Induction of chromosome aberrations in cultured human lymphocytes treated with sand dust storm fine particles (PM2.5)

Toxicology Letters 166 (2006) 37–43

Induction of chromosome aberrations in cultured human lymphocytes treated with sand dust storm fine particles (PM2.5) Aili Wei a,b,1 , Ziqiang Meng a,∗ a

Institute of Environmental Medicine and Toxicology, Shanxi University, Taiyuan 030006, PR China b Department of Biology, Taiyuan Normal University, Shanxi, Taiyuan 030031, PR China Received 9 March 2006; received in revised form 15 May 2006; accepted 15 May 2006 Available online 20 May 2006

Abstract The clastogenic activity of airborne air fine particulate matter (PM2.5, particulates with an aerodynamic diameter ≤2.5 ␮m) has already been demonstrated. However little is known about the health risks associated with sand dust storm PM2.5 and its extract. In order to investigate the clastogenic activity of sand dust storm PM2.5 (include its organic and inorganic extract) on human lymphocytes, the normal PM2.5 and sand dust storm PM2.5 samples were collected in Wuwei city (Gansu Province) and Baotou city (Inner Mongolia), China. The chromosomal aberration (CA) test was employed and the cells were treated with 0, 33, 100, 300 ␮g ml−1 sand dust storm or normal ambient air PM2.5 suspension (physiological saline as solvent control), or inorganic extract (0, 75, 150, 300 ␮g ml−1 , physiological saline as solvent control) or organic extract (0, 20, 40, 80 ␮g ml−1 , DMSO as solvent control) at the beginning of the cell culture. The results indicated that sand dust storm PM2.5 and its extract as well as normal samples can induce increase in CA frequency. With the increase of treatment concentrations the CA frequency increased and the mitotic index (MI) values declined in a dose–response manner. In the same concentrates, the CA frequency of normal ambient air PM2.5 and its extract were significant higher than those of sand dust storm PM2.5 (P < 0.05 or 0.01) except the treatment of Wuwei sample at higher doses (100, 300 ␮g ml−1 ), the treatment of inorganic extract of PM2.5 at the highest dose (300 ␮g ml−1 ) and the treatment of organic extract of PM2.5 at the higher dose (40 and 80 ␮g ml−1 ) either in Baotou or in Wuwei (P > 0.05). The toxicity of sand dust storm PM2.5 and its extract at high dose is very potent. CA frequency of normal PM2.5 (include its organic extract) from Baotou were higher than those of Wuwei especially in low and middle dose (P < 0.05), but the treatment results of sand dust storm PM2.5 (include its all extract) was not significant different between the cities (P > 0.05). © 2006 Elsevier Ireland Ltd. All rights reserved. Keywords: Sand dust storm; Fine particles (PM2.5); Human lymphocytes; CA frequency

1. Introduction ∗

Corresponding author. Tel.: +86 351 7011895; fax: +86 351 7011895. E-mail addresses: [email protected] (A. Wei), [email protected] (Z. Meng). 1 Tel.: +86 351 2275704.

Sand dust storm is defined as having an instantaneous wind velocity of >17 m/s and a sky visibility of <1 km (Middleton, 1997; Chen et al., 2003; Wang et al., 2004). Such storms are common phenomena which occur with great frequency and magnitude over the arid

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and semi-arid regions of the earth’s land surface (Goudie, 1978; Meng, 2001; Meng et al., 2003). In the process of forming and transporting of particles, the chemical and biological pollution occur, and the damage of airborne fine particles (PM2.5) to human health occur too. Epidemiological studies have found that respiratory diseases, mortality, cardiovascular diseases in the elderly and even Al Eskan disease (or Desert Storm pneumonitis) were associated with dust storms (Chen et al., 2004; Hefflin et al., 1991; Kwon et al., 2002; Korenyi-Both et al., 1992). It is speculated that these diseases or deaths might be caused mainly by dust storm PM 2.5 (particles ≤2.5 ␮m in aerodynamic diameter) or ultrafine particles (PM 0.1) since the coarse particles (commonly referred to as particles between 10 and 2.5 ␮m in aerodynamic diameter) are typically filtered by the nose or coughed out of the throat and upper lungs despite that PM10 can in some individuals yield breathing problems or aggravate pre-existing breathing problems, such as asthma (Englert, 2004). Although toxicity may be due to a direct action of PM2.5 on the respiratory tissue, particle composition varies extensively and toxicological effects may also be mediated by compounds present in or associated with PM2.5 (Lei et al., 2004). There are many reports about the toxicological effect of ambient air PM2.5 and its components (organic and inorganic extract) on human lymphocytes, such as chromosome damage, micronuclei form and so on (Buschini et al., 2001; Lucas and Neas, 2000; Zhang et al., 2004), so do the toxicological effect of sand dust storm PM2.5 on rat alveolar macrophages and human lung fibroblasts (Geng et al., 2005; Jin et al., 2004; Huang et al., 2004). Although the respiratory toxicities of PM2.5 from urban atmosphere, coal dust, fly ash, sand dust storm, etc. have been evaluated (Payne et al., 2004; Hamilton et al., 2004; Lei et al., 2004), little is known about the clastogenic activity of sand dust storm PM2.5 (include its organic and inorganic extract) on human lymphocytes. So the chromosomal aberration test was employed in order to know the genotoxicity effect of sand dust storm PM2.5 (include its organic and inorganic extract) from different kind of cities on human lymphocytes. 2. Materials and methods 2.1. Sampling The sand dust storm PM2.5 samples as well as normal PM2.5 ones (collected on sunshiny days and non-blowing sand days) were collected in Wuwei city (101◦ 49 –104◦ 43 E, 36◦ 29 –39◦ 27 N), Gansu Province, northwest China and also collected in Baotou city (109◦ 50 –111◦ 25 E, 41◦ 20 –42◦ 40 N),

Table 1 Air pollution conditions of Baotou and Wuwei city Items Air quality standard Wuwei (n = 23) Baotou (n = 23)

PM10 (␮g/m3 ) 150 68 ± 41.0 80 ± 34.0

SO2 (␮g/m3 )

NO2 (␮g/m3 )

150

120

34.8 ± 26.7 78.9 ± 61.4

12.3 ± 4.0 28.5 ± 15.0

Inner Mongolia, north China. Wuwei is an agricultural city. The city is easily disturbed by sand dust storm because the Badian Jaran Desert and the Tengger Desert are near it. Baotou is an industry city also disturbed by the sand dust storms originating from the Badian Jaran and Tengger Deserts, as well as from the Kubuqiare Desert, Wulanbheand sand, Mus sand and Hunsandken sand. The air quality conditions of the two cities were showed in Table 1. The PM2.5 high volume air sampler (Thermon Anderson) was placed on the rooftop of a building about 10-m tall in Wuwei city and Baotou city and there were no large obstacles and no large pollution sources near the building. From 1 March to 31 March 2004, normal airborne PM2.5 samples and sand dust storm PM2.5 samples were collected on quartz filters (Whatman, American). The flow rate of the sampler was 1.13 m3 min−1 (±10%) and the sampling time was nominally 24 h with sampling starting at 5:00 p.m. Filter papers with fine particles were packaged by aluminum foil and numbered, preserved avoid light in −20 ◦ C. The samples were divided into two groups (normal samples and sand dust storm samples) basing on the PM2.5 standard of ambient air quality of American EPA and the standard of ambient air quality of China (GB3095, 1996), also according to the datum of local weather department and environment protection station. 2.2. Preparation of fine particles (PM2.5) and organic and inorganic extract The filters loading PM2.5 samples were cut into triplet, one for the preparation of total fine particle suspensions, one for the preparation of organic extract and one for inorganic extract. The preparation of fine particles (PM2.5) according to the method of Geng et al. (2005). The filters loading PM2.5 samples were cut and surged in Milli-Q water with sonication. The PM2.5 suspensions were obtained and frozenly dried in vacuum. To obtain inorganic fraction of PM2.5, the above suspensions were filtered through 0.45 ␮m filters (Whatman, American) and dried (Veronesi et al., 1999); to obtain solvent-extractable organics of PM2.5, the extraction procedure was according to Zheng et al. (1997). Briefly, the solvent-extractable organics of samples were extracted using dichloromethane in an ultrasonic bath, then dried. The samples were stored at −20 ◦ C. Prior to use, the dried fine particle (PM2.5) samples were diluted with sterilized 0.9% physiological saline to make suspensions, inorganic extract were made to solution with sterilized 0.9% physiological saline and organic extract were made

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to solution by DMSO. PM2.5 samples were swirled for 5 min before use. 2.3. Cell culture and treatment Chromosome aberration test was carried out according to Edith et al. (1999) with slight modifications. Blood samples from four healthy donors for each treatment were obtained by venipuncture using heparinized syringe lymphocyte cultures were set up by adding 0.5 ml of whole blood to 4.5 ml of RPMI 1640 medium supplemented with 20% heat-inactivated fetal calf serum, l00 U ml−1 antibiotics (penicillin and streptomycin, respectively). Lymphocytes were stimulated by adding 40 ␮g ml−1 phytohaemagglutinin (PHA-M, Sigma Chem. Co., U.S.A.), pH 7.2–7.4. At the beginning of the cell culture, different concentrates of sand dust storm PM2.5 suspension and normal ambient air PM2.5 suspension (0, 33, 100, 300 ␮g ml−1 , physiological saline as solvent control), or inorganic extract (0, 75, 150, 300 ␮g ml−1 , physiological saline as solvent control) or organic extract (0, 20, 40, 80 ␮g ml−1 , DMSO as solvent control) were added to the cultures. After 24 h incubation at 37 ◦ C in 5% CO2 , colcemid solution was present in the cultures at final concentration of 0.3 ␮g ml−1 . At 52 h of incubation, the cultures were harvested according to the method described by Preston et al. (1987) with slight modification. The cells were harvested by centrifugation (1000 rpm) 10 min, given a hypotonic shock in 0.075 mol/l KCl (37 ◦ C) for 25 min, and then fixed three times in a fresh solution of methanol/glacial acetic acid (3:1, v/v). Slides were coded and prepared using usual air-drying technique, stained with 5% Giemsa (Sigma) and analyzed for chromosome aberrations. For each donor, 150 well-spread metaphases cells containing 46 chromosomes for each PM2.5 or its extract concentrate were analyzed for chromosome structure damage. Gaps were not included. Identification of the aberration type was performed according to the International System for Human Cytogenetic Nomenclature (1985). The mitotic index (MI) was calculated as the proportion of metaphases among the total cell population by counting a total of 1000 cells. It was calculated by applying the formula below (Alejandro and Martha, 2002): MI (%) =

no. of cells in division × 100 total no. of cells

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2.4. Statistical analysis The results are presented as the means ± standard deviation (S.D.) of four independent experiments. Statistical analysis of chromosome aberrations frequency was performed on log-transformed values as the data was non-normal, by using a statistical package SPSS Version 11.0 for windows. Mean frequency was compared using t-test for normal ambient air PM2.5 (include its extract) and sand dust storm PM2.5 (include its extract), also for Baotou and Wuwei city, and present the results at 0.05(* ) or 0.01(** ) level of significance. Statistical analysis for effect of dose was compared using ANOVA followed by Duncan’s test for multiple comparisons for correction. Correlation coefficients were calculated to analyze dose–response relationships.

3. Results 3.1. The variation of mitotic index of different treatment As Fig. 1 showed, compared to control, the treatment of different samples from Baotou and Wuwei decreased the mitotic index significantly (P < 0.05 or 0.01). The relationship between treatment dose and CA level was positive correlation and the relationship between treatment dose and MI was negative correlation (Table 2). 3.2. The variation of chromosome aberration frequency of different treatment Compared to control, both the treatment of sand dust storm and normal fine particles samples from Baotou and Wuwei increased the CA frequency of lymphocytes (Fig. 2) in a dose–response manner with the increase of concentrates (Table 2). In the same concentrates, CA frequency of normal ambient air PM2.5 and its extract were significant higher than those of sand dust storm PM2.5 (P < 0.05 or 0.01) except the treatment of Wuwei sample

Fig. 1. Mitotic index of different treatments. (Notes: BN stands for Baotou normal, BS stands for Baotou sand, WN stands for Wuwei normal, WS stands for Wuwei sand; * P < 0.05, ** P < 0.01, compared to control, n = 4.)

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Table 2 Correlation coefficient of CA or MI and dose Samples

BN BS WN WS

Correlation coefficient of CA and dose

Correlation coefficient of MI and dose

PM2.5

Organic extract

Inorganic extract

PM2.5

Organic extract

Inorganic extract

0.8814 0.9512* 0.9195 0.9780*

0.9739* 0.9727* 0.9633* 0.9606*

0.9716* 0.9910** 0.9945** 0.9789*

−0.9794* −0.9935** −0.9845* −0.9967**

−0.9876* −0.9965** −0.9934** −0.9978**

−0.9836* −0.9863* −0.9931** −0.9945**

Notes: BN stands for Baotou normal, BS stands for Baotou sand, WN stands for Wuwei normal, WS stands for Wuwei sand; * P < 0.05, ** P < 0.01, compared to control, n = 4.

Fig. 2. Chromosome aberration frequency of different treatment. (Notes as Fig. 1, # stands for the difference between normal and sand samples of the same city P < 0.05, ## P < 0.01.)

at higher doses (100, 300 ␮g ml−1 ), the treatment of inorganic extract of PM2.5 at the highest dose (300 ␮g ml−1 ) and the treatment of organic extract of PM2.5 at the higher dose (40 and 80 ␮g ml−1 ) either in Baotou or in Wuwei (P > 0.05). The toxicity of sand dust storm PM2.5 and its extract at high dose is very potent. CA frequency of normal PM2.5 (include its organic extract) from Baotou were higher than those of Wuwei especially in low and middle dose (P < 0.05), but the treatment results of sand dust storm PM2.5 (include its all extract) was not significant different between the cities (P > 0.05).

3.3. Chromosome aberration of lymphocytes treated with sand dust storm PM2.5 sample The treatment of different samples can induce CA detected as chromatid break, chromosome break, deletion, acentric fragment, dicentric chromosome, acentric ring, chromosomal and chromatid gaps. But the aberration induced by sand dust storm PM2.5 is mainly of chromatid type (breaks and deletion) and acentric fragment (Figs. 3–5). The aberration number and dose has no directed relationship.

Fig. 3. Number of chromatid break of different treatment. (Notes as Fig. 1, number of structural chromosome aberrations is from four dorners (600 cells) for each treatment dose, analyze 150 cells per dorner.)

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Fig. 4. Number of deletions of different treatment. (Notes as Fig. 1, number of structural chromosome aberrations is from four dorners (600 cells) for each treatment dose, analyze 150 cells per dorner.)

Fig. 5. Number of acentric fragments of different treatment. (Notes as Fig. 1, number of structural chromosome aberrations is from four dorners (600 cells) for each treatment dose, analyze 150 cells per dorner.)

4. Discussion During the last years it has been shown several times that chromosomal aberrations in human peripheral blood lymphocytes are a sensitive biomarker of genotoxic damage (Edith et al., 1999). A large number of human biomonitoring studies are based on the data from the chromosomal aberration assay in human lymphocytes, either alone or in combination with other biomarkers of genetic damage (Alejandro and Martha, 2002). The chromosomal aberration assay has also been proven to be a convenient test for somatic risk assessment. Clear evidence has been presented that an enhanced frequency of chromosomal aberrations correlates with an increased incident of tumour and cancer in epidemiological surveys and is of predictive value for subsequent cancer risk especially blood lymph system tumour risk (Perera et al., 1992; Bonassi et al., 2000). In the present study, sand dust storm PM2.5 and its extract treatments cultures as well as normal PM2.5 and its extract treatments cultures induced increase in CA frequency. The difference was significant among different treatment dose (P < 0.5 or 0.01). With the increase of treatment dose the CA frequency increased and the MI declined in a dose–response manner. This indicated that sand dust storm PM2.5 is an kind of

chromosome clastogen and the toxicity mainly related to dose. The results also showed that the CA frequency of Baotou normal PM2.5 at any dose and Wuwei normal PM2.5 at lowest dose were significant higher than those of sand dust storm PM2.5. But the difference of the treatment of inorganic extract of PM2.5 at the highest dose (300 ␮g ml−1 ) and the treatment of organic extract of PM2.5 at the higher dose (40 and 80 ␮g ml−1 ) either in Baotou or in Wuwei was not significant (P > 0.05). So we think the reason maybe related to normal PM2.5 can absorb a lot of poisons include organic pollutions and inorganic pollutions in normal weather, so the treatment results were higher than those of sand dust storm PM2.5. But when the dose come to some extent, the toxicity of sand dust PM2.5 and its extract is similar to normal PM2.5 and its extract. The toxicity of sand dust PM2.5 and its extract in high dose cannot be ignored. CA frequency of Baotou normal sample were significant higher than those of sand dust storm PM2.5 maybe related to Baotou is an industry city and normal ambient air pollution are relative serious, PM2.5 absorb a lot of poisons, include organic pollutions. Wuwei just in the lowest dose was significant different showed the difference between sand dust storm sample and normal sample was little. It maybe related to Wuwei is an agricultural town, air pol-

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lution was relatively light, sand dust storm PM2.5 and normal PM2.5 all absorb little pollution poisons (pollution condition see Table 1). Compare the difference between the cities, the difference of sand dust storm PM2.5 (include its extract) from the two cities was not significant. It maybe related to the two cities were all near the desert and sand dust storm transport distance are short, so sand dust storm PM2.5 from the two cities all can absorb little pollutants. Lei et al. (2004) have proposed that the chemical composition of dust storm PM2.5 or/and the microorganisms such as fungi and bacteria absorbed onto the surface of the particles might contribute to pulmonary inflammation. According to the analysis of Guo et al. (2003, 2004), the main fractions of solvent-extractable organic compounds of PM2.5 in Asian dust episodes were nalkanes, polycyclic aromatic hydrocarbons (PAHs) and fatty acid. In addition, the solvent-extractable organic compounds, in general, showed much smaller variations in the dust and non-dust samples. However, there was no metabolic activation system (S9 mix) exist in my test, PAHs do not have sufficient metabolic activity, but the results showed that organic extract of sand dust storm PM2.5 can induce CA. All of these suggested that the organic extract may include other direct mutagens. The components of sand dust storm PM2.5 is complex and multiplex. The further test on the components of sand dust storm PM2.5 need to be completed. According to the report of Sun et al. (2005) and Wang et al. (2005), the major inorganic fraction of PM2.5 from the dust days was CaSO4 , while the main chemical species of the inorganic fraction of PM2.5 was NH4 NO3 in the non-dust days. In addition, the average concentrations of Fe, Al, Ca, Na, Ti, Mg in PM2.5 from dust days were 5–8 times higher than those from non-dust days. The results showed that the difference between the inorganic extract of normal and sand dust storm PM2.5 at the highest dose (300 ␮g ml−1 ) was not significant. All of this indicated that the toxicity of inorganic extract at 300 ␮g ml−1 is important and has no direct relationship to components, but the difference between normal and sand dust storm samples at lower dose maybe related to the difference of their components. Airborne PM2.5 mass quality (particles in per unit volume air) was very high during the dust events (Claiborn et al., 2000). In the present study, Wuwei normal ambient air PM2.5 mass quality is 61.94 ␮g/m3 , sand dust storm PM2.5 is 152.47 ␮g/m3 , Baotou PM2.5 mass quality in normal weather is 77.18 ␮g/m3 and sand dust storm weather is 252.56. Because the mass quality concentrate in normal and sand dust storm weather is different, especially when the sand dust storm occurring,

PM2.5 concentrates rise up, PM2.5 concentrates in per unit stere in cities and two kinds of weather are different. In this point of view, the difference between the cities or the normal weather and sand dust storm may be different, the toxicity of sand dust storm PM2.5 and its extract maybe higher than normal sample. Acknowledgements This research program was supported by the National Natural Science Foundation of China (No. 30230310) and by a grant from the Natural Science Foundation of Shanxi Province (No. 20031092). References Alejandro, D.B., Martha, S.B., 2002. Chromosomal response of human lymphocytes to streptozotocin. Mut. Res. 503, 63–68. Bonassi, S., Hagmar, L., Stromberg, U., et al., 2000. Chromosomal aberrations in lymphocytes predict human cancer independently of exposure to carcinogens. European Study Group on Cytogenetic Biomarkers and Health. Cancer Res. 60, 1619–1625. Buschini, A., Cassoni, F., Anceschi, E., 2001. Urban airborne particulate genotoxicity evaluation of different size fractions by mutagenesis tests on microorganisms and comet assay. Chemosphere 44, 1723–1736. Chen, Y.S., Shen, P.C., Chen, E.R., Liu, Y.K., Wu, T.N., Yang, C.Y., 2004. Effects of Asian dust storm events on daily mortality in Taipei, Taiwan. Environ. Res. 95, 151–155. Chen, Y., Cai, Q., Tang, H., 2003. Sand dust storm as an environmental problem in north China. Environ. Manage. 32, 413–417. Claiborn, C.S., Finn, D., Larson, T.V., Koenig, J.Q., 2000. Windblown dust contributes to high PM2.5 concentration. J. Air Waste Manage. Assoc. 50, 1440–1445. Edith, H., Annemarie, G., Teodora, N., 1999. Chromosomal aberrations in humans as genetic endpoints to assess the impact of pollution. Mut. Res. 445, 251–257. Englert, N., 2004. Fine particles and human health—a review of epidemiological studies. Toxicol. Lett. 149, 235–242. Geng, H., Meng, Z.Q., Zhang, Q.X., 2005. Effects of dust storm fine particles on the calcium level and lipid peroxidation of rat alveolar macrophages. Acta Scientiae Circumstantiae 25, 845–850. Goudie, A.S., 1978. Dust storms and their geomorphologic implications. Arid Environ. 1, 291–310. Guo, Z.G., Feng, J.L., Fang, M., Chen, H.Y., Lau, K.H., 2004. The elemental and organic characteristics of PM2.5 in Asian dust episodes in Qingdao, China, 2002. Atmos. Environ. 38, 909–919. Guo, Z.G., Sheng, L.F., Feng, J.L., Fang, M., 2003. Seasonal variation of solvent extractable organic compounds in the aerosols in Qingdao, China. Atmos. Environ. 37, 1825–1834. Hamilton Jr., R.F., Holian, A., Morandi, M.T., 2004. A comparison of asbestos and urban particulate matter in the in vitro modification of human alveolar macrophage antigen-presenting cell function. Exp. Lung Res. 30, 147–162. Hefflin, B.J., Jalaludin, B., McClure, E., Cobb, N., Johnson, C.A., Jecha, L., Etzel, R.A., 1991. Surveillance for dust storms and respiratory diseases in Washington State. Arch. Environ. Health 49, 170–174.

A. Wei, Z. Meng / Toxicology Letters 166 (2006) 37–43 Huang, X.L., Jin, X., Guo, X.B., 2004. Impact of dust storm PM2.5 and PM10 on the phagocytic function of alveolar macrophages of rat. Hyg. Res. 33, 154–157. ISCN, 1985. An International System for Human Cytogenetic Nomenclature. S. Karger, New York. Jin, Y., Guo, X., Huang, X., 2004. Study on the cytotoxicity of dust storm PM (10) and PM (2.5) on human lung fibroblasts. J. Environ. Health 21, 199–201. Korenyi-Both, A.L., Molnar, A.C., Fidelus-Gort, R., 1992. Al Eskan disease: Desert Storm pneumonitis. Mil. Med. 157, 452–462. Kwon, H.J., Cho, S.H., Chun, Y., Lagarde, F., Pershagen, G., 2002. Effects of the Asian dust events on daily mortality in Seoul, Korea. Environ. Res. 90, 1–5. Lei, Y.C., Chan, C.C., Wang, P.Y., Lee, C.T., Cheng, T.J., 2004. Effects of Asian dust event particles on inflammation markers in peripheral blood and bronchoalveolar lavage in pulmonary hypertensive rats. Environ. Res. 95, 71–76. Lucas, M., Neas, 2000. Fine particles matter and cardiovascular disease. Fuel Process. Technol. 65, 55–67. Meng, Z.Q., Hu, M., Guo, X.B., 2003. Effects of dust storms on human health. Chin. J. Public Health 19 (4), 471–472. Meng, L., 2001. Sand dust storm causes and its control in Songhuajiang and Liaohe regions. Soil Water Conserv. China 6, 26–27. Middleton, N., 1997. Desert dust. In: Thomas, D.S.G. (Ed.), Arid Zone Geomorphology, 2nd ed. Wiley, Singapore, 713 pp. Payne, J.P., Kemp, S.J., Dewar, A., Goldstraw, P., Kendall, M., Chen, L.C., Tetley, T.D., 2004. Effects of airborne World Trade Center dust on cytokine release by primary human lung cells in vitro. J. Occup. Environ. Med. 46, 420–427.

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Perera, F.P., Hemminki, K., Gryzbowska, E., Motykiewicz, G., Michalska, J., Santella, R.M., Young, T.L., Dickey, C., Brandt-Rauf, P., De Vivo, I., Blaner, W., Tsai, W.Y., Chorazy, M., 1992. Molecular and genetic damage in humans from environmental pollution in Poland. Nature 360, 256–258. Preston, S.R.J., Sebastian, J.R., McFee, A.F., 1987. The in vitro human lymphocyte assay for assessing the clastogenicity of chemical agents. Mut. Res. 189, 175–183. Sun, Y.L., Zhuang, G.S., Wang, Y., Zhao, X.J., Li, J., Wang, Z.F., An, Z.S., 2005. Chemical composition of dust storms in Beijing and implications for the mixing of mineral aerosol with pollution aerosol on the pathway. J. Geophys. Res. 110, 1–11. Veronesi, B., Oortgiesen, M., Carter, J.D., et al., 1999. Particulate matter initiates inflammatory cytokine release by activation of capsaicin and acid receptors in a human bronchial epithelial cell line. Toxicol. Appl. Pharmacol. 154, 106–115. Wang, X., Dong, Z., Zhang, J., Liu, L., 2004. Modern sand dust storms in China: an overview. J. Arid Environ. 58, 559–574. Wang, Y., Zhuang, G.S., Sun, Y.L., An, Z.S., 2005. Water-soluble part of the aerosol in the dust storm season-evidence of the mixing between mineral and pollution aerosols. Atmos. Environ. 39, 7020–7029. Zhang, J., Yang, W., Xu, Y., 2004. DNA damages in peripheral blood lymphocytes induced by organic extracts from ambient air particles with various diameters. J. Environ. Health 21, 88–90. Zheng, M., Wan, T.S.M., Fang, M., Wang, F., 1997. Characterization of the non-volatile organic compounds in the aerosols of Hong Kong—identification, abundance and origin. Atmos. Environ. 31, 227–237.