Soil petroleum hydrocarbon pollution is increasingly serious. Petroleum pollutants released into the environment due to oil extraction are as high as 4×10⁷ t per year. Petroleum pollutants are extremely harmful to the soil, destroying the surface structure of the soil. Worse still, the pollutants enter the food chain through soil and water cycles, destroying the ecological environment and threatening human health. To effectively prevent and control petroleum hydrocarbon pollution in soil, it is necessary to conduct on-site rapid detection of petroleum hydrocarbon pollution in soil. However, some traditional detection methods of petroleum hydrocarbon in soil, including infrared spectrophotometry, high-performance liquid chromatography, gas chromatography, gas chromatography-mass spectrometry, Soxhlet extraction, and gravimetric method, have to extract soil samples first, which is complicated to operate. Therefore, these traditional technologies cannot be used as on-site detection of petroleum hydrocarbon pollution in soil. Moreover, it is easy to cause secondary pollution during the collection, transportation, and pretreatment of soil samples contaminated by petroleum hydrocarbons. Some components of pollutants are very easy to volatilize, which leads to deviations in the detection results of petroleum hydrocarbon content. Therefore, a real-time in-situ detection of petroleum hydrocarbon pollutants in the soil is an important prerequisite for improving the detection speed and accuracy, and it is urgent to develop a rapid in-situ detection method of petroleum hydrocarbon pollutants in soil. To further improve the efficiency and accuracy of the rapid in-situ detection of petroleum hydrocarbons in soil, this paper applies deep ultraviolet (UV) light emitting diode (LED) as the excitation light source to detect petroleum pollutants in soil based on UV-induced fluorescence technology, which provides a new method for the rapid in-situ detection of petroleum hydrocarbons in soil.

Three types of soil substrates mixed with three types of oil are selected as test samples, and the samples are detected by constructing a UV-induced fluorescence system. The sensitivity, stability, applicability, and accuracy of the detection system are verified. The detection system adopts a deep UV LED driven by a parallel constant current circuit (central emission wavelength of 280 nm, half-wave width of 10 nm, and rated optical power of 8 mW). A dual-lamp-bead combined symmetrical illumination system is constructed. After the sample passes through a 280 nm bandpass filter, an excitation spot with an area of 1 cm² is formed on the surface of the soil sample. The excitation light power measured by the UV irradiance meter is 3.78 mW/cm². The fluorescence detector uses the Hamamatsu H10721-01 photomultiplier tube (PMT) with the detection sensitivity of 200 μA/lm and the PMT voltage of 0.55 V. The sample is loaded into a special circular sample cell, and a flat surface is formed by pressing. The detection system structure is shown in Fig. 4.

Since it is difficult to detect petroleum hydrocarbons in the soil in situ, the deep UV LED-induced fluorescence system is built to detect different types of oil in the soil in this study. The detection system has high sensitivity and stability, and its detection effect is significantly better than that of the laser induced fluorescence spectroscopy (LIF) system. The detection system is utilized to detect different types of engine oils (gasoline engine oil, diesel engine oil, air compressor engine oil) on different soil substrates, and the detection results are as follows. The detection limits of three kinds of engine oils on the soil substrate of red soil are 60.38 mg/kg, 29.91 mg/kg, 8.66 mg/kg, respectively. The detection limits of three kinds of engine oils on the soil substrate of yellow soil are 62.37 mg/kg, 31.39 mg/kg, 8.87 mg/kg, respectively. The detection limits of three kinds of engine oils on the soil substrate of black soil are 104.97 mg/kg, 52.01 mg/kg, 16.75 mg/kg, respectively. The relative standard deviation of oil in different types of soil is less than 4.00%, and the average error of measurement is less than 10.00%. The experimental system constructed in this study completes the accurate quantification of different soil types and different oils, and verifies the feasibility of the UV-induced fluorescence in-situ detection technology of petroleum hydrocarbon pollutants in soil. Using deep-UV LED as the light source and PMT as the detector, the detection system is miniaturized, which provides a new method for the in-situ detection of petroleum hydrocarbon pollutants in soil and provides an important technical reference for the detection of petroleum hydrocarbon pollutants in deep soil in the future.

This study uses UV-induced fluorescence technology to achieve quantitative detection of engine oil in soil. The use of deep-UV LED as the light source and PMT as the detector realizes the miniaturization of the detection system and significantly improves the detection sensitivity of the system. Through quantitative detection of different types of engine oil pollution in the soil, it is verified that there is a good linear relationship between the engine oil fluorescence intensity and its mass fraction. The feasibility of UV-induced fluorescence detection of engine oil under different soil substrates is studied, and the applicability of the method under different soil substrates is verified. The experimental results show that the detection method of engine oil based on UV induction technology can be well applied to the detection of engine oil in the soil, which provides a feasible method for the rapid in-situ detection of petroleum hydrocarbons in soil in the future.