5. RESULTS OF SUBSYSTEM 2: HEALTH EFFECTS AND RISKS RELATED TO DRINKING WATER POLLUTION

5.1 Organisation of monitoring activities

In 2001, subsystem II activities were carried out in all 30 selected areas. Public Health Centres Litoměřice and Pardubice continued their volunteered participation (Table 3.1). Drinking water quality in districts or cities which serve as administrative centres for participants of this monitoring project is likewise monitored as part of the subsystem.

Each of the participating Public Health Centres was required to carry out a minimum quota of complete drinking water analyses (8–20), depending on the size of the population supplied by the public water mains network, and maintain a prescribed set of water quality indicators.

Drinking water quality is monitored both in the water supply network and at the outlet of water treatment plants. Data from analyses performed by drinking water producers (distributors) were included among the other Monitoring System data. Prior to 31. 12. 2000, drinking water quality was assessed according to Czech National Standard CSN 757 111 “Drinking Water”. Since 1. 1. 2001, public health requirements for drinking water quality have been set by Regulation No. 376/2000 of the Ministry of Health, Czech Republic, which respects WHO guidelines from 1993 and partially correlates with Guideline No. 98/83/EC for Quality of Water Intended for Human Consumption. Evaluation of radiological indicators is based on Ordinance No. 184/1997 of the State Office for Nuclear Safety on Requirements for Protection from Radiation.

The Monitoring System includes the immediate reporting of water quality emergencies that may constitute a threat to population health and changes in water quality requiring intervention by Public Health Authorities (water supply outage, for example).

5.2 Monitoring health impairment indicators

The monitoring of health-associated indicators is based on reporting the incidence of selected infectious diseases potentially transmissible through contaminated water and recording cases of poisoning resulting from contamination of drinking water by chemicals. Information is obtained from the EPIDAT epidemiological information system and through direct reports from participating Public Health Centres. Analysis of the present situation shows that no cases of infection or poisoning can be attributed to consumption from any of the monitored public water supply systems; water was confirmed as a vector in only 39 cases from a total of 33 938 registered instances of infection, although none of these involved drinking water from the water supplies monitored, as confirmed by laboratory and epidemiological tests. In the majority of cases these infections were attributed to water from private wells or outdoor swimming activities and several cases were acquired from abroad. Likewise, reports by participating Public Health Centres did not indicate a single case of infection or chemically linked poisoning by drinking water from any of the public water systems in the monitored districts.

5.3 Drinking water quality

In 2001, a total of 4792 analysed samples of drinking water collected from consumer tap-water or treatment plant outlets yielded 96 482 units of data on individual water quality indicators in the monitored districts. Limit values for health-associated water quality indicators – the maximum limit value (MLV) and limit value of reference risk (LVRR) – were exceeded in 121 instances (0.13 %). Limit values (LV) for indicators primarily characterising the sensory qualities of drinking water were below par in 2844 cases (2.9 %). In all, 3490 cases of exceeded limit values for indicators of quality were recorded (3.6 %). Comparison of data obtained in 1994–2001 reveals that the rate at which MLV and LVRR has been exceeded is decreasing slightly (from 0.8 % to 0.1 %) with no marked changes occurring in the other indicators. Changes in the limit values of certain drinking water quality indicators following amendments to public health legislation are effectively negligible.

The most frequent instances of exceeded limits involved drinking water from surface sources. Health-associated indicators MLV or LVRR were exceeded only sporadically in 2001.

Drinking water quality in monitored public water supplies is evaluated in Fig. 5.1a–d and Fig. 5.2. As for biological and microbiological indicators of quality, the limit values for coliform bacteria were once again the most frequently exceeded (Fig. 5.1a). In the case of indicators associated with the sensory characteristics of water (5.1b), 2001 marked a continuing trend of exceeded values for chlorine. The increased number of instances of exceeded values for iron content is primarily caused by the reduction of the legal limit from 0.3 to 0.2 mg/l. Chlorites and TOC are newly introduced indicators. Fig. 5.1c shows levels of health-associated indicators in the water supplies of the monitored cities; the documented cases of exceeded limit values represent isolated findings.

As in previous years, 2001 marked a high rate of non-compliance with limit values for chlorine. For this indicator, failure to meet the limit value for a minimum content of 0.05 mg Cl/L is recorded as well as an exceeded maximum recommended chlorine content of 0.3 mg Cl/L (5.1d). The proportion of over-chlorinated water samples collected from the outlets of water treatment plants reached 69 % in 2001, while the frequency of exceeded minimum chlorine content in water supply systems reached 40 %. However, non-compliance with chlorine limit values should be assessed in relation to other related indicators: if the microbial quality, content of chlorination by-products and sensory qualities of the resulting water are satisfactory then non-compliance with chlorine limits should not be viewed negatively. The recorded maximum chlorine values (about 2 mg/L) do not represent a direct health hazard according to current findings.

A total of 1997 samples of drinking water was collected from the water supplies of the cities monitored. Non-compliance with MLV or LVRR was detected in 21 instances. Evaluation of drinking water quality in the water supplies monitored as related to the total number of analyses is given in Fig. 5.2. MLVs and LVRRs of health-associated indicators were exceeded most frequently in Kolín, Mělník, Znojmo, Havlíčkův Brod and Šumperk. In another 20 cities these indicators were not exceeded.

Table 5.1 details the trends in non-compliance with various limit values in the public water supplies of the administrative centres monitored over the past 5 years (1997–2001). From this it is evident that there have been no significant changes in drinking water quality over the named period in the monitored water systems. Evaluation of the temporal trend by a correlation coefficient of 5 % failed to show a statistically significant increase in values of health-associated MLV and LVRR, with a decrease occurring in 3 cases. Indicators with LV were exceeded in two cities and a decrease was recorded in Ústí n. Orlicí.

In 2001, the National Institute of Public Health continued the monitoring of selected disinfectants in water supplies, a study which is part of subsystem II (Fig. 5.4). The chemicals monitored are those recommended by WHO (Guidelines for Drinking Water Quality, second edition, volume 1, World Health Organisation, Geneva 1993) and included in EU Council Directive 98/83/EC and Regulation No. 376/2000 Coll. of the Ministry of Health of the Czech Republic. These guidelines set requirements for drinking water quality and the extent and frequency of its monitoring. Samples for determining the presence of trihalogenmethanes (trichloromethane – chloroform, dibromochloromethane, bromodichloromethane and tribromomethane – bromoform), bromites and chlorites were collected as planned in February, May and October. A total of 97 results were obtained pertaining to the incidence of each monitored substance in drinking water distributed by the monitored water systems. All samples met WHO, EU and Ministry of Health (Regulation No. 376/2000 Coll.) requirements. Since these contaminants are included in the set of drinking water quality indicators their further monitoring is justified.

5.4 Assessment of exposure to selected contaminants

Population burden by contaminants in drinking water was evaluated for selected substances (arsenic, nitrates, nitrites, aluminium, chloroform, cadmium, manganese, copper, nickel, lead, mercury, selenium, tetrachloromethane, iron) which have been subject to proposed exposure limits by WHO and US EPA. Exposure assessment assumed consumption of 1 litre of tap-water per day (confirmed by NIPH HELEN questionnaire). The results are presented in Fig. 5.3a, b as the percentage of the exposure limit taken up by consumption of drinking water for the median exposure value and 90th percentile. The median value means that one half of the population in monitored cities is exposed to a specific contaminant up to the given value and 90 % of the population up to the value of the 90th percentile. As in the previous monitoring period, exposure to nitrates is predominant. This, however, reaches 6.5 % only of the acceptable daily intake (Fig. 5.3a). The exposure limit did not exceed 1 % of the acceptable daily intake (ADI) for any other substance. Exposure determined for 90 % of the population exceeded this limit for chlorine and chloroform only (Fig. 5.3b). Concentrations of the other contaminants in drinking water often do not exceed the detection limit of the analytical method used (in more than 50 % of cases). Exposure to these substances cannot therefore be assessed with accuracy, although it can be positively stated that it is lower than 1 % of the exposure limit.

Evaluation of the population burden in relation to the size of population supplied by each of the water systems is shown in Fig. 5.3c. Less than 13 % of the population in the monitored cities reached 10–20 % of ADI for nitrates through drinking water, 0.5 % reached over 20 %. Only 1.5 % of the population sample exceeded 10 % of the exposure limit for cadmium. The results for previous years are very similar.

Table 5.2 shows trends in population exposure to selected contaminants in drinking water in 1997–2001. Those contaminants for which exposure limits have been set and whose exposure in aggregate for all monitored cities had reached 1 % of the exposure limit in at least a 1 year period were evaluated. 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. A statistically significant decrease for nitrates was recorded in České Budějovice, Hradec Králové, Most, Sokolov, Svitavy and Šumperk in particular and for the all cities in general. Exposure to other contaminants comprised slight variations counted in decimals at around 1 % ADI and less.

The presence of natural radionuclides in drinking water results in an average population exposure of 0.02 mSv/r, about 1 % of total irradiation from natural sources.

5.5 Carcinogenic risk assessment

To predict probable increase in the risk of contracting cancer resulting from chronic exposure to chemicals in drinking water, a linear no-threshold dose-effect model was applied. Substances selected for monitoring were those with an available carcinogenic potency oral slope factor, chosen from indicators of water quality as set down in Regulation No. 376/2000 Coll.: 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, trichloroethene. Based on median concentrations established in the cities monitored, the contribution to increased risk of developing cancer was estimated for each contaminant. In cases where the majority of results for a given substance were below the detection limit of the analytical method used, that substance was excluded from the final assessment. 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 presented in Fig. 5.5. Consumption of drinking water represents a very low level of cancer risk in the range of 1 case annually per 1 million – 1 milliard population. Altogether, less than 1 additional case of cancer resulting from consumption of drinking water from the public water supply can 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 2001.

As in 2000, limit values for hazardous 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. Intake of nitrates reaches 6.5 % of the exposure limit and does not exceed 1 % of the limit for the other contaminants. The estimated incidence of cancer resulting from chronic exposure to 15 organic substances and compounds of arsenic and mercury in drinking water equals less than one additional case attributable to drinking water from public water supplies.

Statistical evaluation of temporal trends for selected indicators in the 1997–2001 period in the monitored cities has not disproved the random distribution hypothesis in the vast majority of cases. From this fact it may be stated that no significant changes in water quality have occurred during the period described in the water supply networks of the monitored cities.

Table 5.1 Drinking water quality in public water supplies of cities under Monitoring System, 1997-2001

 

Excess of LV [%]

Excess of MLV + LVRR [%]

City/Calendar year

1997

1998

1999

2000

2001

1997

1998

1999

2000

2001

Benešov

0.88

0.84

1.32

1.01

1.51

0.14

0.00

0.00

0.00

0.00

Brno

2.40

1.33

1.10

1.52

2.54

0.10

0.03

0.01

0.00

0.01

České Budějovice

1.07

1.33

3.45

4.85

3.17

0.24

0.00

0.00

0.13

0.10

Děčín

5.36

4.89

4.86

2.80

4.14

0.44

0.00

0.10

0.07

0.00

Havlíčkův Brod

3.09

1.11

0.85

0.31

0.65

0.07

0.46

0.09

0.00

0.24

Hodonín

2.03

0.89

1.60

1.79

1.36

0.00

0.00

0.00

0.00

0.00

Hradec Králové

2.39

2.57

3.78

3.20

3.11

0.18

0.03

0.00

0.04

0.00

Jablonec nad Nisou

4.02

2.57

1.25

1.90

1.32

0.09

0.15

0.05

0.18

0.05

Jihlava

2.02

1.58

1.95

1.13

5.26

0.18

0.02

0.05

0.38

0.13

Jindřichův Hradec

0.42

0.50

0.56

2.10

4.41

0.00

0.00

0.00

0.38

0.00

Karviná

0.82

0.73

0.83

0.74

0.16

0.05

0.00

0.09

0.00

0.00

Kladno

1.88

2.01

2.03

1.37

0.33

0.00

0.00

0.48

0.00

0.00

Klatovy

1.62

2.22

0.49

0.49

1.73

0.41

0.16

0.16

0.00

0.00

Kolín

2.25

0.84

1.55

1.10

4.26

0.17

0.34

0.56

1.25

1.16

Kroměříž

0.00

1.20

2.14

1.52

1.84

0.00

1.20

0.00

0.00

0.00

Liberec

3.30

2.05

1.48

0.43

3.62

0.28

0.22

0.15

0.48

0.10

Litoměřice

1.14

0.55

0.38

0.65

2.52

0.16

0.13

0.19

0.14

0.00

Mělník

1.39

1.91

1.43

0.67

1.19

0.00

0.21

0.00

0.00

0.79

Most

0.71

1.84

1.06

0.45

0.86

0.04

0.05

0.10

0.08

0.00

Olomouc

0.41

0.86

0.99

3.33

4.14

0.00

0.00

0.20

0.00

0.00

Ostrava

2.14

1.79

1.17

1.28

5.41

0.16

0.18

0.05

0.04

0.00

Pardubice

0.37

0.79

6.33

6.55

7.80

0.50

0.10

0.06

0.00

0.00

Plzeň

3.22

1.68

1.20

2.43

3.62

1.49

0.10

0.00

0.02

0.04

Prague

0.22

1.83

1.73

1.10

0.33

0.01

0.00

0.00

0.07

0.08

Příbram

1.97

2.55

2.92

4.84

1.09

0.43

0.36

0.75

0.22

0.00

Sokolov

3.41

3.62

2.83

2.67

0.00

0.68

0.62

0.36

0.00

0.00

Svitavy

5.37

4.30

5.22

6.30

8.22

0.58

0.96

1.03

0.19

0.00

Šumperk

0.80

0.38

0.49

0.16

1.74

0.85

0.32

0.38

0.64

0.31

Ústí nad Labem

1.16

1.17

1.49

1.52

1.78

0.14

0.17

0.56

0.51

0.00

Ústí nad Orlicí

1.74

1.82

1.77

1.39

0.85

0.27

0.12

0.24

0.12

0.00

Znojmo

2.17

3.81

4.34

2.58

8.30

0.36

0.15

0.00

0.74

0.90

Žďár nad Sázavou

0.28

0.66

1.23

1.93

0.49

0.04

0.06

0.11

0.14

0.00

Remark:
LV - limit value
MLV - maximal limit value
LVRR - limit value of reference risk
1997-2000 evaluation of the limit excess according to the Czech national standard ČSN 75 71 11 “Drinking Water”
2001 - 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, 1997-2001

City

Daily intake [% exposure limit]

Chlorine

Nitrates

Manganese

Nickel

Lead

Selenium

Chloroform

Benešov

N

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

N

Havlíčkův Brod

N

N

N

N

N

N

N

Hodonín

N

N

-

-

N

N

N

Hradec Králové

N

-

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

N

Karviná

N

N

N

-

N

N

N

Kladno

N

N

N

N

N

N

N

Klatovy

N

N

N

N

N

N

N

Kolín

+

N

N

N

N

N

N

Kroměříž

N

N

N

N

N

N

N

Liberec

+

N

N

N

N

N

N

Litoměřice

N

N

N

N

+

N

N

Mělník

N

N

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

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

N

Sokolov

N

-

N

N

N

N

N

Svitavy

N

-

N

N

+

N

N

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

N

N

N

N

Žďár nad Sázavou

N

N

N

N

N

N

N

Czech Republic

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

Fig. 5.1a Drinking water quality in consumer network, 2001 - microbiological and biological indicators
Fig. 5.1b Drinking water quality in consumer network, 2001 - indicators with limit value
Fig. 5.1c Drinking water quality in consumer network, 2001 - indicators with maximal limit value and limit value of reference risk
Fig. 5.1d Chlorine content in consumer network, 1994–2001
Fig. 5.2 Exceeding of limit values in the cities, 2001
Fig. 5.3a Population exposure to nitrates from drinking water, 1994–2001
Fig. 5.3b Population exposure to selected significant contaminants from drinking water, 1994–2001
Fig. 5.3c Distribution of the population according to the contaminant exposure from drinking water, 2001
Fig. 5.4 Selected disinfectant by-products in drinking water (trihalogenmethanes), annual arithmetic mean, 2001
Fig. 5.5 Theoretical estimate of relative cancer risk increase from drinking water intake, 1994–2001

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