A review of bioaccumulation of volatile methylsiloxanes in aquatic ecosystems

Cyclosiloxane artifacts explain reported Henry's law constants for nonvolatile fluorotelomer sulfonates

The Henry's Law partition coefficient (KH) is important for understanding and predicting the air-water partitioning and transport of molecules, including per- and polyfluoroalkyl substances (PFAS). Henry's Law constants for three fluorotelomer sulfonates (FTSs) were reported in 2022 by static headspace analysis coupled with gas chromatography (GC)-tandem mass spectrometry. However, FTSs are nonvolatile at the reported experimental pH values (5.0-7.0). We tested the hypothesis that artifacts were responsible for the chromatographic peaks attributed to FTSs. Static air-water partition experiments and controls were conducted with free-acid (neutral) FTS standards with GC-quadrupole time-of-flight mass spectrometry (QTOF). Free acid standards of FTSs directly injected into the GC-QTOF gave no peaks. In contrast, a 10:2 FTOH standard produced a distinct peak and strong match with the NIST23 library. Although FTS homologs are not in the NIST library because they are nonvolatile, accurate mass fragments and formula calculations confirmed that the peaks previously attributed to FTSs were D3, D4, and D5 cyclosiloxanes (74-90 % match). Controls revealed that injection of oxygen and moisture creates the cyclosiloxanes artifacts that were misidentified as FTSs.

Toxicokinetic Profiles and Potential Endocrine Disruption Effects at the Reproductive Level Promoted by Siloxanes Used in Consumer Products

Siloxanes, commonly known as silicones, are polymeric compounds made up of silicon and oxygen atoms bonded together alternately. Within this group of substances are linear methyl-siloxanes and cyclic methyl-siloxanes, with octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) being the most produced and used industrially. Due to their versatility, high production volume, stability, and local presence in environmental matrices and biological fluids such as breast milk, fat, and plasma, siloxanes have been considered persistent organic pollutants, representing a public health problem. This represents a public health concern, especially when different investigations have reported potential endocrine effects at the reproductive level in experimental animals exposed to D4 and D5. The objective of this study was to review the potential reproductive and endocrine effects derived from siloxanes present in personal care products (PCPs). The results of the literature review confirmed that D4 and D5 were the most used siloxanes as additives in PCP because they improve the emollient properties of the cosmetic and the physical appearance of hair and skin. Similarly the toxicological effects of siloxanes, particularly D4, D5, and D6 included significant endocrine disruption, reproductive toxicity, and liver toxicity. Studies in SD and F-344 rats, commonly used to assess these effects, have shown that D4 has low estrogenic activity, binding to ER-α receptors, whereas D5 does not bind to estrogen receptors. D4 exposure has been associated with increased uterine weight and estrous cycle alterations, leading to prolonged exposure to estrogens, which raises the risk of endometrial hyperproliferation and carcinogenesis. Recent research highlights that D5 exposure disrupts follicle growth, endometrial receptivity, and steroidogenesis, resulting in infertility and hormonal imbalances, potentially causing disorders like endometriosis and increased cancer risk. Chronic exposure to D5 has been linked to the development of uterine endometrial adenocarcinoma, with higher doses further elevating this risk.

Volatile methylsiloxanes in beauty and personal care products sold in India and human exposure assessment

This study investigated the presence of cyclic and linear volatile methylsiloxanes in 174 beauty and personal care products (PCPs) sold in India. Siloxanes were detected in all the samples with a detection frequency of 20 to 99 %. The cyclic siloxanes viz. decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6) were predominant in all the samples, and the total concentration of cyclic siloxanes was as high as 773,000 μg g-1. About 40 % of the samples exceeded the European Union guideline value (0.1 %) for wash-off and leave-on products. The estimated per-capita run-off emissions of total siloxanes from beauty and PCPs were between 158,000 and 2,680,000 μg day-1 (average: 988,000 μg day-1). Hair serum, makeup remover, body wash, face wash, and shaving foam showed higher average per-capita run-off emissions for total siloxanes (range: 2950 to 505,000 μg day-1). The estimated per-capita air emissions of siloxanes were between 42,600 to 1,950,000 μg day-1 (average: 551,000 μg day-1). Hair serums, moisturizers, deodorants, foundation, primers, lip colour, makeup removers, and aftershaves were the major contributors to air emissions (0.44 to 56.3 %). The average dermal and inhalation exposure to siloxanes from using beauty and PCPs was 4020 and 642 μg kg-bw-1 day-1, respectively. The average daily dermal and inhalation doses for ∑octamethylmethycyclotertrasiloxane (D4) + D5 were 16.9 and 172 μg kg-bw-1 day-1, respectively, which is higher than the chronic reference dose for inhalation exposure. Among the studied siloxanes, cyclic siloxanes predominantly contributed to consumer exposure from applying beauty and PCPs.

Organic ultraviolet filters in Hainan coral reefs: Distribution, accumulation, and ecological risks

Organic ultraviolet filters (OUVFs) have been widely used as functional ingredients of sunscreen products and have entered into marine ecosystems, particularly in tropical areas where solar UV radiation is strong. These chemicals, with their potential toxicity and ecological risk, have raised widespread concern for the protection of the fragile marine ecosystem of coral reefs. In this study, fourteen OUVFs were analyzed among 24 coral species, together with their habitats including seawater and sediment from the coastal coral reef regions of Hainan Island, South China Sea. Surprisingly, all of fourteen OUVFs were detected in each sample, indicating the wide distribution of OUVFs among sites and samples. Among the fourteen OUVFs, benzophenone-3 (BP-3) and 4-methylbenzylidene camphor (4-MBC) were the most abundant, with concentrations ranging from 35.3 to 75.6 and 38.3 to 61.4 ng/L in seawater, from 13.2 to 25.9 and 7.0 to 17.4 ng/g dw in sediment, and from 4.5 to 21.3 and 4.4 to 19.7 ng/g dw in corals, respectively. Analysis of OUVFs in 24 coral species pointed that OUVFs accumulation in corals is morphology dependent: the highest concentration of OUVFs was identified in Galaxea fascicularis with abundant of polyps and tentacles while the lowest levels of OUVFs were found in Porites mayeri (smooth or lobed surface). In corals, we found that these OUVFs accumulated, depending on the coral species and the types of OUVFs. The ecological risk assessment further indicated that BP-3, 4-MBC and BP-8 had posed risks to corals. In addition, significantly higher concentrations of OUVFs were observed in Sanya (a seaside tourist resort) than in the other sites, suggesting that tourist activity and use of sunscreen products are the key to high inputs of sunscreen agents into marine ecosystem. Overall, our study demonstrates a potential risk role for OUVFs in coral protection in tropical areas where coral bleaching events occur.

Phenylmethylsiloxanes in the typically human-impacted Xiaoqing River of China: Their distribution and degradation in both waterbodies and mussels

Based on sampling from Xiaoqing River of China and elimination experiments, this study first investigated spatial/seasonal profiles and fates of phenylmethylsiloxanes (PMSs), as modified products of dimethylsiloxanes (DMSs), in natural waterbody. Overall, the average water (6.7 ng/L) and sediment (28.5 ng/g dw) concentrations of total six cis-/trans- isomers of 2,4,6-triphenyl-2,4,6-trimethylcyclotrisiloxanes (P3) and 2,4,6,8-tetraphenyl-2,4,6,8-tetramethylcyclotetrasiloxanes (P4) in river segments located in industrial areas were respectively 7.37 and 6.13 times higher than those near residential areas, indicating that industrial activities may have larger contribution to PMSs emission than living activities. Compared with paired DMSs with same Si number, PMSs had lower hydrolysis but faster photolysis, and these two pathways influenced isomeric differences in river water: (1) slower hydrolysis of trans-isomers (t1/2 = 45.6-334 h) than cis-isomers (t1/2 = 38.1-251 h) might cause actual cis/trans ratios (0.18 for P3 and 0.092 for P4) lower than theoretical values (0.33 for P3 and 0.14 for P4) in water, especially in acidic (pH=6.1-6.3) and alkaline (pH=8.0-8.4) segments; (2) faster indirect photolysis of trans-isomers (t1/2 = 54.7-177 h) than cis-isomers (t1/2 = 73.4-191 h) might lead to larger mean cis/trans ratios in summer (0.31 for P3) with stronger illumination than those in winter (0.08 for P3). The Σ(P3 + P4) concentrations in 140 mussels (Anodonta woodiana) from 14 sites of the Xiaoqing River were Collapse

Key Words

• Degradation
• Environmental distributions
• Fresh mussels
• Phenylmethylsiloxanes
• Xiaoqing River

Collapse

MESH Headings

• Water Pollutants, Chemical/analysis
• Water Pollutants, Chemical/metabolism
• Rivers/chemistry
• China
• Siloxanes/metabolism
• Siloxanes/analysis
• Siloxanes/chemistry
• Animals
• Bivalvia/metabolism
• Environmental Monitoring
• Humans
• Photolysis
• Geologic Sediments/analysis

Collapse

Grants Collapse

Affiliation(s)

Nannan Liu School of Environmental and Municipal Engineering, Tianjin Chengjian University, Tianjin 300384, China; State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085, China
Wenxuan Jin School of Environmental and Municipal Engineering, Tianjin Chengjian University, Tianjin 300384, China
Chunsheng Qiu School of Environmental and Municipal Engineering, Tianjin Chengjian University, Tianjin 300384, China
Lin Xu State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085, China; School of Environment, Hangzhou Institute for Advanced Study, UCAS, Hangzhou 330106, China.
Xu Chen School of Environmental and Municipal Engineering, Tianjin Chengjian University, Tianjin 300384, China
Na Li Qilu University of Technology (Shandong Academy of Sciences), Shandong Analysis and Test Center, Key Laboratory for Applied Technology of Sophisticated Analytical Instruments of Shandong Province, Jinan 250014, China
Rusong Zhao Qilu University of Technology (Shandong Academy of Sciences), Shandong Analysis and Test Center, Key Laboratory for Applied Technology of Sophisticated Analytical Instruments of Shandong Province, Jinan 250014, China
Yaqi Cai State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085, China; School of Environment, Hangzhou Institute for Advanced Study, UCAS, Hangzhou 330106, China; University of Chinese Academy of Sciences, Beijing 100049, China

Collapse

Collaborators Collapse

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.

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.

Residual toxins on aquatic animals in the Pacific areas: Current findings and potential health effects

The Pacific Ocean is among the five largest and deepest oceans in the world. The area of the Pacific Ocean covers about 28 % of the Earth's surface. This is the habitat of many marine species, and its diversity is recognized as a fundamental element of Pacific culture and heritage. The ecosystems of aquatic animals are highly affected by climate change and by other factors. Residual toxins on aquatic animals can be categorized into two types based on origin: toxins of marine origin and toxins associated with human activity. Residual toxins have emerged as a global concern in recent years due to their frequent presence in aquatic environments. Furthermore, residual toxins in organisms living in the marine environment in the Pacific Ocean region also seriously affect food safety, food security, and especially human health. In this review we discuss important issues about residual toxins on aquatic animals in the Pacific areas specifically about the types of toxins that exist in marine animals, their contamination pathways in the Asia, Pacific region and the potential health effects for humans, the application of information technology and artificial intelligence in residual toxins on aquatic animal.

Physiological impact of personal care product constituents on non-target aquatic organisms

Personal care products (PCPs) are products used in cleaning, beautification, grooming, and personal hygiene. The rise in diversity, usage, and availability of PCPs has resulted in their higher accumulation in the environment. Thus, these constitute an emerging category of environmental contaminants due to the potential of its constituents (chemical and non-chemical) to induce various physiological effects even at lower concentrations (ng/L). For analyzing the impact of the PCPs constituents on the non-target organism about 300 article including research articles, review articles and guidelines were studied from 2000 to 2023. This review aims to firstly discuss the fate and accumulation of PCPs in the aquatic environment and organisms; secondly provides overview of environmental risks that are linked to PCPs; thirdly review the trends, current status of regulations and risks associated with PCPs and finally discuss the knowledge gaps and future perspectives for future research. The article discusses important constituents of PCPs such as antimicrobials, cleansing agents and disinfectants, fragrances, insect repellent, moisturizers, plasticizers, preservatives, surfactants, UV filters, and UV stabilizers. Each of them has been found to display certain toxic impact on the aquatic organisms especially the plasticizers and UV filters. These continuously and persistently release biologically active and inactive components which interferes with the physiological system of the non-target organism such as fish, corals, shrimps, bivalves, algae, etc. With a rise in the number of toxicity reports, concerns are being raised over the potential impacts of these contaminant on aquatic organism and humans. The rate of adoption of nanotechnology in PCPs is greater than the evaluation of the safety risk associated with the nano-additives. Hence, this review article presents the current state of knowledge on PCPs in aquatic ecosystems.

Identification of Mid-Polar and Polar AhR Agonists in Cetaceans from Korean Coastal Waters: Application of Effect-Directed Analysis with Full-Scan Screening

Major aryl hydrocarbon receptor (AhR) agonists were identified in extracts of blubber, liver, and muscle from six long-beaked common dolphins (Delphinus capensis) and one fin whale (Balaenoptera physalus) collected from Korean coastal waters using effect-directed analysis. Results of the H4IIE-luc bioassay indicated that the polar fractions of blubber and liver extracts from the fin whale exhibited relatively high AhR-mediated potencies. Based on full-scan screening with high-resolution mass spectrometry, 37 AhR agonist candidates, spanning four use categories: pharmaceuticals, pesticides, cosmetics, and natural products, were selected. Among these, five polar AhR agonists were newly identified through toxicological confirmation. Concentrations of polar AhR agonists in cetaceans were tissue-specific, with extracts of blubber and liver containing greater concentrations than muscle extracts. Polar AhR agonists with great log KOA values (>5) were found to biomagnify in the marine food chain potentially. Polar AhR agonists contributed 8.9% of the observed AhR-mediated potencies in blubber and 49% in liver. Rutaecarpine and alantolactone contributed significantly to the total AhR-mediated potencies of blubber, whereas hydrocortisone was a major AhR contributor in the liver of the fin whale. This study is the first to identify the tissue-specific accumulation of polar AhR agonists in blubber and liver extracts of cetaceans.

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.

Chemical Recycling of High-Molecular-Weight Organosilicon Compounds in Supercritical Fluids

The main known patterns of thermal and/or catalytic destruction of high-molecular-weight organosilicon compounds are considered from the viewpoint of the prospects for processing their wastes. The advantages of using supercritical fluids in plastic recycling are outlined. They are related to a high diffusion rate, efficient extraction of degradation products, the dependence of solvent properties on pressure and temperature, etc. A promising area for further research is described concerning the application of supercritical fluids for processing the wastes of organosilicon macromolecular compounds.