Interference of the gas chromatography- mass spectrometry instrumental background on the determination of trace cyclic volatile methylsiloxanes and exclusion of it by delayed injection.

Cyclic volatile methylsiloxanes (cVMS) have been widely found in various types of environmental media and attracted increasing attention as new pollutants. However, there is still a great challenge in the accurate quantification of trace cVMS, due to their volatility, and the high background originating from GC/MS accessories and surroundings. In this work, the main sources of the high background were investigated in detail for octamethylcyclotetrasiloxane (D4), decmethylcyclopentasiloxane (D5) and dodecmethylcyclohexosiloxane (D6). Several effective measures were employed to minimize these backgrounds, including the delayed injection method to minimize the interference from the injection septum. Then, a GC-MS method was developed for the accurate determination of D4, D5 and D6, with a linear range of 2 - 200 µg/L. The coefficient of determination was 0.9982-0.9986, the limit of detection (LOD) was 0.40-0.52 µg/L, and the quantitative range was 1.88-190 µg/L. Good reproducibility and recovery were obtained, indicating the reliability of the established analytical method.

Concentrations of Volatile Methyl Siloxanes in New York City Reflect Emissions from Personal Care and Industrial Use.

Volatile methyl siloxanes (VMS) are a group of organosilicon compounds of interest because of their potential health effects, their ability to form secondary organic aerosols, and their use as tracer compounds. VMS are emitted in the gas-phase from using consumer and personal care products, including deodorants, lotions, and hair conditioners. Because of this emission route, airborne concentrations are expected to increase with population density, although there are few studies in large urban centers. Here, we report summertime concentrations and daily variations of VMS congeners measured in New York City. Median concentrations of the 6 studied congeners, D3 (20 ng m-3), D4 (57 ng m-3), D5 (230 ng m-3), D6 (11 ng m-3), L5 (2.5 ng m-3), and L7 (1.3 ng m-3) are among the highest reported outdoor concentrations in the literature to date. Average congener ratios of D5:D4 and D5:D6 were consistent with previously reported emissions ratios, suggesting that concentrations were dominated by local emissions. Measured concentrations agree with previously published results from a Community Multiscale Air Quality model and support commonly accepted emissions rates for D4, D5, and D6 of 32.8, 135, and 6.1 mg per capita per day. Concentrations of D4, D5, D6, L5, and L7 and total VMS were significantly lower during the day than during the night, consistent with daytime oxidation reactivity. Concentrations of D3 did not show the same diurnal trend but exhibited a strong directional dependence, suggesting that it may be emitted by industrial point sources in the area rather than personal care product use. Concentrations of all congeners had large temporal variations but showed relatively weak relationships with wind speed, temperature, and mixing height.

Cyclic and linear siloxane contamination in sediment and invertebrates around a thermal power plant in Korea: Source impact, distribution, seasonal variation, and potential for bioaccumulation.

Siloxanes have been commonly used as additives in a variety of industrial and consumer products. Media and government investigations have revealed that defoamers containing siloxanes are used in the effluent of thermal power plants in Korea. However, investigations of the source impact of siloxane contamination from the discharge of thermal power plants into coastal environments are scarce. In this study, sediment and invertebrates were collected around a thermal power plant to assess source impact, seasonal variation, and a potential for bioaccumulation. Although siloxanes were detectable in sediment and invertebrates, the spatial distribution and composition (which differed between the siloxanes found in sediment and invertebrates and those in defoamer used in the plant) suggest they were likely transported by long-distance migration as well as the discharge of thermal power plant. Seasonal differences might affect sedimentary contamination and the bioaccumulation potential of siloxanes. Specifically, octamethylcyclotetrasiloxane (D4) may have limited adsorption capacity and potential for long-distance migration, as its contribution in sediment far from the coastline was greater than that of decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6). However, higher D5 accumulation in invertebrates, and D5 has a potential bioaccumulation. A molecular docking analysis showed that the binding affinity between D5 and the cytochrome enzyme in invertebrates was weaker than that with other siloxanes, which could lead to higher D5 accumulation in invertebrates.

Bioaccumulation of Linear Siloxanes in Fish.

The bioaccumulation behavior, including the uptake, internal distribution, depuration, and biotransformation rates, of three widely used linear methyl-siloxanes was investigated in rainbow trout. Dietary uptake efficiencies of octamethyltrisiloxane (L3), decamethyltetrasiloxane (L4), and dodecamethylpentasiloxane (L5) were 15% (3.3% standard error [SE]), 8.6% (1.4% SE), and 15% (1.8% SE), respectively, and for L3 and L4 were well below those of nonmetabolizable reference chemicals with similar octanol-water partition coefficients, suggesting significant intestinal biotransformation of L3 and L4. Somatic biotransformation rate constants were 0.024 (0.003 SE) day-1 for L3 and 0.0045 (0.0053 SE) day-1 for L4 and could not be determined for L5. Lipid-normalized biomagnification factors for L3, L4, and L5 were 0.24 (0.02 SE), 0.24 (0.01 SE), and 0.62 (0.05 SE) kg-lipid kg-lipid-1 , respectively. Bioconcentration factors standardized to a 5% lipid content fish for water in Canadian oligotrophic lakes with a dissolved organic carbon content of 7.1 mg L-1 were 2787 (354 SE) for L3, 2689 (312 SE) for L4, and 1705 (418 SE) L kg-wet weight-1 , respectively, and 3085 (392 SE) for L3, 4227 (490 SE) for L4, and 3831 (938 SE) L kg-wet weight-1 in water with a dissolved organic carbon content of 2.0 mg L-1 . A comparison of 238 bioaccumulation profiles for 166 different chemicals shows that the bioaccumulation profiles for L3, L4, and L5 are vastly different from those of other very hydrophobic compounds found in the environment. Environ Toxicol Chem 2024;43:42-51. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Factors determining contamination and time trends in cyclic and linear siloxanes in sediments from an industrialized lake in Korea.

Siloxanes, widely used in various consumer and industrial products, are emerging concerns of contaminants. Despite this, limited studies have been conducted on contamination and time trends on siloxanes in coastal environments. In the present study, four cyclic and 15 linear siloxanes were measured in sediments collected from an artificial saltwater lake in Korea during 2001-2016 to investigate contamination, time trends, and ecotoxicological concerns. Cyclic siloxanes were detected in all sediment samples, whereas linear siloxanes were not frequently detected. The highest siloxane concentrations were observed in creeks passing through various industrial complexes, indicating that industrial activities predominantly contributed to siloxane contamination in coastal environments. Decamethylcyclopentasiloxane (D5) and dodecylcyclohexasiloxane (D6) were predominant siloxanes in sediments over the last two decades. Siloxane concentrations significantly increased in creek sediments from 2008 to 2016, whereas those in inshore and offshore regions significantly decreased due to a strong dilution effect by the operation of tidal power plant. This suggests that consumption patterns and coastal development activities are crucial factors determining the contamination and time trends in the sedimentary siloxanes. The sedimentary concentrations of octamethylcyclotetrasiloxane (D4) and D5 exceeded several thresholds, raising the potentials for ecological risks to aquatic organisms.

Siloxane Emissions and Exposures during the Use of Hair Care Products in Buildings.

Cyclic volatile methyl siloxanes (cVMS) are ubiquitous in hair care products (HCPs). cVMS emissions from HCPs are of concern, given the potential adverse impact of siloxanes on the environment and human health. To characterize cVMS emissions and exposures during the use of HCPs, realistic hair care experiments were conducted in a residential building. Siloxane-based HCPs were tested using common hair styling techniques, including straightening, curling, waving, and oiling. VOC concentrations were measured via proton-transfer-reaction time-of-flight mass spectrometry. HCP use drove rapid changes in the chemical composition of the indoor atmosphere. cVMS dominated VOC emissions from HCP use, and decamethylcyclopentasiloxane (D5) contributed the most to cVMS emissions. cVMS emission factors (EFs) during hair care routines ranged from 110-1500 mg/person and were influenced by HCP type, styling tools, operation temperatures, and hair length. The high temperature of styling tools and the high surface area of hair enhanced VOC emissions. Increasing the hair straightener temperature from room temperature to 210 °C increased cVMS EFs by 50-310%. Elevated indoor cVMS concentrations can result in substantial indoor-to-outdoor transport of cVMS via ventilation (0.4-6 tons D5/year in the U.S.); thus, hair care routines may augment the abundance of cVMS in the outdoor atmosphere.

Directed evolution for Si-C bond cleavage of volatile siloxanes in glass bioreactors.

Volatile methylsiloxanes (VMS) are a class of non-biodegradable anthropogenic compounds with propensity for long-range transport and potential for bioaccumulation in the environment. As a proof-of-principle for biological degradation of these compounds, we engineered P450 enzymes to oxidatively cleave Si-C bonds in linear and cyclic VMS. Enzymatic reactions with VMS are challenging to screen with conventional tools, however, due to their volatility, poor aqueous solubility, and tendency to extract polypropylene from standard 96-well deep-well plates. To address these challenges, we developed a new biocatalytic reactor consisting of individual 2-mL glass shells assembled in conventional 96-well plate format. In this chapter, we provide a detailed account of the assembly and use of the 96-well glass shell reactors for screening biocatalytic reactions. Additionally, we discuss the application of GC/MS analysis techniques for VMS oxidase reactions and modified procedures for validating improved variants. This protocol can be adopted broadly for biocatalytic reactions with substrates that are volatile or not suitable for polypropylene plates.

Occurrence, time trends, and human exposure of siloxanes and synthetic musk compounds in indoor dust from Korean homes.

Siloxanes and synthetic musk compounds (SMCs) have been widely used as additives in household and personal care products. Humans are easily exposed to siloxanes and SMCs originating from these products through ingestion and dermal absorption of indoor dust. In the present study, indoor dust samples were analyzed for 19 siloxanes (cyclic and linear) and 12 SMCs (polycyclic, macrocyclic, and nitro musks) to assess their occurrence, time trends over time, source, and health risks. A total of 18 siloxanes and 10 SMCs were detected in all indoor dust samples obtained from 2011⎯2021, indicating widespread and long-term contamination. Higher detection frequencies and concentrations were associated with siloxanes and SMCs with higher use and strong resistance against degradation processes. Indoor dust samples were dominated by linear siloxanes (L11-L13), 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta-(g)-2-benzopyran (HHCB), musk ketone (MK), and 7-acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphthalene (AHTN). The frequent use of household and personal care products is likely an important source of siloxane and SMC contamination in indoor environments. The concentrations of siloxanes and SMCs in indoor dust increased from 2011 to 2021, particularly, those of linear siloxanes, reflecting the impact of regulatory actions addressing cyclic siloxanes. The profiles of siloxanes remained stable throughout the study period, whereas those of SMCs shifted from nitro to polycyclic musks. The estimated daily intakes (EDIs) of siloxanes and SMCs arising from ingestion were greater than from dermal absorption of indoor dust. The EDIs of siloxanes and SMCs associated with indoor dust indicated that children are exposed to these pollutants.

Mechanism of bonding, surface property, electrical behaviour, and environmental friendliness of carbon/ceramic composites produced via the pyrolysis of coal waste with polysiloxane polymer.

A simple mixing-pressing followed by thermal curing and pyrolysis process was used to upcycle coal waste into high-value composites. Three coal wastes of different physicochemical properties were investigated. The hypothetical mechanisms of bonding between the coal particles and the preceramic polymer are presented. The textural properties of the coals indicated that the lowest volatile coal waste (PCD) had a dense structure. This limited the diffusion and reaction of the preceramic polymer with the coal waste during pyrolysis, thereby leading to low-quality composites. The water contact angles of the composites up to 104° imply hydrophobic surfaces, hence, no external coating might be required. Analysis of the carbon phase confirmed that the amorphous carbon structure is prevalent in the composites compared to the coal wastes. The dc volume resistivity of the composites in the range of 22 to 82 Ω-cm infers that the composites are unlikely to suffer electrostatic discharge, which makes them useful in creating self-heating building parts. The leached concentrations of heavy metal elements from the composites based on the end-of-life scenario were below the Toxicity Characteristic Leaching Procedure regulatory limits. Additionally, the release potential or mobility of the metals from the composites was not influenced by the pH of the eluants used. On the basis of the reported results, these carbon/ceramic composites show tremendous prospects as building materials due to these properties.

Helping WWTP managers to address the volatile methylsiloxanes issue-Behaviour and complete mass balance in a conventional plant.

Volatile methylsiloxanes (VMSs) are a group of additives employed in different consumer products that can affect the quality of the biogas produced in wastewater treatment plants (WWTPs). The main objective of this study is to understand the fate of different VMSs along the treatment process of a WWTP located in Aveiro (Portugal). Thus, wastewater, sludge, biogas, and air were sampled in different units for two weeks. Subsequently, these samples were extracted and analyzed by different environment-friendly protocols to obtain their VMS (L3-L5, D3-D6) concentrations and profiles. Finally, considering the different matrix flows at every sampling moment, the mass distribution of VMSs within the plant was estimated. The levels of ∑VMSs were similar to those showed in the literature (0.1-50 µg/L in entry wastewater and 1-100 µg/g dw in primary sludge). However, the entry wastewater profile showed higher variability in D3 concentrations (from non detected to 49 µg/L) than found in previous studies (0.10-1.00 µg/L), likely caused by isolated releases of this compound that could be related to industrial sources. Outdoor air samples showed a prevalence of D5, while indoor air locations were characterized by a predominance of D3 and D4. Differences in sources and the presence of an indoor air filtration system may explain this divergence. Biogas was characterized by ∑VMSs concentrations (8.00 ± 0.22 mg/m3) above the limits recommended by some engine manufacturers and mainly composed of D5 (89%). Overall, 81% of the total incoming mass of VMSs is reduced along the WWTP, being the primary decanter and the secondary treatment responsible for the highest decrease (30.6% and 29.4% of the initial mass, respectively). This reduction, however, is congener dependant. The present study demonstrates the importance of extending sampling periods and matrices (i.e., sludge and air) to improve sample representativity, time-sensitivity, and the accuracy of mass balance exercises.

Seasonal and latitudinal variability in the atmospheric concentrations of cyclic volatile methyl siloxanes in the Northern Hemisphere.

Field data from two latitudinal transects in Europe and Canada were gathered to better characterize the atmospheric fate of three cyclic methylsiloxanes (cVMSs), i.e., octamethyl-cyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6). During a year-long, seasonally resolved outdoor air sampling campaign, passive samplers with an ultra-clean sorbent were deployed at 15 sampling sites covering latitudes ranging from the source regions (43.7-50.7 °N) to the Arctic (79-82.5 °N). For each site, one of two passive samplers and one of two field blanks were separately extracted and analyzed for the cVMSs at two different laboratories using gas-chromatography-mass spectrometry. Whereas the use of a particular batch of sorbent and the applied cleaning procedure to a large extent controlled the levels of cVMS in field blanks, and therefore also the method detection and quantification limits, minor site-specific differences in field blank contamination were apparent. Excellent agreement between duplicates was obtained, with 95% of the concentrations reported by the two laboratories falling within a factor of 1.6 of each other. Nearly all data show a monotonic relationship between the concentration and distance from the major source regions. Concentrations in source regions were comparatively constant throughout the year, while the concentration gradient towards remote regions became steeper during summer when removal via OH radicals is at its maximum. Concentrations of the different cVMS oligomers were highly correlated within a given transect. Changes in relative abundance of cVMS oligomers along the transect were in agreement with relative atmospheric degradation rates via OH radicals.

Per- and polyfluoroalkyl substances and volatile methyl siloxanes in global air: Spatial and temporal trends.

The study reports on the atmospheric concentrations of per- and polyfluoroalkyl substances (PFAS) and volatile methyl siloxanes (VMS) measured using sorbent-impregnated polyurethane foam disks (SIPs) passive air samplers. New results are reported for samples collected in 2017, which extends temporal trend information to the period 2009-2017, for 21 sites where SIPs have been deployed since 2009. Among neutral PFAS, fluorotelomer alcohols (FTOHs) had higher concentrations than perfluoroalkane sulfonamides (FOSAs) and perfluoroalkane sulfonamido ethanols (FOSEs) with levels of ND‒228, ND‒15.8, ND‒10.4 pg/m3, respectively. Among ionizable PFAS, the sum of perfluoroalkyl carboxylic acids (PFCAs) and perfluoroalkyl sulfonic acids (PFSAs) in air were 0.128-781 and 6.85-124 pg/m3, respectively. Longer-chain i.e. C9-C14 PFAS, which are relevant to the recent proposal by Canada for a listing of long-chain (C9-C21) PFCAs to the Stockholm Convention, were also detected in the environment at all site categories including Arctic sites. Cyclic and linear VMS ranged between 1.34‒452 and 0.01-12.1 ng/m3, respectively, showing dominance in urban areas. Despite the wide range of levels observed across different site categories, geometric means of the PFAS and VMS groups were fairly similar when grouped according to the five United Nations regions. Variable temporal trends in air (2009-2017) were observed for both PFAS and VMS. PFOS, which has been listed in the Stockholm Convention since 2009, is still showing increasing tendencies at several sites, indicating constant input from direct and/or indirect sources. These new data inform international chemicals management for PFAS and VMS.

Occurrence of methylsiloxanes in indoor store dust in China and potential human exposure.

Methylsiloxanes are synthetic molecules with versatile and extensive applications. Because of their volatile properties, they are easily released from manufactured products and contaminate indoor environments, causing high human exposure. However, available information on their presence in specific microenvironments, and on the related potential risks for human health, is limited. We conducted a survey of sixteen methylsiloxanes species, including three cyclic (D4-D6) and thirteen linear (L4-L16) chemicals, in indoor dust samples from twenty-eight stores representative of six store categories in Beijing, China. Total methylsiloxane concentrations in store dust were 176-54,825 ng/g, depending on the store, with a median of 2196 ng/g. Linear chemicals represented a median proportion of 90.8% of total methylsiloxanes. The measured methylsiloxane concentrations in this study were marginally higher than those reported previously for standard living and working environments. The highest linear and total methylsiloxane concentrations were measured in electronic stores, while the highest cyclic methylsiloxane concentrations were measured in department stores. The presence of methylsiloxanes in the store dust samples was attributed mainly to their release from chemical additives in marketed products. Estimated median total exposure doses under normal and worst-case exposure scenarios were 0.237 and 0.888 ng/kg bw/d, respectively. Further investigation is needed to characterize methylsiloxane distribution in other microenvironments and to evaluate the associated health risks.

Occurrence and fate of chlorinated methylsiloxanes in surrounding aqueous systems of Shengli oilfield, China.

Mono-chlorinated products of cyclic volatile methylsiloxanes (cVMS), i.e., Monochlormet-hylheptamethylcyclotetrasiloxane [D3D(CH2Cl)], monochlormethylnonamethylcyclopenta-siloxane [D4D(CH2Cl)], and monochlormethylundemethylcyclohexasiloxane [D5D(CH2Cl)], were detected in water [

Assessment of cyclic volatile methyl siloxanes (CVMSs) in indoor dust from different micro-environments in northern and central Vietnam.

Comprehensive studies on emerging contaminants like volatile methyl siloxanes in settled dust from different micro-environments are still limited. In this study, concentrations and distribution of cyclic volatile methyl siloxanes (CVMSs) including D3, D4, D5, and D6 were examined in indoor dust samples collected from various micro-environments in northern and central Vietnam. Concentrations of total CVMSs in the dust samples ranged from 86.0 to 5890 (median 755) ng/g and decreased in the order: waste processing workshops (median 1560; range 329-5890) > common houses (650; 115-1680) > university classrooms (480; 86.0-1540) > vehicle repair shops (295; 126-1950) ng/g. This observation suggests that informal waste processing activities are sources of CVMSs. Among the studied CVMSs, D5 was the most predominant compound (41 ± 14%), followed by D6 (26 ± 13%), D4 (23 ± 12%), and D3 (11 ± 11%). Moderate positive correlations between D3/D4, D4/D5, and D5/D6 were found. Median daily intake doses of D3, D4, D5, and D6 through dust ingestion were 0.016, 0.051, 0.11, and 0.054 ng/kg/d, respectively, which were comparable to water consumption and markedly lower than the air inhalation pathway.

Volatile Methyl Siloxanes and Other Organosilicon Compounds in Residential Air.

Volatile methyl siloxanes (VMS) are ubiquitous in indoor environments due to their use in personal care products. This paper builds on previous work identifying sources of VMS by synthesizing time-resolved proton-transfer reaction time-of-flight mass spectrometer VMS concentration measurements from four multiweek indoor air campaigns to elucidate emission sources and removal processes. Temporal patterns of VMS emissions display both continuous and episodic behavior, with the relative importance varying among species. We find that the cyclic siloxane D5 is consistently the most abundant VMS species, mainly attributable to personal care product use. Two other cyclic siloxanes, D3 and D4, are emitted from oven and personal care product use, with continuous sources also apparent. Two linear siloxanes, L4 and L5, are also emitted from personal care product use, with apparent additional continuous sources. We report measurements for three other organosilicon compounds found in personal care products. The primary air removal pathway of the species examined in this paper is ventilation to the outdoors, which has implications for atmospheric chemistry. The net removal rate is slower for linear siloxanes, which persist for days indoors after episodic release events. This work highlights the diversity in sources of organosilicon species and their persistence indoors.

Occurrence and Behavior of Methylsiloxanes in Urban Environment in Four Cities of China.

Methylsiloxanes (MSs), used in industrial production and personal care products, are released in various environmental media. In this study, we combined monitoring and modeling to investigate the occurrence and behavior of MSs in the urban environment in China. MSs were widely found in the air, water, soil and sediment of four cities in China. The concentrations of MSs in all four environmental media of Zhangjiagang were higher than those in the other three cities (Beijing, Kunming and Lijiang), indicating that the siloxane production plant had a significant impact on the pollution level of MSs in the surrounding environment. The samples with high MS concentrations were all from the sample sites near the outlet of the WWTPs, which showed that the effluent of the WWTPs was the main source of MS pollution in the surrounding environment. The modeling results of the EQC level III model showed that D4 discharged into the environment was mainly distributed in the air, while D5 and D6 were mainly distributed in the sediment. CMSs (D4-D6) discharged into various environmental media could exist in the urban environment for a long time with low temperatures in cities. When the temperature was 0 °C, the residence time of D5 and D6 could be 68.1 days and 243 days in the whole environmental system in Beijing. This study illustrates the importance of CMSs (D4-D6) in low-temperature environments and the potential environmental risks that they may pose.

Seasonal occurrence, concentrations, and occupational exposure to VMSs in different environments of a WWTP.

In the present study, indoor and outdoor environments of a wastewater treatment plant (WWTP) were monitored by passive air samplers to assess the presence and seasonal trends of three linear (L3-L5) and four cyclic (D3-D6) volatile methylsiloxanes (VMSs). Furthermore, passive sampling rates (PSRs) were estimated from literature values to calculate VMSs air concentrations and occupational exposure to potentially toxic (D4-D6) congeners. Results showed a seasonal pattern of VMSs in outdoor locations (especially in the aeration tank and preliminary treatment), being the highest levels of total VMSs reached in Summer and the lowest in Spring, caused by the confluence of changing weather conditions and VMSs consumption patterns. This seasonality was not found in indoor sites. The congener profiles of VMSs were consistent throughout the year, showing a prevalence of D5 outdoors, and of D3 and D4 in strictly indoor environments. Different sources of VMSs, together with an air filtering system installed in the sampled buildings explain these differences. Estimated PSRs yielded lower values indoors (0.16-0.21 m3/day) than outdoors (0.32-0.49 m3/day), due to different wind speeds. Overall, outdoor locations showed higher VMSs concentrations in air than indoors. However, the values detected in both environments (∑VMSs between 8.00 and 2000 ng/m3) were within the ranges described in the literature for these locations. The occupational exposure to D4-D6 estimated for three different activities in the WWTP showed the highest values for Maintenance Technicians (8010 ± 722 ng/(kg·year)) and the lowest for Laboratory Technicians (5410 ± 874 ng/(kg·year)), in direct correlation with the higher amount of time spent outdoors by the former. In any case, the exposure was below the inhalation threshold of 150 µg/(kg·day) proposed as safe by other authors.

Nationwide monitoring of cyclic and linear siloxanes in sediment and bivalves from Korean coastal waters: Occurrence, geographical distribution, and bioaccumulation potential.

Contamination of coastal environments by siloxanes is of growing concern. Sediment and bivalves were collected from 50 locations along the Korean coast to assess the geographical distribution, sources, and bioaccumulation potential of siloxanes. Cyclic and linear siloxanes were detectable in all sediment and bivalve samples. The highest siloxane concentrations were detected in sediment (656 ng/g dw) and bivalves (3273 ng/g dw) from highly industrialized bays and harbor-zones, suggesting that industrial and shipping activities are major sources of siloxanes in coastal environment. The geographical distribution of siloxanes was similar in sediment and bivalves. Sedimentary siloxanes were dominated by cyclic siloxanes, while linear siloxanes were predominant in bivalves. Bioaccumulation of linear siloxanes in bivalves originated mainly from the sedimentary environment. Mean biota-sediment accumulation factors (BSAFs) of seven siloxanes ranged from 1.26 to 6.03, indicating potential for bioaccumulation. This is the first report on the nationwide survey on siloxanes in Korean coastal waters.

Activated Porous Carbon Fiber: New Adsorbent for Sampling and Analysis by Thermal Desorption of Siloxanes in Biogas and Biomethane.

The growing global energy demand requires the continuous development and optimization of the production of alternative energy sources. According to the circular economy approach, waste conversion into biogas and biomethane represent an interesting energy source. The input into the distribution network and energy conversion systems of biomethane requires quality monitoring and the use of cleaning up systems. Therefore, there is a need to constantly invest in the development of sampling and analysis systems that save time, costs, and materials. The purpose of this study was to use activated porous carbon fiber (APCF), an extremely versatile material for sampling and analysis by thermal desorption, to show the advantages it has over the adsorbents traditionally used for siloxane monitoring. Siloxanes are among the contaminating compounds that are mainly present in biogas and biomethane, and if not removed sufficiently, they endanger the quality and use of the gas. These are highly harmful compounds since during combustion, they produce quartz particles that are abrasive to the surfaces of the materials involved in the energy production process. In addition, siloxanes directly hinder the energy properties of biomethane during combustion, due to their radical scavenger properties. In this work, the efficiency of APCF tube was evaluated by comparing it with common multilayer tube thought sampling and analyzing siloxanes in lab scale and in real scale (biogas plant). Thermal desorption analysis coupled with GC-MS for the determination of siloxanes showed that the use of APCF allows to obtain better performance. This allows to deduce that APCF is an innovative material for the establishment of a better sampling and analysis method than the current ones, enabling better results to be achieved in the process of monitoring fuel quality in biomethane production and storage facilities.