Our surrounding environment consists of several hazardous particulates that are frequently polluting the breathable air, water bodies, and sediments. This ubiquity, coupled with a wide range of distinctive characteristics (e.g., density, surface treatment, particulate dimensions and shapes, and tensile properties), has begun to pique the research community's curiosity.
Several particle analysis techniques, such as microscopic analysis, spectroscopy, X-ray techniques, and chromatography, are extensively utilized for particle monitoring. These methods are also useful for environmental monitoring for the discovery and characterization of particles such as plastics, pesticides, pharmaceutical particles, heavy metals, etc. The article focuses on the applications of particle analysis utilized for the process of environmental monitoring.
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Surface Enhanced Raman Spectroscopy for Environmental Monitoring
The conventional (and highly effective) approach for detecting micro-pollutants in the environment is chromatography as a separation approach which is followed by mass spectrometry (preferably high-resolution). Typically, environmental contamination is tracked using mass spectrometry-based techniques.
An article published in the journal Science of the Total Environment states that conventional methods are typically intricate, demand a high level of specialization, and necessitate constant, costly oversight and maintenance. Typically, considerable sample pretreatment needs to be performed before analysis.
It is extremely useful to have an approach that could identify target compounds more quickly and without extensive specimen preparation. Raman Spectroscopy is one such technique, and Surface Enhanced Raman Spectroscopy (or SERS) is the method of choice for environmental monitoring.
SERS is a spectroscopic technique that utilizes electronic and chemical connections between the stimulated beam of the spectrometer, the reagent of interest, and a specific substrate to specifically enhance the signal, and thus the facilitation of target molecules.
Endocrine-disrupting chemicals (EDCs) are one of the most pervasive groups of marine contaminants and have garnered considerable attention. 17ß-estradiol has been detected using SERS in both laboratory and environmental samples.
Pesticides consist of compounds designed to kill or dissuade insects. Pesticides are frequently used as analytes in Raman spectroscopy-based detection investigations. Determining which pesticides to investigate is one of the challenges involved in pesticide monitoring. Developing highly specific methods for each would be an expensive endeavor. One method to combat this is to develop a SERS sensor that targets a component shared by multiple pesticides.
Chromatography for Detection of Micro-Plastics in the Environment
The ubiquitous nature of micro-plastics (MPs) found in ecological sites, living creatures and end products has necessitated their both quantitative and qualitative evaluation to supply information about their prevalence and polymer variety specifications in various substrates.
An article focusing on micro-plastics and their monitoring by chromatographic approaches has been published in the journal Science of the Total Environment. As per the article, microplastics (MPs) are responsible for 51 trillion plastic particles. Chromatographic analytical methods are potent instruments for the molecular and thermodynamic examination of polymer substances, and so their application to the analysis of MPs is also feasible.
Due to its adequate specificity and high adaptability, Gas Chromatography-Mass Spectrometry (GC-MS) is one of the most enticing and innovative methods for routine analysis of some ubiquitous and flammable organic pollutants. It is the most renowned analytical instrument for the identification and quantification of MPs, as it detects small-sized MPs and is unaffected by the impurities of the sample.
Analytical pyrolysis is also suitable for analyzing compounds of micro- and nano-plastics (plastic particles <100 nm).
Soil and Sediment Analysis via Particle Analysis
Evaluation of soil particulate size distribution and roughness offers knowledge about soil characteristics, fertility, and its ability for water retention. The evaluation of soil contamination mobility is essential for ecological risk assessment. Methods for particle detection aid in determining the presence of contaminants, examination of their binding capacity with organic particulates, and forecasting their possible runoff or discharge.
In addition, particle analysis is the preferred method for investigating sediment constituents and accumulation trends in aquatic settings.
Applied Sciences has an article that mentions the use of a Laser-Induced Breakdown Spectroscopy (LIBS) system and multivariate chemometric analysis for the identification of heavy metals in sediments.
The recorded LIBS spectra contained 10,239 peaks from spectral bands spanning 187 to 894 nm and peaks for Cadmium, and Chromium were most frequent, depicting the abundance of these heavy metals. PLSR, one of the multidimensional chemometric techniques, was utilized for assessing the fundamental makeup of soil specimens because it is an efficient dimension-reduction technique. R2 should be close to 1 for an ideal model, while RMSEC should be close to 0. The experimental results yield the values of R2 to be 0.9963 and 0.9406, respectively while RMSE obtained was 0.0063 and the RMSE of cross-validation turned out to be 0.0264. This demonstrated the model's effectiveness.
Particle Analysis for Monitoring of Water
Methods of particle analysis aid in determining the existence of pollutants and microbes in water. By examining particulates and associated chemical compounds, researchers can identify contaminants such as pesticides, etc. thereby facilitating the administration of water quality.
An article published in Process Safety and Environmental Protection focuses on residue analysis of pharmaceuticals in water bodies by utilizing liquid chromatography-mass spectrometry. The environmental presence of pharmaceutically active compounds (PhACs) is a growing cause for concern. The environmental presence of PhACs is a growing cause for concern. A multi-residue technique for identifying 70 PhACs of regional significance in Latin America was developed for aqueous samples.
A total of 23 substances were identified, with a detection frequency of 19.0% on average. The group with the highest frequency was the central nervous system (CNS) stimulants, with caffeine at 66.7% and 1,7-dimethylxanthine at 55.5%. The group of antibiotics also contained six compounds, although at reduced frequencies. The pharmaceutical concentrations detected in the surface water varied from 0.013 µg/L to 53.8 µg/L. The majority of L. sativa samples indicated cytotoxicity in germination experiments. The correlation between germination suppression and medicinal danger was greater than that reported in prior wastewater studies.
An article in Talanta focuses on the analysis and detection of Fluorine and Chlorine particles in water bodies by utilizing molecular Laser-induced Breakdown Spectroscopy (LIB).
Fluorine and chlorine are the two most influential factors in water quality. Laser-induced breakdown spectroscopy (LIBS) is a spectro-chemical analytical technique that deduces the elemental composition of a sample through analysis of the spectra of plasmas created by a pulsed laser beam. CaF and CaCl molecular emission bands were created in place of fluorine and chlorine atomic lines to identify fluorine and chlorine in water solutions using LIBS methods in the open air.
The coefficient of determination R2 indicates the analytical linearity. The R2 values of the calibration curves for F (685.6 nm) and Cl (837.5 nm) were 0.965 and 0.986, respectively, which were less than CaF (0.996) and CaCl (0.995). The results demonstrated that the calibration of the model precision of molecular LIBS analyses was superior to that of atomic LIBS analyses.
Future Outlook
Within the modern Industry 4.0 era, the domain of particle analysis is also undergoing automation. Researchers are developing neural networks as well as utilizing reinforced learning and machine learning to boost the efficiency of the systems, develop superior data management and data pre-processing methods, and facilitate automated classification of particles. Nano-sensing techniques are also gaining popularity these days with scientists all over the world studying the risks associated with the utilization of engineered nanoparticles.
In short, particle analysis provides major benefits to the domain of environmental monitoring and is essential for sustainable development.
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References and Further Reading
Yoon S. et al. (2021). Determination and Quantification of Heavy Metals in Sediments through Laser-Induced Breakdown Spectroscopy and Partial Least Squares Regression. Applied Sciences. 2022. 11(15):7154. Available at: https://doi.org/10.3390/app11157154
Ainali, N. et. Al. (2021). Micro-plastics in the environment: Sampling, pretreatment, analysis and occurrence based on current and newly-exploited chromatographic approaches. Science of The Total Environment, 794, 148725. Available at: https://doi.org/10.1016/j.scitotenv.2021.148725
Ong, T et. al. (2020). Surface Enhanced Raman Spectroscopy in environmental analysis, monitoring and assessment. Science of The Total Environment, 720, 137601. Available at: https://doi.org/10.1016/j.scitotenv.2020.137601
Ramirez. D. et. al. (2021). Multi-residue analysis of pharmaceuticals in water samples by liquid chromatography-mass spectrometry: Quality assessment and application to the risk assessment of urban-influenced surface waters in a metropolitan area of Central America. Process Safety and Environmental Protection, 153, 289-300. Available at: https://doi.org/10.1016/j.psep.2021.07.025
Tang, Z et. al. (2021). Sensitive analysis of fluorine and chlorine elements in water solution using laser-induced breakdown spectroscopy assisted with molecular synthesis. Talanta, 224, 121784. Available at: https://doi.org/10.1016/j.talanta.2020.121784
Caldwell, J et. al. (2022). The micro-, submicron-, and nano-plastic hunt: A review of detection methods for plastic particles. Chemosphere, 293, 133514. Available at: https://doi.org/10.1016/j.chemosphere.2022.133514
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