Konrad Hungerbuehler

Hazard assessment of fluorinated alternatives to long-chain perfluoroalkyl acids (PFAAs) and their precursors: Status quo, ongoing challenges and possible solutions

Because of concerns over the impact of long-chain perfluoroalkyl acids (PFAAs) on humans and the environment, PFAAs and their precursors are being substituted by alternative substances including fluorinated alternatives that are structurally similar to the substances they replace. Using publicly accessible information, we aimed to identify the status quo of the hazard assessment of identified fluorinated alternatives, to analyze possible systemic shortcomings of the current industrial transition to alternative substances, and to outline possible solutions. Fluorinated alternatives, particularly short-chain PFAAs and perfluoroether carboxylic and sulfonic acids (PFECAs and PFESAs), possess high environmental stability and mobility implying that they have a high global contamination potential. In addition to their potential for causing global exposures, certain fluorinated alternatives have been identified as toxic and are thus likely to pose global risks to humans and the environment. Various factors, particularly the information asymmetry between industry and other stakeholders, have contributed to the current lack of knowledge about the risks posed by fluorinated alternatives. Available cases show that a non-fluorinated substitution strategy (employing either chemical or functionality substitutions) can be a possible long-term, sustainable solution and needs to be further developed and assessed.

Aggregate consumer exposure to UV filter ethylhexyl methoxycinnamate via personal care products.

Ultraviolet (UV) filters are substances designed to protect our skin from UV-induced damage and can be found in many categories of personal care products (PCPs). The potential endocrine-disrupting effects attributed to UV filter ethylhexyl methoxycinnamate (EHMC) are being debated. We evaluated the aggregate exposure of the Swiss-German population (N=1196; ages ≤1-97years) to EHMC via the use of PCPs; thus we provide the first comprehensive information about the current EHMC exposure sources and aggregate exposure levels. In our probabilistic modeling method performed at an individual level, PCP use data obtained by a postal questionnaire were linked to concentration data on EHMC gained from chemical analyses of PCPs used by the questionnaire respondents. The modeled median and 99.9th percentile of the internal aggregate exposure for the general population were 0.012 and 0.873mgday(-1)kg(-1) and 0.008 and 0.122mgday(-1)kg(-1) for the summer/autumn and winter/spring period, respectively. The major contributors to internal aggregate exposure were sunscreen products in summer/autumn (females: 64%; males: 85%; children aged ≤12years 93%). In winter/spring, lip care dominated for females (30%) and sunscreen for males (38%) and children aged ≤12years (50%). Overall, the internal aggregate exposure estimates for the studied population are shown to be below the Derived No Effect Level (DNEL) for EHMC i.e., the level of exposure above which humans should not be exposed; however, when an intense short-term exposure via sunscreen is accounted for during a sunbathing day, at the high-end percentiles (99.9th) the predicted aggregate exposure exceeds the DNEL for thyroid-disrupting effects such as for children aged ≤4years, who might be particularly susceptible to endocrine disrupting events. It is nevertheless critical to acknowledge that quantitative data on transdermal penetration of EHMC from PCPs are currently insufficient. Since long-term effects of endocrine disruptors are not known, future studies are warranted to provide accurate quantitative data on transdermal penetration of EHMC and to determine its metabolic fate in humans.

The probabilistic aggregate consumer exposure model (PACEM): validation and comparison to a lower-tier assessment for the cyclic siloxane D5

Current practice of chemical risk assessment for consumer product ingredients still rarely exercises the aggregation of multi-source exposure. However, focusing on a single dominant source/pathway combination may lead to a significant underestimation of the risk for substances present in numerous consumer products, which often are used simultaneously. Moreover, in most cases complex multi-route exposure scenarios also need to be accounted for. This paper introduces and evaluates the performance of the Probabilistic Aggregate Consumer Exposure Model (PACEM) applied in the context of a tiered approach to exposure assessment for ingredients in cosmetics and personal care products (C&PCPs) using decamethylcyclopentasiloxane (D5) as a worked example. It is demonstrated that PACEM predicts a more realistic, but still conservative aggregate exposure within the Dutch adult population when compared to a deterministic point estimate obtained in a lower tier screening assessment. An overall validation of PACEM is performed by quantitatively relating and comparing its estimates to currently available human biomonitoring and environmental sampling data. Moderate (by maximum one order of magnitude) overestimation of exposure is observed due to a justified conservatism built into the model structure, resulting in the tool being suitable for risk assessment.

The Dynamic Structure of Gold Supported on Ceria in the Liquid Phase Hydrogenation of Nitrobenzene

With regard to heterogeneous catalysis by gold and, in particular, hydrogenation reactions, there is no consensus on the oxidation state of the catalytically active species. By means of high‐resolution X‐ray absorption spectroscopy, we determined in situ the oxidation state of gold in the functioning catalyst Au/CeO2 in the slurry phase of the hydrogenation of nitrobenzene at high pressure. The conversion of nitrobenzene was monitored simultaneously by means of online attenuated total reflectance–Fourier transform infrared spectroscopy. We found that catalysts without measurable amounts of cationic gold were more active than catalysts with cationic gold. Any cationic gold that remained after pretreatment was reduced under reaction conditions, without any loss of activity. No evidence was found that the cationic gold contributed to the catalytic activity.

Exploring the Use of Molecular Docking to Identify Bioaccumulative Perfluorinated Alkyl Acids (PFAAs)

Methods to predict the bioaccumulation potential of per- and polyfluorinated alkyl substances (PFAS) are sorely needed, given the proliferation of these substances and lack of data on their properties and behavior. Here, we test whether molecular docking, a technique where interactions between proteins and ligands are simulated to predict both bound conformation and interaction affinity, can be used to predict PFAS binding strength and biological half-life. We show that an easy-to-implement docking program, Autodock Vina, can successfully redock perfluorooctanesulfonate (PFOS) to human serum albumin with deviations smaller than 2 Å. Furthermore, predicted binding strengths largely fall within one standard deviation of measured values for perfluorinated alkyl acids (PFAAs). Correlations with half-lives suggest both membrane partitioning and protein interactions are important, and that serum albumin is only one of a number of proteins controlling the fate of these chemicals in organisms. However, few data are available for validation of our approach as a broad screening tool, and available data are highly variable. We therefore call for collection of new data, particularly including proteins other than serum albumin and substances beyond perfluorooctanoic acid (PFOA) and PFOS. The methods we discuss in this work can serve as a framework for guiding such data collection.

Swelling Constrained Control of an Industrial Batch Reactor Using a Dedicated NMPC Environment: OptCon

This work presents the application of nonlinear model predictive control (NMPC) to a simulated industrial batch reactor subject to safety constraint due to reactor level swelling. The reactions are equilibrium limited, one of the products is in vapor phase, and the catalyst decomposes in the reactor. The catalyst is fed in discrete time steps during the batch, and the end-point objective is the maximum conversion in a fixed time. The reaction kinetics is determined by the temperature profile and catalyst shots, while the chemical equilibrium is shifted by operating at low pressure and removing one of the products. However, the formed vapor causes liquid swelling, due to the gas or vapor stream resulted from the reaction. As a result reaction mass may enter in the pipes and condenser, creating productivity losses and safety hazard. The end-point objective function (maximum conversion) of this problem can be converted into a level set point tracking problem. The control method is based on the moving horizon NMPC methodology and a detailed first-principles model of reaction kinetics and fluid hydrodynamics is used in the controller. The NMPC approach is based on the sequential quadratic programming (SQP) algorithm implemented in a user-friendly software environment, OptCon. The application of the fast real-time iteration scheme in the NMPC allows the use of small sampling period minimizing this way the violation of the maximum level constraints, due to disturbances within sampling period.

Real time Takagi-Sugeno fuzzy model based pattern recognition in the batch chemical industry

This contribution describes the real time pressure check pattern recognition of an industrial batch dryer. The goal is to identify the start of the drying process and to calculate the time elapsed between two consequent batch starts (batch time) right after the batch has completed. The presented pattern recognition method implements a supervised learning approach based on Takagi-Sugeno fuzzy (TS) models. The decision maker design is based on plant data compressed by the PI algorithm (OSI Software, Inc). It is concluded that the developed classifier is able to perform real time classification and the compressed PI data can be used in order to design data analysis tools which are useful for chemical batch plant operation investigations.

Modeling the dynamics of DDT in a remote tropical floodplain: indications of post-ban use?

Significant knowledge gaps exist regarding the fate and transport of persistent organic pollutants like dichlorodiphenyltrichloroethane (DDT) in tropical environments. In Brazil, indoor residual spraying with DDT to combat malaria and leishmaniasis began in the 1950s and was banned in 1998. Nonetheless, high concentrations of DDT and its metabolites were recently detected in human breast milk in the community of Lake Puruzinho in the Brazilian Amazon. In this work, we couple analysis of soils and sediments from 2005 to 2014 at Puruzinho with a novel dynamic floodplain model to investigate the movement and distribution of DDT and its transformation products (dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane (DDD)) and implications for human exposure. The model results are in good agreement with the accumulation pattern observed in the measurements, in which DDT, DDE, and DDD (collectively, DDX) accumulate primarily in upland soils and sediments. However, a significant increase was observed in DDX concentrations in soil samples from 2005 to 2014, coupled with a decrease of DDT/DDE ratios, which do not agree with model results assuming a post-ban regime. These observations strongly suggest recent use. We used the model to investigate possible re-emissions after the ban through two scenarios: one assuming DDT use for IRS and the other assuming use against termites and leishmaniasis. Median DDX concentrations and p,p′-DDT/p,p′-DDE ratios from both of these scenarios agreed with measurements in soils, suggesting that the soil parameterization in our model was appropriate. Measured DDX concentrations in sediments were between the two re-emission scenarios. Therefore, both soil and sediment comparisons suggest re-emissions indeed occurred between 2005 and 2014, but additional measurements would be needed to better understand the actual re-emission patterns. Monte Carlo analysis revealed model predictions for sediments were very sensitive to highly uncertain parameters associated with DDT degradation and partitioning. With this model as a tool for understanding inter-media cycling, additional research to refine these parameters would improve our understanding of DDX fate and transport in tropical sediments.

Evaporation of decamethylcyclopentasiloxane (D5) from selected cosmetic products: Implications for consumer exposure modeling.

Consumer exposure to leave-on cosmetics and personal care products (C&PCPs) ingredients of low or moderate volatility is often assumed to occur primarily via dermal absorption. In reality they may volatilize from skin and represent a significant source for inhalation exposure. Often, evaporation rates of pure substances from inert surfaces are used as a surrogate for evaporation from more complex product matrices. Also the influence of partitioning to skin is neglected and the resulting inaccuracies are not known. In this paper we describe a novel approach for measuring chemical evaporation rates from C&PCPs under realistic consumer exposure conditions. Series of experiments were carried out in a custom-made ventilated chamber fitted with a vapor trap to study the disposition of a volatile cosmetic ingredient, decamethylcyclopentasiloxane (D5), after its topical application on either aluminum foil or porcine skin in vitro. Single doses were applied neat and in commercial deodorant and face cream formulations at normal room (23°C) and skin temperature (32°C). The condition-specific evaporation rates were determined as the chemical mass loss per unit surface area at different time intervals over 1-1.25h post-dose. Product weight loss was monitored gravimetrically and the residual D5 concentrations were analyzed with GC/FID. The release of D5 from exposed surfaces of aluminum occurred very fast with mean rates of 0.029 mg cm(-2)min(-1) and 0.060 mg cm(-2)min(-1) at 23°C and 32°C, respectively. Statistical analysis of experimental data confirmed a significant effect of cosmetic formulations on the evaporation of D5 with the largest effect (2-fold decrease of the evaporation rate) observed for the neat face cream pair at 32°C. The developed approach explicitly considers the initial penetration and evaporation of a substance from the Stratum Corneum and has the potential for application in dermal exposure modeling, product emission tests and the formulation of C&PCPs.

Tracking pesticide fate in conventional banana cultivation in Costa Rica: A disconnect between protecting ecosystems and consumer health

Conventional banana cultivation in Costa Rica relies on heavy pesticide use. While pesticide residues in exported bananas do not generally represent a safety concern for consumers abroad, ecosystem and human health in producing regions are not likewise protected. In Costa Rica, most studies on pesticide residues in the environment are snapshots, limiting our ability to identify temporal dynamics that can inform risk mitigation strategies. To help bridge this gap, we created a dynamic multimedia model for the Caño Azul River drainage area, which is heavily influenced by banana and pineapple plantations. This model estimates chemical concentrations in water, air, soil, sediments, and banana plants through time, based on pesticide properties and emission patterns and on variable environmental conditions. Case studies for three representative chemicals-the herbicide diuron, the nematicide ethoprofos, and the fungicide epoxiconazole-show that concentrations in fruit remain below EU and US maximum residue limits set to ensure consumer health, while those in the environment are highly variable, reaching peak concentrations in water that can exceed thresholds for ecosystem health. Critical research needs, including incorporating sediment dynamics and the effects of adjuvants on the properties and transport of active ingredients into multimedia models, were identified.