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

The problem of soil environmental pollution in China is serious.In order to improve the soil environment and promote the construction of ecological civilization,the State Council issued"ten soil rules",which clearly pointed out that the key supervision of polycyclic aromatic hydrocarbons（PAHs）pollutants in soil should be carried out in order to achieve comprehensive census and dynamic monitoring.Therefore,it is urgent to develop a rapid and on-site detection method for PAHs contaminants in soil.Due to its advantages of non-contact,no pretreatment,suitability for on-site and on-line detection,fluorescence analysis has become a research hotspot in the field of agricultural environmental safety.However,soil moisture has a serious impact on the fluorescence intensity of PAHs,which is undoubtedly a challenge to the development of rapid real-time fluorescence detection technology for PAHs in soil.Based on the study of the fluorescence characteristics of PAHs and the influence of soil moisture on its fluorescence intensity,a correction method was proposed to reduce the influence of soil moisture on the fluorescence intensity of PAHs in this paper.The details are as follows:（1）The overlapping peaks of benzoapyrene,benzo[ghi]perylene and benzo[k]fluoranthene solutions were effectively resolved based on two-dimensional（2D）correlation fluorescence spectra.Three experimental systems were designed to construct synchronous and asynchronous 2D correlation fluorescence spectra under the external disturbance of PAHs concentration.The source of characteristic fluorescence peaks were identified according to the positive and negative cross peaks in synchronous spectra and whether there were cross peaks in asynchronous spectra.The effective analysis of three overlapping peaks of PAHs was realized.（2）A correction method was established to reduce the influence of soil moisture on PAHs fluorescence intensity.The near infrared diffuse reflectance spectra,ultraviolet-visible diffuse reflectance spectra,and fluorescence spectra of typical PAHs pollutants phenanthrene in soils were studied with different humidity.On this basis,the fluorescence intensity of PAHs in soil was corrected by diffuse reflectance spectroscopy based on soil moisture content as a bridge.On this basis,the fluorescence intensity of PAHs was corrected in soil based on diffuse reflectance spectroscopy using soil moisture as a bridge.The results show that the fluorescence intensity can be corrected by near infrared diffuse reflectance spectra at 5184cm^-1,which can effectively reduce the effect of soil moisture on the fluorescence intensity of PAHs.（3）The validity of the above correction method was verified.Firstly,a standard curve was established for quantitative analysis of phenanthrene in soil under different humidity and concentration.The uncorrected and corrected results were also compared and analyzed.It was pointed out that there was a significant linear correlation between the correction fluorescence intensity of phenanthrene and the concentration of phenanthrene in soil based on the near infrared diffuse reflectance s spectra at 5184 cm^-1,which accorded with the law that the fluorescence intensity was proportional to the concentration of phenanthrene.The validity of correction method was verified for single-component PAHs in soil.Secondly,for more complex soils with mixed phenanthrene and benzoapyrene at different concentrations and humidity,quantitative prediction models were established based on uncorrected and corrected fluorescence spectra using partial least squares（PLS）and multi-dimensional partial least squares（NPLS）,respectively.For uncorrected PLS models,the root mean square error of prediction（RMSEP）of phenanthrene and benzoapyrene were 18.7164 and 2.1003,the coefficient of determination（R²）were 0.6821 and 0.5274;for uncorrected NPLS models,RMSEP were 11.1167 and 1.5120,R² were 0.88 and 0.8182;For corrected PLS models,RMSEP of phenanthrene and benzoapyrene were 10.8700 and 1.4806,R² were 0.9025 and0.8933;for corrected NPLS models,RMSEP were 6.7616 and 0.8182,R² were 0.9628 and0.8309.The results show that the predictive ability of the corrected model is better than that of the uncorrected model.It is further proved that the fluorescence intensity of PAHs in soil can be corrected by near infrared diffuse reflectance spectra at 5184 cm^-1,which can effectively reduce the influence of soil moisture content on the fluorescence intensity of PAHs,and improve the accuracy of quantitative analysis.