate concentrations were found to be at the upper limit of the mean annual values of 1998–2003 in Prague, Kladno, Kroměříž and Jihlava. In 2001, in Hodonín there were closed the old waterworks, and the city was connected to a new source, the Bzenec complex.
5.4 Assessment of exposure to selected contaminants
Population burden of contaminants from drinking water intake was evaluated for selected substances (arsenic, nitrates, nitrites, aluminium, free chlorine, chloroethene, chloroform, cadmium, manganese, copper, nickel, lead, mercury, selenium, tetrachloromethane, iron) with exposure limits recommended by WHO and US EPA. Consumption of 1 litre of tap-water per person and day was considered and confirmed by the NIPH HELEN questionnaire investigation (see Chapter 9). As in the previous monitoring period, exposure to nitrates is predominant. Its median and 90th percentile, however, only reach about 8 % and almost 10 % of the acceptable daily intake, respectively (Fig. 5.4a). Chloroform exposure is moderately above 1 % of the total acceptable daily intake. Concentrations of the other contaminants analyzed in drinking water often do not exceed the detection limit of the analytical method used and therefore exposure to these substances cannot be assessed with accuracy, although it can be positively stated that it is lower than 1 % of the exposure limit. The degree of exposure to selected substances is presented in Fig. 5.4a and 5.4b as the percentage of tapping the daily exposure limit from the drinking water of public water mains in the cities under monitoring, obtained with the aid of the median value and the 90% quantile of the concentration of those substances, both weighed by the number of inhabitants supplied in each of the cities.
Distribution of the population monitored by the burden of exposure to contaminants from drinking water intake is given in Fig. 5.4c. In the year 2003 almost 60 % of the population tapped up to 10 % of the acceptable daily intake of nitrates through drinking water. This portion of drinking water exposure of 10 % in the total oral intake of nitrates is recommended as the limit by the WHO. Moderately above 40 % of the population in the cities under monitoring tapped through drinking water more than 10 % of the acceptable daily intake of nitrates, of these 0.4 % of the population tapped more than 20 %. The daily exposure limit between 1 % and 10 % was tapped by a greater portion of the population in chloroform (40 %), in the other contaminants the absolute majority of the population of the cities under monitoring tapped less than 1 % of the daily exposure limit through drinking water.
Table 5.2 shows trends in population exposure to selected contaminants from drinking water intake in 1999–2003. Those contaminants for which exposure limits have been set and exposure in aggregate for all monitored cities had been close to 1 % of the exposure limit in at least 1 year were evaluated. To assess trends, a correlation coefficient at the 5 % level of significance was used. Data in this Table shows that in the majority of cases no correlation was found and that the hypothesis of random distribution of values is not disproved. If in isolated cases any either positive or negative correlation was recorded, there was either an increase or a decrease reaching tenths percent, the burden being close to 1 % of the total ADI or less.
The presence of natural radionuclides in drinking water results in an average population exposure of 0.03 mSv/r. Drinking water intake accounts for about 1 % of total irradiation from natural sources.
5.5 Carcinogenic risk assessment
To predict probable increase in the risk of cancer resulting from chronic exposure to chemicals in drinking water, a linear no-threshold dose-effect model was applied. Among drinking water quality indicators listed in Decree of MoH No. 376/2000, the following substances for which a carcinogenic potency oral slope factor is available were selected for carcinogenic risk assessment: 1,2-dichloroethane, 1,2-dichloroethene, arsenic, benzene, benzo[a]pyrene, benzo[b]fluorantene, benzo[k]fluorantene, bromodichloromethane, bromoform, dibromochloromethane, chloroethene (vinyl chloride), chloroform, indeno[1,2,3-cd]pyrene, mercury, tetrachloroethene (PCE), tetrachloromethane and trichloroethene. Based on median concentrations, the contribution to increased risk of developing cancer was estimated for each contaminant and each city monitored. If the majority of results for a given substance were below the detection limit of the analytical method used, the contribution of such a substance was not taken into account. The overall estimate of increased cancer risk for each area was then expressed as the sum of contributions by all contaminants assessed. The risk estimates for each of the cities monitored are given in Fig. 5.5. Consumption of drinking water is associated with a very low level of cancer risk; in the cities monitored, it could contribute to an increase of cancer risk in the range of 1 case annually per 1 million – 1 milliard population. In 2003, less than 1 additional case of cancer resulting from consumption of drinking water from the public water supply could be expected in all cities monitored (about 3.5 million population).
5.6 Partial conclusions
As in previous years, no cases of infectious disease or poisoning through consumption of drinking water from the public water supplies monitored were reported in 2003.
The most commonly exceeded biological and microbiological indicators of drinking water quality were coliform bacteria counts. As in 2002, limit values for hazardous chemical contaminants were exceeded only in isolated instances.
Long-term population exposure to selected organic and inorganic substances poses no significant health hazard. The burden of nitrates reaches 8 % of the acceptable intake and that of chloroform slightly over 1 %. In the other contaminants the burden does not exceed 1 % of the acceptable intake. Based on calculation of theoretical increase in cancer risk from chronic exposure to 15 organic substances and arsenic and mercury compounds in drinking water from the public supply systems, about less than one additional case of cancer is to be expected in 2003 for the total of the cities monitored.
Statistical evaluation of trends in selected indicators in the cities monitored between 1999 and 2003 did not reveal any significant increase in their concentrations and thus in exposure for the vast majority of cases. Therefore, it may be stated that no significant changes were found in water quality from the water supply systems of the cities monitored within this period and that in general the water supplied is of very good quality.
Tab. 5.1 Drinking water quality in public water supplies, 1999–2003
|
Excess of LV [%] |
Excess of MLV + LVRR [%] |
||||||||
City/Calendar year |
1999 |
2000 |
2001 |
2002 |
2003 |
1999 |
2000 |
2001 |
2002 |
2003 |
Benešov |
1.32 |
1.01 |
1.51 |
2.24 |
0.69 |
0.00 |
0.00 |
0.00 |
0.22 |
0.00 |
Brno |
1.10 |
1.52 |
2.54 |
2.52 |
2.24 |
0.01 |
0.00 |
0.01 |
0.04 |
0.05 |
České Budějovice |
3.45 |
4.85 |
3.17 |
5.83 |
2.10 |
0.00 |
0.13 |
0.10 |
0.00 |
0.08 |
Děčín |
4.86 |
2.80 |
4.14 |
3.41 |
2.62 |
0.10 |
0.07 |
0.00 |
0.05 |
0.04 |
Havlíčkův Brod |
0.85 |
0.31 |
0.65 |
0.18 |
0.17 |
0.09 |
0.00 |
0.24 |
0.09 |
0.08 |
Hodonín |
1.60 |
1.79 |
1.36 |
2.35 |
2.01 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
Hradec Králové |
3.78 |
3.20 |
3.11 |
2.00 |
3.71 |
0.00 |
0.04 |
0.00 |
0.00 |
0.08 |
Jablonec nad Nisou |
1.25 |
1.90 |
1.32 |
3.68 |
1.45 |
0.05 |
0.18 |
0.05 |
0.00 |
0.21 |
Jihlava |
1.95 |
1.13 |
5.26 |
1.37 |
0.00 |
0.05 |
0.38 |
0.13 |
0.11 |
0.00 |
Jindřichův Hradec |
0.56 |
2.10 |
4.41 |
2.29 |
1.57 |
0.00 |
0.38 |
0.00 |
0.00 |
0.00 |
Karviná |
0.83 |
0.74 |
0.16 |
0.35 |
1.10 |
0.09 |
0.00 |
0.00 |
0.00 |
0.11 |
Kladno |
2.03 |
1.37 |
0.33 |
0.44 |
0.35 |
0.48 |
0.00 |
0.00 |
0.44 |
0.17 |
Klatovy |
0.49 |
0.49 |
1.73 |
12.64 |
4.26 |
0.16 |
0.00 |
0.00 |
0.14 |
0.10 |
Kolín |
1.55 |
1.10 |
4.26 |
1.67 |
1.26 |
0.56 |
1.25 |
1.16 |
0.00 |
0.42 |
Kroměříž |
2.14 |
1.52 |
1.84 |
2.69 |
2.53 |
0.00 |
0.00 |
0.00 |
0.27 |
0.00 |
Liberec |
1.48 |
0.43 |
3.62 |
1.84 |
1.68 |
0.15 |
0.48 |
0.10 |
0.06 |
0.08 |
Litoměřice |
0.38 |
0.65 |
2.52 |
1.24 |
1.35 |
0.19 |
0.14 |
0.00 |
0.52 |
0.00 |
Mělník |
1.43 |
0.67 |
1.19 |
0.50 |
0.34 |
0.00 |
0.00 |
0.79 |
0.33 |
0.00 |
Most |
1.06 |
0.45 |
0.86 |
1.57 |
1.47 |
0.10 |
0.08 |
0.00 |
0.05 |
0.00 |
Olomouc |
0.99 |
3.33 |
4.14 |
5.05 |
4.51 |
0.20 |
0.00 |
0.00 |
0.00 |
0.18 |
Ostrava |
1.17 |
1.28 |
5.41 |
2.75 |
1.52 |
0.05 |
0.04 |
0.00 |
0.14 |
0.00 |
Pardubice |
6.33 |
6.55 |
7.80 |
5.22 |
3.48 |
0.06 |
0.00 |
0.00 |
0.00 |
0.50 |
Plzeň |
1.20 |
2.43 |
3.62 |
2.94 |
3.30 |
0.00 |
0.02 |
0.04 |
0.06 |
0.04 |
Prague |
1.73 |
1.10 |
0.33 |
0.31 |
0.19 |
0.00 |
0.07 |
0.08 |
0.06 |
0.00 |
Příbram |
2.92 |
4.84 |
1.09 |
4.44 |
0.93 |
0.75 |
0.22 |
0.00 |
0.44 |
0.00 |
Sokolov |
2.83 |
2.67 |
0.00 |
3.79 |
2.28 |
0.36 |
0.00 |
0.00 |
0.00 |
0.00 |
Svitavy |
5.22 |
6.30 |
8.22 |
6.25 |
3.11 |
1.03 |
0.19 |
0.00 |
0.00 |
0.00 |
Šumperk |
0.49 |
0.16 |
1.74 |
4.65 |
3.37 |
0.38 |
0.64 |
0.31 |
0.66 |
0.28 |
Ústí nad Labem |
1.49 |
1.52 |
1.78 |
1.33 |
1.21 |
0.56 |
0.51 |
0.00 |
0.00 |
0.07 |
Ústí nad Orlicí |
1.77 |
1.39 |
0.85 |
1.78 |
4.82 |
0.24 |
0.12 |
0.00 |
0.00 |
0.00 |
Znojmo |
4.34 |
2.58 |
8.30 |
7.87 |
2.68 |
0.00 |
0.74 |
0.90 |
1.31 |
0.00 |
Žďár nad Sázavou |
1.23 |
1.93 |
0.49 |
0.41 |
1.34 |
0.11 |
0.14 |
0.00 |
0.00 |
0.00 |
Remarks:
LV – limit value
MLV – maximum limit value
LVRR – limit value of reference risk
In 1999–2000 exceeding of the limit values was reviewed according to the Czech National Standard ČSN 75 71 11 “Drinking Water”, since 2001 according to the Regulation No. 376/2000 Coll. of the Ministry of Health
Tab. 5.2 Trends of exposure to selected significant contaminants from drinking water, 1999–2003
City |
Daily intake [% exposure limit] |
|||||
Chlorine |
Nitrates |
Manganese |
Nickel |
Lead |
Chloroform |
|
Benešov |
N |
N |
N |
N |
N |
N |
Brno |
N |
N |
N |
N |
N |
N |
České Budějovice |
N |
N |
N |
N |
N |
N |
Děčín |
N |
N |
N |
N |
N |
N |
Havlíčkův Brod |
N |
N |
N |
N |
– |
N |
Hodonín |
N |
– |
N |
– |
N |
– |
Hradec Králové |
N |
N |
N |
N |
N |
N |
Jablonec nad Nisou |
+ |
N |
N |
N |
N |
N |
Jihlava |
N |
N |
N |
N |
N |
– |
Jindřichův Hradec |
N |
– |
N |
N |
N |
N |
Karviná |
N |
N |
N |
N |
– |
N |
Kladno |
N |
N |
0 |
0 |
N |
N |
Klatovy |
N |
N |
N |
N |
N |
N |
Kolín |
N |
N |
0 |
N |
N |
N |
Kroměříž |
N |
N |
N |
N |
N |
N |
Liberec |
N |
N |
N |
N |
N |
N |
Litoměřice |
N |
N |
N |
N |
N |
0 |
Mělník |
N |
N |
N |
N |
N |
N |
Most |
N |
– |
N |
N |
N |
N |
Olomouc |
N |
N |
N |
N |
N |
N |
Ostrava |
N |
N |
N |
N |
N |
N |
Pardubice |
N |
N |
N |
N |
N |
N |
Plzeň |
N |
N |
N |
N |
N |
+ |
Prague |
– |
N |
N |
N |
N |
+ |
Příbram |
N |
N |
N |
N |
N |
0 |
Sokolov |
N |
N |
N |
N |
N |
0 |
Svitavy |
+ |
N |
+ |
N |
N |
0 |
Šumperk |
N |
N |
N |
+ |
N |
N |
Ústí nad Labem |
N |
N |
N |
N |
N |
N |
Ústí nad Orlicí |
N |
N |
N |
N |
N |
N |
Znojmo |
N |
N |
N |
0 |
N |
+ |
Žďár nad Sázavou |
N |
N |
N |
N |
N |
N |
CZ |
– |
N |
N |
N |
N |
+ |
Remarks:
„+“ – statistically significant increase (tested by correlation coefficient at a significance level of 5 %)
„–“ – statistically significant decrease (tested by correlation coefficient at a significance level of 5 %)
„N“ – random distribution of values
„0“ – exceeding of the limit value not detected