Molecular Products from the Thermal Degradation of Selected Tobacco Components: Lignin, Tyrosine, Glutamic Acid, and Modeling of Lignin Pyrolysis using CHEMKIN Combustion Suite

This study explores the thermal decomposition behavior of selected tobacco components: lignin, tyrosine, and glutamic acid using the system for thermal diagnostic studies (STDS) in an in-line gas chromatography-mass spectrometer analytical technique. The pyrolysis conditions employed in this study were a flowing atmosphere of nitrogen and 4% O2 in nitrogen at a residence time of 0.2 seconds for a total pyrolysis time of 3 minutes. The results identified common relationships between the two modes of reaction atmospheres, as well as some differences. While some products were favored by an inert regime, some were favored under an oxidative regime. Oxidative pyrolysis of tyrosine for instance yielded compounds of interest, e.g., hydroquinone, p-benzoquinone, dibenzofuran, and dibenzo-p-dioxin, although no such products were observed under pyrolysis. A comprehensive product distribution at distinct pyrolysis and oxidative pyrolysis temperature of various compounds is presented. The mechanistic channels for the formation of compounds of biological concern such as phenols, and polycyclic aromatic hydrocarbons (PAHs) have also been discussed in detail. Of the classes of compounds analyzed from the thermal degradation of lignin, the phenolic compounds were the most abundant, accounting for over 60% of the total compounds detected. The principal products from pyrolysis of tyrosine were phenol, p-cresol, o-cresol, and benzaldoxime. For the oxidative pyrolysis, the main products were p-tyramine, phenol, p-cresol, and benzonitrile. The principal products from pyrolysis of glutamic acid in order of decreasing abundance were succinimide, pyrrole, 2-pyridone, and acetonitrile. On the other hand, succinimide, propiolactone, ethanol, and hydrogen cyanide were the key products under oxidative pyrolysis. CHEMKIN combustion Suite was used to model the pyrolysis of lignin and consequently, a 15 reaction model was developed to determine the kinetics as well as the thermodynamic parameters of reaction products. By use of pseudo first order rate law, the rate coefficients for various products were evaluated. Arrhenius equation was used to compute the pre-exponential factor A, as well as the activation energy Ea for numerous reaction products including phenol, syringol, 4-vinylguaiacol, furfural, toluene, and benzene. Experimental reaction conditions were used to constrain the model. Simulation data reproduced experimental results with reasonable accuracy

The analysis of the essential metal contents in khat (Catha edulis Forsk) from Meru County, Kenya

Background: Chemical composition of plants has attracted considerable interest in recent years with considerable research tailored into determining metal contents in food substances. Particularly, essential elements which are necessary for normal human body functioning and are strongly recommended in optimal proportions for better health. This study determined the levels of essential elements; calcium (Ca), magnesium (Mg), sodium (Na), potassium (K) and manganese (Mn) in eleven khat (Catha edulis Forsk) samples collected from Meru County. Methodology: 1.0 g of dry ground khat samples were wet-digested in a solvent mixture of 10 mL of HCl, HNO3 and 20 vol of H2O2 for 3 h at variable temperature of 50–90 °C and later reconstituted in 25 mL 0.05 molL−1 HCl before analysis. The samples were analyzed using inductively coupled plasma atomic emission spectrometry (ICP AES) after acid digestion whereas Hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used to investigate elemental characteristics and determine the sources of essential metals in khat. In addition, Pearson correlation coefficient (PCC) was used to evaluate the relationships between the essential metals. Results: Spinach leaves certified reference material (CRM 1750a) was analyzed and the percentage recoveries (%) of 98.4 and 101.7 determined showing that the digestion method employed in this work had adequate accuracy. The validated method was employed for the analysis of all the khat samples. The analyzed metal concentration ranges (mg100g−1) in fresh-weight basis per day of five metals were 160.9–267.3, 44.6–81.7, 2.0–3.0, 237.6–393.6, and 220.3 -349.0 for Ca, Mg, Mn, K, and Na, respectively. Both HCA and PCA results showed that these elements could be linked to natural soils and anthropogenic sources. PCC reported significant correlations between Na and K indicating they may have been derived from the same source. The daily metal intakes were below the World Health Organization (WHO) permissible limits implying no associated health risks for khat users. Conclusion: Based on the findings of this study, the consumption of khat from regions of Meru County may be a potential source for essential elements required for human biological processes

Geochemical survey of the Nyamyumba and Bugarama hot springs in the western province of Rwanda

The focus of the current study was to investigate the presence of selected trace metals (Pb, Cd, Mn, Ni, and Cu) and to determine the major cation and anion levels in Nyamyumba and Bugarama hot springs in the Western Province of Rwanda. The trace metals were determined using micro plasma atomic emission spectroscopy. The mean Cu concentrations in Nyamyumba and Bugarama were found to be 0.1 mg/L and were within the permissible limits of the World Health Organization (WHO) for potable water. Similarly, Mn concentrations were within acceptable WHO limits with mean concentrations being 0.04±0.02 and 0.11±0.03 mg/L in Nyamyumba and Bugarama, respectively. The lead concentration was found to be above the WHO limits with mean results of 0.01±0.001 and 0.013±0.01 mg/L in Nyamyumba and Bugarama, respectively. The mean concentration of cadmium was 0.01 mg/L in both sampling sites, which is observed to be above the allowed WHO limit. Nickel, on the other hand, was found to be below the detection limit. The fluoride concentration was determined using the SPADNS Ultra Violet Spectroscopic (UV-VIS) method and its mean levels were found to be 1.07±0.05 and 0.85±0.07 mg/L in Nyamyumba and Bugarama, correspondingly, which is within the acceptable limit of the WHO. Due to the potential pollution trends identified in this study, it is recommended that biosorption remediation techniques be applied for potable and therapeutic water usage to reduce the levels of Pb and Cd, which can have serious etiological risks to both flora and fauna due to possible trace metal bioaccumulation

GC/EI-MS and UV-Vis analysis of pesticide residues in cultivated Catha edulis Forsk (Khat) from selected farms in Meru County, Kenya

In this study, an analysis of pesticide residues was performed using a gas chromatography/ electron impact mass spectrometer (GC/EI-MS) to qualitatively assess and characterize pesticide residues in khat leaves sampled from selected agricultural farms in Meru County, Kenya. A solid-phase microextraction (SPME) procedure followed by GC/EI-MS analysis led to the detection and identification of six pesticide compounds from the sample-ion chromatograms. They include cypermethrin, acephate, cyhalothrin, cyfluthrin, chlorpyrifos, and chlorfenvinphos. The prevalence rate of pesticide contamination was determined to be 54.5% of the sample size. Of the identified pesticide residues, 50% were compounds based on pyrethroids and the other 50% were based on organophosphate. Four of the six identified pesticides were chlorinated compounds. A quick, easy, cheap, effective, rugged, and safe UV-vis double beam spectrophotometric technique based on copper (II) chelation reactions leading to colored copper pesticide complexes was developed, validated, and applied to quantify and compare the levels of selected pesticide compounds found in the khat samples. UV-vis wavelength-scan measurements performed on pesticide compounds chelated with copper (II) ions revealed maximum absorption of Cu-cypermethrin and Cu-acephate at 321 and 207 nm, respectively. The standards calibration curves developed from the UV-Vis quantitation technique showed excellent linearity in the concentration range of 0.5-10.0 µg/L (R2 = 0.99) for both cypermethrin and acephate standards. The estimated limits of quantification (LOQ) were 0.25-0.26 µg/L, respectively. The UV-Vis quantitation results from the selected samples (in which residues were confirmed to be present) revealed that acephate (an organophosphate residue) occurred at higher concentration levels (range 2.897-7.978 µg/L) than cypermethrin (2.145 µg/L). For the pesticides quantitatively analysed in the selected samples, the levels were below the maximum residue limit (MRL). The hazard quotients (HQ) were in the range of between 0.247-0.797

Organic contaminants in the groundwater of the Kerio Valley water basin, Baringo County, Kenya

Currently, groundwater is largely becoming the main source of fresh water in most developing countries. However, various deleterious impacts resulting from anthropogenic activities beneath the earth’s surface have significantly affected groundwater quality, as evidenced in several areas endowed with mineral and hydrocarbon deposits, agricultural activities, and industrial processes. The possible etiological impacts may include cancer and genetic aberrations which result from the toxic effects of organic waterborne contaminants ingested by humans and animals over time. The motivation behind this study was to identify and determine the concentration profiles of various organic pollutants in the wells located along the Kerio Valley water basin near the exploratory wells for hydrocarbons and mining activities. Therefore, this study is necessary in unraveling the level of organic contaminants in the sampled borehole water, which can then be extrapolated to cover other boreholes within the Kerio Valley basin. The study was carried out during the dry season of December 2022. The water samples from the boreholes were extracted using a solid phase extraction procedure and characterized using a gas chromatograph interfaced with a mass selective detector. The findings indicate that benzene derivatives which were mainly xylenes, 1,3,5-trimethylbenzene, 1-ethyl-3-methylbenzene, 1-methyl-2-propylpentylbenzene and polycyclic aromatic hydrocarbons such as naphthalene, phenanthrene, fluoranthene, azulene, and pyrene were found in most of the boreholes sampled. Furthermore, long-chain hydrocarbons were present in all groundwater samples with varying concentrations. The concentration of benzene derivatives ranged from 2.84 to 20.47 ppm. However, polycyclic hydrocarbons exhibited the highest concentrations of all organic pollutants, with pyrene giving a concentration of 23.14 ppm, fluoranthene (18.54 ppm), phenanthrene (14.13 ppm) and anthracene (11.06 ppm). According to the findings reported in this study, most of the borehole water in the Kerio Valley basin is contaminated and may be unsafe for drinking. Most of the reported concentration levels were several times higher than the standards of the U.S. Environmental and Protection Agency. However, it is necessary to develop a policy framework on the assessment and monitoring of water quality in the region and propose urgent measures to ensure a clean water supply for the benefit of residents