| This research investigates the physicochemical characteristics and toxicity of indoor particles including PM10, PM2.5, and size-segregated particles in different areas of Xuanwei with high(Hutou) and low(Xize) lung cancer mortality rates by individual particle analysis, elemental analysis, and toxicology analysis. The range of 24 h average mass concentrations of PM10 in Xuanwei in summer was 203.06μg/m3 to 365.26μg/m3, which is higher than that outlined in the second of China Ambient Air Quality Standards(150μg/m3). In samples from winter, the mass concentration of biomass-burning particles was the highest(350μg/m3), followed by electricity-fuel(coal-burning during the night), then coal-burning particles. In summer samples, the mass concentration of coal-burning particles was the highest(350μg/m3), followed by electricity-fuel, biomass-burning particles and outdoor particles. Differences between average mass concentrations of particles in the two locations in winter and summer are small. The mass ratio of indoor to outdoor particles(I/O) of coal-burning PM2.5(Hutou), electricity-fuel PM2.5(Hutou) and biomass-burning PM10(Xize) were 1.10, 1.78, and 2.27 respectively. All ratios are greater than one, meaning that indoor particles in Xuanwei originate from indoor pollution. The range of mass concentrations of indoor and outdoor PM2.5 in Hutou was 38.54 to 102.64μg/m3, while that in Xize was 32.94 to 54.70μg/m3. The mass concentration of PM2.5 in the coal-burning house in Hutou was higher than in houses using other fuels. The range of mass concentrations of indoor and outdoor PM10 in Hutou was 84.09 to 355.75μg/m3, while that in Xize was 51.23 to 661.49μg/m3. The mass concentration of PM10 in the biomass-burning house in Xize was almost three times greater than in the other houses, thus burning biomass produces more particles than burning coal. The average mass of PM10 in Hutou in the winter of 2013 was almost half of that in 2011, both during the day and at night. The average PM2.5 mass in Hutou in the winter of 2013 was almost one third of that in 2011 in daytime samples, the mass of samples taken at night remained at the same level. Consequently, after three years the average mass concentration of particles has dramatically decreased, and indoor air pollution has been reduced.The analysis of individual particles by a transmission electron microscope with energy dispersive X-ray(TEM-EDX) showed that the size range of individual particles in both Hutou and Xize was from 0.2μm to 3μm, though few particles in either location were larger than 2μm. The size distribution of samples in the two locations showed the same pattern, and the majority of particles were smaller than 1μm.Sulphur(S) and silica(Si) were the most abundant elements in Hutou and Xize. Xize, which has low lung cancer incidence, has eight fewer elements present than Hutou, though arsenic(As) is only detected in Xize. According to morphology information and chemical compositions obtained by TEM-EDX, individual particles were classified into five types: fly ash, organics(soot, tar ball, and bioparticle), mineral particles, sulphates and mixed particles. Mixed particles were the most common at both locations. Solid particles such as fly ash, organics, and mineral particles react with acid gas and water in the atmosphere, forming ions such as H+, SO42- and NO3-. Further reactions generate mixed particles including core–shell particles. Most mixed particles have an external or internal mixture including soot, organics, minerals and sulphate. The aging degree of core–shell particles, and the core–shell ratio, partly showed the aging status of mixed particles. The equivalent diameter range of core–shell particles was from 0.5 to 2.5μm, with an average diameter of 1.6μm. Almost all core–shell ratios fell between 0.4 and 0.8, the average value was 0.6.The toxicity of indoor particles was analysed by plasmid scission assay(PSA). Under dosages of 50, 100, 150, 200, and 250μg/m L, the DNA damage rate by PM10 in winter ranged from 6 to 98%, the peak winter value was found in biomass-burning particle samples in Xize. The range in summer was 24 to 72%, the peak summer value was found in coal-burning particle samples in Hutou. Overall, particle toxicity was higher in summer than in winter. The DNA damage rate by PM10 in the biomass-burning house in Xize was relatively high regardless of season. Under dosages of 50, 100, 150, 200, 250, 500, and 1000μg/m L, the DNA damage rate by PM10 ranged from 15 to 95%, and there was a dosedamage response. In samples from Hutou in winter, the DNA damage rate of particles sampled during cooking was higher than those sampled at other times. Night-time particles were more toxic than those during the day, especially in Xize. Comparison of DNA damage rates of particles from different burning methods concludes that coalburning particles are the most toxic, followed by biomass and electricity. Some residents in Xuanwei do not have kitchens with chimneys; instead they cook directly in the living room. Particles sampled in rooms with chimneys were less toxic than those without. There is no correlation between DNA damage rate and mass concentration of particles, mainly because the harm exerted on the human body by particles is connected to chemical composition and the toxic substances on the surface of particles, thus mass concentration cannot be used to evaluate particle toxicity.In cell apoptosis assay, under dosages of 6.25, 12.5, 25 and 50μg/m L, the percentage of apoptosis cells in Xuanwei was low and showed weak rising trend, and the highest apoptosis percentage was under dosage of 50μg/m L. In haemolysis assay, under dosages of 50, 250, 500, 1000, 2000μg/m L, the percentage of haemolysis cells in Xuanwei was low which showed that even when the dosage is 2000μg/m L, it is not high enough to cause high haemolysis percentage, so for samples in Xuanwei, only when human inhale particles of enough high concentration, the red blood cells can be damaged.Elemental composition analysis conducted by inductively coupled plasma mass spectrometry(ICP-MS) showed that zinc, titanium, and nickel content was high in all samples: zinc content in winter samples ranged from 676 to 16978 ppm, titanium content ranged from 577 to 25560 ppm, and nickel content ranged from 459 to 6508 ppm. Zinc content in summer samples ranged from 2013 to 22220 ppm, titanium from 755 to 1620 ppm, and nickel from 1058 to 9200 ppm. The content of each element in samples from the electricity-fuel house in Hutou and the biomass-burning house in Xize was relatively high, the total elemental content of the former was very high(81841.96ppm), because the residents burn coal for heating during the night. The total elemental content of samples in winter is higher than that in summer, the maximum value is found in the Hutou electricity-fuel house(36590.45ppm) and the minimum value in the Hutou coalburning house(8157.45ppm). The peak value in summer samples is 30318.82ppm(Hutou outdoor sample), the lowest value is 9226.74ppm(Hutou coal-burning house). The zinc content in the samples was positively correlated with DNA damage rate; the correlation coefficient is 0.67 at the 0.05 significance level, therefore soluble zinc may be one of the main contributors to particle toxicity. Converting the elemental content in particles into standard atmospheric conditions(ng/m3) gives the most abundant elements in the atmosphere as Zn, Ni, and Ti. The concentration ranges of Zn, Ni, and Ti in the air were 11.1916 to 424.4598ng/m3, 8.9197 to 118.1527ng/m3, and 16.3403 to 639.0148ng/m3 respectively. The elemental content of particles in the air was lower in 2013 than in 2011, 2013 had most elemental contents measuring less than 10ng/m3 and no elemental content higher than 500ng/m3. Zinc was the highest elemental content in both years, but was lower in 2013. The results of energy dispersive X-ray(EDX) echo those of ICP-MS. Zinc can be used as the fundamental element to define particle toxicity using the correlation coefficients between the elements and DNA damage rate, and between different elements. |
