Abstract
OBJECTIVES:
Exposure to lead and cadmium in developing countries is considered to be a public health emergency. The present study was designed to investigate children’s exposure to lead and cadmium in Changchun, China.
METHODS:
A total of 1619 blood samples were collected at random from 1426 children between one and 14 years of age, and 204 adults from Changchun, China. Blood lead and cadmium levels were determined using atomic absorption spectrophotometry.
RESULTS:
The average blood lead level in children was 60.29 μg/L, with boys exhibiting higher blood lead levels than girls. The average blood cadmium level in children was 1.26 μg/L, and differences were not observed between boys and girls.
CONCLUSIONS:
Children from Changchun exhibited relatively low blood lead and cadmium levels compared with children from other cities, and higher lead and lower cadmium levels than adults. This may be related to leaded gasoline environmental pollution and children’s hand-to-mouth activities.
Keywords: Blood, Cadmium, Changchun, Children, Lead
Abstract
OBJECTIFS :
L’exposition au plomb et au cadmium est considérée comme une urgence de santé publique dans les pays en développement. La présente étude était conçue pour examiner l’exposition des enfants de Changchun, en Chine, au plomb et au cadmium.
MÉTHODOLOGIE :
Les chercheurs ont colligé au hasard un total de 1 619 prélèvements de sang auprès de 1 426 enfants de un à 14 ans et de 204 adultes de Changchun, en Chine. Ils ont déterminé leur taux de plomb et de cadmium dans le sang au moyen de la spectrophotométrie d’absorption atomique.
RÉSULTATS :
La plombémie moyenne des enfants s’élevait à 60,29 μg/L et était plus élevée chez les garçons que chez les filles. Le taux moyen de cadmium dans le sang des enfants s’élevait à 1,26 μg/L et n’était pas différent entre les garçons et les filles.
CONCLUSIONS :
Les enfants de Changchun présentaient un taux relativement faible de plomb et de cadmium dans le sang par rapport aux enfants d’autres villes, et un taux plus élevé de plomb et plus faible de cadmium que les adultes. Ce phénomène peut être lié à la pollution environnementale par l’essence au plomb et au fait que les enfants portent beaucoup leurs mains à leur bouche.
Global health concerns span a wide range of issues, from prevention of infectious disease to environmental contamination. In this Global Health article, Dr Jianling Xu and colleagues from Changchun, an industrialized city in Northeastern China with a special focus on the automotive industry, report on lead and cadmium concentrations in the blood of more than 1400 children. This is one of the first studies to systematically evaluate heavy metal exposure in Chinese children. Interestingly, these investigators have found that the concentrations of lead and cadmium were, on average, lower than the limited data available for other Chinese cities, despite Changchun being dry, dusty and a centre for heavy industry. Among children with higher lead and cadmium concentrations, risk factors appeared to mirror the risk factors associated with exposure to these metals in other countries.
Michael J Rieder, Associate Editor, Paediatrics & Child Health
Long-term exposure to lead may cause serious health problems, particularly in young children (1–3). Lead is toxic to many organs and tissues including the immunological, neurological and reproductive systems (4). The hazards of lead exposure in children are more extensive than in adults, and their growing bodies make them more susceptible to absorbing and retaining lead (5–7). The WHO has placed lead as the leading factor among the 13 environmental factors that are hazardous to the health of children. It has been reported that a decrease in IQ of more than six to seven points can result from mean blood lead concentrations >100 μg/L (5).
The United States has made tremendous advances against lead exposure in children, as demonstrated by two nationwide surveys of blood lead levels conducted in the United States in 1976 and 1991, respectively. According to these surveys, the number of cases with blood lead levels >100 μg/L dropped from 88.3% to 11.5% among one- to two-year-old children, and from 88.1% to 7.3% among three- to five-year-old children (7).
The persistent toxicity of lead in children was observed to result in significant and serious impairment of cognitive development as well as level of intelligence (5,8,9). In addition, osseous lead exposure may be the cause of the high incidence of rickets among children and the failure of some conventional treatments for the disease (10).
Exposures in these situations or absorption from contaminated food, water and air could result in cadmium accumulation in the human body. In newborns, increases in blood cadmium levels are mainly caused by recent contact with cadmium (11). Acute exposure to cadmium fumes may cause symptoms such as headache, dizziness, loss of appetite, coughing and asthma. The incidence of stomach and duodenal ulcers, bronchitis, urinary stones and several other chronic diseases are significantly higher in cadmium-contaminated areas (12). Ingestion of any significant amount of cadmium or compounds containing cadmium may have toxic effects on lung, bone, kidney, heart, brain blood vessels, liver and reproductive organs (13).
In the present study, we measured blood lead and cadmium levels in children living in Changchun, Jilin Province, China. Samples from adults were also analyzed as corresponding controls. Factors that contribute to lead and cadmium exposure in children were analyzed.
METHODS
Subjects
A total of 1619 blood samples were randomly collected from 1426 children (one to 14 years of age) and 204 adults in Changchun, Jilin Province, China. The present study was conducted in accordance with the Declaration of Helsinki, with approval from the Ethics Committee of Northeast Normal University (Changchun, China). Written informed consent was obtained from all participants’ guardians.
Measurement of blood lead and cadmium levels
After all participants disinfected their hands, 2% iodine was used for skin disinfection by wiping for 20 s, followed by deiodination using 70% ethanol. 40 μL of blood was drawn from the tips of their left ring fingers and immediately transferred to 0.36 mL dilution buffer (H2O, [NH4]2HPO4, Triton X-100). Blood lead and cadmium levels were determined using a BH 2100 atomic absorption spectrometer (Beijing BoHui Innovation Optical Company, China), which is faster, more convenient and more reliable compared with traditional instruments. There were no differences in the results between the BH 2100 atomic absorption spectrometer and the traditional instruments.
In the present study, as shown in Table 1, the results indicated that the blood lead and cadmium content at different ages were different. The blood lead and cadmium levels of adults were also determined. The exposure rates were calculated for all ages; the classification was performed according to the criteria of the United States Centers for Disease Control and Prevention (CDC) (Georgia, USA) (14). The lead and cadmium measurements were performed simultaneously and the results were analyzed at the same time. The blood was appropriately stored before the experiment so as not to affect the results.
TABLE 1.
Blood lead and cadmium levels in the 1426 children surveyed
| Age, years | n | Lead poisoning, n (%) | Blood lead, μg/L | Cadmium poisoning, n (%) | Blood cadmium, μg/L |
|---|---|---|---|---|---|
| <1 | 196 | 13 (6.63) | 53.93±0.126 | 10 (5.10) | 1.27±0.045 |
| 1 | 187 | 20 (10.70) | 60.88±0.258 | 8 (4.27) | 1.53±0.072 |
| 2 | 125 | 10 (8.00) | 56.70±0.161 | 7 (5.60) | 1.54±0.216 |
| 3 | 81 | 10 (12.35) | 59.78±0.235 | 9 (11.11) | 1.70±0.113 |
| 4 | 98 | 10 (10.20) | 54.44±0.099 | 3 (3.06) | 1.10±0.107 |
| 5 | 110 | 11 (10.00) | 60.48±0.115 | 2 (1.82) | 0.93±0.201 |
| 6 | 104 | 10 (9.61) | 62.90±0.169 | 6 (5.77) | 1.21±0.156 |
| 7 | 101 | 3 (2.97) | 54.90±0.085 | 0 (0) | 0.78±0 |
| 8 | 89 | 10 (11.24) | 69.03±0.093 | 3 (3.37) | 1.24±0.127 |
| 9 | 103 | 13 (12.62) | 61.30±0.136 | 3 (2.91) | 1.22±0.049 |
| 10 | 44 | 9 (20.45) | 74.80±0.352 | 0 (0) | 1.12±0 |
| 11 | 70 | 11 (15.71) | 65.49±0.151 | 2 (2.86) | 0.96±0.042 |
| 12 | 56 | 11 (19.64) | 67.38±0.173 | 7 (12.5) | 1.73±0.142 |
| 13 | 62 | 6 (9.68) | 64.29±0.315 | 2 (3.23) | 0.99±0.056 |
| Female | 585 | 54 (9.23) | 58.04±0.163 | 27 (4.62) | 1.24±0.096 |
| Male | 841 | 93 (11.06) | 61.83±0.199 | 33 (3.92) | 1.27±0.123 |
| All children | 1426 | 147 (10.31) | 60.29±0.191 | 60 (4.38) | 1.26±0.109 |
| Adults | 204 | 17 (8.33) | 56.09±0.266 | 19 (9.31) | 1.73±0.167 |
Data presented as mean ± SD unless otherwise indicated. The standard limits for the concentration of blood lead poisoning was 100 μg/L, and 5.0 μg/L for blood cadmium poisoning
Blood lead and cadmium concentrations were evaluated according to the criteria of the CDC (14). Five blood lead exposure levels were used in the diagnosis: level I (<100 μg/L), safe and no clinical treatment required; level II (100 μg/L to <200 μg/L), asymptomatic or mild lead exposure; level III (200 μg/L to <450 μg/L), moderate lead exposure; level IV (450 μg/L to 700 μg/L), severe lead exposure; and level V (≥700 μg/L), very severe lead exposure. For blood cadmium, levels >5.00 μg/L were considered to be toxic and levels below this were considered to be safe. Children of different ages were randomly tested to analyze the lead and cadmium levels. Statistical analyses (both Student’s t test and Pearson correlation analysis) were performed using SPSS version 13.0 (IBM Corporation, USA). Statistical analysis was used to determine the normality of the sampled data, and t tests and Pearson correlation analyses were used to analyze the relevance of lead and cadmium content; P<0.05 was considered to be statistically significant.
RESULTS
Blood lead and cadmium levels in children
The detailed blood test results for the 1426 children surveyed are presented in Table 1. The mean blood lead concentration among children was 60.29 μg/L. Ninety per cent (1279 of 1426) were in the safe range (<100 μg/L), while the rest (10% [147 of 1426]) were at unsafe exposure levels according to the diagnostic criteria (14). Ninety-six per cent (140 of 147) and 4% (six of 147) of the exposure group exhibited mild (level II) and moderate lead exposure (level III), respectively. According to the experimental results, the maximum concentration of lead in blood was 123.1 μg/L, and 1.88 μg/L for blood cadmium (Table 2). No samples with severe lead exposure were observed in the survey. The average blood cadmium concentration in children was 1.26 μg/L, and the cadmium exposure rate was 4.4% (62 of 1426). The correlation was positive based on Pearson correlation analysis (P<0.05). The linear correlation coefficient of blood concentrations for lead and cadmium was >0, which was considered to be a positive correlation. However, the correlation coefficient was small (P<0.05) and not obvious.
TABLE 2.
Blood lead and cadmium levels in lead poisoning and non-lead poisoning subjects in the 1426 children surveyed
| Groups | n | Lead, μg/L | n | Cadmium, μg/L |
|---|---|---|---|---|
| Lead poisoning (blood lead level ≥100 μg/L) | 146 | 123.06±0.267 | 62 | 1.88±0.155 |
| Non-lead poisoning (blood lead level <100 μg/L) | 1269 | 53.07±0.169 | 1364 | 1.18±0.101 |
| All samples | 1415 | 60.29±0.191 | 1426 | 1.26±0.109 |
Data presented as mean ± SD unless otherwise indicated
Age distribution of blood lead and cadmium levels
As shown in Table 1, the range of blood lead concentrations was between 54 μg/L and 75 μg/L; the data were relatively concentrated and the range was narrow. However, from the statistical analysis of the experimental results, the lead concentration and exposure rate generally changed according to age, as did the cadmium concentration and exposure rate. Because the data changed little, age was not the main factor affecting the concentration of and exposure rates to lead and cadmium.
The blood cadmium levels in all children were <2 μg/L. Children at three and 12 years of age appeared to exhibit the highest levels of cadmium exposure. However, there was no significant correlation between blood cadmium levels and age. The lead and cadmium content varied according to age and their correlation was minimal.
In adults, both the blood lead levels and exposure rate were lower than those in children (Table 1), while blood cadmium levels and exposure rate were higher than those in children. The lead and cadmium concentrations and toxicity rate in men were commonly higher than those in women.
DISCUSSION
Nationwide epidemiological surveys of blood lead levels in children have not been conducted in China. There have been only a few small-scale local investigations, which have indicated that the blood lead levels of children in urban areas are within the range of 50 μg/L to 90 μg/L and the lead exposure rate is approximately 10% to 50%, but worse in some more heavily polluted industrial areas, with an average lead exposure rate as high as 70% (6).
Sex differences in blood lead and cadmium exposure in children
The mean blood lead levels in boys and girls were 61.71 μg/L and 57.75 μg/L, respectively (Table 1), and the exposure rate was higher in boys than in girls (11.06% versus 9.23%). The results of the statistical analysis showed that the exposure rate in boys was very similar to that in girls, but was higher numerically in boys than that in girls.
In contrast, there were no sex differences in blood cadmium levels between boys (1.27 μg/L) and girls (1.24 μg/L). The cadmium exposure rates in boys and girls were 3.92% and 4.62%, respectively.
Possible sources of lead pollution
Automobile exhaust:
The total suspended particle (TSP) counts in ambient air decreased significantly since leaded petroleum was banned in Changchun on July 1, 1998. However, 94.8% of lead still came from automobile exhaust in the TSP detected (15). This high TSP level in the air is likely attributable to the fact that 37.5% of the nonleaded gasoline on the market exceeds the lead level limit of 0.5 g/L to 0.7 g/L (16). The lead concentration is 10 times higher than that in the upper air above the ground where children breathe. Consequently, children who are more frequently exposed to the urban streets have a higher risk of lead exposure.
Coal burning:
Coal, a fossil fuel, is the largest source of energy for the generation of electricity in China. Approximately one billion tons of coal is directly combusted each year, which represents 84% of the annual total coal consumption. Changchun, located in the northeast region of China, has a winter heating period of approximately six months per year, which is currently coal based. Some power plants in Changchun are also coal based. However, data regarding the amount of coal combustion in Changchun are unavailable. Each ton of coal burned in an energy plant or combusted in a coal-fired boiler could emit approximately 19.84 g or 20.35 g of lead, respectively, and approximately two-thirds of the lead resulting from the burning of coal are released into the air (17). The enormous amount of lead from coal burning likely contributes to high blood lead levels in children.
Industrial enterprises:
Heavy industrial activity correlated with lead concentration. A study conducted in Nanjing (Jiangsu, China) revealed a 2.2-fold increased soil lead level in a typical industrial area compared with a typical residential area, which suggests that a greater hazard of lead exposure is correlated with industrial enterprises (18). Also, villagers and children have been found to exhibit toxic levels of lead exposure, mostly caused by pollution from battery factories. In a battery scrap processing-intensive region, high lead content was detected in the air, soil, drinking water and wheat (15). Although data from similar studies in Changchun are lacking, the impact of industrial enterprises cannot be ignored.
Household decoration:
Household paint, wood coating and wall-papers may contain cadmium salts, chromium oxides, yellow lead, white lead or red lead. Decoration-based lead pollution can be of particular concern to children because their rooms are normally painted more colourfully than adults’ rooms.
Dust:
The most common lead hazard is lead-contaminated dust. Lead exposure can occur anywhere – in suburban and rural areas, as well as cities – because it is often caused by lead dust, which results when lead-based paint is sanded or chipped, typically during a renovation. Changchun, located in the northeast region of China, is windy and dusty, especially in the spring. Studies have shown that blood lead levels of children are positively correlated with the amount of outdoor dust (16). Anyone can be exposed to lead, but children between six months and six years of age are at the highest risk because they often put their hands and toys in their mouth.
In addition to the factors listed above, there are more children-specific sources of lead pollution. These include colourful toys, clothes and school supplies, which are often linked with high lead content (19). Some countries set a limit of 250 mg/kg soluble lead in paint layers used for toys and school supplies (20). The brown-black colour of paint on desks and chairs can contain lead exceeding the limit by 36.7-fold (21). The lead content of coloured paper is 500 times higher than that of white paper. Children have increased risk for exposures to lead via these materials. Smoke (20) and diet (22) could also add to the risks of lead pollution and exposure. Studies found that lead levels of embryos in women who smoked were 15 to 92 times those of women who did not smoke. The lead levels of embryos in women exposed to secondhand smoke were 4.21 times and 10.66 times those in nonsmoking women (23). As with the factors discussed above, either specifically designed surveys or laboratory experiments involving animal models are needed to clarify the postulated connections between the two. It is worth noting that the rapid industrialization process in Changchun and any factors that (potentially) contribute to lead and cadmium pollution and exposure will play much larger roles over time. Children are in more danger than adults because their bodies are still developing. Therefore, it is necessary for yearly surveys to be conducted to better monitor the risks. In addition, the main sources of cadmium include phosphate fertilizers, fossil fuel combustion, electroplating, mining, smelting, and the production and use of dyes and batteries, as well as some industrial activities.
SUMMARY
Our survey revealed that 89.7% of blood lead levels measured among children in Changchun were considered to be safe, which was not as severe as in other cities in China. The cadmium exposure rate in Changchun was 4.4%, which was also lower than in many other cities. This was related to the different living conditions of the children in different cities. A weak correlation exists between the lead and cadmium levels and the age of the child. In the sampled population, the blood lead levels increased in children ≤11 years of age and decreased in children >11 years of age. Cadmium levels were highest in three- and 12-year-old children. Interestingly, boys appear to have a higher risk of lead and cadmium exposure than girls. The exposure rates of lead in boys and girls were very similar, but were higher numerically in boys than that in girls. Children have higher blood lead levels and exposure rates, but lower cadmium levels and exposure rates than adults. In the present study, we analyzed the risk factors (which include automobile exhaust, coal burning, industrial enterprises, etc) that contribute to lead pollution. However, the direct links need further investigation.
Acknowledgments
This project was supported by a Scientific Innovation Grant from Northeast Normal University (No. NENU-STC08016), and partially supported by the Education Department of Jilin Province, and a Scientific Development Program of Jilin Province (No. 20130102039JC). It was also supported by Jilin Province Environmental Protection Bureau (No. 2010-01). The authors appreciate this support.
Footnotes
DISCLOSURES: The authors have no conflicts of interest to declare.
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