Analysis Method And Distribution Of Polycyclic Aromatic Hydrocarbons In Soil-plant System

Polycyclic aromatic hydrocarbons(PAHs)are a group of persistent organic pollutants consisting of two or more fused aromatic rings and formed during the incomplete combustion of fossil fuel.They are teratogenic,carcinogenic and mutagenic toxicity with high lipid solubility and strong hydrophobicity.PAHs are stable and difficult to be degraded in soils thus posing a serious threat to ecological security and human health through the soil-plant system.It's significant to figure out the distribution of PAHs in soil-plant system,so as to prevent the soil pollution and ensure the safety of agricultural products.Previous researchers used a single ultraviolet or fluorescence detector in high performance liquid chromatography(HPLC)analysis technology to analyze the PAHs in soil and plant samples.However,when using a single detector to test the multiple PAHs contained samples,limited by the standard curve linear range,detection limits,PAHs optical properties and the concentration of each kind of PAH,we have to operate many times and even a sample dilution process is needed.The operation is complicated,time-consuming and expensive.Developing of HPLC/UV-FLD analysis technology is expected to overcome these problems and simultaneously detect many kinds of PAHs in one sample injection.In this paper,a tandem method of ultraviolet and fluorescence detector in high performance liquid chromatography analysis is established to test 16 kinds of polycyclic aromatic hydrocarbons in soil and plant samples.The PAHs accumulation and absorption in several crops planted in 16 PAHs contained soils are investigated as well as the residual regularity of PAHs through a pot experiment in the greenhouse.The main results are as followed:(1)Building an analysis method of 16 polycyclic aromatic hydrocarbons in soils and plants by high performance liquid chromatography with ultraviolet-fluorescence detector.The ultrosonication extraction combined with HPLC/UV-FLD analysis technique was introduced to determine 16 PAHs of the priority pollutants named by the US Environmental Protection Agency(USEPA)in soil and plant samples.The analysis method is simple to operate,time saving,high recovery rate,good repeatability and implements that a variety of large differences in the concentration of PAHs in the sample are simultaneously detected after one sample injection.The recoveries of 16 test PAHs in Chinese cabbage and rice were 55.68%?106.2%,with relatively standard deviations(RSD)of 0.555%?12.5%.The recoveries of these PAHs in soils were 65.59%?104.4%with RSD of 0.589%?15.8%.This potentially useful and prospective analysis method can be utilized in understanding the transport and fate of PAHs in soil-plant system.(2)Revealing the residual regularity of PAHs in vegetated soil.The soil sample was prepared and initial concentration of ?PAHs are 102(S1)?172(S2)?351 mg/kg(S3).The crops tested were Chinese cabbage(Brassicachinensis L.),celery cabbage(Brassica pekinensis Rupr.),potato(Solanum tuberosum L.),water spinach(Ipomoea aquatica Forsk)and crowndaisy chrysanthemum(Chrysanthemum coronarium L.)After planting Chinese cabbage,celery cabbage or potato,within 35?75 d,the concentration of ?PAHs in soil S1(low concentration of PAHs)decreased more slowly than in soil S2(middle concentration of PAHs)and S3(high concentration of PAHs).After planting Chinese cabbage,the residual concentration of ?PAHs in soil S1 is the lowest compared to panting celery cabbage or potato.The residual concentration of ?PAHs in soil S2 and S3 decreased the fastest,in the order of celery cabbage>Chinese cabbage or potato.At the end of the experiment(75 d),the residual concentration of ?PAHs in soil S1,S2 and S3 was 17.1?32.9?46.1?72.1 and 63.0?90.8 mg/kg,reduced 21.7%?59.0%?22.5%?50.4%and 21.0%?45.2%compared to the CK(control group).At the end of the 75 d experiment,different ring number PAHs differed in the residual ratio in S1?S2 and S3.After 35 d,the concentration of 2 ring PAHs were lower than the detection limits as a result that 2 ring naphthalene is strong volatile and biodegradable.The residual ratio of 3 ring PHAs in vegetated soil decreased,however,the residual of 4-6 ring PAHs increased after 75 d.In soils,the greater is the lgKow of PAH,the higher is the residual rate.(3)Analyzing several crops' accumulation and transmission characteristics of PAHs in soil.The height,root length and biomass of the crops have been affected by PAHs in soil.The height of Chinese cabbage,celery cabbage and potato decreased in S2 and S3 compared to the CK after 35 days.PAHs had an obvious repression on the elongation of roots of Chinese cabbage and celery cabbage.The fresh weight of Chinese cabbage and celery cabbage had a tendency to decrease as the concentration of PAHs in soil increased.The uptake,accumulation and translocation behavior of PAHs in plants was investigated using pot experiments.Soil culture experiment of the five kinds of crops(Chinese cabbage,celery cabbage,potato,water spinach,crowndaisy chrysanthemu)showed that,PAHs concentrations in the five crops were significantly positive correlated to the added PAHs levels in the soil and under the same treatment conditions,concentrations of PAHs in the shoot were lower than in the root.However,the increasing trend of PAHs concentrations in shoot is greater than in the root with in 35?75 days.The potato's and water spinach's root concentration factors of PAHs were significantly lower than Chinese cabbage,celery cabbage or crowndaisy chrysanthemu.At the end of the experiment(75 d),4 and 5-6 ring PAHs dominated in roots,accounted for 21.9%?58.1%and 58.1%?15.5%respectively.However,distribution ratio were different between roots and leaves or stems.'The 3 ring PAHs in crops leaves or stems in the polluted soils were in higher proportion of 41.2%?82.6%.