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

Spatiotemporal trends and ecological risk assessment of volatile methylsiloxanes in Tokyo Bay catchment basin, Japan: River water and sewage treatment plant samples

The large production volume of volatile methylsiloxanes (VMSs) and their high mobility and persistence present significant environmental-pollution concerns. Although the temporal trends of the persistent-compound concentrations of the environment have been considerably explored, those of surface water, namely surface water VMSs, have been barely investigated. Thus, we investigated the 2013-2021 spatiotemporal trends of the VMS (cyclic VMSs (cVMSs; D3-D6) and linear VMSs (L3-L6)) concentrations of river water and sewage treatment plant (STP) samples from the Tokyo Bay catchment basin, Japan. Our findings indicated the widespread concentrations of VMSs in the river water (2.3-1190 ng/L); the highest VMS levels were detected downstream of the STP discharges. However, no elevated VMS concentrations were detected downstream of silicone-manufacturing facilities, except for D3. The temporal trend analysis revealed statistically significant decreases in the D4, D5, and D6 concentrations within the monitoring period, with annual changes ranging from -7.7 % to -6.4 %, probably reflecting the impact of regulatory actions to address cVMSs. Our risk assessment of the adverse effects of surface water D4, D5, and D6 on aquatic organisms revealed that their distributions did not overlap between the 95th percentile field-water concentration and 5th percentile chronic no-observed-effect water concentration, whereas their cVMS levels were close to their predicted no-observed-effect concentrations. Furthermore, their risks of the aquatic environment to cVMS exposure displayed decreasing temporal trends during the study period. Overall, understanding temporal trends of surface water VMS is key to implementing necessary emission regulations and evaluating the effectiveness of future restrictions on these silicone materials.

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

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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

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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

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Assessing the impact of mining on cyclic and linear methylsiloxane distribution in Tibetan soils: Source contribution and transport pattern

The pervasive presence of methylsiloxanes (MSs), comprising linear and cyclic congeners, in the environment poses significant ecological risks, yet the understanding of their transport mechanisms and deposition patterns remains limited. This study analyzed the concentrations of 12 linear-MSs (L3-L14) and 7 cyclic-MSs (D3-D9) in 29 surface soil samples collected across varying altitudes (3726 to 4863 m) near the Jiama mining sector in Tibet, aiming to investigate the distribution and transport dynamics of MSs from the emission source. The distribution of total MS concentration (ranging from 50.1 to 593 ng/g) showed a remarkable correlation with proximity to the mining site, suggesting the emergent source of mining activities for the MSs in the remote environment of the Tibetan Plateau. Employing the innovative model of robust absolute principal component scores-robust geographically weighted regression (RAPCS-RGWR), the analysis predicted that the mining operations contributing 57.1 % of the total soil MSs, would significantly surpass contributions from traffic emissions (14.7 %), residential activities (13.2 %), and the environmental factor of total organic matter content (14.9 %). The Boltzmann equation effectively modeled the distribution pattern of soil MSs, highlighting atmospheric transport and gravitational settling as key distribution mechanisms. However, linear-MSs exhibited longer transport distances than cyclic-MSs and were more profoundly affected by prevailing wind directions, suggesting their differential environmental behaviors and risks. Our study underscored that the mining sector possibly emerged as a significant source of Tibetan MSs, and provided insights into the transport and fate of MSs in remote, high-altitude environments. The findings emphasize the need for targeted pollution control strategies to mitigate the environmental footprint of mining activities in Tibet and similar regions.

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.