5. HEALTH EFFECTS AND RISKS RELATED TO DRINKING WATER POLLUTION |
5.1 Organization of monitoring activities
In 2002, subsystem II activities were carried out in all 30 selected localities. The District Public Health Centres Litoměřice and Pardubice continued their volunteered participation (Table 3.1).
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 January 1, 2001, public health requirements for drinking water quality have been set by Regulation No. 376/2000 of the Ministry of Health, Czech Republic, compliant with the 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 2002. 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 62 out of 32 952 reported cases of infections, but none of these 62 cases was accociated 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 2002, analyses of 2,449 drinking water samples collected either at the consumer’s tap in the monitored cities or the most important district water supplies or at the outlet of a water treatment plant yielded 53,986 data on drinking water quality indicators. In all, 1,645 failures to comply with the limit values for drinking water quality indicators (LV, MLV and LVRR) were recorded. From the total of 48,059 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 41 instances. Limit values (LV) for indicators of sensory qualities of drinking water were not met in 1,493 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.
As many as 2242 water samples were collected from the supply systems in the monitored cities. Failure to comply with the MLV or LVRR for at least one water quality indicator was recorded in 38 samples.
The highest frequency of limit exceedances irrespective of LV type was found in drinking water produced from surface sources.
The highest rate of limit values (LV) exceedances was recorded in Klatovy (12 %), while the lowest rates were reported in Havlíčkův Brod (see Table 5.1). As in 2001, MLV or LVRR for indicators with significance for health were exceeded only sporadically in 2002, the highest exceedance rate reaching 1.3 % in Znojmo.
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); and were exceeded at a higher rate compared to 2001. Speaking of the indicators associated with the sensory characteristics of water for which limit values had been set up (Fig. 5.1b), an upward tendency in failure to meet the limit value for free chlorine continued in 2002. Fig. 5.1c shows levels of indicators significant for health in the water supply systems of the monitored cities. MLV and LVRR are most frequently exceeded for acrylamide and epichlorohydrin but this means one exceedance per 7 and 8 analyses, respectively. The rates with which the limit values for other indicators are exceeded are very low, e.g. two and five exceedances for nitrates and NEL, respectively.
As in previous years, a high rate of non-compliance with limit values for chlorine was recorded in 2002 (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 over-chlorinated water samples collected at the outlets of water treatment plants reached 68 % in 2002, while the rate of failures to meet the minimum chlorine content in water supply systems exceeded 40 %, showing an upward tendency since 1998. 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. The recorded maximum chlorine values (about 2 mg/L) do not represent a direct health hazard according to latest knowledge.
Drinking water quality in the water supply systems monitored by total rates of limit value exceedances is represented in Fig. 5.2. MLVs and LVRRs of indicators significant for health were exceeded most frequently in Znojmo (4 times per 98 analyses), Šumperk (3 times per 116 analyses) and Litoměřice (5 times per 287 analyses). In 14 cities none of these indicators was exceeded.
NO3 concentrations close to the upper limit of mean annual values for nitrates obtained for the 9-year period of monitoring were found in 2002 in Ústí nad Orlicí, Brno, Havlíčkův Brod, Benešov, Praha, Šumperk and Kladno; a significant interannual increase was not found for any of these localities. Compared to 2001, relatively higher differences in the mean values were recorded in Praha and Šumperk. The other cities show medians of annual concentrations close to the lower limit of mean annual values. The most marked decrease in mean annual concentrations of nitrates at the consumer’s outlet was recorded in Hodonín that started to be supplied with water from a new source called Bzenec after the old water treatment plant was closed (see Fig. 5.3).
In 2002, a three-year study was completed the objective of which was to map the levels of selected disinfection byproducts in the water supply systems. The chemicals monitored were those recommended by WHO (Guidelines for Drinking Water Quality, second edition, volume 1, World Health Organization, Geneva 1993) and included in EU Council Directive 98/83/EC and Regulation No. 376/2000 of the Ministry of Health of the Czech Republic which sets requirements for drinking water quality and the extent and frequency of its monitoring. Samples to be analyzed for the presence of trihalomethanes (THM), i.e. trichloromethane – chloroform, dibromochloromethane, bromodichloromethane and tribromomethane – bromoform, bromites and chlorites were collected three times a year as planned, i.e. in February, May and October. Eventually, a total of 297 data were obtained.
The study revealed a progressive increase in the content of trihalomethanes in most water supply systems monitored between 2000 and 2002. The mean sum THM contents were 11.7 µg/L, 15.3 µg/L and 21.3 µg/L in 2000, 2001 and 2002, respectively, the total increase equaling to 97.4 % (see Fig. 5.6b). Chloroform continues to be the most important part of THM and its mean concentrations for all water supply systems monitored were 7.5 µg/L, 10.4 µg/L and 15.5 µg/L in 2000, 2001 and 2002, respectively, the total increase equaling to 106.7 %. The proportion of chloroform in the sum THMs is represented in Fig. 5.6a.
Although all THM levels found in drinking water of the supply systems monitored meet the requirements of Regulation of MoH No. 376/2000 (allowing higher contents of chloroform in compensation for lower contents of bromo THM), their upward tendency is definitely undesirable. Concentrations of chloroform and THMs will continue to be monitored according to the requirements of the amended Regulation of MoH No. 376/2000.
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. The results are presented in Fig. 5.4a, 5.4b as percentages of the exposure limit accounted for consumption of drinking water from the public water supply systems monitored for the median exposure level and 90th percentile. 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). The median exposure levels did not exceed 1 % of the acceptable daily intake (ADI) for any other contaminant (Fig. 5.4b). Exposure determined for 90 % of the population in the cities monitored slightly exceeded the limits for free chlorine and chloroform only, as in previous years. 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.
Distribution of the population monitored by the burden of exposure to contaminants from drinking water intake is given in Fig. 5.4c. In 2002, this burden reached under 10 % and more than 10 % of the total ADI for nitrates in less than 60 % and 40 % of population in the monitored cities, respectively, a burden over 20 % of the total ADI being found for 0.6 % of population only. As for other contaminants monitored, a burden above 10 % of the total ADI was recorded for lead and vinylchloride only in 2–4 % of the population monitored.
Table 5.2 shows trends in population exposure to selected contaminants from drinking water intake in 1998–2002. 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 per cent, 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 0.02 mSv/y. 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 Regulation 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 2002, 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 2002. As in 2001, limit values for hazardous chemical contaminants were exceeded only in isolated instances. The most commonly exceeded biological and microbiological indicators of drinking water quality were coliform bacteria counts.
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 the other contaminants 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 one additional case of cancer is to be expected in 2002 for the total of the cities monitored.
A three-year study of the content of disinfection byproducts – trihalomethanes – in drinking water did not show any exceedance of the limit values according to Regulation of MoH No. 376/2000 but did show a marked upward tendency in their presence for most public water supply systems monitored.
Statistical evaluation of trends in selected indicators in the cities monitored between 1998 and 2002 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.
Table 5.1 Drinking water quality in public water supplies of cities under Monitoring System, 1998–2002
|
Excess of LV [%] |
Excess of MLV + LVRR [%] |
||||||||
City/Calendar year |
1998 |
1999 |
2000 |
2001 |
2002 |
1998 |
1999 |
2000 |
2001 |
2002 |
Benešov |
0.84 |
1.32 |
1.01 |
1.51 |
2.24 |
0.00 |
0.00 |
0.00 |
0.00 |
0.22 |
Brno |
1.33 |
1.10 |
1.52 |
2.54 |
2.52 |
0.03 |
0.01 |
0.00 |
0.01 |
0.04 |
České Budějovice |
1.33 |
3.45 |
4.85 |
3.17 |
5.83 |
0.00 |
0.00 |
0.13 |
0.10 |
0.00 |
Děčín |
4.89 |
4.86 |
2.80 |
4.14 |
3.41 |
0.00 |
0.10 |
0.07 |
0.00 |
0.05 |
Havlíčkův Brod |
1.11 |
0.85 |
0.31 |
0.65 |
0.18 |
0.46 |
0.09 |
0.00 |
0.24 |
0.09 |
Hodonín |
0.89 |
1.60 |
1.79 |
1.36 |
2.35 |
0.00 |
0.00 |
0.00 |
0.00 |
0.00 |
Hradec Králové |
2.57 |
3.78 |
3.20 |
3.11 |
2.00 |
0.03 |
0.00 |
0.04 |
0.00 |
0.00 |
Jablonec nad Nisou |
2.57 |
1.25 |
1.90 |
1.32 |
3.68 |
0.15 |
0.05 |
0.18 |
0.05 |
0.00 |
Jihlava |
1.58 |
1.95 |
1.13 |
5.26 |
1.37 |
0.02 |
0.05 |
0.38 |
0.13 |
0.11 |
Jindřichův Hradec |
0.50 |
0.56 |
2.10 |
4.41 |
2.29 |
0.00 |
0.00 |
0.38 |
0.00 |
0.00 |
Karviná |
0.73 |
0.83 |
0.74 |
0.16 |
0.35 |
0.00 |
0.09 |
0.00 |
0.00 |
0.00 |
Kladno |
2.01 |
2.03 |
1.37 |
0.33 |
0.44 |
0.00 |
0.48 |
0.00 |
0.00 |
0.44 |
Klatovy |
2.22 |
0.49 |
0.49 |
1.73 |
12.64 |
0.16 |
0.16 |
0.00 |
0.00 |
0.14 |
Kolín |
0.84 |
1.55 |
1.10 |
4.26 |
1.67 |
0.34 |
0.56 |
1.25 |
1.16 |
0.00 |
Kroměříž |
1.20 |
2.14 |
1.52 |
1.84 |
2.69 |
1.20 |
0.00 |
0.00 |
0.00 |
0.27 |
Liberec |
2.05 |
1.48 |
0.43 |
3.62 |
1.84 |
0.22 |
0.15 |
0.48 |
0.10 |
0.06 |
Litoměřice |
0.55 |
0.38 |
0.65 |
2.52 |
1.24 |
0.13 |
0.19 |
0.14 |
0.00 |
0.52 |
Mělník |
1.91 |
1.43 |
0.67 |
1.19 |
0.50 |
0.21 |
0.00 |
0.00 |
0.79 |
0.33 |
Most |
1.84 |
1.06 |
0.45 |
0.86 |
1.57 |
0.05 |
0.10 |
0.08 |
0.00 |
0.05 |
Olomouc |
0.86 |
0.99 |
3.33 |
4.14 |
5.05 |
0.00 |
0.20 |
0.00 |
0.00 |
0.00 |
Ostrava |
1.79 |
1.17 |
1.28 |
5.41 |
2.75 |
0.18 |
0.05 |
0.04 |
0.00 |
0.14 |
Pardubice |
0.79 |
6.33 |
6.55 |
7.80 |
5.22 |
0.10 |
0.06 |
0.00 |
0.00 |
0.00 |
Plzeň |
1.68 |
1.20 |
2.43 |
3.62 |
2.94 |
0.10 |
0.00 |
0.02 |
0.04 |
0.06 |
Prague |
1.83 |
1.73 |
1.10 |
0.33 |
0.31 |
0.00 |
0.00 |
0.07 |
0.08 |
0.06 |
Příbram |
2.55 |
2.92 |
4.84 |
1.09 |
4.44 |
0.36 |
0.75 |
0.22 |
0.00 |
0.44 |
Sokolov |
3.62 |
2.83 |
2.67 |
0.00 |
3.79 |
0.62 |
0.36 |
0.00 |
0.00 |
0.00 |
Svitavy |
4.30 |
5.22 |
6.30 |
8.22 |
6.25 |
0.96 |
1.03 |
0.19 |
0.00 |
0.00 |
Šumperk |
0.38 |
0.49 |
0.16 |
1.74 |
4.65 |
0.32 |
0.38 |
0.64 |
0.31 |
0.66 |
Ústí nad Labem |
1.17 |
1.49 |
1.52 |
1.78 |
1.33 |
0.17 |
0.56 |
0.51 |
0.00 |
0.00 |
Ústí nad Orlicí |
1.82 |
1.77 |
1.39 |
0.85 |
1.78 |
0.12 |
0.24 |
0.12 |
0.00 |
0.00 |
Znojmo |
3.81 |
4.34 |
2.58 |
8.30 |
7.87 |
0.15 |
0.00 |
0.74 |
0.90 |
1.31 |
Žďár nad Sázavou |
0.66 |
1.23 |
1.93 |
0.49 |
0.41 |
0.06 |
0.11 |
0.14 |
0.00 |
0.00 |
Remark:
LV – limit value
MLV – maximal limit value
LVRR – limit value of reference risk
1998–2000 evaluation of the limit excess according to the Czech national
standard ČSN 75 71 11 “Drinking Water”
2001 and 2002 – evaluation of the limit excess according to the Regulation
No. 376/2000 Coll. of the Ministry of Health
Table 5.2 Trends of exposure to selected significant contaminants from drinking water, 1998-2002
City |
Daily intake [% exposure limit] |
||||||
Chlorine |
Nitrates |
Manganese |
Nickel |
Lead |
Selenium |
Chloroform |
|
Benešov |
N |
N |
N |
N |
N |
+ |
N |
Brno |
- |
N |
N |
N |
N |
N |
N |
České Budějovice |
N |
- |
- |
N |
N |
N |
- |
Děčín |
N |
N |
N |
N |
N |
N |
N |
Havlíčkův Brod |
N |
N |
N |
- |
N |
N |
N |
Hodonín |
- |
- |
- |
- |
N |
N |
N |
Hradec Králové |
N |
- |
N |
- |
N |
N |
N |
Jablonec nad Nisou |
N |
N |
N |
- |
N |
N |
N |
Jihlava |
N |
N |
N |
N |
- |
N |
N |
Jindřichův Hradec |
N |
- |
N |
N |
N |
N |
N |
Karviná |
N |
N |
N |
- |
N |
N |
N |
Kladno |
N |
N |
N |
N |
N |
N |
N |
Klatovy |
N |
N |
N |
N |
N |
N |
+ |
Kolín |
N |
- |
N |
N |
N |
N |
N |
Kroměříž |
N |
N |
- |
N |
N |
N |
N |
Liberec |
+ |
N |
N |
- |
N |
N |
N |
Litoměřice |
N |
N |
+ |
N |
N |
N |
N |
Mělník |
N |
N |
- |
- |
N |
N |
N |
Most |
N |
- |
N |
N |
N |
N |
N |
Olomouc |
- |
N |
N |
- |
N |
N |
N |
Ostrava |
N |
N |
N |
N |
N |
N |
N |
Pardubice |
N |
N |
N |
N |
N |
N |
N |
Plzeň |
N |
N |
N |
N |
- |
N |
+ |
Prague |
N |
N |
- |
N |
N |
+ |
N |
Příbram |
N |
- |
N |
N |
N |
N |
N |
Sokolov |
N |
- |
N |
N |
N |
N |
N |
Svitavy |
N |
N |
N |
N |
+ |
N |
N |
Šumperk |
N |
N |
N |
+ |
N |
N |
N |
Ústí nad Labem |
N |
N |
N |
N |
N |
N |
N |
Ústí nad Orlicí |
N |
N |
N |
- |
N |
+ |
N |
Znojmo |
N |
N |
N |
N |
N |
N |
+ |
Žďár nad Sázavou |
N |
N |
N |
N |
N |
N |
N |
CR |
N |
N |
- |
- |
N |
N |
N |
Remark:
“+” - 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 in monitoring period