5. RESULTS OF SUBSYSTEM 2: HEALTH CONSEQUENCES AND RISKS RELATED TO POLLUTION OF DRINKING WATER |
5.1 Organization of the monitoring activities
Working on the tasks for 1998 took place in all 30 selected localities; the Public Health Center in Tábor which terminated its cooperation was replaced by that in Jindřichův Hradec. The Public Health Centers in Litoměřice and Uherské Hradiště continued in their volunteer cooperation and the Public Health Center in Pardubice joined in newly (Tab. 3.1). Drinking water quality is followed up within the framework of this subsystem also in other important cities or district water mains networks 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 minimum 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 is followed up in the water mains network as well as at the outlets from the respective water treatment plant. Into the Monitoring System there are also included results of analyses performed by the producers of the drinking water (so-called distributors). The binding basis for the evaluation of drinking water quality is the hitherto valid Czech national standard ČNS 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.
A constituent of the monitoring activity is also the immediate reporting of cases of disrepair altering water quality which could endanger the health of the population, or reporting changes that have led to measures taken by the Public Health Service, including the removing of the water mains from operation.
5.2 The Monitoring of impair indicators of 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 the Public Health Centers. From the analysis of the situation it can be said that was not one confirmed any case of infection or poisoning which could be attributed to the consumption of water from the public water networks under follow-up. Of the 33 308 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 69 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 study in question. In most cases, the water from private wells was in question or the infection was acquired during outdoor bathing and swimming. In several cases the infection was acquired abroad (Tunisia, Egypt, India, etc.). Likewise, from reports by collaborating Public Health Centers it follows that in the districts under monitoring there was not demonstrated a single case of infection through drinking water from the public water mains under monitoring.
From reports that have been sent in by the Public Health Centers it also follows 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 to be the source of infection or poisoning.
5.3 Drinking water quality
Through the analysis of 8 343 samples of drinking water taken in 1998, more than 188 thousand 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 597 cases. The limit values of quality indicators mostly characterizing the organoleptic properties of drinking water were not met in 3 370 findings. In all, 10 420 cases were registered in which the limit values of quality indicators were exceeded. From a comparison of values obtained in the course of 1994 through 1998 it is apparent that a decrease in the proportion of exceeded limit values in indicators limited by NMH or MHPR from 0.80% to 0.32% occurred, no outstanding changes occurring in the other indicators.
A fundamental 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. Of 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 and 1997 was likewise confirmed in 1998. In indicators with limit values having the character of a recommended value (DH) or of an indicative value (IH), the results obtained in 1998 are comparable with those from previous years (Fig. 5.2b). As regards indicators influencing the sensorically detectable properties of water (Fig. 5.2c), there the frequency decreased in exceeding the limit for aluminium content with a frequency of less than in 10% of samples analyzed, the exceeding of the limit values of manganese content showing a continued decreasing tendency. The situation with indicators important to health in the water mains networks of the cities under follow-up is described in Fig. 5.2d. The frequency of the exceeding of limit values for selenium from 1997 (3.10%) has dropped in 1998 to 0.65%. There was also a decrease to 3.7% in the case of chloroform. The increased frequency of exceeding the limit values for beryllium continued into 1998 and reached 1.3%.
Just as in previous years, so in 1998, 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 (0.05 mg Cl/l), as well as the exceeding of the recommended maximum chlorine content (0.3 mg Cl/l). The increase in frequency of not meeting the minimum content of active chlorine in the distribution networks has stopped, in 1998 it fell below 20%. Likewise, the proportion of hyperchlorinated water at the outlets of water treatment plants has been decreasing in recent years, in 1998 it was less than 50%.
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 (10 findings), Kroměříž (3), Sokolov (21), Havlíčkův Brod (12) and Šumperk (11). There was no exceeding found in nine cities (Benešov, České Budějovice, Hodonín, Jindřichův Hradec, Karviná, Kladno, Olomouc and Prague). Nonconformity with the limit value in at least one indicator limited by NMH or MHPR was found in 3% of samples.
In Tab. 5.1 there is presented the statistical evaluation of trends that 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 1998. 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 iron content was found in Hradec Králové (from 12 to 20%) and of chlorine in Ústí n/O (from 0 to 24%). There was a statistically significant decrease in 18 cases over the five years of follow-up. In the evaluation of the sum of cities under monitoring there was found a decrease in the proportion of exceeding the limit values in enterococci (from 1.3 to 0.5%) and in coliform bacteria (from 4.5 to 1.8%).
The year 1998 was the final year of working on the partial task of Subsystem 2 the objective of which was to detect the occurrence of selected trace elements in drinking water from the public supply in districts under monitoring in the Czech Republic. In the period of 1995 through 1998 1 334 results for each element under follow-up were obtained. Only 25 samples, i.e. 1.9% contained more than 300 µg B/l; concentrations exceeding the limit value set by European legislation (1 000 µg B/l) were found in four samples. Although the results obtained confirm that findings of this element in drinking water are only singular, it is purposeful to follow-up the boron content because most washing powders contain optical whitening agents based on compounds of boron. The limit value for beryllium content (1 µg/l) which is being introduced into the legislation of the Czech Republic, was exceeded in only nine cases (0.7%). Results show that mainly in small water mains systems with a minimum of water treatment, there exists a direct link between the beryllium content in drinking water and the content of this element in the geological substratum. Results of lithium findings confirmed that this element occurs mostly in low concentrations in the drinking water of the Czech Republic. Almost 75% of the samples contained less than 10 µg Li/l and in only less than 5% of the samples was there more than 50 µg Li/l. The newly recommended limit for nickel content (20 µg/l) was exceeded in 20 cases (1.5%). The exceeding of the limit for antimony (5 µg Sb/l) that is being introduced was found in 2 cases (2.2%). In 1334 samples analyzed for vanadium content, a level of more than 10 µg V/l was found in only eight cases. Therefore, the inclusion of this element among indicators of drinking water quality in the legislative ruling which is in preparation, is not necessary.
In 1998 the NIPH survey conducted within the framework of Subsystem 2 continued, the objective of which is the follow-up of selected by-products of disinfection, the so-called trihalogen methanes (THM): trichloromethane (chloroform), bromodichloromethane, dibromochloromethane and tribromomethane (bromoform). In all, 69 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. The limit value of the sum of THM (according to the rule 98/83/EC) was met in 100% of samples taken. However, the fact that there has been demonstrated the mere presence of these serious contaminants merits their further follow-up.
5.4 Assessment of exposure to selected pollutants
In selected contaminants (barium, chloroform, nitrites, nitrates, hexachlorobenzene, aluminium, 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 evaluation 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), was the US EPA limit (RfD) 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 previous period, in 1998 exposure to nitrates unequivocally dominates (median = 7.5% ADI). The exposure median for barium is 1.3% ADI. Exposure determined from 90% quantile values exceeded 1% of the exposure limit, besides the above mentioned substances, also in the case of chloroform, cadmium, nickel and lead. Often the concentration levels of other treated contaminants in drinking water do not reach the detection limit of the analytical method employed. Exposure to such contaminants in essence cannot be evaluated quantitatively, but it can be said that it is less than 1% of the exposure limit.
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 less than 15% of the population living in 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 1997, are very similar and with no marked changes.
In Tab. 5.2 there is presented the evaluation of trends in the exposure of the population in the cities under monitoring, to selected pollutants through the intake of drinking water in the period of 1994 through 1998. Assessed were important pollutants for which there are set exposure limits 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 there was not been found any correlation for the majority of the data and that the hypothesis of random distribution was not rejected. In the case of lead there was recorded a statistically significant increase in exposure in Havlíčkův Brod only (from 0.2 to 1.1% ADI) but a decrease in Prague, Hradec Králové and Příbram. As regards nitrates, there has been registered a significant increase in Hodonín (from 9.5 to 18.1% ADI) and in Kroměříž (from 3.3 to 5.5% ADI). To the contrary a significant decrease was found in Děčín, Most, Ostrava, Sokolov and Šumperk. There occurred a significant increase in exposure to nickel in two cities, in Klatovy and Olomouc. Generally, these increases in exposure, with the exception of nitrates, have materialized in the region of under 1% ADI. A statistically significant decrease in exposure was found in 26 instances and generally applied to selenium, barium, manganese, and the cases already mentioned.
In consequence of the presence of natural radionuclides in drinking water the population was exposed with 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-dichloroethene, 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 analyses of a pollutant were below the detection limit, the contribution of such a chemical substance was not included in the evaluation. The overall estimate of increased risk of tumor diseases in each of the cities was then expressed as the sum of the contributions of all the pollutants assessed. Calculations carried out in relation to the numbers of inhabitants supplied from the individual public water mains network are presented in Fig. 5.5 for each individual city. 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 (3.4 million inhabitants) it is possible to expect, form the exposure in 1998, less than one additional case of tumor disease attributable to the consumption of drinking water from the public water mains.
5.6 Partial conclusions
In 1998 there was no case of infection or poisoning 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 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. Regardless of improvement, there was still found a rather high frequency of nonconformity with the limit value of active chlorine content in the distribution networks.
The exposure of the population to selected inorganic and organic substances does not pose any significant risk. By the consumption of drinking water 7.5% of the exposure limit in nitrates is drawn upon, in barium 1.3% 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 1998, 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 developmental trends in the indicators monitored during the period of 1994 through 1998 in the cities under monitoring has shown that in the vast majority of cases the hypothesis of random distribution of the values followed up cannot be 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.
Tab. 5.1 Trends of limit values excess of selected consequential indicators of quality
in public water supplies of cities under follow-up, 1994 - 1998
(Selection of indicators follow to health consequence and frequency of limit values excess)
City |
Excess of limit value [%] |
|||||||
Entero- |
Bacteria |
Bacteria |
Organisms |
Chlorine |
Chloro- |
Alumi- |
Iron |
|
Benešov |
0 |
0 |
n |
0 |
n |
0 |
0 |
n |
Brno |
n |
0 |
- |
n |
n |
0 |
0 |
- |
České Budějovice |
n |
n |
n |
0 |
n |
n |
0 |
n |
Děčín |
n |
- |
- |
n |
n |
0 |
n |
n |
Havlíčkův Brod |
n |
n |
n |
n |
n |
0 |
n |
n |
Hodonín |
n |
0 |
n |
0 |
- |
0 |
0 |
n |
Hradec Králové |
- |
n |
n |
n |
n |
0 |
n |
+ |
Jablonec n/N |
n |
n |
n |
n |
n |
n |
n |
n |
Jihlava |
n |
n |
n |
n |
n |
n |
0 |
n |
Jindřichův Hradec |
0 |
0 |
n |
0 |
- |
0 |
0 |
- |
Karviná |
n |
0 |
n |
0 |
- |
n |
n |
n |
Kladno |
n |
0 |
n |
0 |
n |
0 |
0 |
n |
Klatovy |
n |
n |
n |
n |
n |
n |
n |
n |
Kolín |
n |
0 |
n |
n |
n |
n |
0 |
n |
Kroměříž |
0 |
n |
n |
n |
n |
n |
0 |
n |
Liberec |
n |
n |
n |
n |
n |
n |
n |
n |
Litoměřice |
n |
n |
- |
0 |
n |
0 |
0 |
n |
Mělník |
n |
n |
- |
0 |
n |
0 |
0 |
0 |
Most |
- |
0 |
0 |
n |
n |
n |
n |
n |
Olomouc |
0 |
0 |
0 |
0 |
n |
0 |
0 |
n |
Ostrava |
- |
n |
n |
n |
n |
- |
n |
- |
Pardubice |
n |
n |
n |
n |
n |
n |
n |
n |
Plzeň |
n |
n |
n |
n |
n |
n |
n |
n |
Praha |
n |
0 |
n |
n |
n |
n |
n |
n |
Příbram |
n |
n |
n |
n |
n |
n |
n |
n |
Sokolov |
n |
n |
n |
n |
n |
n |
n |
n |
Svitavy |
n |
n |
n |
0 |
n |
0 |
0 |
n |
Šumperk |
n |
n |
n |
n |
n |
0 |
n |
- |
Uherské Hradiště |
0 |
n |
- |
n |
n |
n |
0 |
n |
Ústí n/L |
n |
n |
n |
0 |
n |
n |
n |
n |
Ústí n/O |
n |
n |
n |
n |
+ |
0 |
n |
n |
Znojmo |
n |
n |
n |
0 |
n |
- |
0 |
n |
Žďár n/S |
n |
n |
n |
n |
n |
n |
n |
n |
Czech Republic |
- |
n |
- |
n |
n |
n |
n |
n |
Remark:
“+” statistically meaningful increase
“-” statistically meaningful decrease
“0” excess of limit value was not found in a period under monitoring
“n” temporal correlation was not found, random distribution of values in monitoring period
Tab. 5.2 Exposure trends of citizens in cities under follow-up to selected consequential
contaminants from drinking water ingestion, 1994 - 1998
(Selection of contaminants with exposure higher than 1% exp. limit only)
City |
Daily intake [% exp. limit] |
|||||
Barium |
Nitrates |
Manganese |
Nickel |
Lead |
Selenium |
|
Benešov |
n |
n |
- |
n |
n |
n |
Brno |
n |
n |
- |
n |
n |
- |
České Budějovice |
n |
n |
n |
n |
n |
n |
Děčín |
- |
- |
n |
n |
n |
n |
Havlíčkův Brod |
n |
n |
n |
n |
+ |
n |
Hodonín |
- |
+ |
- |
n |
n |
n |
Hradec Králové |
n |
n |
n |
n |
- |
n |
Jablonec n/N |
n |
n |
n |
n |
n |
n |
Jihlava |
n |
n |
n |
n |
n |
n |
Jindřichův Hradec |
n |
n |
n |
n |
n |
- |
Karviná |
n |
n |
- |
n |
n |
n |
Kladno |
n |
n |
n |
n |
n |
n |
Klatovy |
n |
n |
n |
+ |
n |
n |
Kolín |
n |
n |
- |
n |
n |
n |
Kroměříž |
n |
+ |
n |
n |
n |
n |
Liberec |
n |
n |
n |
n |
n |
n |
Litoměřice |
n |
n |
- |
n |
n |
n |
Mělník |
n |
n |
- |
n |
n |
n |
Most |
n |
- |
- |
n |
n |
n |
Olomouc |
n |
n |
n |
+ |
n |
n |
Ostrava |
n |
- |
- |
n |
n |
n |
Pardubice |
|
n |
n |
n |
n |
n |
Plzeň |
n |
n |
- |
n |
n |
n |
Praha |
n |
n |
n |
n |
- |
n |
Příbram |
n |
n |
n |
n |
- |
n |
Sokolov |
n |
- |
- |
n |
n |
n |
Svitavy |
n |
n |
n |
n |
n |
n |
Šumperk |
n |
- |
n |
n |
n |
n |
Uherské Hradiště |
n |
n |
n |
n |
n |
n |
Ústí n/L |
n |
n |
n |
n |
n |
n |
Ústí n/O |
n |
n |
n |
n |
n |
- |
Znojmo |
n |
n |
- |
n |
n |
n |
Žďár n/S |
- |
n |
n |
n |
n |
n |
Czech Republic |
n |
n |
n |
n |
n |
n |
Remark:
“+” statistically meaningful increase
“-” statistically meaningful decreases
“n” temporal correlation was not found, random distribution of values in monitoring period