Tissue-specific distribution and bioaccumulation of cyclic and linear siloxanes in South Korean crucian carp (carassius carassius)

Distribution and spatial variation of volatile methylsiloxanes in surface water and wastewater from the Yangtze River Basin, China

Volatile methylsiloxanes (VMSs) earned serious concerns due to their detection and toxicities after their release to the environments. They were also detected in rivers around the globe, but their distribution remained to be explored in larger rivers with longer length, higher water volume and wider watershed. In the present study, 8 cyclic VMSs (cVMSs) and 7 linear ones (lVMSs) were investigated in 42 water samples (27 surface water (including 7 drinking source water) and 15 wastewater) from the Yangtze River Basin, China. Results showed that VMSs were detected in all sampling sites. In surface water, the concentrations of total cVMSs ranged from 17.3 to 4.57 × 103 ng/L, while those of lVMSs ranged from 1.72 to 81.6 ng/L. In wastewater, the total concentrations of cVMSs and lVMSs showed ranges of 17.6-1.66 × 103 ng/L and 2.59-252 ng/L, respectively. Apparently, cVMSs showed significantly higher concentrations than lVMSs. The concentrations of cVMSs followed an order of lower > upper > middle reaches, while those of lVMSs did not show clear distribution patterns. Among cVMSs, those with less Si numbers were dominant, while those with more Si numbers were dominant in lVMSs. Notably, the VMSs were also detected in 7 surface waters that served as drinking source waters, which earned them further concerns. In addition, the VMSs in surface water showed positive correlation with those in wastewater, which led to necessity in management on industrial emissions in the future.

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.

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.

Lead induced structural and functional damage and microbiota dysbiosis in the intestine of crucian carp (Carassius auratus)

Lead (Pb) is a hazardous pollutant in water environments that can cause significant damage to aquatic animals and humans. In this study, crucian carp (Carassius auratus) were exposed to waterborne Pb for 96 h; then, histopathological analysis, quantitative qPCR analysis, and 16S high-throughput sequencing were performed to explore the effects of Pb on intestinal bioaccumulation, structural damage, oxidative stress, immune response, and microbiota imbalance of C. auratus. After Pb exposure, the intestinal morphology was obviously damaged, including significantly increasing the thickness of the intestinal wall and the number of goblet cells and reducing the depth of intestinal crypts. Pb exposure reduced the mRNA expressions of Claudin-7 and villin-1 while significantly elevated the level of GST, GSH, CAT, IL-8, IL-10, IL-1, and TNF-α. Furthermore, 16S rRNA analysis showed that the Shannon and Simpson indices decreased at 48 h after Pb exposure, and the abundance of pathogenic bacteria (Erysipelotrichaceae, Weeksellaceae, and Vibrionaceae) increased after Pb exposure. In addition, the correlation network analysis found that Proteobacteria were negatively correlated with Firmicutes and positively correlated with Bacteroidetes. Functional prediction analysis of bacteria speculated that the change in intestinal microbiota led to the PPAR signaling pathway and peroxisome function of the intestine of crucian carp was increased, while the immune system and membrane transport function were decreased. Finally, canonical correlation analysis (CCA) found that there were correlations between the intestinal microbiota, morphology, antioxidant factors, and immune factors of crucian carp after Pb exposure. Taken together, our results demonstrated that intestinal flora dysbiosis, morphological disruption, oxidative stress, and immune injury are involved in the toxic damage of Pb exposure to the intestinal structure and function of crucian carp. Meanwhile, Pb exposure rapidly increased the abundance of pathogenic bacteria, leading to intestinal disorders, further aggravating the damage of Pb to intestinal structure and function. These findings provide us a basis for the link between gut microbiome changes and heavy metal toxicity, and gut microbiota can be used as biomarkers for the evaluation of heavy metal pollution in future.

Exploring eco-friendly approaches for mitigating pharmaceutical and personal care products in aquatic ecosystems: A sustainability assessment

Global water scarcity is exacerbated by climate change, population growth, and water pollution. Over half of the world's population will be affected by water shortages for at least a month annually by 2050 due toa lack of clean water sources. Even though recycling wastewater helps meet the growing demand, new pollutants, including pharmaceuticals and personal care products (PPCPs), pose a health threat since conventional methods cannot remove them and their environmental monitoring regulations are yet in place. Therefore, the current review aims to investigate and propose eco-friendly technologies for removing PPCPs from wastewater and their implementation strategies for ecosystem safety. Findings indicated the absence of a single wastewater treatment technology that can remove all PPCPs in a single operation. Instead, biotechnological methods are one of the alternatives that can remove PPCPs from aquatic environments. In this context, community involvement and knowledge transfer are identified keys to clean water resources' long-term sustainability.

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.

Evaluation of sample preparation methods for suspect and non-target screening in water, sediment, and biota samples using gas chromatography coupled to high-resolution mass spectrometry

In this study, the sample preparation methods were proposed for the suspect and non-target screening (SNTS) using gas chromatography coupled to high-resolution mass spectrometry in the aquatic environment. The pretreatment methods were evaluated based on detection rates, recoveries, and screening detection limits (SDLs) for 316 substances spiked into surface water, sediment, and biota samples. The detection rates of the spiked compounds were 92.1 % and 98.7 % by the sample preparation methods for water (solid-phase extraction using HLB cartridge) and sediment (ultrasonic extraction (USE) with HLB cartridge clean-up), respectively. Similarly, USE with HLB cartridge clean-up gave the highest detection rate (87.9 %) for biota samples; however, additional pretreatment method using deactivated silica gel clean-up was necessary for the detection of persistent organic pollutants (POPs). The SDL ranges of spiked compounds by the suggested pretreatment methods were 0.01-23.5 ng/L for surface water, 0.02-37.5 ng/g dry weight for sediment, and 0.01-12.2 ng/g wet weight for biota. Although some pollutants, such as POPs had SDLs that were higher than the levels normally detected in the aquatic environment as reported in previous studies, the analytical methods suggested in the present study were satisfactory for the SNTS of most pollutants originated from anthropogenic sources.

Are silicone foul-release coatings a viable and environmentally sustainable alternative to biocidal antifouling coatings in the Baltic Sea region?

To combat unwanted fouling on immersed hulls, biocidal antifouling coatings are commonly applied to vessels trafficking the Baltic Sea. Here, the efficacy, environmental sustainability and market barriers of silicone foul-release coatings (FRCs) was assessed for this region to evaluate their viability as replacements for biocidal coatings. Coated panels were exposed statically over a 1 year period at three locations in the Baltic Sea region to assess the long-term performance of a biocide-free FRC and two copper coatings. The FRC was found to perform equally well or significantly better than the copper coatings. Even though most silicone FRCs on the market are biocide-free, a review of the literature regarding toxic effects and the identity and environmental fate of leachables shows that they may not be completely environmentally benign, simply for the lack of biocides. Nonetheless, FRCs are substantially less toxic compared to biocidal antifouling coatings and their use should be promoted.

Spatial distribution and benthic risk assessment of cyclic, linear, and modified methylsiloxanes in sediments from Tokyo Bay catchment basin, Japan: Si-based mass profiles in extractable organosilicon

We investigated the spatial distribution, mass profiles, and benthic risk assessment of a wide range of methylsiloxanes (MSs), including 7 cyclic MSs (CMSs; D3-D9; the number refers to the number of SiO bonds), 13 linear MSs (LMSs; L3-L15), and 15 modified and other MSs (MMSs) in sediments from the Tokyo Bay catchment basin, Japan. We observed widespread distribution of MSs (ΣCMS, ΣLMS, and ΣMMS) in the sediment samples, with concentrations of 1.0-6180 ng/g dry weight (dw), 1.8-10,100 ng/g dw, and < 0.31-210 ng/g dw, respectively. Our study is the first to measure various MMSs modified with hydrogen, vinyl, or phenyl groups; however, only methyltris(trimethylsiloxy)silane and phenyltris(trimethylsiloxy)silane were detected with high occurrence frequency. Notably, no elevated concentrations of MSs were observed downstream of silicone manufacturers, whereas the sediment was characterized by a specific D4/D5 ratio. With the Si-based mass profiles in extractable organosilicon (EOSi), the measured CMSs, LMSs, and MMSs accounted for 5.4%, 7.8%, and 0.2%, respectively. Unidentified EOSi (unknown fraction) constituted a major proportion of the EOSi in the sediment, with a mean of 87%, suggesting that the organosilicon environmental emissions were more than the measured MSs. In risk assessment of the adverse effects of D4, D5, and D6 in sediment on benthic organisms, the respective distributions indicated no overlap between the 95th percentile field sediment concentration and the 5th percentile chronic sediment no-effect concentration in organic carbon-normalized concentration. Although the hazard quotient compared with the predicted no-effect concentration for D5 and D6 exceeded the threshold level (hazard quotient ≥1), the results of probabilistic risk assessment for the three CMSs were not high enough to indicate a threat to benthic organisms in the study area.

Silicones in dermatological topical drug formulation: Overview and advances

Silicones, more specifically those of the polydimethylsiloxane type, have been widely used in the pharmaceutical industry for decades, particularly in topical applications. In the dermatological field, in addition to provide undeniable textural and sensory benefits, they can play important functions in the physicochemical properties, stability and biopharmaceutical behavior of these formulations. However, despite the notable advances that can be attributed to the family of silicones, the reputation of these compounds is quite bad. Indeed, silicones, even if they derive from sand, are synthetic compounds. Moreover, they are not biodegradable. They flow into our wastewater and oceans, accumulating in the fauna and flora. This obviously raises many concerns in the common imagination. Do silicones represent a danger for our environment? Should the human species worry about long term toxic effects? Are the claimed benefits really that important? After exploring the various applications of silicone excipients in topical dermatological formulations with a special focus on recent advances which open breathtaking prospects for dermatological applications, this paper shed light on the specific challenges involved in preparation of silicone-based drug as well as, the in vivo behavior of these polymers, the toxicological and environmental risks associated with their application.

Developmental effects of siloxane exposure in zebrafish: a comparison study using laboratory-mixed and environmental water samples

Siloxanes are used in personal care, biomedical, and industrial products. Their worldwide use and persistence in the environment cause consistent exposure for both humans and aquatic animals. Two siloxane congeners, decamethylcyclopentasiloxane (D5; CAS 541-02-6) and octamethylcyclotetrasiloxane (D4; CAS 556-67-2), are among the most prevalent, with measurable levels in air, sediment, water, and biological samples. However, few studies have examined the impact of developmental (embryo/larva) exposure. To address this gap, we performed parallel experiments using wildtype zebrafish (Danio rerio). One set of experiments used laboratory-mixed individual solutions containing either D4, D5, or 2,4,6,8-tetramethylcyclotetrasiloxane (D₄ ^H ; CAS 2370-88-9); the other used environmental water samples containing a mixture of siloxanes, including D4 and D5. These samples were collected from Bladensburg Waterfront Park (BWP) a site along the Anacostia River, Washington, DC. In both experiments, zebrafish (24-48 hours postfertilization, hpf) were exposed until 7 or 14 days (d)pf. Chronic exposure to D4, D5, or BWP water until 7 dpf caused stress-like behaviors and reduced swim velocities; anatomical differences were noted only in BWP-exposed larvae. At 14 dpf, BWP-treated larvae still showed slower swimming velocities and increased immobility; anatomical differences were no longer evident and thigmotactic behavior was reduced. D4 and D5-exposed larvae did not survive after 10 dpf. Larvae exposed to D₄ ^H showed no decreases in behavior or growth at either age. These results suggest early developmental sensitivity to siloxane exposure and point to the need to consider embryonic/larval endpoints when assessing aquatic contaminants.

A review of bioaccumulation of volatile methylsiloxanes in aquatic ecosystems

Volatile methylsiloxanes (VMSs) are found in a broad range of industrial and consumer products. They are categorized as "high production volume chemicals" by the U.S. Environmental Protection Agency and listed as candidates of substances of very high concern in 2018, by the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH). Industrial wastewater and treated effluents may contain VMSs in different amounts, which can be discharged in the receptor media and may lead to environmental contamination. This can result in direct exposure to aquatic receptors in the water column or to benthic invertebrates from contact and/or ingestion of sediments, and indirect exposures through the aquatic food chain. The possible toxicological effects of VMSs for the aquatic biota and human ecology are not very well known since published information regarding this topic is scarce. VMSs have been subjected to regulatory scrutiny for environmental concerns and have already been screened to determine their environmental risk and ecological harm. This paper aims to assess VMSs bioaccumulation and potential biomagnification on food webs, using several bioaccumulation metrics. The result is a high-level overview of all the collected data, comparing the findings and the experimental conditions applied during the assessments. Several studies present conflicting results regarding the bioaccumulation categorization. Some aquatic organisms demonstrated a high bioconcentration and bioaccumulation of these contaminants. Trophic magnification factors (TMFs) have been suggested as the most reliable tool to assess a chemical behaviour in food webs. However, bioaccumulation studies in food webs provided mixed information, with some studies indicating trophic dilution and others presenting a potential of trophic biomagnification of VMSs. Efforts should be directed to obtain field-based levels of VMSs at different trophic levels and a wider range of linear VMSs should be analysed, since most studies focused on D4, D5 and D6.

Spatial distribution and accumulation profiles of volatile methylsiloxanes in Tokyo Bay, Japan: Mass loadings and historical trends

We investigated mass loading and the spatial distribution of volatile methylsiloxanes (VMSs) including four cyclic VMSs (D3-D6; cVMSs, the number refers to the number of SiO bonds) and three linear VMSs (L3-L5; lVMSs) in Tokyo Bay, Japan, which is one of the most industrialized, urbanized, and populated areas in the world. Based on the VMS concentrations determined in eight main inflow rivers to the bay, the mass loading of VMSs via inflow rivers and sewage treatment plants located in Tokyo Bay was estimated at 2500 kg/y for total VMSs. Elevated mass loadings of VMSs were found in three of the rivers, inflowing to the inner west of Tokyo Bay. The distribution and deposition characteristics of VMSs were observed depending on the estuarine condition. Estuarine sediments were found to be efficient and effective traps for VMSs and the salting-out effect is one possible mechanism to explain this phenomenon. The overall profiles of D4, D5, and D6 in surface water and sediment were observed across Tokyo Bay; elevated concentrations were identified in the inner west bay with dispersed low concentrations in the outer bay, except for one hotspot of D4 in the sediment, indicating a major emission route of VMSs via inflow rivers. Additionally, the historical pollution profiles of VMSs in Tokyo Bay were reconstructed based on the VMS concentrations determined in a dated sediment core. VMSs were identified throughout the upper 40 cm of the sediment core (representing the mid 1980s); the profiles correspond with the historical use of VMSs in wash-off personal care-products. The noted decreasing trend of D4 might be a reflection of the early 2000s replacement of D4 with D5 in such products. The elevated VMS concentrations in the estuarine sediment raise concerns about the impact on the aquatic environment.