Research On The Distribution, Sources And Risk Assessment Of Alkanes And Polycyclic Aromatic Hydrocarbons Of Xi’an Outskirt

The types of organic pollutants in environment were complex and diverse, and theirnatures were not same, their sources were also difficult to differentiate. As a class of toxicpollutants, n-alkanes and polycyclic aromatic hydrocarbons were concerned by researchers.Xi’an was an important industrial and agricultural production base of Weihe Plain, with theincreasing of population and the urbanization of Xi’an, the ecological environment has alsoundergoned great changes. Under long-term industrial activities, large amounts of waste water,waste gas, waste, etc. has been produced, which resulted in serious contamination of soil andcrops in the city and the surroundings.In order to strengthen the pollution prevention and control about the alkanes andpolycyclic aromatic hydrocarbons (PAHs) in media of Xi’an outskirt, provide basic data forenvironmental protection about alkanes and PAHs in the system of soil-irrigation water–vegetable,37soil samples,36vegetable samples and38water samples were collected fromXi’an typical suburban vegetable base, then n-alkanes and PAHs were extracted from soil andvegetable samples using accelerated solvent extraction device (ASE), extracted from watersamples using solid phase extraction method, silica/alumina column purification were used tocleansing, last, n-alkanes and PAHs were analyzed quantitatively using gaschromatography/mass spectrometry (GC/MS). The sources of n-alkanes and PAHs wereanalysed using their geochemical parameters and multivariate statistical methods. Based onthe results of toxicity tests, Nisbet proposed that the toxic equivalent (TEQBaP) can becalculated according to the components of PAHs in soil with respect to the TEF which wasabout BaP, then TEQBaP canbe used to assess the health risks about soil. The main results asfollows:(1) The concentration of n-alkanes in soil of Xi’an outskirt ranged from1.06to4.01μg/g,the carbon number range was nC10to nC36, nC31was the main peak carbon. The resultindicated there was a certain degree of pollution about soil of Xi’an outskirt, which wascompared with other regions and abroad. The concentration of ΣPAH16in soil ranged from27.26to935.32μg/kg,3to5ring PAHs were dominant. The pollution level of PAHs in soil was low or middle, which compared with the standards about soil. There was an impact aboutorganic matter, moisture, carbon/phosphorus ratio, carbon/nitrogen ratio to the distribution ofn-alkanes in soil soil, and the impact was significant correlation between the organic matterand the concentration of n-alkanes, the same result also found between the concentration ofΣPAH16and organic matter in soil.(2) The n-alkanes in soil of Xi’an outskirt was mainly derived from the incompletecombustion of fossil fuels, vehicle emissions and the input of terrigenous higher plants(herbaceous plants were dominant), especially the last one. Oil, coal and high-temperaturecombustion of biomass were the main input source of PAHs in soil. The result according tofactor analysis/multivariate regression analysis indicated that traffic emissions and burning ofcoal and straw were the two main sources, and the average contribution rates were55.23%and41.98%.(3) The concentration of n-alkanes, ΣPAH16and ΣPAH7C in vegetables wererespectively ranged from20.02to284.72μg/g, ranged from121.92to2507.19μg/kg, andranged from20.61to214.77μg/kg. Low molecular weight of PAHs (3ring) were dominant invegetables. Celery has the highest levels of PAHs, which related to its own structure in someextent. The level of PAHs in vegetables of Xi’an outskirt was slightly higher, which comparedwith the other vegetables from differnt regions.(4) The concentrations of n-alkanes and ΣPAH16were respectively ranged from9.2to99.35μg/L and ranged from247.05to1867.18ng/L in groundwater. The concentrations ofPAHs in Baqiao district was higher than Weiyang district and Lintong district, which may berelated to the more developed industry. The percentage of5~6ring PAHs was ranged from46.83%to64.89%in ΣPAH16.