Environ. Sci. Technol. 2010, 44, 4760–4765
Lead in Children’s Blood Is Mainly Caused by Coal-Fired Ash after Phasing out of Leaded Gasoline in Shanghai F E N G L I A N G , † G U I L I N Z H A N G , * ,† MINGGUANG TAN,† CHONGHUAI YAN,‡ X I A O L I N L I , † Y U L A N L I , † Y A N L I , * ,† YUANMAO ZHANG,§ AND ZUCI SHAN§ Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China, Shanghai Jiao Tong University School of Medicine, Shanghai 200092, China, and Shanghai Environmental Monitoring Centre, Shanghai 200030, China
Received December 29, 2009. Revised manuscript received April 30, 2010. Accepted May 10, 2010.
Lead (Pb) is a highly toxic element to the human body. After phasing out of leaded gasoline we find that the blood lead level of children strongly correlates with the lead concentration in atmospheric particles, and the latter correlates with the coal consumption instead of leaded gasoline. Combined with the 207 Pb/206Pb ratio measurements, we find that the coal consumption fly ash is a dominate source of Pb exposure to children in Shanghai, rather than vehicle exhaust, metallurgic dust, paint dust, and drinking water. Those particles are absorbed to children’s blood via breathing and digesting their deposition on ground by hand-to-mouth activities. Probably the same situation occurs in other large cities of developing countries where the structure of energy supply is mainly based on coal-combustion.
Introduction It is well-known that lead is a highly toxic element to the human body and that even at low concentrations it will have severe physiological or neurological effects, particularly for children (1, 2). Lead is absorbed into the body following ingestion and inhalation exposure. Human exposure to Pb occurs through various middle routes, but there are four main pathways of lead from the environment to humans, these are inhaled aerosol particles, dusts, food, and drinking water (3). One of the main pathways of lead assimilation by the human body is through breathing, and for children, the ingestion through hand-to-mouth activities is also important. In 1986, the United States Environmental Protection Agency (U.S. EPA) reported a strong correlation between blood lead levels and the amount of lead used in gasoline between 1976 and 1980 (4), later on, Thomas et al. (5) also found that correlation. This means that the largest source of anthropogenic Pb in that period was derived from the combustion of leaded petrol exhausted from vehicles. After the phaseout of leaded gasoline, concentrations of lead in the air of * Address correspondence to either author. Phone: 0086-2139194768. Fax: 0086-21-59553021. E-mail:
[email protected] (G. Z.);
[email protected] (Y. L.). † Chinese Academy of Sciences. ‡ Shanghai Jiao Tong University School of Medicine. § Shanghai Environmental Monitoring Centre. 4760
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urban environments in the U.S. have dropped more than 90% (3, 6). But we found that lead concentrations in Shanghai dropped only around 50% since the use of tetraethyl lead was phased out much later, in 1997. The concentration of lead in Shanghai’s air was still high, with average Pb concentration in PM10 (aerodynamic diameter e10 µm) of 224 ( 45 ng · m-3 in the winter of 2003 (7), which was above the value of 200 ng · m-3 recommended by the World Health Organization. Blood lead level (BLL) of children has been gradually reduced since phasing out leaded gasoline in Shanghai, but it is still much higher than that of 1.9 µg dL-1 in U.S. during 1999-2004 with 1-5 years olds (8). Now the average value of children’s BLL in cities of China is in a range of 5.0-9.0 µg dL-1 (9), and the prevalence rate of childhood lead poisoning (BLL is higher than 10 µg dL-1 which is the level of concern according to the U.S. Centers for Disease Control and Prevention) is in a range of 5-20%, much lower than recent reported values in Bombay, India (10). The average value of children’s BLL in Shanghai in 2007 is 6.2 µg dL-1, which is somewhat higher than the past few years. As is known, BLL is highly dependent on the lead contained in atmospheric particles, paint dust, soil, food, and drinking water. Therefore, the impacts associated with the lead pollutant on BLL are quite different in different countries, different areas, as well as different in time periods because of the variation in the main pollutants. For the areas using coal combustion as a main energy supply, the coal-fired dust and its deposition may become an important source (11) and a predominate exposure to children’s blood. For areas using Pb-based paint, the paint dust would be the major intake of lead for children. Moreover, BLLs correlate most closely with recent environmental exposure. The excretory half-life of lead in adult blood is approximately 40 days, but estimates in children are somewhat longer than that (12). Therefore BLL could be a good marker of recent lead pollution in the environment. As is known, various pollutants were formed originally by different ores and rocks which have different Pb isotopic composition (13). Isotopic ratio of Pb is a reliable index for studying the origin of lead in the environment (14). In this article, we tried to find out the predominate source of Pb exposure to children’s blood in Shanghai by studying the relationships among lead in children’s blood and lead in atmospheric particles, paint, water, and annual combustion coal of city as well as lead in soil.
Materials and Methods Lead Data in Atmospheric Particles and Coal Consumption. Total suspended particles (TSP) samples were collected every day at 19 monitoring sites in Shanghai carried out by Shanghai Environmental Monitoring Center. The annual average Pb concentrations and Pb isotopic ratios were analyzed by inductively coupled plasma mass spectrometry (ICP-MS)(X7; Thermo, U.S.), the experimental details can be found in our previous work (7, 15, 16). Lead concentrations in TSP were determined in 1991-2005. Because of the lack of a few monitoring sites in 2006 and 2007, the data of those two years were not taken into account. The annual coal consumption data of the city were released by the China Energy Statistical Yearbook (17) and the Shanghai Statistical Yearbook on Industry, Energy, and Transport (18). Blood Lead of Children. The BLLs were determined by samples taken from children under 6 years of age using an epidemiological protocol in that period, and those values were 10.1021/es9039665
2010 American Chemical Society
Published on Web 05/18/2010
collected from our previous (16, 19) and recent work, as well as other published literature (20). All published data are quite limited because people did not pay much attention on systematic study of the children’s blood one decade ago. However its variation tendency with years could be clearly found by the data shown in later figures. For the lead isotope ratio measurement, a total of 382 samples of normal children’s blood, aged less than 6 years, were randomly collected from kindergartens distributed in 15 administrative districts in Shanghai in the period of 2005-2006. For each child, venous blood samples taken from the arm (5 mL) were drawn into vacutainers containing sodium heparin anticoagulant, after thoroughly cleaning the arm with an ethanol swab. Lead in 0.5 mL blood samples was leached with 1 mL 10% HNO3 for one day, then diluted digestate by ultrapure water (MiliQ A10, Milipore, U.S.) to total volume of 5 mL. After centrifugation, the supernatant was analyzed for isotopic composition. Soil Sampling and Preparation. In order to study the impact of deposition of coal combustion fly ash on the ground we chose a coal-fired plant as an emission source to measure its lead contamination to soil. Among the 19 power plants in Shanghai, 17 are coal-fired plants, scattered along the midline across the city from the north to the south. The wind in Shanghai is mainly southeaster/east (E) in summer and northwest (W) in winter, with a frequency ratio of WindE to WindW being about 2 (21). We select a 4 × 600 MW power plant (Shi Dong Kou), which has been burning coal ever since it is establishment in 1988; it is located in the northern part of Shanghai in an area closed to the Yangtze River. It consumes 6.3-6.4 million tonnes of coal per year. The flue gases after electrostatic precipitator are released through 240 m-high stacks. The fly ash in large sizes, such as PM10 and TSP, descends from the stacks over a wide area. Soil samples were collected at 19 sites along a sector from the stacks of Shi Dong Kou Power Plant through a distance of 26 km at the leeward area. Around this area there are no significant sources from coal combustion. Sampling points were selected at the undisturbed place. Before sampling at each point, vegetation was removed from the surface by hand over a radius of 20 cm. The sampler is a cylindrical tube 20 cm long and 5 cm in diameter. Two layers of soil sample with 0-4 cm and 4-8 cm depth were collected into separated plastic bags. Samples were dried at 60 °C in an oven, then ground in an agate mortar and sieved by a nylon sieve into 100 mesh powders, then put into polyester bottles and kept in desiccators. The prepared soil samples were digested by a mixture solution of HNO3-HF-HClO4-H2O2 and subjected to a microwave digestion process. After the microwave digestion, the vessels were heated on a hot plate for evaporating the excess HF until near dry. Finally, the residue was dissolved in 1 mL of HNO3 and diluted with 50 mL of pure water for ICP-MS analysis. Paint Collection and Preparation. There are varieties of paints in the markets, but the paints used for the normal residential area, and particularly dealing with children can mainly be divided to three kinds of paints. They are for toys, indoor decorating, and refurbishing materials included the wall paint. Under the help of Shanghai Institute of Paint Research a total of 69 paint samples were collected. Those samples include different uses, brands, and colors, occupying ∼90% of the retail market. Each sample was stirred and applied by a brush to individual glass plates. After dried by an oven, it was peeled off carefully by a scraper. The preparation procedure of dried powder was conforming to ASTM standard through microwave digestion (22). First, 0.2 g of sample was weighed and mixed with 5 mL of concentrated nitric acid. Then, the mixtures were put into a microwave oven (Ethos 320; Milestone, Italy) to digest. The microwave system reaches to 180 °C in 10 min and then stays at this temperature for 15
min. The digestates were dissolved with ultrapure water to a final volume of 100 mL, and then were filtrated after cooling. Water Sample Collection and Preparation. There are many drinking water supply companies in Shanghai, but just three supply ∼84% of the total of 7.60 million m3 per day. Those companies mainly supply urban Shanghai. Fourteen water samples of 1 L each were collected randomly from different families, covering nearly all water suppliers in Shanghai. After adding two drops of HNO3, the water was kept in clean plastic bottles until analysis. Water was transferred into Teflon vials, evaporated to dryness at 200 °C, and redissolved in 1% HNO3 for concentration and isotopic compositions analysis. Lead Concentration Analysis. Lead concentrations in all samples were measured by ICP-MS, and thallium was added online by a Y-type canal as an internal standard subjected to lead concentration measurement. Analysis of Pb Isotope Ratio. Lead isotope ratios were determined by quadrupole ICP-MS.Their relative abundances were expressed as the ratios of 207Pb/206Pb, 208Pb/206Pb, and 206 Pb/204Pb. NIST 981 (National Institute of Standards and Technology, Gaithersburg, MD) was used to determine the mass bias correction factors. The blank subtraction was taken into account for the final intensity of each isotope in the sample. The uncertainty levels for SRM 981 were mostly under 0.2% for 207Pb/206Pb and 208Pb/206Pb, and 1% for 206Pb/204Pb, respectively. Prior to isotope ratio measurement, lead concentrations in the extracts for blood and digested samples were adjusted in the range of 1-25 ng mL-1 by appropriate dilution with 1% HNO3. Each sample was measured three times. The isotope ratio in water sample after concentrating was measured directly by ICP-MS. Because of its low concentration of lead, each water sample was measured 15 times. High purity water was also measured as a blank. All reagents used are high purity. Statistical Analyses. The correlation coefficients r between BLL of children and lead concentration in TSP in 1991-2005 and between lead concentration in TSP and amount of coal consumed annually in Shanghai in a period of 2000-2005 were calculated by the formula of Pearson correlation coefficient. The average values were obtained by arithmetic mean, and standard deviation is used for indicating the variability of data.
Results Figure 1a shows the relationship between BLL of children and lead concentration in TSP in 1991-2005. A correlated decrease in BLL of children and lead concentration in TSP is evident from Figure 1a, suggesting that the BLL in children is positively correlated with atmospheric particulate matter (PM). It was found that their correlation coefficient (r) and p value are 0.979 and
