Propylene Glycol Degradation Research Articles

Electrochemical degradation of a methyl paraben and propylene glycol mixture: Interference effect of competitive oxidation and pH stability

Endocrine disrupting compounds (EDCs) are one of the many classes of harmful pollutants frequently found in water resources. Even at low concentrations, EDCs might accumulate in the organisms and interfere on numerous processes controlled by hormones. Parabens, for example, are preservatives widely used in pharmaceutical and cosmetic industries, but several studies related them to human breast cancer. It is well-known that electrochemical technologies are an efficient alternative for wastewater treatment, promoting the appropriate destruction of EDCs. However, most studies are applied to single target contaminant solutions, which may neglect the impact from co-exited inorganic/organic pollutants. Based on that, this study aimed to elucidate the interfering effects of two target organic contaminants of very different nature during electrochemical mediated process. For that, methyl paraben (MeP) and propylene glycol (PG) were selected as models of aromatic/phenolic and carboxylate compounds versus low-molecular aliphatic alcohols. These two compounds are often together used in preservative blends and cosmetic/pharmaceutical formulations. PG is not a harmful chemical, but it is present in several types of effluents in relatively high concentrations. Thus, it may interfere on the degradation of numerous pollutants of low concentrations. The electrochemical treatment of a mixture containing 100 mg L−1 MeP +1000 mg L−1 PG showed that both contaminants suffered interfering effects. The presence of MeP negatively interfered on PG degradation; the carboxylate compound is more easily oxidized even at lower molecular concentration. On the other hand, the presence of PG showed an unexpected positive effect on MeP degradation, that was not reflected on its mineralization. The results indicate that in addition to the expected effect of anodic competition, polymerization and copolymerization reactions may also occur in the studied system. The use of an acidic buffer medium increased the removal of both contaminants and favored the oxidation pathway over the polymerization. In this case, the increase in the removal was reflected in the mineralization process, which increased up to 6 times when the mixture was treated in the buffered medium.

Low-temperature (

Electronic cigarette usage has spiked in popularity over recent years. The enhanced prevalence has consequently resulted in new health concerns associated with the use of these devices. Degradation of the liquids used in vaping have been identified as a concern due to the presence of toxic compounds such as aldehydes in the aerosols. Typically, such thermochemical conversions are reported to occur between 300 and 400 °C. Herein, the low-temperature thermal degradation of propylene glycol and glycerol constituents of e-cigarette vapors are explored for the first time by natural abundance 13C NMR and 1H NMR, enabling in situ detection of intact molecules from decomposition. The results demonstrate that the degradation of electronic nicotine delivery system (ENDS) liquids is strongly reliant upon the oxygen availability, both in the presence and absence of a material surface. When oxygen is available, propylene glycol and glycerol readily decompose at temperatures between 133 and 175 °C over an extended time period. Among the generated chemical species, formic and acrylic acids are observed which can negatively affect the kidneys and lungs of those who inhale the toxin during ENDS vapor inhalation. Further, the formation of hemi- and formal acetals is noted from both glycerol and propylene glycol, signifying the generation of both formaldehyde and acetaldehyde, highly toxic compounds, which, as a biocide, can lead to numerous health ailments. The results also reveal a retardation in decomposition rate when material surfaces are prevalent with no directly observed unique surface spectator or intermediate species as well as potentially slower conversions in mixtures of the two components. The generation of toxic species in ENDS liquids at low temperatures highlights the dangers of low-temperature ENDS use.

Abstract 17100: Effects of Electronic Cigarette Solvents on Endothelial Dysfunction

Introduction: After a decade of electronic cigarettes (E-cig) in the U.S., 3 elements remain: 1) E-cigs evolve; 2) E-cigs use propylene glycol (PG) and vegetable glycerin (VG); and, 3) uncertainty about E-cig use and CVD risk. Because all E-cigs use PG:VG, we tested for vascular effects of PG:VG-derived aerosol alone. Methods: Female C57BL/6 mice were exposed by inhalation (6h/d*4d) to filtered air (n=10) or to PG:VG-derived aerosol (n=10). After exposures, blood and aortas were examined for changes in: circulating immune and stem cells and platelets by flow cytometry, and vascular function by isometric myography. Results: PG:VG exposure significantly decreased WBC (-47±7%); increased RBC (+6±1%) and hemoglobin (+4±1%), but had no effect on circulating angiogenic cells or platelet-leukocyte aggregates. In aorta, vascular smooth muscle (VSM) function measured as aortic contractility to phenylephrine (PE) was unaltered. However, acetylcholine (ACh)-induced, endothelium-dependent relaxation was significantly decreased (air: -75.5±4.2%; PG:VG: -61.8±4.2%; P<0.05), whereas sensitivity of ACh-induced relaxation was variably depressed (air EC 50 : 166±54nM; PG:VG EC 50 : 1020±435nM; 0.05<P<0.10). Because loss of ACh-induced relaxation may reflect VSM desensitization to NO, we measured relaxation of NO donor, sodium nitroprusside (SNP). Both sensitivity and efficacy of SNP-induced relaxations were unchanged in the PG:VG group (EC 50 : 8.8±0.8nM; % relaxation: -99.0±0.3%) vs air group (EC 50 : 11.1±1.0nM; % relaxation: -99.1±0.3%) indicating a loss of ACh responsiveness was independent of VSM. To test whether eNOS was altered by PG:VG, PE response was done in presence of eNOS inhibitor (LNAME). The ‘PE contraction ratio’ (i.e., Tension PE+LNAME / Tension PE alone ) was significantly decreased in PG:VG group (1.28±0.03) vs air group (1.39±0.20; P<0.05) re-enforcing that PG:VG depressed eNOS function and/or NO bioavailability. Conclusions: Acute exposure to E-cig solvent aerosol alone led to endothelial dysfunction and immune cell changes suggesting that E-cig use may increase CVD risk independently of nicotine and flavor constituents. Perhaps thermal degradation of PG and VG into aldehydes may contribute to endothelial dysfunction.

Biodegradation of Propylene Glycol Wastewater Using Bacterial Consortia Isolated from Municipal Wastewater Treatment Sludge–Process Kinetics and Optimization

Propylene glycol (PG), commonly used in the food, cosmetics and pharmaceutical industries and considered non-PBT, is still an emerging contaminant of concern due to its widespread use. In this study, an isolate of a bacterial consortium obtained from an effluent treatment plant, MC1S, was used to degrade PG. The growth kinetics of the isolate was studied under aerated and non-aerated conditions. The isolate was able to effectively grow in saline water under aerated conditions using PG as the substrate. Using response surface methodology (RSM), the effect of pH, salinity, PG concentration, phosphate and nitrate concentration on cell growth and PG degradation was investigated. The isolated bacterium, MC1S, was capable of degrading PG with a maximum of 79% COD reduction observed and was able to withstand comparatively high salinity of the medium. Solution pH and salinity were the most important parameters affecting degradation. Salinity less than 0.1 M and pH close to 8 appeared to be the optimum conditions for PG degradation. HPLC analysis of the treated sample appeared to show the presence of three daughter products. Using RSM, a quadratic equation model between COD reduction and the process variables was developed. The results indicated that aerobic treatment of PG under specific conditions was the best approach for the specific isolate.

Triacetin Enhances Levels of Acrolein, Formaldehyde Hemiacetals, and Acetaldehyde in Electronic Cigarette Aerosols.

The health effects of inhaled electronic cigarette (e-cigarette) flavoring compounds are largely unknown. Earlier reports of their chemical reactivity have been conflicting, with some claiming, for example, that the degradation of flavoring chemicals in e-cigarettes to aldehydes is statistically insignificant. It is thus important to understand how these molecules react to afford enhanced aerosol products. The purpose of the current study was to investigate the origin of formaldehyde, acrolein, and acetaldehyde in e-cigarettes that contain the popular additive, triacetin (TA). By using 13C labeling and a combination of 1H NMR and 13C NMR, we were able to identify that ester hydrolysis of TA occurs to form acetic acid (HOAc) during aerosolization. The released HOAc acts as a catalyst in the degradation of propylene glycol (PG) and glycerol (GLY), increasing the formation of formaldehyde hemiacetals, acrolein, and acetaldehyde. A solution of 10% TA in 1:1 PG/GLY e-liquid was aerosolized using two different e-cigarettes at two wattages. Each device exhibited a significant increase in aldehyde levels, of up to 185% compared to the aerosol from a 1:1 PG/GLY e-liquid. In addition, the GLY formaldehyde hemiacetal was more predominant within the presence of HOAc, indicating that GLY may be relatively more prone to degradation from protonation.

Constraints of propylene glycol degradation at low temperatures and saturated flow conditions.

During snowmelt, the infiltration of large amounts of propylene glycol (PG), the major compound of many aircraft deicing fluids, affects redox processes and poses a contamination risk for the groundwater. To gain a better understanding about the degradation of PG and the associated biogeochemical processes under these conditions, we conducted saturated soil column experiments at 4 °C. During two successive PG pulses, we monitored the effect of the runway deicer formate (FO) and changing redox conditions on PG degradation. Furthermore, we applied first-order and simplified Monod kinetics to describe PG and FO transport. The transport of 50 mg l(-1) PG showed three stages of microbial degradation, which were defined as lag phase, aerobic phase, and anaerobic phase. During the second pulse, lag effects diminished due to the already accomplished microbial adaption, and the initial degradation rate of PG increased. Degradation of PG was most efficient during aerobic conditions (aerobic phase), while the subsequent drop of the redox potential down to -300 mV decreased the degradation rate (anaerobic phase). Formate addition decreased the overall degradation of PG by 50 and 15 % during the first and second pulse, illustrating the inhibitory effect of FO on PG degradation. The concurrent increase of Fe(III), organic carbon, and the turbidity in the column effluent after PG and FO application suggest the combined export of Fe adsorbed to fragments of detached biofilm. Neither the first-order nor the simplified Monod model was able to reconstruct the dynamic breakthrough of 50 mg l(-1) PG. The breakthrough of 1,000 mg l(-1), however, was described reasonably well with first-order kinetics. At low temperature and high water saturation, the application of first-order degradation kinetics seems therefore appropriate to describe the transport of high concentrations of PG.

Degradation of deicing chemicals affects the natural redox system in airfield soils

During winter operations at airports, large amounts of organic deicing chemicals (DIC) accumulate beside the runways and infiltrate into the soil during spring. To study the transport and degradation of DIC in the unsaturated zone, eight undisturbed soil cores were retrieved at Oslo airport, Norway, and installed as lysimeters at a nearby field site. Before snowmelt in 2010 and 2011, snow amended with a mix of the DICs propylene glycol (PG) and formate as well as bromide as conservative tracer was applied. Water samples were collected and analyzed until summer 2012. Water flow and solute transport varied considerably among the lysimeters but also temporally between 2010 and 2011. High infiltration rates during snowmelt resulted in the discharge of up to 51 and 82% PG in 2010 and 2011, respectively. The discharge of formate remained comparatively low, indicating its favored degradation even at freezing temperatures compared with PG. Manganese (Mn) and iron (Fe) were observed in the drainage in autumn owing to the anaerobic degradation of residual PG during summer. Our findings suggest that upper boundary conditions, i.e., snow cover and infiltration rate, and the extent of preferential flowpaths, control water flow and solute transport of bromide and PG during snowmelt. PG may therefore locally reach deeper soil regions where it may pose a risk for groundwater. In the long term, the use of DIC furthermore causes the depletion of potential electron acceptors and the transport of considerable amounts of Fe and Mn. To avoid an overload of the unsaturated zone with DIC and to maintain the natural redox system, the development of suitable remediation techniques is required.

Transport and degradation of propylene glycol in the vadose zone: model development and sensitivity analysis

Transport and degradation of de-icing chemical (containing propylene glycol, PG) in the vadose zone were studied with a lysimeter experiment and a model, in which transient water flow, kinetic degradation of PG and soil chemistry were combined. The lysimeter experiment indicated that aerobic as well as anaerobic degradation occurs in the vadose zone. Therefore, the model included both types of degradation, which was made possible by assuming advection-controlled (mobile) and diffusion-controlled (immobile) zones. In the mobile zone, oxygen can be transported by diffusion in the gas phase. The immobile zone is always water-saturated, and oxygen only diffuses slowly in the water phase. Therefore, the model is designed in a way that the redox potential can decrease when PG is degraded, and thus, anaerobic degradation can occur. In our model, manganese oxide (MnO2, which is present in the soil) and NO3- (applied to enhance biodegradation) can be used as electron acceptors for anaerobic degradation. The application of NO3- does not result in a lower leaching of PG nor in a slower depletion of MnO2. The thickness of the snowcover influences the leached fraction of PG, as with a high infiltration rate, transport is fast, there is less time for degradation and thus more PG will leach. The model showed that, in this soil, the effect of the water flow dominates over the effect of the degradation parameters on the leaching at a 1-m depth.

Natural and enhanced biodegradation of propylene glycol in airport soil

Aircraft de-icing fluids (ADF) are a source of water and soil pollution in airport sites. Propylene glycol (PG) is a main component in several commercial formulations of ADFs. Even though PG is biodegradable in soil, seasonal overloads may result in occasional groundwater contamination. Feasibility studies for the biostimulation of PG degradation in soil have been carried out in soil slurries, soil microcosms and enrichment cultures with and without the addition of nutrients (N and P sources, oligoelements), alternative electron acceptors (nitrate, oxygen releasing compounds) and adsorbents (activated carbon). Soil samples have been taken from the contaminated area of Gardermoen Airport Oslo. Under aerobic conditions and in the absence of added nutrients, no or scarce biomass growth is observed and PG degradation occurs by maintenance metabolism at constant removal rate by the original population of PG degraders. With the addition of nutrient, biomass exponential growth enhances aerobic PG degradation also at low temperatures (4°C) that occur at the high season of snowmelt. Anaerobic PG degradation without added nutrients still proceeds at constant rate (i.e. no biomass growth) and gives rise to reduced fermentation product (propionic acid, reduced Fe and Mn, methane). The addition of nitrate does not promote biomass growth but allows full PG mineralization without reduced by-products. Further exploitation on the field is necessary to fully evaluate the effect of oxygen releasing compounds and adsorbents.

Degradation of propylene glycol wastewater by Fenton's reagent in a semi-continuous reactor

Propylene glycol (PG) wastewater seriously threatens aquatic lives and causes health damage to human beings. Several early studies for PG degradation focused on biological process, which usually proceeds at a slow rate and is often inhibited by substances which are toxic to the microorganisms. In this paper, Fenton method was exploited for treating PG wastewater in a semi-continuous reactor with adding ferrous sulfate (FeSO 4) and hydrogen peroxide (H 2O 2) to the reactor, respectively. Semi-continuous applications of H 2O 2 and Fe 2+ could result in low steady state of HO , which would minimize HO scavenging and further increase PG oxidation efficiency. Under the optimal conditions, 99.1% of PG conversion and 88.4% of COD removal were achieved. In addition, pseudo-first-order model, in which the concentration of HO was assumed to remain constant, was established. The intrinsic activation energy of HO with PG, calculated by Arrhenius-equation was 35.18 kJ/mol. The intrinsic reaction rate constant of HO with PG around optimal conditions was 1.56–1.72 × 10 8 M −1 s −1. After Fenton's reaction, PG molecules could not be thoroughly oxidized to H 2O and CO 2. Intermediates, such as aldehyde, acetone, methanol, formic acid, and acetic acid, were checked by GC–MS, which all had a very low content and toxicity. As a homogeneous catalytic oxidation, Fenton oxidation is a feasible treatment for PG wastewater for its low toxicity, low price, and high efficiency.

Transport and anaerobic biodegradation of propylene glycol in gravel-rich soil materials

Continued input of airplane de-icing/anti-icing fluids (ADAF) to runway adjacent soils may result in the depletion of soil-borne terminal electron acceptors. We studied the transport and transformation of propylene glycol (PG), the major constituent of many ADAF, in topsoil and subsoil samples using saturated column experiments at 4 °C and 20 °C. The export of soil-borne DOC was generally high, non-exhaustive and rate limited. Retardation of added PG was negligible. Rapid PG degradation was observed only in topsoil materials high in organic matter at 20 °C. At 4 °C, no significant degradation was observed. Thus, under unfavorable, i.e., wet and cold conditions typical for winter de-icing operations, PG and its metabolites will be relocated to deeper soil horizons or even to the groundwater. In subsoil materials, PG degradation was very slow and incomplete. We found that subsoil degradation depended on the import of active microorganisms originating from the organic-rich topsoil material. The degradation efficiency is strongly influenced by the flow velocity, i.e., the residence time of PG in the soil column. Poorly crystalline iron(III) and manganese(IV) (hydr)oxides are used during microbial respiration acting as terminal electron acceptors. This results in the formation and effective relocation of reduced and mobile Fe and Mn species. Long-term application of ADAF to runway adjacent soil as well as the lasting consumption of Fe and Mn will tend to decrease the soil redox potential. Without proper counteractive measures, this will eventually favor the development of methanogenic conditions.

Sequential kinetic parameter estimation of anaerobic fluidized bed bioreactor using an optimization technique

Mathematical model parameters for the methanogenic degradation of propylene glycol were estimated in a sequential manner by means of an optimization technique. Model parameters determined from an initial experimental data set using one bioreactor were then verified with the results from a second bioreactor. The proposed methodology is a useful tool to obtain model parameters for continuous flow reactors with completely mixed regime.

Transport and degradation of propyleneglycol and potassium acetate in the unsaturated zone

De-icing chemicals used during the winter season are potential pollutants for the groundwater underneath the new main airport of Norway. Several field experiments examining the transport and degradation of propyleneglycol (PG), potassium acetate (KAc) and non-reactive tracers were performed in a lysimeter trench under natural snowmelting conditions. Chemicals were applied underneath the snow cover and the transport in a heterogeneous coarse sandy soil was examined by extracting soil water from 30 or 40 suction cups placed at five depths between 0.4 and 2.4 m depth. Transport and degradation was analysed by spatial moment calculations. The de-icing chemicals showed the same basic displacement as chemically inactive tracers, an initial fast transport during the melting period followed by a period of stagnation throughout the summer season. PG seemed to be displaced to greater depths compared to non-reactive tracer after the first application. However, computer simulations of transport and degradation in a heterogeneous unsaturated soil showed that decreasing degradation constants with depth can generate a downward movement of the centre of mass without any flow occurring in the system. Potassium acetate showed some adsorption, with calculated retardation factors of approximately 1.3 and 1.2. The degradation rate constant for PG was calculated to be 0.015 day −1 in 1994 and increased to 0.047 day −1 in the second application made in 1995. The degradation rate constant for acetate was estimated to be 0.02 day −1. Increased manganese concentrations seem to be a good indicator of degradation of PG and Ac.