Kinetics Of Bisphenol Research Articles

Catalytic effect of N-phenylaminopropyl polyheadral oligomeric silsesquioxane in the synthesis of hybrid nanocomposites based on polycyanurate

Organic-inorganic nanocomposites based on heat-resistant crosslinked polycyanurate (PCN) and N-phenylaminopropyl polyhedral oligomeric silsesquioxane (NPAP-POSS), containing eight reactive secondary amino groups, were synthesized using the in situ reactive formation method. Fourier transmission infrared (FTIR) spectroscopy and dynamic differential scanning calorimetry (DSC) methods were used to study the effect of NPAP-POSS on the kinetics of bisphenol E dicyanate ester (DCBE) polycyclotrimerization during the formation of PCN in PCN/NPAP-POSS nanocomposites. The content of the nanofiller was varied from 0.05 to 1.00 wt.%. Based on the results of FTIR spectral studies, the main kinetic peculiarities of PCN formation were found and their changes under the action of NPAP-POSS nanofiller were determined. A significant catalytic effect of NPAP-POSS on the polycyclotrimerization of DCBE was found, which is confirmed by a decrease in the time of the onset of auto-acceleration, an acceleration of the conversion of cyanate groups of DCBE and the formation of triazine cycles of PCN, an increase in the values of the maximum reaction rate, a decrease in the duration of the reaction, etc. The dynamic DSC method also confirmed the catalytic effect of NPAP-POSS on the formation of PCN in the nanocomposites and established the main kinetic characteristics depending on the content of the nanofiller: a significant decrease in the temperature of the exothermic maximum, an increase in the reaction enthalpy, non-monotonic changes in the induction period and reaction rate, etc. From the analysis of the experimental data, it was concluded that the detected changes in the kinetics of the in situ reaction formation of PCN/NPAP-POSS nanocomposites and the recorded catalytic effect of the nanofiller are due to the fact that two chemical processes occur during the synthesis of the nanocomposites: chemical interaction of –O–C≡N groups of DCBE with secondary –NH groups of NPAP-POSS, which led to further embedding of nanoparticles into the resulting polymer matrix and the direct polycyclotrimerization of DCBE with formation of hybrid polycyanurate network. Schemes of the sequential reactions explaining the catalytic effect of the nanofiller in the synthesis of hybrid PCN/NPAP-POSS nanocomposites are proposed. It was concluded that under the selected conditions of the synthesis, the greatest catalytic effect of the nanofiller is manifested at its content of 0.10 wt.%, since for this sample the maximum shift of the reaction exothermic peak towards lower temperatures, the maximum reaction rate, and the minimum induction period and reaction start temperature were recorded. The results of the research make it possible to optimize the synthesis of heat-resistant materials promising for use in special-purpose structures.

Sonolytic degradation of bisphenol S: Effect of dissolved oxygen and peroxydisulfate, oxidation products and acute toxicity

In this paper, the kinetics of bisphenol S (BPS) degradation in the presence of peroxydisulfate (PDS) or dissolved oxygen (DO) in ultrasound (US) system were investigated. For PDS (US/PDS), increased PDS concentration result in faster BPS degradation, but the enhancement was not remarkable with multiplying PDS dosages. Therefore, heterogeneous PDS activation model based on a Langmuir-type adsorption mechanism was proposed to explain the trait of BPS abatement. The equilibrium constant of PDS (KPDS) was calculated to be 2.91 × 10−4/μM, which was much lower than that of BPS, suggesting that PDS was hard to adsorb on the gas-liquid interface of the cavitation bubble following by activation. Besides, the formation of •OH and SO4•− in US/PDS system was reinvestigated. The result showed that SO4•− rather than •OH was the predominant radical, which was quite different from previous study. Dissolved oxygen largely improve the degradation of BPS in US system and •OH rather than O2•− was proved to be the main reactive oxygen species (ROS). The improvement of •OH generation possibly caused by the reaction of DO with •H so that it cannot recombine with •OH. The transformation of the BPS in US system mainly included BPS radical polymerization, hydroxylation and hydrolysis. Frustratingly, the acute toxicity assay of Vibrio fischeri suggests that the degradation products of BPS are more toxic. These results will improve the understanding on the activation mechanisms of PDS and the role of dissolved oxygen play in US. Further investigations may need to explore other treatment ways of BPS and evaluate the acute toxicity of degradation products.

Migration Characteristics and Degradation Kinetics of Bisphenol A

This paper study the migration characteristics and degradation kinetics of bisphenol A using TGA - gas chromatography - mass spectrometry and found that bisphenol A polycarbonate in the thermal oxidative aging conditions of 130 °C de-gradated to bisphenol A. At the range of 0 h to 120 h, the bisphenol A content of environmental hormones increased with time. When it reached 120 h, bisphenol A environmental hormone content decreased slightly with aging time. The content of bisphenol A reached 495mg/kg when the thermal oxidative aging time was 168 h, which was decreased compared to the content of 442mg/kg at 120 h. Polycarbonate thermal decomposition kinetics study showed that the thermal decomposition of polycarbonate can be divided into three phases. The first thermal decomposition occurred at the range of 415° C to 425 ° C, the polycarbonate end groups fracture of the second stage at 493.6°C , the main fracture of the main chain rearrangement and crosslinking, and the third stage at 598.7°C, the degradation of the chain continues to decompose and the decomposition of the crosslinked carbon precursor; thermal oxidation aging of polycarbonate decreased the heat stability and promote the thermal decomposition of polycarbonate. Comparing the oxidation induction period, thermal weight loss rate and activation energy of polycarbonate before and after thermal oxidative aging, it c found that the thermal stability of the hot oxygen aging of polycarbonate is reduced.

Report on the two‐phase public consultation on the draft EFSA scientific opinion on bisphenol A (BPA)

Report on the two‐phase public consultation on the draft EFSA scientific opinion on bisphenol A (BPA)

Oral Argument: Sublingual Findings Challenge Key Assumptions about BPA Exposure

Key assumptions about bisphenol A (BPA) exposure and bioavailability may be off base, according to a new report in EHP that questions the traditional interpretation of biomonitoring data underlying current risk assessments of the chemical.1 Laboratory research suggests that BPA, a widely used chemical for polycarbonate plastics and other products, is an endocrine disruptor with potential adverse health effects involving reproduction, metabolism, and cancer.2,3 Median daily intake of the chemical through the diet is estimated to be 0.01–0.12 µg/kg body weight, based on urinary concentrations of BPA metabolites.4 These metabolites, particularly BPA glucuronide (BPAG), are not biologically active like the parent compound. Nearly all ingested BPA has been thought to be absorbed in the small intestine and rapidly converted to BPAG in the liver prior to bodywide distribution.5,6 Given the estimated daily intake and assumption of rapid conversion, the European Food Safety Authority set a tolerable daily intake of BPA at 0.05 mg/kg.1 However, the current study indicates that BPA can be completely absorbed directly into the bloodstream from the mouth, thus bypassing early rapid metabolism and remaining biologically active for an extended period of time. “Most previous studies have relied on the gavage method, where BPA is distributed directly into the gut,” says Laura Vandenberg, a postdoctoral fellow at the Tufts University Center for Regenerative and Developmental Biology, who was not involved in the study. “This isn’t how food actually enters our bodies. We chew it, move it around in our mouths, and it interacts with numerous surfaces—our tongue, cheeks, etc.—before it enters the stomach.” Gavage studies suggest there should not be detectable levels of unmetabolized BPA in the blood after exposure, yet dozens of other studies report otherwise, she says. The researchers compared the bioavailability of BPA given sublingually (under the tongue) versus intravenously or by gavage. In one experiment 6 dogs received a dose of 5 mg/kg first intravenously, then a week later sublingually either all at once or one drop at a time. In another experiment, conducted in three parts, the same dogs received a dose of 0.05 mg/kg first intravenously, then sublingually, and finally a 20-mg/kg dose delivered by gavage. After each administration, blood samples were collected to measure BPA and BPAG and calculate various parameters such as maximum concentration, time to maximum concentration, and mean residence time.1 BPA was readily absorbed from both the mouth and the gut, but bioavailability throughout the body differed significantly depending on the absorption site. Over the 2 hours following dosing, 5 mg/g and 0.05 mg/kg sublingual BPA yielded ratios of biologically inactive BPAG to biologically active BPA of 1:1–13:1 and 1:1–6:1, respectively, compared with 237:1–634:1 for the dose placed directly in the stomach.1 If confirmed, new findings on sublingual BPA dosing could have important implications for human exposures to BPA. “The sublingual route is a rather well-known route of absorption for those who are involved in the development of drugs but not for those working with contaminants in general and BPA in particular,” says study coauthor Pierre-Louis Toutain, a professor of physiology and therapeutics at the National Veterinary School of Toulouse, France. He says dogs were chosen as the study animals because their oral tissue closely resembles that of humans. The sublingual dosing used in the study may present different conditions from the exposure that occurs while eating or drinking. It also does not reflect potential nonfood exposures from sources such as dust, cigarette filters, thermal papers, and dental sealants that previous research has suggested occur.7 However, “the authors have shown very clearly that when BPA comes into contact with the mucosa under the tongue, it can be rapidly absorbed into the bloodstream. When this happens, it enters the bloodstream without being metabolized,” says Vandenberg. Additionally, this study may explain previous biomonitoring reports of plasma BPA levels deemed impossible or incorrect based on assumptions about gut-only absorption. This is important because plasma levels found in biomonitoring studies are similar to those found to cause adverse health effects in animal studies.7 Urinary BPAG serves as an index of external BPA exposure in biomonitoring studies, but it tells us nothing about the route of absorption, says Toutain. Given the researchers’ findings, he says it would be unacceptable to assume that only a negligible fraction of BPAG circulated as active BPA before it was converted to the inactive form measured in urine. He says, “It is clear that our data suggesting that BPA bioavailability can be high should raise some questions and possibly lead some agencies to reconsider their risk analysis on BPA.”

Bisphenol A levels in blood depend on age and exposure

We present two approaches to estimate blood concentrations of Bisphenol A (BPA). Simple kinetic principles were applied to calculate steady state plasma concentrations. A physiologically based model was used to simulate the blood concentration time profile in several age groups exploring the influence of not yet fully developed metabolic capacity on the blood concentrations in the newborn. Both approaches gave concordant results and are in excellent agreement with experimental results [Völkel, W., Colnot, T., Csanady, G.A., Filser, J.G., Dekant, W., 2002. Metabolism and kinetics of bisphenol A in humans at low doses following oral administration. Chem. Res. Toxicol. 15, 1281–1287]. The predictions also agree with published results obtained with a different physiologically based model. According to model simulations, BPA is present in the blood of the normal population at concentrations several orders of magnitude lower than most measurements reported in the literature. At the same external exposure level, the newborn is predicted to have 3 times greater blood concentration than the adult. This is due to the not yet fully developed glucuronidation activity in the newborn, not fully compensated by the unimpaired sulfation pathway. For the highest measured external BPA exposure, the predicted blood concentrations of 2.6 pg/ml (steady state concentration) and 8.2 pg/ml (peak concentration) in the adult are lower than the in vitro concentrations at which inhibiting adiponectin release from human adipocytes and stimulation of β-cell production and secretion were observed.

Bisphenol A and Risk Assessment

In a recent article, vom Saal and Hughes (2005) proposed that a new risk assessment on bisphenol A (BPA) is needed because of the availability of extensive new literature, including “recent epidemiologic evidence that BPA is related to disease in women.” Specifically, the only research that vom Saal and Hughes cited as evidence relating BPA to disease is a study by Takeuchi et al. (2004), which they describe as a case–control study that reports that ovarian disease in women is related to blood levels of BPA. Vom Saal and Hughes (2005) have misrepresented the Takeuchi study (Takeuchi et al. 2004): It is not a case–control study, and it does not demonstrate that BPA is specifically associated with ovarian disease. Takeuchi et al. (2004) conducted a small cross-sectional descriptive study that assessed 73 women with respect to serum BPA, hormone concentrations, and their clinical condition at a single point in time. Women were categorized clinically as normal (either obese or nonobese), or as having hyper-prolactinemia, hypothalamic amenorrhea, or polycystic ovary syndrome (PCOS) (again, either obese or nonobese). The six groups in the study each contained as many as 19 subjects (nonobese normal group) and as few as 6 subjects (PCOS obese group). The authors reported that serum BPA was higher in women with PCOS (both obese and not obese) and obese normal women than normal women who were not obese. There were also significant positive correlations between serum BPA and various androgens. Takeuchi et al. (2004) concluded that there is a strong relationship between serum BPA and androgen, and they noted that there are a number of possible explanations for this relationship. Takeuchi et al. (2004) appropriately acknowledged that their study was a hypothesis-generating study and they did not attempt to draw conclusions about causal relationships. Vom Saal and Hughes (2005) overstated the importance of this low-level epidemiologic evidence by referring to it as a case–control study. A case–control study is a more rigorous epidemiologic study in which a group of cases (i.e., with the disease of interest) is compared to a group of controls (i.e., without the disease of interest) with respect to exposures that occurred before the development of disease. Rather, Takeuchi et al. (2004) conducted a cross-sectional study in which both exposure and disease were assessed at a single point in time. When both exposure and outcome are assessed at a single point in time, it is not possible to determine whether the exposure preceded the clinical condition or whether the clinical condition affected the individual’s level of exposure. A cross-sectional study cannot test hypotheses; at most, it can merely examine correlations. Furthermore, cross-sectional studies cannot control for confounding factors that may obscure the true relationship between exposure and disease (Hennekens and Buring 1987). Vom Saal and Hughes (2005) overlooked the intended primary focus of the paper by Takeuchi et al. (2004), which is that there is a relationship between serum BPA and androgen levels. The exact nature of this relationship is not known at this time and Takeuchi et al. (2004) speculate that BPA may stimulate androgen production, or, more likely, androgen may suppress the metabolism of BPA. Consequently, women who have clinical conditions that are associated with elevated androgen (e.g., PCOS or obesity) may have elevated levels of BPA as a result of their elevated androgen. The cross-sectional study by Takeuchi et al. cannot shed light on the time course of events and, therefore, cannot address causal relationships among any of the variables studied in these women. In addition, a number of recent studies have reported that several of the ELISA kits available for measurement of serum BPA [the analytic method used by Takeuchi et al. (2004)] overestimate BPA concentrations and exhibit considerable cross-reactivity, calling into question the validity of results generated by such methods (Fukata and Mori 2004; Fukata et al. 2003; Kawaguchi et al. 2003). Furthermore, it is well known that BPA is metabolized and eliminated rapidly (Volkel et al. 2002), so serum levels provide only a snapshot of BPA exposure within the last day. It is not meaningful to correlate an acute exposure (serum BPA at one time-point) with a chronic disease that took years to develop. Chronic exposure to BPA would have to be demonstrated and not assumed. The Takeuchi et al. (2004) study suggests a hypothesis that could be further examined in an appropriately controlled analytic study. It should not be portrayed as recent epidemiologic evidence that demonstrates an association between blood levels of BPA and clinical disease in women.

Metabolism of bisphenol A in zebrafish ( Danio rerio) and rainbow trout ( Oncorhynchus mykiss) in relation to estrogenic response

The kinetics of bisphenol A (BPA) were investigated in zebrafish ( Danio rerio) exposed to 100 μg BPA/l. BPA uptake was measured during a 7-day period followed by an elimination phase of similar duration. After 2, 6, 12, 24, 48, 72, 120 and 168 h of uptake/elimination, fish were analysed for their content of BPA, bisphenol A glucuronic acid (BPAGA) and bisphenol A sulfate (BPAS). Within the first 24 h steady state levels of BPA, BPAGA and BPAS were reached and the total body concentrations were calculated to be 569, 12 600 and 39.9 ng/g fish, respectively. Elimination rates of the three compounds in zebrafish were estimated by fitting the data to a compartment model. An initial rapid elimination phase was observed for BPA and BPAS with total body half lives (T 1/2) of <1.1 h and 30 min, followed by a slower second elimination phase with T 1/2 values of 139 and 71 h, respectively. Excretion of BPAGA occurred from a single compartment with a T 1/2 of 35 h. The steady state concentration of BPA and its metabolites were investigated in rainbow trout ( Oncorhynchus mykiss) exposed to 100 μg BPA/l. The toxicokinetic parameters from zebrafish and rainbow trout were compared; including previously published data on the rainbow trout. The data indicate that the smaller estrogenic sensitivity observed for the zebrafish may be caused by a more rapid metabolism of BPA in the zebrafish liver.

Thermal degradation of bisphenol A polysulfone by high-resolution thermogravimetry

The thermal degradation and kinetics of bisphenol A polysulfone (PSF) have been studied by high-resolution thermogravimetry (TG). The influence of the testing atmosphere and heating rate on the thermal degradation characteristics of the PSF has been discussed. The thermal degradation temperature of the PSF increases slightly with an increase of heating rate or with the variation of testing atmosphere in the order of: in air<in nitrogen<in vacuum<in argon. The activation energy of the thermal degradation for the PSF also increase from 140, 258 to 293 kJ/mol with variation of the testing atmosphere from air, nitrogen to argon. The activation energy of thermal degradation calculated by high-resolution TG in nitrogen and air are almost the same as those by traditional isothermal or constant heating rate TG. The isothermal weight loss in a certain temperature range could be correctly predicted on the basis of the kinetic parameters determined by nonisothermal high-resolution TG.