5. HEALTH EFFECTS AND RISKS RELATED TO DRINKING WATER POLLUTION


5.1 Organization of monitoring activities

Since 2004, an information system acronymed IS PiVo and administered by the Ministry of Health has been used for processing data on drinking water quality collected within the nationwide monitoring of water supply systems in the Czech Republic. Data from 2002 and 2003 were also entered into IS PiVo. The basic unit for drinking water assessment in a water supply system is the size of the supplied area (defined by Decree No. 252/2004 as the area supplied from one or more sources, with water considered to be of approximately equal quality, by one operator or one owner). In 2005, more than 4,000 supplied areas were monitored, including over 3,200 small areas supplying less than 1,000 population. Nevertheless, 80 % of the population are connected to public water systems supplying more than 5,000 population.

Comparison of the population supplied with drinking water from the monitored areas in 2005 (9.49 million) and that connected to the public water supply system (based on the Czech Statistical Office data from 2004, as many as 9.36 million (91.8 %) population of the Czech Republic were connected to the public water supply) shows that the monitoring covered the vast majority of public water supply systems in the Czech Republic. In more detail, distribution of the supplied population and numbers of samplings in 2005 by water supply system size is given in Fig. 5.1 Water invoiced to households was 103 l/person/day in 2002 and 2003 and 102 l/person/day in 2004.

Since 2004, the major source of data for the nationwide monitoring have been analyses carried out by operators at intervals and in the extent required by law. Pursuant to Act No. 258/2000 (as last amended by Act No. 274/2003 in force from October 1, 2003) water analysis data can only be entered into IS PiVo when provided by an accredited or authorized laboratory. In line with Decree 252/2004, drinking water samples for analysis have to be collected to be representative of drinking water quality throughout the year and within the entire water supply system. Samples are collected at the outlets providing water for human consumption. Available data on drinking water quality indicators characterize the monitored water supply system under standard conditions. Data relating to possible accidents are not included in the primary data sets.

The binding background document for drinking water quality assessment is Decree No. 252/2004 of the Ministry of Health of the Czech Republic which is fully harmonized with Council Directive 98/83/EC on the quality of water intended for human consumption. The background document for the assessment of water radiological indicators is Decree No. 307/2002 on radiation protection of the State Office for Nuclear Safety. Compliance with guidance levels for volume activity is assessed.

5.2 Monitoring indicators of health damage

Data on the incidence of waterborne infectious diseases are obtained from the epidemiological information system EPIDAT. Reported cases of potential waterborne diseases were retrieved from the EPIDAT database. Water was identified as the route of transmission in only 107 of 73,700 reported cases of infections. Nevertheless, based on laboratory and epidemiological analyses, drinking water from the monitored public supply systems was not implicated in any of the reported cases of infection (Table 5.1).

5.3 Drinking water quality

Compliance with limits for drinking water quality indicators was assessed separately for smaller areas supplying 5,000 or less population and larger areas supplying more than 5,000 population.

In 2005, almost 36 thousand drinking water samples were collected and more than 846 thousand pieces of data on drinking water quality indicators were obtained, i.e. more than 332 thousand pieces of data for larger areas and less than 514 thousand pieces of data for smaller areas. The maximum limit values or limit values were exceeded for 1.0 % of samples from larger areas supplying more than 5,000 population and for 3.0 % of samples from smaller areas supplying 5,000 or less population. Distribution of areas by population supplied (see Fig. 5.2a) shows that the rate of failures to comply with the limit values (related to the total of samples analysed) is decreasing with the increasing population number supplied. Fig. 5.2b shows the trend in the quality of drinking water supplied by the public water systems over the last four years. In the period 2002–2005 the rate of exceedances of the maximum limit values for indicators with health significance in water systems in larger areas was below 1 % and that in smaller areas ranged between 1.3 % and 2 %.

Distribution of the population by the rate of exceedances of the limit values for various indicators is shown in Fig. 5.2c. Almost 6.4 million (67 %) population were supplied with drinking water from systems where no maximum limit value was exceeded in 2005. On the other hand, 80 thousand inhabitants were supplied with water where the maximum limit value was exceeded for at least one indicator in all samples analyzed. Sixty-six water systems supplying 22,000 inhabitants had a temporary derogation granted for an indicator while water from other ten systems supplying 1,300 inhabitants was fully or partially prohibited for use as drinking water in 2005.

In the Czech Republic, 42 %, 30 % and 26 % of the population are supplied with drinking water produced from groundwaters, surface water sources and mixed sources, respectively (see Fig. 5.3). In 2002–2005, the maximum limit values were relatively most frequently exceeded for drinking water produced from groundwaters.

In larger areas, apart from failure to comply with the recommended water hardness (Ca + Mg) range recorded for more than half of samples analysed, the limit values were exceeded most frequently for iron (7.3 %) and trichloromethane (chloroform) (3.3 %). As for microbiological quality indicators, the limit values were most frequently exceeded for colony count at 36 °C (4.4 %), coliform count (1.5 %) and colony count at 22 °C (1.4 %). When considering the indicators with health significance, the maximum limit value was exceeded most frequently for the pesticide Atrazin (3.9 %).

In smaller areas, failure to comply with the recommended water hardness range was recorded for 73 % of samples analysed. The limit values were often exceeded for the following indicators: pH (16 %), iron (9.3 %) and manganese (6.4 %), and the following microbiological quality indicators: coliform count (8.1 %) and colony count at 36 °C (7.2 %). When considering the indicators with health significance, the maximum limit value was most frequently exceeded for nitrates (5.8 %) and the pesticides Desethylatrazin (7.4 %) and Atrazin (2.3 %). As for microbiological quality indicators, the maximum limit value was most frequently exceeded for enterococci (3.7 %) and Escherichia coli (2.9 %) (Fig. 5.4a Fig. 5.4b Fig. 5.4c). The limit value for trichloromethane is more frequently exceeded in larger areas while the limit values for most other drinking water quality indicators are more frequently exceeded in smaller areas.

The highest health risk is posed by nitrates and trichloromethane. In 2005 the presence of nitrates was detected in nearly all of the monitored areas (99.9 %). The maximum limit value (50 mg/l) was exceeded in 1,153 of 31,743 analyzed samples. In 234 areas the mean concentration ranged between 50 and 113 mg/l, i.e. was as high as or higher than the maximum limit value for this indicator (these areas supply 67,000 population and only two of these are larger areas supplying more than 5,000 population).

In 2005, trichloromethane (chloroform) was detected in drinking water samples from 3,056 (75.7 %) areas. In 26 areas supplying a total of 81,000 population, the mean concentration of chloroform was not lower than the limit value of 30 µg/l (5 of these areas were larger areas supplying more than 5,000 population).

Health significance of drinking water calcium and magnesium is currently of concern. Based on the monitoring data, only 6 % of the population (Fig. 5.5) are supplied with drinking water with the recommended optimal magnesium concentration, i.e. 20–30 mg/l. Water supplied to most of the population (91 %) from public water systems is low in magnesium whose levels are below the recommended lower limit. Water optimal in calcium (40–80 mg/l) is available to 20 % of the population, while 32 % of the population are supplied with water too high in calcium and water too low in this element is distributed to 48 % of the population. Water optimal in hardness (2–3.5 mmol/l) is supplied to 28 % of the population, softer water is distributed to 61 % of the population and harder water is available to 11 % of the population.

The presence of natural radionuclides in drinking water results in an effective dose of 0.05 mSv/yr on average, a substantial part of which is ascribed to the presence of radon (0.04 mSv/yr). Mean irradiation by radon from drinking water is about 100 times as low as irradiation by radon migrating into homes from the ground.

5.4 Assessment of exposure to selected contaminants

The population exposure from drinking water was assessed for selected contaminants (arsenic, chloroethene, nitrites, nitrates, aluminium, cadmium, manganese, copper, nickel, lead, mercury, selenium, trichloromethane), using exposure limits recommended by the World Health Organization or US Environmental Protection Agency (see Annexe). Based on the health and lifestyle questionnaire survey HELEN, daily consumption of water from the public water supply system was estimated to be 1 litre. Exposure in each of the supplied areas was calculated from the annual median concentration and 90th percentile of concentrations of the given contaminant. The mean exposure for all areas was weighed by the number of the supplied population.

In the Czech Republic, nitrates are clearly predominant among the drinking water contaminants entering the body, with their intake reaching 6.1 % of the exposure limit (5.9 % for larger areas and 6.6 % for smaller areas). For a higher than mean estimate of exposure (based on the 90th percentile of concentrations), 7.7 % and 8.2 % of the exposure limit were reached in larger and smaller areas, respectively. Exposure slightly above 1 % of the exposure limit was determined for trichloromethane. Exposure to nitrates remains more or less unchanged while exposure to trichloromethane decreased from 1.9 % to 1 % (Fig. 5.6). As concentrations of the other monitored contaminants are often close to or below the detection limit of the analytical method used, the exposure level is difficult to assess; nevertheless, it can be stated that it falls below 1 % of the exposure limit. Distribution of exposure to nitrates and trichloromethane by area is represented in Figures 5.7a and 5.7b. Based on exposure levels calculated for different areas, the arithmetic mean for each district weighed by the population number was calculated. Distribution of the population by exposure to drinking water contaminants is shown in Fig. 5.8. Exposure to nitrates from drinking water reaches more than 10 % of the allowable daily intake in 25 % of the population in the Czech Republic while exposure to other contaminants remains below 10 % of the allowable daily intake. Acute health damage caused by the monitored contaminants was not observed.

5.5 Cancer risk assessment

The linear no-threshold dose-response model based on the health risk assessment method was used for calculating the theoretical incremental cancer risk from chronic exposure to drinking water contaminants. Based on Decree 252/2004, the following contaminants were selected as drinking water quality indicators to be monitored: 1,2-dichloroethane, benzene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, bromodichloromethane, bromoform, chloroethene (vinyl chloride), dibromochloromethane, indeno[1,2,3-cd]pyrene, tetrachloroethene and trichloroethene. Data on carcinogenic potential of the contaminants (oral slope factors) were taken from the US EPA guidelines.

Two incremental cancer risk estimates were calculated, i.e. the minimum risk estimate Rmin (values below the detection level were considered as zero) and the maximum risk estimate Rmax (values below the detection limit were considered as equal to the detection limit). The ranges of mean Rmin and Rmax values for the monitored indicators weighed by the population number of each area supplied are represented in Fig. 5.9. The incremental cancer risk from chronic drinking water exposure does not exceed 10-7 for any of the chemicals monitored, with the maximum risk estimate Rmax ranging between 10-8–10-7 for bromodichloromethane, chlorethene (vinyl chloride), dibromochloromethane, tetrachloroethane and trichloroethene. The overall incremental cancer risk estimate was calculated as the sum of the incremental cancer risk estimates for all contaminants assessed. Consequently, drinking water consumption might theoretically result in an annual incremental cancer risk of about 2*10-7, i.e. 2 incremental cancer cases per 10 million inhabitants.

The exposure and risk calculations were performed using the standard procedures; nevertheless, the exposure factors used are always affected by some uncertainty due to the limited range of the contaminants monitored, interindividual variation in tap drinking water consumption and absorption of substances, etc.

5.6 Drinking water quality in public and commercial wells

Within the nationwide monitoring, data on drinking water quality from public and commercial wells are also entered into IS PiVo. In 2005, 4,313 samples were collected from 313 public wells and 1,737 commercial wells, i.e. from about a half of the registered public and commercial wells. Failure to comply with the limit values for drinking water quality indicators was observed for 5,971 of more than 94,000 samples analyzed. The maximum limit values for water quality indicators with health significance were exceeded in 743 samples analyzed.

Failure to comply with the limit values for microbiological quality indicators was observed relatively frequently: Clostridium perfringens (4.3 %), enterococci (9.2 %), E. coli (6.5 %), coliforms (18.1 %), colony count at 22 °C (11.3 %) and colony count at 36 °C (16.4 %). The most frequent failure to comply with the limit values for other indicators was observed for pH (19.4 %), iron (17.6 %), manganese (15.6 %), nitrates (8.6 %) and recommended water hardness (77 %).

5.7 Partial conclusions

The maximum limit values for indicators with health significance were exceeded in 2,384 (0.3 %) analyzed samples from the public water supply systems. Failure to comply with the limit values for sensorial quality indicators was observed in 16,500 (2 %) analyzed samples. The rate of failures to comply with the limit values decreases with the increasing number of the population supplied in the area.

In 2005, almost 6.4 million (67 %) inhabitants were supplied from the public water systems with no reported exceedance of the maximum limit values. The maximum limit value was exceeded for at least one indicator in all analyzed samples from water systems supplying 80,000 inhabitants.

The highest drinking water exposure in the Czech Republic was determined for nitrates, the levels of which reached 5.9 % and 6.6 % of the exposure limit in larger and smaller supplied areas, respectively. In larger supplied areas, 1 % of the trichloromethane exposure limit was also exceeded. Acute damage to population health caused by the monitored contaminants was not observed.

The linear no-threshold dose-response model based on the health risk assessment method was used for calculating the theoretical incremental cancer risk from chronic drinking water exposure to 12 organic contaminants. The calculations revealed that the drinking water intake might theoretically result in an annual incremental cancer risk of about 2*10-7, i.e. 2 incremental cancer cases per 10 million inhabitants.

Based on the data obtained within the nationwide water quality monitoring in 2002–2005, it can be stated that no marked changes have been observed in the quality of drinking water supplied by the public distribution systems.

Tab. 5.1 Incidence of notified waterborne infectious diseases in 2005

Diagnosis

Code*

No. of cases

Total

Transmission water**

Public water supply

Amoeboisis A06

13

not stated

0

Ankylostomosis B76.0

8

not stated

0

Enteroviral meningitis A87.0

389

0

0

Gastroenteritis vs. infections A09

2,877

1

0

Campylobacteriosis A04.5

30,268

25

0

Giardiosis A07.1

92

0

0

Other bacterial intest. infections A0.4

2,704

7

0

Legionellosis A48.1

9

5

0

Leptospirosis A27

50

8

0

Salmonellosis A02

32,927

6

0

Shigellosis A03

278

34

0

Tularaemia A21

83

18

0

Viral intest. infections A08

3,670

3

0

Viral hepatitis A B15

322

0

0

Typhoid fever A01

3

0

0

Total

73,700

107

0

* ICD, 10. revision
** not solely drinking water


Fig. 5.1 Distribution of supplied population and drinking water samplings by size of supply area, 2005
Fig. 5.2a Drinking water quality by size of supply area, 2005
Fig. 5.2b Exceeded limit values in supply areas (below 5,000 and over 5,000 population) in 2002–2005
Fig. 5.2c Distribution of the supplied population by the maximum number of limit value exceedances for same indicator, 2005
Fig. 5.3 Distribution of the population by type of crude water source, 2005
Fig. 5.4a Microbiological and biological indicators of drinking water quality, 2005
Fig. 5.4b Drinking water quality in consumer network, 2005 chemical and physical indicators with limit value
Fig. 5.4c Drinking water quality in consumer network, 2005 chemical and physical indicators with maximum limit value
Fig. 5.5 Population distribution by magnesium and calcium concentrations in drinking water, 2005
Fig. 5.6 Contribution of drinking water to population exposure to selected contaminants, 2002–2005
Fig. 5.7a Contribution of drinking water to population exposure to nitrates, 2005
Fig. 5.7b Contribution of drinking water to population exposure to trichloromethane, 2005
Fig. 5.8 Distribution of the population by the exposure to contaminants from drinking water, 2005
Fig. 5.9 Theoretical estimate of relative cancer risk increase from drinking water intake, 2005

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