5. RESULTS OF SUBSYSTEM 2: HEALTH CONSEQUENCES AND RISKS RELATED TO POLLUTION OF DRINKING WATER |
5.1 Organization of the monitoring activities
Work on the tasks for 1999 took place in all 30 selected localities. The Public Health Centers in Litoměřice and Pardubice continued in their volunteer cooperation, and the Public Health Center in Uherské Hradiště terminated its cooperation (Tab. 3.1). Drinking water quality was followed up within the framework of this subsystem and also in other important water mains networks of the cities of whose districts the municipal centers of which participate in the Monitoring System.
Each of the participating Public Health Centers had a prescribed minimum number of required complex analyses of drinking water (8 - 20) to be carried out and a minimum set of indicators to be determined. The set of drinking water quality indicators to be determined was the same for all the Public Health Centers. The required numbers of complex analyses were prescribed for each Public Health Center individually according to the size of the population supplied with drinking water from the public water mains network in each respective city under monitoring.
Drinking water quality was followed up in the water mains network as well
as at the outlets from the respective water treatment plant. Results of
the analyses performed by the producers of the drinking water (so-called
distributors) were also included in the Monitoring System. The binding
basis for the evaluation of drinking water quality is the hitherto valid
Czech national standard ČSN 757111 “Drinking Water”. The basis for evaluating
radiological indicators is the Public Notice of the State Office for
Nuclear Safety No. 184/97 Dig. on the requirements for ensuring protection
from radiation.
5.2 The monitoring of indicators of impaired health
The Monitoring System is focused on the notification of selected infectious diseases potentially transmissible through contaminated water and on the registration of eventual poisonings caused by chemical contamination of drinking water. Information is obtained from the epidemiological information system EPIDAT and through direct notification by collaborating Public Health Centers. From the analysis of the situation it can be said that there was not one confirmed case of infection or poisoning which could be attributed to the consumption of water from the public water networks under follow-up. Of the 32 667 cases of infectious diseases potentially transmissible by way of water (so-called waterborne diseases) registered in the system EPIDAT in the districts under monitoring, in only 64 cases was water found to be the carrier. This was demonstrated either by laboratory tests or epidemiologically that not in a single case was drinking water from the public water mains under monitoring in question. In most cases, the water from private wells was in question or the infection was acquired during outdoor bathing or swimming. In several cases the infection was acquired abroad (Egypt, India, Vietnam, Syria, Pakistan, Thailand, Kenya). Likewise, from reports by collaborating Public Health Centers it can be said that in the districts under monitoring a single case of infection through drinking water from the public water mains under monitoring was not demonstrated.
From reports that have been sent in by the Public Health Centers it can
also be seen that in the districts under follow-up there was no demonstrated
case in which intake of water from public water mains under monitoring
was branded the source of infection or poisoning.
5.3 Drinking water quality
Through the analysis of 7 577 samples of drinking water taken in 1999, more than 177 471 records on individual indicators of drinking water quality in the public water mains under monitoring were obtained in all the districts under follow-up. The limits for quality indicators important to health, the maximum limit value (NMH) and the limit value of reference risk (MHPR) were exceeded in 486 cases (0.27 %). The limit values (MH) of quality indicators mostly characterizing the organoleptic properties of drinking water were not met in 3 336 findings (1.9 %). In all, 9 509 cases were registered in which the limit values of quality indicators were exceeded (8.4 %). From a comparison of values obtained in the course of 1994 through 1999 it is apparent that a decrease in the proportion of exceeded limit values in indicators limited by NMH or MHPR from 0.80 % to 0.27 % occurred, no outstanding changes occurring in the other indicators.
The evaluation of the quality of the drinking water classified according to the character of the source of raw water from which it was produced, is presented in Fig. 5.1. The meeting of recommended values of quality indicators is still the best in water produced from underground sources, while in indicators significant for health the frequency of exceeding NMH or MHPR, just as in previous years, was the lowest in drinking water produced from surface water sources.
The evaluation of the quality of drinking water in the public mains network of cities under monitoring is documented in Fig. 5.2a - 5.2e. From among the biological and microbiological indicators of quality, the limit values for coliform bacteria were most frequently exceeded, although the decrease in the frequency of their detection observed in the years 1996 through 1998 was likewise confirmed in 1999. For indicators with limit values having the character of a recommended value (DH) or of an indicative value (IH), the results obtained in 1999 are comparable with those from previous years (Fig. 5.2b). As regards indicators influencing the organoleptic properties of water (Fig. 5.2c), the exceeding of the limit values of aluminum and manganese content showing a continued decreasing tendency in 1999. The situation with the indicators important to health in the water mains networks of the cities under follow-up is described in Fig. 5.2d. The frequency of exceeding of the limit values for selenium from 1997 (3.10 %) has dropped to 0.52 % in 1999. In the case of chloroform the decrease stopped, in 1999 there was obtained the same value as in 1998 (3.7 %). By comparing with previous years, in 1999 any exceeding of NMH for beryllium concentration was not found. In comparison with the year 1998 the number of findings of exceeded limit values in dichlorobenzenes (from 0.74 % to 1.79 %) and nonpolar extractable compounds (from 0.37 % to 1.85 %) has increased.
Just as in previous years, also in 1999 a higher frequency of non-conformation with limit values for active chlorine content was detected (Fig. 5.2e). Herein is evaluated the failure to meet the limit value for the minimum content of 0.05 mg Cl/l, as well as the exceeding of the recommended maximum chlorine content, 0.3 mg Cl/l (Fig. 5.2e). Likewise, the proportion of hyperchlorinated water at the outlets of water treatment plants has been decreasing in recent years, in 1999 it reached the value of 45 %. However, the frequency of not meeting the minimum chlorine content in the distribution networks in 1999 has risen again to over 20 %.
In water mains networks of the individual cities under monitoring (Fig. 5.3) the indicators most important to health, NMH and MHPR, were exceeded most often in Svitavy (3.9 %), Ústí n/L (3.2 %) and Příbram. On the other hand, no exceeding was found in nine cities (Benešov, České Budějovice, Hodonín, Hradec Králové, Jindřichův Hradec, Kroměříž, Mělník, Prague and Znojmo). In summary, nonconformity with the limit value in at least one indicator limited by NMH or MHPR was found in 2.9 % of samples analyzed.
In Tab. 5.1 the statistical evaluation of trends is presented which refers to not meeting the limit values of selected indicators of drinking water quality in public water mains networks of the cities under monitoring in the years 1994 through 1999. The selection of the evaluated indicators was carried out in view of their public health importance and the revealed frequency of not keeping with the limit values. A statistically significant increase in not keeping with limit values of chlorine content was found in Olomouc (from 4 % in 1994 to 18 % in the year 1999) and a repeated correlation in Ústí n/O (from 0 % to 36 %). Significant is also the increased frequency of exceeding the NMH for chloroform concentrations in Liberec. A significant decrease came about in 27 cases and of these in 15 there was a repetition of the correlation found in the previous year 1998. In the evaluation of the sum of the cities under monitoring, a decrease in the proportion of exceeding the limit values in enterococci and in coliform bacteria was found. Newly was found a decrease in findings of fecal coliform bacteria, too.
Tab. 5.1 |
Trends of limit values excess of selected consequential indicators of quality in public water supplies of cities under Monitoring system, 1994 - 1999 (Selection of indicators follow to health consequence and frequency of limit values excess) |
Evaluation of the trends in nonconformity with individual types of limit values in the public water mains networks of the cities under monitoring over the period of routine operation of the Monitoring system (1994 through 1999) is presented in Tab. 5.2. In the case of the most important indicators limited by NMH or MHPR, no significant increase was found, a decrease having occurred in 13 cities. In indicators limited by MH a significant increase was found in Děčín and Ústí n/O, a decrease being registered in 13 cities. The proportion of cases of not keeping with recommended or indicative values increased significantly in six cities, a decrease being recorded in two.
Tab. 5.2 | Drinking water quality in public water supplies of cities under Monitoring System, 1994 - 1999 |
In 1999 the NIPH survey conducted within the framework of this Subsystem, the objective of which is the follow-up of selected by-products of disinfection in the water mains networks of the cities under monitoring. Followed up are substances recommended by WHO (Guidelines for Drinking Water Quality, Geneva 1993) and included in an EU directive (Council Directive 98/83/EC) and in a Public Notice being prepared by the Ministry of Health of the Czech Republic: trihalogen methanes (trichloromethane, bromodichloromethane, dibromochloromethane and tribromomethane), bromates and chlorites. Samplings were carried out according to a time schedule set beforehand, three times a year (February, May, October), by the staff of Public Health Centers, and analyses of the samples were performed by the laboratory of the Research group for drinking water at the NIPH. In all, 98 records were obtained on the occurrence of each of the substances followed up in drinking water distributed in water mains networks of the cities under monitoring. WHO and EU requirements were met in 100 % of the samples taken. The fact that these contaminants have been newly included in the set of indicators of drinking water quality, merits their further follow-up.
5.4 Assessment of exposure to selected pollutants
In selected contaminants (barium, chloroform, nitrites, nitrates, hexachlorobenzene, aluminum, cadmium, manganese, copper, nickel, lead, mercury, selenium, tetrachloromethane, zinc and iron) for which there are established exposure limits, the population exposure from the intake of drinking water was assessed. The starting point of the assessment was the assumption that on the average a human drinks one litter of drinking water from the public water supply per day (Summary Report 1995). The acceptable daily intake (ADI) was applied as the exposure limit. Only in such cases where the ADI was not established (manganese, selenium), the US EPA limit (RfD) was applied. The results are presented in Fig. 5.4a as the total population exposure for the median and 90% quantile of the content of contaminants in the public water supply under monitoring. Just as in the whole previous period, exposure to nitrates unequivocally dominates (median = 7.7 % ADI). The median of exposure to barium is 1.4 % ADI. Exposure determined from 90% quantile values moderately exceeded 1 % of the exposure limit, besides the above mentioned contaminants, also in the case of chloroform, nickel and lead. Often the concentration levels of the other contaminants in drinking water do not reach the detection limit of the analytical method employed (in more than 50 % of cases). Exposure to such contaminants cannot be evaluated quantitatively and they are not presented in Fig. 5.4a.
The evaluation of exposure in relation to the size of the population supplied by each water mains network is documented in Fig. 5.4b. In the case of nitrates, just as in 1998, less than 15 % of the inhabitants of the cities under monitoring had consumed more than 10 % of the ADI through the intake of drinking water. In other cases the median exposure did not exceed 10 % of the exposure limit in any of the cities under monitoring. The results from preceding years, 1994 through 1998, are very similar and with no marked changes.
In Tab. 5.3 the evaluation of trends in the exposure of the inhabitants of the cities under monitoring to selected pollutants through the intake of drinking water in the period of 1994 through 1999 is presented. Evaluated were important pollutants for which the exposure limits were set down and the existence of which in the aggregation for all the cities under monitoring exceeded, in at least one year of monitoring, the value of 1 % of the exposure limit. 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 rejected. In the case of barium, a statistically significant decrease in exposure was recorded in Hodonín (repeated correlation in the past two years). As regards nitrates, a significant increase in Havlíčkův Brod, Hodonín (repeatedly), Kolín, Kroměříž (repeatedly) and Mělník was registered. To the contrary, a significant decrease was found in Havlíčkův Brod, Děčín (repeatedly), Jihlava, Most (repeatedly), Ostrava (repeatedly), Sokolov (repeatedly), Šumperk (repeatedly) and Žďár n/S. In the case of other pollutants evaluated (manganese, nickel, lead and selenium), in question is an increase or decrease at the level of tenths of a percent in the range of up to 1 % ADI at most.
Tab. 5.3 |
Exposure trends of citizens in cities of Monitoring System to selected consequential contaminants from drinking water ingestion, 1994 - 1999 (Evaluation of contaminants with exposure higher than 1 % exp. limit only) |
In consequence of the presence of natural radionuclides in drinking water the population was exposed with the value of an average dose equivalent of 0.02 mSv per year. The ingestion of drinking water represents about 1 % of the total irradiation in the population from natural sources.
5.5 Carcinogenic risk assessment
For calculating the theoretical estimate of the probability of an increase
in the number of tumor affections due to chronic exposure to selected pollutants
by ingesting drinking water, a linear non-threshold model of dose-response
relationships was applied. The following were assessed: 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. For each city under monitoring an estimate
of the contribution to the increased risk in the number of tumor affections
through each of the contaminants was calculated separately. In cases when
most of the results of pollutant analyses were below the detection limit,
the contribution of such a compound was not included in the evaluation.
The overall estimate of increased risk of tumor diseases in each of the
localities was then expressed as the sum of the contributions of all the
pollutants assessed. The thus calculated estimates of the risk for each
city are presented in Fig. 5.5. Consumption of drinking water
could have contributed in the individual cities to the increase in cancer risk in the
range of one case a year per one million to one thousand million of the
population. In all the cities under monitoring together (3.5 million inhabitants)
less than one additional case of tumor disease attributable to the consumption
of drinking water from the public water mains could be expected.
5.6 Partial conclusions
In 1999 no case of infection or poisoning was confirmed, which could be attributed to the consumption of drinking water from the public water mains of the cities under monitoring.
Just as in the previous year, the most frequent exceeding of the limit values of chemical pollutants important to health, was found in chloroform. As regards biological and microbiological indicators of drinking water quality, this was in coliform bacteria. Just as in previous years so in 1999, the frequency of nonconformity with the limit value of active chlorine content in the distribution networks was found to be rather high.
The exposure of the population to selected inorganic and organic substances does not pose any significant risk. By the consumption of drinking water 7.7 % of the exposure limit in nitrates is drawn upon, in barium 1.4 % of the limit, and in other pollutants this does not exceed 1 % of the limit. A theoretical estimate of the probability of increased tumor disease incidence as a result of chronic exposure to 15 organic substances and to compounds of arsenic by the ingestion of drinking water has shown that in all of the cities under monitoring together, in 1999, it is possible to expect less than one additional case of tumor disease caused by the ingestion of drinking water from the public water supply.
The statistical evaluation of temporal trends in the indicators monitored during the period of 1994 through 1999 in the cities under monitoring has shown that in the vast majority of cases the hypothesis of random distribution of the values followed up is not rejected. From this fact it can be stated that in the period under follow-up there did not take place any significant changes in the quality of drinking water in the distribution networks of the cities under follow-up.