Effect Of Soil Type On Fluorescence Characteristics Of Polycyclic Aromatic Hydrocarbons And Its Correction Method

Polycyclic aromatic hydrocarbons（PAHs）,as important environmental pollutants,pollute 77%of China’s soil to varying degrees.In order to improve the environment pollution of the soil,the"Soil Pollution Control Action Plan",which was issued by the State Council in2016,clearly stated that it is important to supervise the polycyclic aromatic hydrocarbons in soil.Fluorescence spectroscopy,which has the characteristics of good selectivity,high sensitivity,and low detection limit,has been applied to the detection of PAHs in the environment.However,soil type has serious effects on the fluorescence intensity of PAHs,which restricts the application of fluorescence spectroscopy in the detection of PAHs.In this paper,eight typical PAHs in soil were as the research object.The fluorescence characteristics of the eight PAHs were studied,a correction method was proposed and established to reduce the effect of soil types on the PAHs fluorescence intensity.And the effectiveness of the correction method was verified.The specific research contents and related results are as follows:（1）The"characteristic fluorescence information libraries"of eight PAHs were constructed.According to the type and degree of PAHs pollution in China’s soil,the eight PAHs were selected as research object,including:naphthalene（bicyclic）,anthracene,fluorene（tricyclic）,fluorene,fluoranthene（tetracyclic）,benzo[a]pyrene,benzo[b]fluoranthene（pentacyclic）,benzo[ghi]pyrene（hexacyclic）.The one-dimensional and three-dimensional fluorescence spectral characteristics of eight PAHs in simple aqueous solution system and complex soil system were studied.The optimal excitation and emission wavelengths were determined.Based on the above research,the"characteristic fluorescence information library"of eight PAHs were established,which provided a theoretical and experimental basis for the selection of excitation wavelength and the establishment of correction methods.（2）The correction method to reduce the effect of soil type on PAHs fluorescence intensity was established.Taking benzo[ghi]pyrene as the research object,samples with same concentration and different soil types were prepared to study the effects of soil type on fluorescence,near-infrared and ultraviolet-visible diffuse reflectance spectra.Based on the single wavelength reflectance or the average reflectance of the entire band of the near-infrared and ultraviolet-visible diffuse reflectance spectra,the fluorescence intensities of PAHs were corrected,and a comparative analysis was performed.The results show that the ratio of fluorescence intensity to exp（near-infrared spectral diffuse reflectance×10）as the corrected fluorescence intensity is the best method to reduce the effect of soil type on the fluorescence intensity of PAHs.（3）The effectiveness of the correction method was verified.Taking benzo[ghi]pyrene and fluoranthene as research objects,the established correction method was used to correct the fluorescence intensity of PAHs soils with different concentrations and different soil types to establish a standard curve for quantitative analysis.The fitted linear relationships were compared and analyzed before and after correction.For benzo[ghi]pyrene,the determination coefficients R~2 of linear fitting between the fluorescence intensities and concentrations of benzo[ghi]perylene are 0.783 and 0.938 before and after correction,respectively For fluoranthene,the R~2 of linear fitting between fluorescence intensities and concentrations of fluoranthene are 0.758 and 0.916 before and after correction,respectively.The above research results show that correcting PAHs fluorescence intensity based on near-infrared diffuse reflectance spectrum can effectively reduce the effect of soil type on PAHs fluorescence intensity.