Determination of toxic molecular products and heavy metals from combustion of unprocessed and processed commercial cigarettes sold in Kenya: computational modeling and experimental studies

Abstract

There is substantial evidence that inhaled toxicants such as cigarette smoke can cause irreparable damage to body cells, genetic material and the general respiratory landscape in smokers. Cigarette smoke contains organic and inorganic carcinogenic compounds that pose danger to human life. This study seeks to describe the toxic compound formation mechanism during cigarette smoking. Accordingly, this study computed the global energies and entropies, performed geometry optimization, estimated the toxicity indices of selected molecular products and investigated the heavy metal content in the solid and gas phase of cigarettes commonly sold in Kenya. Two cigarette brands with one unprocessed cigarette coded SM1, ES1 and Trd respectively, were selected for this study. To simulate actual cigarette smoking conditions, smoking apparatus were designed according to ISO 3402: 1999 standards. The heavy metals content was qualitatively and quantitatively determined using Atomic Absorption Spectrometry, AAS, (Shimadzu 6200) while Gas Chromatography-Mass Spectrometry (GC-MS), was used to analyze molecular by-products. Standard solutions for each of the heavy metals were prepared in the range 0.1 ppm to 8.0 ppm from which calibration curves were obtained with R2 values of 0.995±0.003 appropriately for quantification of each metal. Quantitative means for the three cigarette brands were compared using Analysis of variance (ANOVA) and significant levels measured at 95% confidence level with significant differences recorded at p < 0.05. Gaussian ‘03 computational program was used to perform thermochemical calculations at the Density Functional Theory (DFT) and Moller Plesset Perturbation (MP2) analytical gradient. The toxicity indices were determined using Quantitative Structural Activity Relationship (QSAR) technique incorporated in HyperChem computational platform. The results showed that lead (Pb) had the highest concentration in all cigarette brands; 6.776±0.02, 6.984±0.03 and 7.119±0.05μg.g-1 for Trd, SM1 and ES1cigarettes respectively. Pb concentration was not significantly different in the three cigarette brands, F (2, 15) = 2.555, p = 0.111 while Cr was significantly higher in both Trd (3.6254μg.g-1) and SM1 (3.5527μg.g-1) compared to ES1 cigarette (2.0882μg.g-1) smoke. GC-MS results indicated that the yield of propanol and phenol at retention times of 4.04 and 8.88 minutes respectively reached a maximum of 7.2 x 108 and 2.2 x 108 at about 400 °C before decreasing exponentially to about1.2 x 108 and9.0 x 107 GC area counts at 700 °C respectively. The enthalpy data revealed that the exothermicity process for converting propanol and phenol to their respective deadly radicals decreased with increase in temperature. The estimated toxicity indices for propanol and phenol with their corresponding radicals were 0.55, 0.57, 2.31 and 1.99 respectively. The primary heavy metal component was Pb whereas propanoxy radical was estimated to be the most toxic by-product from cigarette smoking. There is a need for cigarette manufacturers to design cigarettes that can be smoked at lower temperatures to minimize the formation of lethal radicals and investigate sources of carcinogenic metals in cigarettes