Environmental Contaminant Detection - EPR (ESR) Applications
Updated 2022-07-21

As one of the global crises, environmental pollution is affecting human life and health. There is a new class of environmentally harmful substances among the air, water, and soil pollutants - Environmentally Persistent Free Radicals (EPFRs). EPFRs are ubiquitous in the environment and can induce the generation of reactive oxide species (ROS), which cause cell and body damage and are one of the causes of cancer and have strong biohazard effects. Electron paramagnetic resonance (EPR or ESR) technology can detect EPFRs and quantify them to find the source of the hazard and solve the underlying problem.



What are EPFRs


EPFRs are a new class of environmental risk substances that are proposed relative to the traditional concern of short-lived free radicals. They can exist in the environment for tens of minutes to tens of days, have a long lifetime, and are stable and persistent. Its stability is based on its own structural stability, not easy to decompose, and difficult to react with each other to burst. Its persistence is based on the inertness that it is not easy to react with other substances in the environment, so it can persist in the environment. Common EPFRs are cyclopentadienyl, semiquinone, phenoxy, and other radicals.



Common EPFRs


Where do EPFRs come from?


EPFRs are found in a wide range of environmental media, such as atmospheric particulate matter (e.g. PM 2.5), factory emissions, tobacco, petroleum coke, wood and plastic, coal combustion particulates, and soluble fractions in water bodies and organically contaminated soils, etc. EPFRs have a wide range of transport pathways in environmental media and can be transported through vertical ascent, horizontal transport, vertical deposition to water bodies, vertical deposition to land, and landward migration of water bodies. And in the process of migration, new reactive radicals may be generated, which directly affect the environment and are contributors to the natural sources of pollutants.


Formation and Multimediated Transfer of EPFRs (Environmental Pollution 248 (2019) 320-331)

Application of EPR Technique for the Detection of EPFRs


EPR (ESR) is the only wave spectroscopy technique that can directly detect and study substances containing unpaired electrons, and it plays an important role in the detection of EPFRs due to its advantages such as high sensitivity and real-time in situ monitoring. For the detection of EPFRs, EPR (ESR) spectroscopy provides information in both spatial and temporal dimensions.The spatial dimension refers to the EPR spectra that can prove the presence of free radicals and obtain information on molecular structure, etc. The EPR test allows the analysis of species such as free radicals in the sample, where continuous wave EPR spectra can provide information such as g-factor and hyperfine coupling constant A, which in turn allows researchers to obtain information such as the electronic structure of free radicals. The time dimension means that the half-life of EPFRs can be inferred by monitoring the present time of EPR signals.

Application of EPR Technology in Detecting EPFRs in the Soil Environment


Petroleum processing, storage, transportation, and possible leakage from storage tanks are all susceptible to soil contamination. Although thermal treatment techniques can be used to remediate soils contaminated by various volatile, semi-volatile, pesticides and PCBs, heating may alter soil physicochemical properties. The effect of low-temperature thermal treatment on PCPs and EPFRs in soils can be studied using EPR techniques.


Soils were heat treated and tested for EPR (ESR) using two types of heating: closed heating (anoxic conditions) and open heating (oxygen-rich conditions). The test results showed a slightly broader and weaker EPR (ESR) radical signal in open heated soils, indicating that open heating resulted in the formation of a PCP radical or other similar radical with an oxygen-centered structure. The highest EPFR concentration was 10 × 1018 spin/g under open heating at 100 °C and 12 × 1018 spin/g under closed heating at 75 °C. The results suggest that low-temperature treatment of PCP-contaminated soil can convert PCP to more toxic EPFRs that may be present in the environment for a long enough time.



EPR spectra of Closed-heated and Open-heated Soils and the Corresponding Concentrations of EPFRs and PCP (Environ Sci Technol, 2012, 46(11): 5971-5978)


Application of EPR Technology for Detection of EPFRs in Tobacco Smoke


Tobacco smoke is an aerosol composed of particles/droplets (TPM, total particulate matter) and gas-phase chemicals (toxic gases, volatile organic compounds, short-lived radicals, etc.) TPM contains high concentrations of long-lived EPFRs, stable radicals that cause DNA damage through the formation of hydroxyl radicals (-OH), resulting in long-term negative effects on human health.

For conventional cigarettes, the presence of carbon-centered free radicals makes them detectable by EPR techniques. For modern e-cigarettes, the EPR technique allows the determination of free radicals generated during the inhalation of e-cigarettes and the quantification of the generation of EPFRs and the production of ROS in TPM, respectively.



The Amount of Hydroxyl Radicals Formed by Electronic Cigarette TMP (Environmental Science and Technology 2020 54 (9), 5710-5718)


Application of EPR Technology in Detecting EPFRs in Coal-Fired Mining Areas


Xuanwei, Yunnan, China, is a region with a high incidence of lung cancer. The area is rich in bituminous coal reserves and residents use bituminous coal in their daily life and industrial production. The combustion of bituminous coal produces pollutants containing substances such as polycyclic aromatic hydrocarbons (PAHs), which are considered to be the main cause of the high incidence of lung cancer. Polycyclic aromatic hydrocarbons (PAHs) are the most widely distributed potentially carcinogenic and teratogenic chemical pollutants in the environment. The molecules themselves are not paramagnetic but are easily oxidized to the corresponding cationic radicals under the action of silica-aluminum catalysts. Such cationic radicals adsorbed on the catalyst surface are stable and can be detected by EPR spectroscopy. Meanwhile, the signal intensity of EPR is linearly related to the concentration of PAHs, so the total concentration of PAHs can be monitored by EPR spectroscopy.


CIQTEK Electron Paramagnetic Resonance (EPR) Spectroscopy


The CIQTEK EPR (ESR) spectroscopy provides a non-destructive analytical method for the direct detection of paramagnetic materials. It can study the composition, structure, and dynamics of magnetic molecules, transition metal ions, rare earth ions, ion clusters, doped materials, defective materials, free radicals, metalloproteins, and other substances containing unpaired electrons, and can provide in situ and non-destructive information on the microscopic scale of electron spins, orbitals, and nuclei. It has a wide range of applications in the fields of physics, chemistry, biology, materials, and industry.