12. IMPORTANCE OF THE ROUTE OF EXPOSURE TO SELECTED INORGANIC SUBSTANCES FOR THE POPULATION OF THE CZECH REPUBLIC |
Based on the results of the Monitoring System, the importance of the individual routes of exposure was estimated for selected inorganic substances, which are monitored in several subsystems, with respect to the drawing of recommended exposure limits and to the health risks of these substances. In view of the complexity of this theme, for the purpose of approximation the problem a certain simplifications were applied.
12.1 Arsenic
Anthropogenic sources of arsenic in the environment include steel foundries and metallurgy (such as metallurgy of copper), combustion of fossil fuels, in particular of low-quality brown coal, and the use of pesticides (especially insecticides); drinking water contains arsenic mainly of natural origin.
The IARC classifies arsenic in group I as a known human carcinogen. Cumulative exposure to arsenic is associated with the risk of development of bladder cancer, skin cancer and cancer of other organs. Higher exposure to airborne arsenic increases the risk of lung cancer. Data from scientific literature also proves the influence of arsenic on the increased occurrence of laryngitis and bronchitis and on the development of cardiovascular diseases.
Inhalation is considered to be a non-significant source of exposure to arsenic for the general population. However, lung cancer is considered to be the critical effect of arsenic inhalation. According to the WHO, the usual concentrations in city air range from several up to tens of nanograms per m3. The concentration of airborne arsenic in Czech cities ranged from 0,1 up to 6 ng/m3 in 2001, which represents a potential exposure up to 0.015 µg per kg and week according to a conservative scenario. This intake of arsenic is lower by three orders of magnitude than that stated by JECFA FAO WHO as a limit of ingestion exposure PTWI of 15 µg/kg/week for inorganic arsenic (arsenic in the air is mostly inorganic). Smokers are subject to increased exposure; when smoking 20 cigarettes a day, the daily exposure can increase, according to WHO, by 0.8 to 2.4 µg. Since arsenic is a carcinogenic substance, no safe inhalation exposure can be recommended. For life-long exposure to 1 µg/m3 of arsenic in the air, the WHO estimates the probability of the increased occurrence of a tumor disease at 1.5x10-3 (which is 1.5 cases per 1000 people). At the maximum concentration found in the year 2001 (6 ng/m3), the risk would be up to 1 : 100 000.
The intake of arsenic via drinking water can be substantial in locations with a high natural occurrence of arsenic in the underground water. However, the content of arsenic in the public water mains under monitoring is very low; the limit value has not been exceeded in any sample collection since 1994 (with the exception of 1997), and in 2001, the median concentration in all water mains monitored was 0.5 µg/L. In 2001, the mean exposure to arsenic from drinking water, obtained as the average of medians weighted by number of people supplied, was 0.09 % of the PTWI; the exposure was lower than 0.22 % PTWI in 90 % of the population monitored (from approximately 3.5 million of people supplied from the public water mains under monitoring).
Compared to other sources, the intake of arsenic via food is dominant in the general population. The highest arsenic concentrations are found in seafood and products; the dietary exposure is thus considerably affected by the frequency of consumption of fish/seafood. However, fish/seafood contains arsenic primarily in organic form (such as arsenobetaine) which has no acute effects given its low biological activity and is rapidly eliminated from the organism. The other foodstuff which is important with respect to concentrations of, and exposure to, arsenic is rice treated with pesticides containing arsenic which is readily available for the plants grown on permanently flooded fields. Rice is the main source of arsenic in our population given its lower consumption of fish/seafood than elsewhere in Europe. Exposure to arsenic from rice is more important as the rice contains primarily inorganic arsenic compounds, which are more toxic than organic ones. The other source of arsenic in the diet is beer.
Exposure limits as recommended by the WHO and US EPA are related to the quantity of inorganic arsenic, or in other words, to the quantity of arsenic and its inorganic compounds. The mix of compounds determined and evaluated as “toxic” arsenic is closer to the format of exposure limits than total arsenic content. In 2000, the value of dietary exposure to ”toxic” arsenic was 0.08 µg/kg b.w./day (5 µg/person/day), which is 3.8 % of the PTWI or 27 % of the RfD.
While the arsenic blood level is suitable for identifying only exposure within several hours, the content of arsenic in urine provides information about exposure within several days. In the year 2000, the median value of toxicologically-significant arsenic (inorganic arsenic, mono, and dimethyl-arsenic acid) in the urine of adult population was 3.2 µg per g of creatinine and 3.7 µg per g of creatinine in the urine of children; the values up to 7.7 µg/g or 9.0 µg per g of creatinine were found in 90 % of adults and children, respectively.
12.2 Chromium
Chromium has a varied importance for humans depending on its valence. While trivalent chromium is an essential element, necessary for the functioning of the metabolism, hexavalent chromium is classified by the IARC as a substance with sufficient proof of carcinogenity for humans (group I). However, total chromium is determined from different media of the environment for analytical reasons.
The bronchial tree is the first target for the carcinogenic effects of inhaled hexavalent chromium. Inhalation of aerosols containing hexavalent chromium is considered, in terms of overall exposure to chromium, as being the most important due to the risk of cancer in humans. Different studies show chromium concentrations ranging from 4 to 70 ng/m3 in the urban environment. During the years of monitoring, the air of Czech cities was found to contain average annual concentrations of chromium ranging from 0.1 to 40 ng/m3. In the year 2001, the range of average annual concentrations within the cities being monitored was 0.1 to 14 ng/m3. Considering the daily inhalation average of 20 m3, this corresponds to an intake of 0.01 to 0.28 µg per day. The theoretical risk of the increased probability of contracting cancer over a lifetime exposure to 1 µg/m3 of hexavalent chromium is 4x10-2 (4 cases per 100 inhabitants) according to the WHO; however, as the total chromium concentrations are measured, this risk would be heavily overestimated. The amount of intake through inhalation depends also on other factors such as smoking and the size distribution of dust particles.
Concentrations of chromium in the drinking water from the water mains under the Monitoring System is around the mean annual value of 1.5 µg/l; 90 % of samples were under 3 µg/L in 2001, which represents no deviation compared to the values in the literature (0.4–8.0 µg/L). Intake of chromium from drinking water is non-significant amounting to 0.02 µg/kg/day, which is 0.7 % of the exposure standard US EPA (RfD 3.0 µg/kg/day for hexavalent chromium).
In the year 2000, the average dietary exposure to total chromium in the Czech Republic was approximately 48 µg/day, which was 25 % of the US EPA exposure standard for hexavalent chromium. Beer and common baked goods are among the larger sources of exposure. Absorption in the body of chromium in food is estimated at 5 %.
12.3 Cadmium
Cadmium is released into the environment primarily during the production and utilization of cadmium, the combustion of fossil fuels and wastes, the storage of cadmium-containing wastes, and fertilization with phosphate fertilizers or waste sludge. The intake of cadmium by plants from the soil increases with the decreasing pH of the soil, therefore the soil acidification (e.g. by acid rain) can lead to the increased content of cadmium in food.
The kidneys are the critical target organ in the long-term exposure to low cadmium concentrations. Higher exposure to cadmium results in the disorders of calcium metabolism, hypercalciuria and the formation of renal stones, in combination with nutritional deficits the development of osteoporosis. The IARC classifies cadmium and its compounds as a human carcinogen in group I, based on the relationship between inhalation exposure and lung cancer.
In non-smokers, the main route of cadmium into the body is intake in food. The average daily dietary intake of cadmium in European countries is expected to be 15–25 µg; in the year 2000 the average daily intake of cadmium in adults was estimated at 12 µg, which is approximately 19 % of the WHO (PTWI 7 µg/kg b.w./week) or US EPA (RfD 1µg/kg b.w./day) limits, and corresponds to the WHO statement that exposure to cadmium in the European population for the most part is at the lower end of the 10–25 µg/day interval. The average percentage of absorption of the dose taken in is approximately 5 % and depends on nutritional factors (i.e., could be up to 15 % upon in people with iron deficiency). However, there may be a large difference in the cadmium intake depending on age and dietary habits. The most important sources of cadmium in Czech Republic include plant products, common baked goods, and other cereals, as well as potatoes.
Drinking water from the public water supply network contains very low concentrations of cadmium. In the year 2001, the limit values were exceeded in 0.3 % of samplings, the annual mean concentrations range in the tenths of µg/L, in 2001 it was 0.25 µg/L. In the year 2001, using average median exposure weighted by number of people supplied, the exposure limit was utilized in 0,01 %; 90 % of the population in the places under monitoring (a total of approx. 3.5 million people) reached less than the 1 % of the limit.
The contribution of airborne cadmium to the total cadmium exposure is very low compared to the dietary intake, although the pulmonary absorption exceeds that in the gastrointestinal tract and can amount to up to 50 %. The concentration of cadmium in the urban air of Northern Europe for example is reported within the range of 1–10 ng/m3. The highest annual concentrations of cadmium in the airborne dust of the Czech Republic’s cities under monitoring were identified in the first half of 1990s and ranged up to dozens of ng/m3. In the year 2001, the average annual concentration of cadmium ranged from 0.1 to 4.6 ng/m3, which complied with the WHO’s recommended value of 5 ng/m3, and upon a conservative scenario, represents the inhalation exposure of 0.002 to 0.09 µg per day. In smokers, one cigarette represents the inhalation intake of approximately 0.1 to 0.2 µg of cadmium.
Blood cadmium concentrations express the actual overall exposure. Blood cadmium levels in adults varied during the years under monitoring from 0.5 µg/L to 1.0 µg/L, while the blood cadmium levels reported in the literature are usually lower than 5 µg/L. In several recent years of monitoring, blood cadmium levels in children were lower than the detection limit (0.2 µg/L) in more than one half of samples (the total is 400 children a year). Blood cadmium levels in smokers are significantly higher than those in the non-smoking population. The blood cadmium levels in the Czech Republic’s adult population show no significant difference from the values reported in the literature for the European population. The proposal of reference values for the Czech population, based on the 95th percentile of results of measurement from 1996–2000, is 1.2 µg/L (1.0 µg/L in Germany) in the blood of adults and 0.6 µg/L in the blood of children (0.5 µg/L in Germany).
Cadmium urine levels correspond proportionally to the body burden of cadmium, although the percentage in the urine is very low compared to the concentration in the organism given the long half-life of cadmium, amounting to 20–40 years. The mean cadmium concentration in urine of adults in the Czech population within the years of monitoring ranged from 0.3 to 0.6 µg/g of creatinine; and the cadmium levels up to 0.8 µg/g of creatinine were found in 90 % of the adult population monitored, while the tolerable limit is 2 µg/g of creatinine due to the subclinical effects on the kidneys.
Given the deposition in the kidneys, especially in the renal cortex, of 30 to 50 % of cadmium taken, this indicator of the body burden of cadmium is also examined within the biological monitoring. Cadmium concentrations in the renal cortex are known to increase up to the age of 50 to 60 years, when the increase of cadmium stops or a reduction in these levels occurs. In the European population of 40 to 60 year-olds, the mean cadmium concentrations in the renal cortex are reported to be 15–50 mg per g of tissue. The monitoring in the Czech Republic during the years 1999–2000 revealed median value of 18.5 mg/kg in deceased persons in the age of 28 to 64 years (0.6 to 58.6 mg/kg). This result showed no significant difference compared to the median concentration 14.7 mg/kg identified in the year 1996.
12.4 Manganese
Metallurgy (steel works and foundries) and coal combustion are considered the major anthropogenic sources of manganese entering the environment. In the production of iron alloys one half of all manganese emissions from industry and combustion should originate; in the combustion of fossil fuel it is one tenth. A source can be the incineration of communal waste and waste sludges, a natural source being secondary particulate matter in ambient air. The major source of manganese in drinking water is the geological bedrock.
The toxicity of manganese depends on the pathway of exposure. By ingestion at typical exposure levels manganese has low toxicity and is considered to be a beneficial element. The essential character of manganese has been confirmed in animals, however, in humans no manganese deficiency appeared. Although the amount of airborne manganese, which humans are exposed to, is small in comparison with that ingested in food, the absorption of manganese and transfer to target organs may be relatively higher through inhalation than ingestion. The respiratory effects of airborne manganese at higher concentration levels, especially in the most sensitive population groups, may be the increase in frequency of upper respiratory tract affections and bronchitis, as well as the deterioration of pulmonary function. These potential effects, however, in view of their non-specificity and mildness, and the lack of knowledge of the relation of low-dose – long-term effects in ambient air, cannot be unambigouesly ascribed to manganese.
In the year 2001, airborne manganese concentration levels in Czech cities were found in the range of from 2 to 54 ng/m3. In principle that is in agreement with typical levels in urban ambient air as described by the WHO, i.e. 10–70 ng/m3. The detected maximum mean annual level was three times as low as that recommended by the WHO (150 ng/m3). With the contemplated volume of 20 m3 inhaled daily and with identical levels indoors and outdoors, manganese exposure through inhalation should, at the most, amount to 1 µg/person/day.
The major source of manganese for the general population are foodstuffs, namely of plant origin. The exposure limit value for manganese has not been identified by the WHO. The US EPA (IRIS 2001) determined the reference dose (RfD) at the level of 140 µg/kg b.w./day. In the year 2000, the average dietary exposure in the Czech Republic was approximately 67 µg/kg b.w./day), i.e. approximately 48 % of the RfD. The major source of manganese in our population is whole-grain pastry, flour and potatoes. Since the majority of manganese is found in bran, the processing of plant products decreases its amount. Thus, a diet rich in whole-grain products and shell fruits is rich in manganese. WHO considers the daily intake of 2.5–5 mg per person to be sufficient, that is met in the average person through the intake found.
In 2001, a median manganese concentration of 15 µg/L of drinking water in the public water mains under monitoring was determined, ranging of less than 2.5 up to 30 µg/L. With a contemplated consumption of 1 liter a day of water from the public water supply, the exposure to manganese from drinking water consumption ranges from thousadths of % up to 0.33 % RfD. However, such a situation is not typical for small drinking water sources, namely subterranean, in which water treatment plays no role in decreasing the manganese content.
12.5 Nickel
The major anthropogenic source of nickel into the environment is the combustion of fossil fuels, namely coal, nickel-ore processing, and waste incinerators.
Nickel is probably an essential element, although there are no data on symptoms of its deficiency in the organism. The most frequent effect on population health, under increased exposure, an allergic skin reaction (dermatitis) that is found namely in females. According to the WHO about 11 % of females suffer dermal hypersensitivity to nickel. The carcinogenic effects of nickel have been demonstrated in epidemiological studies of inhalation exposure to high nickel concentrations. The respiratory tract is the target organ in which nickel retention occurs with the risk of contracting respiratory tract cancer. Nickel compounds are therefore classified by IARC as a proven human carcinogens in group 1, metallic nickel as a possible carcinogen in group 2B. There is no experimental nor epidemiological proof of carcinogenic effects of nickel via oral exposure.
Airborne nickel concentrations in various European and American cities were found to be between 9 and 60 ng/m3, and over 100 ng/m3 in industrialized areas. In 32 cities under the Monitoring System, nickel levels are in the range of 1 to 86 ng/m3; applying 20 m3 as the volume of air inhaled daily and a conservative scenario, that represents a potential intake of 0.02–1.8 µg/day. Various compounds of nickel have different absorption rates, therefore retention or absorption in the lungs cannot be determined. In the published studies can be found that the smoke of one cigarette contains about 40 to 580 ng of nickel. The unit risk of inhaled nickel (risk of contracting cancer over a lifetime inhalation of air with 1 µg nickel per m3) is estimated by WHO to be 3.8x10-4; for cities in the Czech Republic the theoretical estimate of the probability of contracting respiratory tract cancer upon life-long inhalation exposure makes up for 3.8 persons per 10 million to 3.3 persons per 100 000 of the population (3.8:107–3.3:105).
In the drinking water of some European countries have been found nickel levels of 2–13 µg/L. In the Czech cities under monitoring (in which there lives about 1/3 of the country’s population), the annual median nickel concentrations range from less than 0.5 µg/L to 5.0 µg/L with a mean value of 1.5 µg/L. The maximum intake was found to be 5 µg/day assuming a consumption of 1 L/d of drinking water from public water supply and an annual maximum median concentration value. However, nickel can be released into water from nickel-containing water distribution piping and fittings, giving a concentration of several tens of µg/L overnight.
No acceptable daily dietary intake has been determined by JECFA FAO WHO. The US EPA (IRIS 2001) RfD for nickel and its soluble salts is 20 µg/kg b.w./day. In 2000, the mean dietary intake of nickel in the Czech population was about 1.9 µg/kg b.w./day (9.3 % RfD). Absorption of nickel in the gastrointestinal tract is estimated to be 15 %. Important sources of nickel in our country are shell fruits, chocolate, bread and legumes.
12.6 Lead
The most significant indiscriminate source of lead into the environment was the combustion of alkylated lead in petroleum, which has thus got through the ambient air into all the components of environment. The source of local increases in lead content can be foundries, steel works, waste incineration, as well as the combustion of coal.
Effects of lead at higher exposures (at higher blood lead levels of over about 150–200 µg/L, respectively) are more or less known: inhibition of certain enzymes, effects on erythropoiesis, neurological effects, impairment of kidney function, etc. Effects under chronic exposure to low levels in the environment have been described in small children in whom there have been demonstrated effects on neurobehavioral functions. Likewise, effects on blood pressure and auditory quality have been observed. There is insufficient evidence on the carcinogenity of lead in humans; IARC classifies lead into group 2B.
The overall intake of lead in the general population is within a very broad interval depending on habits or unavoidable circumstances, such as the consumption of crops grown in heavily contaminated areas, living in the vicinity of the sources (foundries or heavy transportation traffic), smoking, etc.
The intake of lead via food is dominant in the adult population. The average person in the Czech Republic has a dietary exposure of 3.8 µg/kg b.w./week (35 µg/day), that representing about 15 % of the tolerable weekly intake (PTWI 25 µg/kg b.w./week). That corresponds to the intake found in other countries, i.e. below 100 µg/day. Among the most important sources are cereal products, potatoes, and fruit vegetables. Gastrointestinal absorption is greatly influenced by nutrition factors, a low intake of calcium, vitamin D and iron increases the proportion of lead absorbed into the blood.
Intake of lead in drinking water from the water mains under follow-up is negligible, in the year 2001 it amounted to 0.04 % PTWI (median concentration 1 µg/L, 90 % of samplings below 3 µg/L). Such a content in drinking water is at the lower end of the interval given in the literature 1–60 µg/L. In older buildings with lead piping a significant increase of intake can occur, namely by soft or otherwise aggressive water. Presently, in collaboration with the Ministry for Local Development, a program of targeted seeking out is being prepared, including evaluation of the state of the lead water mains in buildings.
Over the years of monitoring, the lead burden from ambient air is stable without any oscillations, rather indicating a mild decline in concentrations, in 2001 not exceeding 0.1 µg/m3. The concentration range in the most cities 0.01–0.06 µg/m3 represents (applying a conservative scenario) an intake of about 0.2–1.2 µg/day, i.e. 0.08–0.4 % of the PTWI. According to a WHO recommendation the mean annual concentration of lead in ambient air should not exceed 0.5 µg/m3.
In small children the greatest exposure pathway does not have necessarily to be diet. Under low standards of hygienic habits, through unintentional (in cases of geophagy, even intentional) ingestion of upper soil and soil dust in children’s sporting grounds and playgrounds there may occur a significant increase in the overall exposure to lead. In the association and pilot studies of the project Health risks from urban soil pollution (Subsystem 8), an assessment of the hazards to health due to the contamination of playgrounds has been carried out in the kindergartens in the cities Olomouc and Karviná. Applying the exposure factors elaborated by the US EPA (1998), i.e. an estimated soil ingestion of 200 mg/d with frequency of exposure 210 days in a year by a child of an average weight of 15 kg, the exposure of children could amount to 17 % or 14 % of the exposure limit, respectively. In the most contaminated kindergarten the exposure to lead could amount to about 19 µg/day, that being 36 % of the exposure limit.
Blood lead level is a good indicator of the present and recent lead burden from the environment (in view of the relatively short half-life of lead in the organism, 28–36 days). In adults hematological and neurological effects can probably not be expected at levels below 200 µg/L. In children, however, there have been demonstrated effects on the central nervous system (cognitive deficit, impaired hearing) at levels of 100–150 µg/L already. The lower end of the range is therefore considered to be a limit acceptable for children as well as adults. In order to ensure a maximum level of 100 µg/L in at least 98 % of the population, the median value should not exceed 54 µg/L blood.
Since 1996, the lead content in the blood of the Czech population has been oscillating at a stable median level around 40–50 µg/L blood (according to the WHO the usual value is 10–30 µg/L), in 90 % of the population the level is below 80 µg/L. Since 1996, in children the median blood lead level has been below 40 µg/L, 90 % of children having a level of below 60 µg/L. In question are children of school age in whom there is manifested a gradual decline in the blood lead level as against around 2-year-olds who generally have a maximum of lead intake reflected in maximum of blood lead levels. Reference values proposed for the Czech population on the basis of the monitoring results from the period of 1996 through 2000, are 95 µg/L for males, 80 µg/L for females, and 60 µg/L for children.
A good biomarker of exposure to lead in early childhood is the first dentition. The median concentration of lead in the milk teeth of children from four cities in the Czech Republic in the year 2000, was 1.39 µg/g (0.4–18.6 µg/g), not differing from results in preceding years of monitoring or data published on the European population.