Gastric acid | EPFL Graph Search

Gastric acid, gastric juice, or stomach acid is a digestive fluid formed within the stomach lining. With a pH between 1 and 3, gastric acid plays a key role in digestion of proteins by activating digestive enzymes, which together break down the long chains of amino acids of proteins. Gastric acid is regulated in feedback systems to increase production when needed, such as after a meal. Other cells in the stomach produce bicarbonate, a base, to buffer the fluid, ensuring a regulated pH. These cells also produce mucus – a viscous barrier to prevent gastric acid from damaging the stomach. The pancreas further produces large amounts of bicarbonate and secretes bicarbonate through the pancreatic duct to the duodenum to neutralize gastric acid passing into the digestive tract. The primary active component of gastric acid is hydrochloric acid (HCl), which is produced by parietal cells in the gastric glands in the stomach. The secretion is a complex and relatively energetically expensive pro

Bioavailability of steroid hormones sorbed on microplastics for aquatic organisms through biological fluids

Florian Frédéric Vincent Breider, Yang Liu, Thibault Béranger Masset, Cécilia Laetitia Carla Siri

Many studies have reported that hydrophobic organic contaminants have the ability to sorb on microplastics in aquatic ecosystem via different mechanisms of sorption. However, a lack of studies investigating desorption of such contaminants in organism fluids has been disclaimed. The bioavailability of potential risk-compounds for aquatic organisms has to be assessed. It has been largely reported that adsorption onto microplastics is directly linked with hydrophobicity property of contaminants; the more hydrophobic the pollutant, the higher the sorption capacity. However, it is expected that the least hydrophobic molecules desorb more easily from microplastics. In our study, steroid hormones with different hydrophobicities, namely progesterone and testosterone, are used and their respective desorption from different types of microplastics is investigated in gastric and gut fluids. The idea is to discern if the ingestion of microplastics by organisms might promote desorption of potential sorbed micropollutants and therefore their bioavailability for such species. By using more complex composition of gastric and intestinal fluids separately and then sequentially, the purposes are to reproduce realistic digestive conditions and furthermore determine the organ which is the most prompt to enhance bioavailability of pollutants. Our results show that a higher desorption efficiency (58.6-73.0%, depending on plastic types) is reached in intestinal fluid than in freshwater (31.1-53.6%) or in gastric fluid (18.7-43.9%). Bile salts in intestinal fluid form micelles able to promote the solubilization of pollutants. Adsorption of pepsin onto microplastics has also been revealed, suggesting a competition between pollutant and pepsin for sorption sites and a potent reduction of pollutant solubilization. Our results indicate that progesterone daily intake via microplastics exposure is equal to 16.0μg/kg/day upon intestinal digestion, which represents about 13% of daily intake via water exposure. This observation suggests that ingestion is an additional route of exposure of pollutants and therefore emphasizes pollutants bioavailability for aquatic organisms.

2020

The adsorption and desorption behaviors of phenanthrene and pyrene onto microplastics in the aquatic environment and digestive fluids

Florian Frédéric Vincent Breider, Yang Liu, Thibault Béranger Masset, Cécilia Laetitia Carla Siri

The adsorption and desorption behaviors of Phenanthrene and Pyrene onto polyethylene (PE), polypropylene (PP), polystyrene (PS), and poly (methyl methacrylate) (PMMA) microplastics in the simulated freshwater and digestive fluids (simulated gastic fluid (SGF), simulated intestinal fluid (SIF)) were studied. The second-order kinetic model described the sorption kinetics of polycyclic aromatic hydrocarbons (PAHs), and the Langmuir model fitted the sorption isotherms of PAHs better, which indicated the surface sorption as the main mechanism. The sorption capacity was in the order of PMMA > PS > PE > PP, which may due to the specific surface area and particle size of microplastics. Various environmental conditions were considered, including pH, salinity and dissolved organic matters (DOM). Although higher salinity would bring negative effects on the adsorption of PAHs onto microplastics, the adsorption behaviors were not significantly influenced by pH and DOM. The desorption rate of PAHs from microplastics in SGF was lower than that in the SIF, with the desorption equilibrium time of 12 h in SIF. For the desorption in simulated freshwater, a secondary adsorption occurred around 3 h. Our work for the first time comparing the desorption behaviors between freshwater and two kinds of digestive fluids, indicating the negative effects of microplastics bring to aquatic organisms through digestive tracts. Further studies are needed to quantify the toxicity threshold of aquatic organisms through ingestion of microplastics combined with persistent organic pollutions.

2020

Adsorption of progesterone onto microplastics and its desorption in simulated gastric and intestinal fluids

Florian Frédéric Vincent Breider, Dominique Grandjean, Yang Liu, Thibault Béranger Masset, Cécilia Laetitia Carla Siri

The sorption of Hydrophobic Organic Compound (HOC) onto microplastics is relatively well reported in the literature, while their desorption remains poorly investigated, and especially in biological ﬂuids. The present study investigated the sorption and desorption of progesterone on polyethylene (PE), polypropylene (PP) and polystyrene (PS) microplastics. The sorption experiments showed that the equilibrium was reached in a few hours for all plastics. A sorption efﬁciency of 357.1 µg/g was found for PE and PS and 322.6µg/g for PP. Sorption experiments indicated that adsorption would happen certainly via surface sorption and potentially pore-ﬁlling mechanism. The desorption was carried out in Simulated Gastric Fluid (SGF) and Simulated Intestinal Fluid (SIF), whose formulations were more complex than similar models reported so far. It has been found that the desorption was higher in SIF compared to SGF, surely due to micelle formation in SIF promoting the pollutant solubilization. Sorption of pepsin onto microplastics has also been revealed, suggesting a competition between pollutant and pepsin for sorption sites and a potent reduction of pollutant solubilization. This study indicates that microplastics ingestion could be considered as as additional route of exposure of pollutants and therefore emphasizes pollutants bioavailability for aquatic organisms.

2021

Bioavailability of steroid hormones sorbed on microplastics for aquatic organisms through biological fluids

Florian Frédéric Vincent Breider, Yang Liu, Thibault Béranger Masset, Cécilia Laetitia Carla Siri

2020