Environmental and socioeconomic factors contributing to elevated blood lead levels in children from an industrial area of Upper Silesia

INTRODUCTION

Lead (Pb) is an element with significant toxic effects on living organisms 1 and is known to have accompanied the development of civilization over approximately 5000 yr 2. Currently, despite significant progress in protecting the environment, Pb pollution of soil and dust emissions from industry and transport continues to cause serious, long-term medical problems for populations living in industrial areas and in many developing countries 3-5.

The pathomechanism of Pb toxicity is multifactorial and leads to damage of many important tissues and organs. Lead has an affinity to blood proteins and the ability to supersede metal cations from other chemical structures. Heavy metals such as Pb disrupt metabolic processes by oxidative stress and interactions at the deoxyribonucleic acid (DNA) level 6, 7. Lead may cause such adverse health effects as anemia, weakness, colicky abdominal pain, hearing and renal impairment, peripheral nerve palsy, and encephalopathy 8-12.

Absorption of Pb in children occurs primarily through the gastrointestinal tract. It is believed that 50% to 70% of the dry weight of absorbed Pb enters the body of a child by the oral route, and 10% to 20% through the lungs. The overall efficiency of Pb absorption in the gastrointestinal tract depends on diet. A diet rich in calcium, magnesium, phosphorus, iron, and vitamins, especially vitamins C and D3, reduces Pb absorption, whereas malnutrition and smoking increase absorption. It is estimated that Pb remains in the bloodstream for approximately 30 d and for more than 40 yr in bone tissue. Circulating blood contains 5% to 10% of the total Pb pool and is filtered by the liver and kidneys. Elimination of Pb occurs primarily by the urinary tract and gastrointestinal tract 13, 14.

Children are particularly vulnerable to the toxic effects of Pb. This increased sensitivity is related to intensive metabolic processes, increased Pb absorption through the digestive tract, and a deficient blood–brain barrier. Increased Pb exposure is a serious threat for the fetus because Pb has the ability to cross the placenta and cause permanent abnormalities in the developing central nervous system of a child 13. Because of the known neurotoxicity of even low blood Pb concentrations, it is now argued that there are no safe concentrations; Pb in any amount might contribute to a risk of permanent damage to the nervous system, diminished cognitive functions, and reduced intelligence quotient 15.

The area of Upper Silesia is one of the most industrialized regions in Poland. The economy of this region is still based on mining and metallurgical industries involving carbon, steel, zinc, and Pb, as well as other types of heavy industry, all of which are related to major environmental pollution in the region 16. A Polish study conducted by Jarosińska et al. in the 1990s showed that the average Pb concentration in the blood of children in Silesia living near industrial areas exceeded 200 µg/L 17. In another study conducted by Jarosińska et al., it was shown that 13% of children aged 2 yr to 7 yr had blood Pb levels exceeding 100 µg/L 18. In numerous studies, factors such as hand-to-mouth activities, malnutrition, unemployment, lower education of parents, parents' occupational Pb exposure, smoking at home, Pb-based paint and leaded gasoline intoxication, and longer outdoor playing periods have been associated with the risk of increased Pb exposure 17-27. In the present study, we aimed to assess the most recent exposure to Pb and to evaluate socioeconomic conditions in the pediatric population living in Upper Silesia.

MATERIALS AND METHODS

RESULTS

The average age of the children was above 9 yr (9.23 yr). The geometric mean of Pb blood concentrations was 28.67 μg/L (range 6.0–360.0 μg/L), median 28.0 μg/L; 4258 (87%) children had Pb blood concentrations levels below 50 μg/L (which is the current level of concern according to the US Centers for Disease Control and Prevention); 576 (12%) children had levels between 50 μg/L and 100 μg/L; 47 (1%) children had levels between 100 μg/L and 200 μg/L; and 1 child had a Pb blood concentrations of 360 μg/L. The present study group consisted of 2564 girls and 2311 boys. The average Pb blood concentrations level of boys was 3.1 μg/L higher than in the girls (Table 1).

The group was divided into 4 subgroups (quartiles) depending on Pb blood concentration level, as follows: quartile I: 1365 children with Pb blood concentration levels from 6.0 μg/L to 21.0 µg/L; quartile II: 1109 children with Pb blood concentration levels from 21.1 μg/L to 28.0 µg/L; quartile III: 1279 children with Pb blood concentration levels from 28.1 μg/L to 40.0 µg/L; and finally, quartile IV: 1129 children with Pb blood concentration levels from 40.1 μg/L to 360 µg/L (Table 2).

With the increase in blood Pb levels, a significantly higher percentage of boys in subsequent quartiles was observed (p < 0.001; Table 2). A significantly lower percentage of maternal employment activity (p < 0.001) was observed in children in quartiles III and IV. A similar relation was found for parental employment activity for quartile IV (p < 0.001; Table 2). Significantly more frequent parental occupational contact with Pb was found (p < 0.001) in quartile IV children. In quartile III and IV children, a significantly higher percentage of parents smoked cigarettes at home (p < 0.001). The influence of locally grown fruit and vegetable consumption was associated with a statistically significant increase in Pb blood concentration levels for children in quartiles II, III, and IV (p < 0.001; Table 2). A significantly higher percentage of physically working mothers and fathers was found for children in quartiles III and IV (p < 0.001; Table 3). A significantly higher percentage of low-educated mothers was observed for children in quartiles III and IV (p < 0.001). A similar relation was observed for low-educated fathers in quartiles II, III, and IV (p < 0.001; Table 4). A significantly higher percentage of poor economic status of the family was found in children in quartiles III and IV (p < 0.001) A significantly longer period of time spent outdoors by children was observed in the quartiles II and IV children (p < 0.001; Table 5). A significantly higher percentage of children living on the ground floor of the home was observed for children in quartiles II and III (p = 0.007; Table 6). It was observed that a low level of education of the child's mother and father had the most significant impact on higher Pb blood concentration levels (Table 7).

In multivariable regression analysis, any potentially significant variables affecting Pb blood concentration levels were evaluated (Table 8). The model explains 11% of the variation in Pb levels (R²_adj = 11%). The p value of the model was <0.001.

DISCUSSION

Our cross-sectional analysis of questionnaires and blood samples was conducted on a large population of children from Upper Silesia. The present study evaluated the effects of environmental and socioeconomic factors on Pb blood concentration levels in children. In spite of a generally observed downward tendency for elevated Pb blood concentration levels, the present study demonstrated that environmental exposure to Pb in Upper Silesia continues to be the cause of Pb toxicity in children.

Male gender is an important determinant of higher exposure to Pb. Studies have shown that boys have higher Pb blood concentration levels than girls in general 3, 28. The higher percentage of automotive and technical activities within boys' population in comparison to the similar population of girls can be linked to the higher environmental exposure to Pb. In addition, it seems that boys have a greater sensitivity of the central nervous system toward increased Pb exposure 29. Sobini et al. demonstrated that delta-aminolevulinic acid dehydratase polymorphism and a specific protein transporter haplotype in male homozygotes predisposes boys to greater neurotoxic intoxication 30.

The influence of socioeconomic factors on Pb toxicity is complex and multifactorial. Poverty and a low level of education is associated with economic deprivation of basic life needs, worse living conditions, and more frequent child malnutrition, and parents with a lower level of education more often have an insufficient level of awareness of environmental health risks and more frequently work in conditions of higher environmental exposure to dust and heavy metals 20.

In the present study, the influence of a number of socioeconomic factors was assessed, and it was shown that a low level of education of parents was 1 of the most important factors responsible for increased Pb blood concentration levels. Among other factors, low economic status of the family associated with unemployment and physical work contributed to higher Pb blood concentration levels in children. Similar results were found by Szymik 20. Likewise, Ureirolo et al. emphasized the relationship among parents' low level of education, poverty, young maternal age, and elevated Pb blood concentration levels 21. Along with the above-mentioned factors, Liu et al. added having siblings and living in a densely populated area 22. Jarosińska et al. also observed that having siblings correlated with higher Pb blood concentration concentrations 18. This observation seems to be related with uncontrolled hand-to-mouth behaviors of less vigilantly supervised young children 14.

The type of house inhabited, its height, and location are significant socioeconomic factors that are also related to increased Pb exposure. Various authors have confirmed that poor housing conditions are associated with higher Pb blood concentration levels in children 18, 25. These data are consistent with the results of the present study. Location of the house near sources of emissions of heavy metals is a well-known risk factor 31. Living in old houses, especially with old water pipes containing Pb elements, may result in increased Pb exposure from contaminated drinking water 23. Striph observed that worse household economic status and living in houses built before 1960 in the United States contributed to higher Pb exposure 32. Another type of indoor exposure may come from painted surfaces that contain Pb compounds 24. During the renovation of such old houses, considerable amounts of dust containing harmful Pb compounds may be released very quickly 33.

Living on the ground floors of buildings also has an impact on environmental Pb exposure. Jiang et al. determined that living on the ground floor was associated with higher Pb blood concentration levels in children 19. Similar findings were observed in the present study, presumably associated with higher concentrations of Pb dust closer to the ground. Densely populated residential areas are also mentioned as a risk factor by some authors 22, 34.

Increased Pb exposure is seasonal in nature, according to the release of Pb particles from the soil during the warm summer months. As temperature increases and soil moisture decreases, wind power influences the transition of Pb particles into the air, which results in environmental exposure to Pb dust 26. The summer is also conducive to long outdoor playtime periods for children, which is associated with prolonged Pb exposure. Futhermore, concentrations of indoor Pb dust on the floors and windowsills of households also increase in the summer. Studies have shown a connection between increased amounts of house Pb dust and elevated Pb blood concentration levels in children 35, 36.

Van Wijnen et al. observed that children can consume up to 200 mg of soil per day 37. During dry, hot weather, the amounts of absorbed soil tend to be the highest. Children absorb Pb via the gastrointestinal and respiratory tracts and are exposed to both outdoor and indoor Pb. Jarosińska et al. observed that Pb blood concentration levels of children in the summer were higher by 10% than in the winter 18. The present study did not assess Pb fluctuations during the year, but confirmed the fact that longer outdoor playtime spells in the contaminated industrial area were associated with higher Pb blood concentration levels. These data are consistent with the observations of other authors 18, 36.

Numerous studies have confirmed that parental occupational exposure to Pb is associated with increased Pb blood concentration levels in children 20-22. This is consistent with the results of the present study. Well-documented facts confirm that Pb compounds deposited on the clothes and skin of an employee can be transferred to households and then absorbed by the respiratory or gastrointestinal tract of a child 23.

Cigarette smoking is considered to be a significant factor in Pb exposure 20, 22. Passive smoking is especially dangerous. This was confirmed in several studies as well as in the present study. Mannino et al. found that children with higher levels of cotinine had higher levels of Pb blood concentrations 38. Younger children exposed to tobacco smoke at home not only inhale toxic and volatile substances through respiration, but can also absorb dust and smoke settlement from the floor 23. Liu et al. observed higher Pb concentrations in the house dust of parents who smoked cigarettes at home 22.

Another important source of exposure to heavy metals is from food. Contamination of food occurs through contaminated irrigation systems, crop contamination, industrial wastes, and emission of toxic dust. Studies have shown that vegetables grown on farmlands in Southern China, Iran, and India contained high concentrations of Pb and other heavy metals, levels that significantly exceeded the legal limits recommended by the World Health Organization 39-41. Sharma et al. also observed that the vegetables sold in local markets contained higher concentration of Pb than those bought at the place of production, which indicated an additional contamination of food during transport and at the marketplace 41. Contamination of food may also occur during its preparation at home 42. Cikrt et al. found that consumption of local vegetables and fruits from Pb-contaminated areas of the Czech Republic was associated with higher concentrations of this heavy metal in blood of children 27. This is consistent with our observations.

The strength of the present study is the fact that it was conducted with a large group of children, residing in 1 region. The other advantage is that the present study focused on a wide-range analysis of different socioeconomic and environmental factors modifying Pb blood concentrations. The present study has some limitations. First, because of the cross-sectional nature of the study, it was not possible to clarify some of the survey questions and verify some answers. Second, certain factors affecting Pb blood concentrations were not taken into account in the survey, such as number of siblings, consumption of dietary supplements, and the influence of air, soil, and water pollution.

The results of the present study illustrate potential sources of environmental risks for the pediatric population living in Upper Silesia. The present study provides important information for primary prevention of exposure to Pb. From a public health perspective, it is necessary to implement measures that aim to reduce risk factors for increased Pb exposure, promote education, and organize social campaigns. This will undoubtedly lead to improvement in the epidemiological situation of increased Pb exposure in children.

CONCLUSIONS

Environmental exposure to Pb is still the cause behind chronic toxicity of this metal in children in Upper Silesia. Selective screening allows identification of children from risk groups that require different ranges of medical intervention. Factors that correspond with increased exposure to Pb include lower education of parents, unemployment, parents' occupational Pb exposure, poor socioeconomic status of the family, smoking at home, living on the ground floor of the home, consumption of locally grown vegetables and fruits, longer outdoor playing periods in the polluted environment, and male gender. The most important socioeconomic factor that influences the concentration of Pb in children's blood is a lower level of education of the child's mother and father.