Environmental Contaminant Detection - EPR (ESR) Applications

Environmental pollution is one of the global crises and is affecting the quality of living and health of the entire population. A new class of harmful substances, the environmentally persistent free radicals (EPFRs). These pollutants are pervasive and can be found in air, water, and soil. The EPFRs can be recognized as biohazard since it can produce reactive oxide species (ROS), which causes cell and tissue damages and ultimately cancer. To mitigate and eventually find a solution to this problem, tracing the origin of such pollutants is needed. Electron paramagnetic resonance (EPR) spectroscopy is a powerful tool and can be used for such tasks.

What are EPFRs

The conventionally recognized free radicals are often transient with a short lifetime. On the contrary, EPFRs can be stable in the environment for tens of minutes to tens of days without being oxidized or quenched. The commonly found EPFRs include, 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, 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. In the process of migration, new reactive radicals may be generated, which directly affects the environment and are precursors to other pollutants.

Formation and Multimediated Transfer of EPFRs

(Environmental Pollution 248 (2019) 320-331)

Application of EPR Technique for the Detection of EPFRs

EPR spectroscopy is extremely sensitive to unpaired electrons, and a directly measurement of signals from these radicals make it an ideal method for monitoring the presence of EPFRs in different samples.  . For the detection of EPFRs, EPR (ESR) spectroscopy provides information in both spatial and temporal dimensions. By measuring and analyzing the continuous-wave EPR spectra of samples, the researchers are able to not only verifying the presence of radicals but also obtain g-values and hyperfine coupling constants of electrons, which can be used for inferring electronic structure of measured molecules. The temporal resolution refers to the half-life of EPFRs, which can also be obtained from monitoring their EPR signals over time.  

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 pentachlorophenol (PCP) , 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 before  EPR  measurements 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 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 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 can be detected 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 can be  easily oxidized to the corresponding cationic radicals by 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 be used for studying 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 of electron spins, orbitals, and nuclei on the microscopic scale, with a wide range of applications in the fields of physics, chemistry, biology, materials, and industry.