Distribution and evaluation of the fate of cyclic volatile methyl siloxanes in the largest lake of southwest China

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 volatile methyl siloxanes (D4, D5, and D6) as the emerging pollutants in environment: environmental distribution, fate, and toxicological assessments

Cyclic volatile methyl siloxanes (cVMS) have now become a subject of environmental contamination and risk assessment due to their widespread use and occurrence in different environmental matrices. Due to their exceptional physio-chemical properties, these compounds are diversely used for formulations of consumer products and others implying their continuous and significant release to environmental compartments. This has captured the major attention of the concerned communities on the grounds of potential health hazards to human and biota. The present study aims at comprehensively reviewing its occurrence in air, water, soil, sediments, sludge, dusts, biogas, biosolids, and biota and their environmental behavior as well. Concentrations of cVMS in indoor air and biosolids were higher; however, no significant concentrations were observed in water, soil, and sediments except for wastewaters. No threat to the aquatic organisms has been identified as their concentrations do not exceed the NOEC (maximum no observed effect concentration) thresholds. Mammalian (rodents) toxicity hazards were not very evident except for the occurrence of uterine tumors in very rare cases under long-term chronic and repeated dose exposures in laboratory conditions. Human relevancy to rodents were also not strongly enough established. Therefore, more careful examinations are required to develop stringent weight of evidences in scientific domain and ease the policy making with respect to their production and use so as to combat any environmental consequences.

Dimethylcyclosiloxanes in Mobile Smart Terminal Devices: Concentrations, Distributions, Profiles, and Environmental Emissions

Dimethylcyclosiloxanes (DMCs) are utilized as vital monomers in the synthesis of organosilicon compounds, integral to the manufacture of mobile smart terminal devices. Toxicological studies have revealed potential endocrine-disrupting activity, reproductive toxicity, neurotoxicity, and other toxicities of the DMCs. This study investigated the concentrations and composition profiles of seven DMCs, including hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6), and tetradecamethylcycloheptasiloxane (D7), hexadecamethylcyclooctasiloxane (D8), and octadecamethylcyclononasiloxane (D9) in three types of mobile smart terminal device components (silicone rubber, adhesive, and plastics). Environmental emissions of DMCs from silicone rubber materials were also estimated to improve the recognition of their potential fate within the environment. D5-D9 were widely present in silicone rubber and adhesives with detection rates ranging from 91-95.5% and 50-100%, respectively, while D3 and D4 were more frequently detected in plastics, both showing a detection rate of 61.1%. Silicone rubber had the highest total DMCs (∑7DMCs) and a concentration of 802.2 mg/kg, which were dominated by D7, D8, and D9. DMCs detected in adhesives were dominated by D4, D5, and D6. The estimated emission of ∑DMCs released into the environment in China from silicone rubber used in mobile smart terminal devices exceeds 5000 tons per year. Further studies are needed on the presence of DMCs in various commodities and environmental media to assess their ecological and human health impacts, as well as the toxicological effects of D7-D9 for the appropriate regulation of these chemicals.

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.

Dimethylsiloxanes in dust from nine indoor microenvironments of Henan Province: Occurrence and human exposure assessment

Dimethylsiloxanes (MSs) are widely used in daily life and industry, with indoors being the main release site. Detecting the levels of MSs in indoor dust is essential for assessing the risks of human exposure. In this study, the content of MSs (D3-D8 and L3-L16) was quantified in indoor dust samples from nine microenvironments of Henan Province. The detection frequency of the targets ranged from 5.00 % to 100 %. The sum concentration of dimethylsiloxanes (TSi) was in a range of 463-3.32 × 104 ng·g-1 (median: 1.92 × 103 ng·g-1). The sum concentration of linear dimethylsiloxanes (TLSi) from all microenvironments was higher than the sum concentration of cyclic dimethylsiloxanes (TCSi), which was consistent with previously reported results. D7 and D8 were the main cyclic dimethylsiloxane, which had similar sources based on Spearman correlation analysis (p < 0.001). Moreover, D8 was detected with high levels in indoor dust for the first time, which warrants further exploration. L8-L16 were the main linear dimethylsiloxanes, which may have been due to their widespread use in electronic equipment and office equipment. The Spearman analysis found that total organic carbon (TOC) in indoor dust had weak effect on MSs. Additionally, relatively high MS levels were recorded in high people-flow working microenvironments. Accordingly, the exposure doses of MSs via indoor dust intake were estimated for different age groups using the model of worst-case exposure and median concentration. Toddlers had the highest EDIs (95th percentile concentration, 90.7 ng·kg-1-bw·d-1) to MSs.

Co-occurrence of phthalic acid esters (PAEs) and cyclic volatile methylsiloxanes (cVMSs) in fine particulate matter (PM0.5 and PM0.1) collected from an industrial area in Vietnam

Distribution patterns of 10 phthalic acid diesters (PAEs) and four cyclic volatile methylsiloxanes (cVMSs) were investigated in fine particulate matter (PM0.1 and PM0.5) collected from Bac Ninh, an industrial province in Vietnam during September-October in 2021. Total concentrations of PAEs found in PM0.1 and PM0.5 were in the ranges of 1.76-372 (median: 34.0 ng/m3) and 2.23-895 ng/m3 (median: 15.4 ng/m3), respectively. Among PAEs, di-n-butyl phthalate (DBP) was the most abundant compound found in PM0.1, whereas, di-2-(ethyl)hexyl phthalate (DEHP) was measured at the highest concentration in PM0.5. Total concentrations of cVMSs measured in PM0.1 and PM0.5 were in the ranges of method quantification limit (MQL)-203 (median: 2.10 ng/m3) and MQL-537 ng/m3 (median: 0.389 ng/m3), respectively. Among cVMSs, decamethylcyclopentasiloxane (D5) was found at the highest concentration in both PM0.1 and PM0.5 fractions of particulate matter. The concentration ratios between PAEs and cVMSs in PM0.1/PM0.5 were greater than 1 (except di-n-octyl phthalate: DnOP), suggesting that these chemicals tend to sorb to PM0.1 more preferentially than PM0.5. Among sampling locations, high concentrations of PAEs and cVMSs were found at traffic intersections (Que Vo district) and a craft village (Tu Son city). Relatively stronger correlations existed between cVMSs pairs in PM0.1 and PM0.5 (correlation coefficient: 0.73-1) than those of PAEs (-0.83-0.90). The human exposure doses to PAEs and cVMSs through inhalation of particulate matter were estimated based on the measured concentrations in PM0.1 and PM0.5 fractions. The estimated exposure doses of PAEs and cVMSs for infants (7.1 ng/kg-bw/d and 2.5 ng/kg-bw/d) were higher than those for adults (2.6 ng/kg-bw/d and 0.9 ng/kg-bw/d).

A method for simulating spatial fates of chemicals in flowing lake systems: Application to phthalates in a lake

In order to describe spatio-temporal distribution of chemicals in flowing lake systems, a dynamic multimedia fate model of chemicals with spatial differentiation was constructed by coupling the level IV fugacity model with lake hydrodynamics. It was successfully applied to four phthalates (PAEs) in a lake recharged by reclaimed water and its accuracy was verified. Results show that under the long-term influence of flow field, the distributions of PAEs in both lake water and sediment have significant spatial heterogeneity of 2∼5 orders of magnitude, but present different distribution rules, which was explained by analysis of PAE transfer fluxes. The spatial distribution of PAEs in the water column depends on hydrodynamic conditions and whether the primary source is reclaimed water or atmospheric input. Slow water exchange and flow speed promote the migration of PAEs from water to sediment, causing them to always accumulate in sediments far away from the recharging inlet. Uncertainty and sensitivity analysis show that the PAE concentrations in water phase are mainly affected by emission and physicochemical parameters, while those in sediment phase are also sensitive to environmental parameters. The model can provide important information and accurate data support for the scientific management of chemicals in flowing lake systems.

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.

Methylsiloxanes risk assessment combining external and internal exposure for college students

Methylsiloxanes (MSs) are widely used as solvents or emollients in various personal care products (PCPs) and may pose a health risk. In this study, we assessed external and internal exposure to MSs among students at two universities in southwestern China. Samples of air, dust, and PCPs were collected to evaluate indoor non-dietary exposure to MSs via multiple pathways among the students. Indoor MS levels were approximately 1-3 orders of magnitude higher in the dormitories of female students than in either classrooms or the dormitories of male students. Lipstick contained the highest MS levels. Cyclic MS (CMS: D4-D6) levels were 1 order of magnitude higher in female students than in male students. Among the three CMSs, D5 levels were highest in the plasma of all students (1.3-15 ng/mL). In dormitories, dermal contact with PCPs was the major route of exposure to CMSs for all students. Among linear MSs (LMSs: L5-L16), dermal PCP absorption and dust ingestion were the predominant exposure routes for male and female students, respectively. Although the overall risk of exposure to D4 and D5 was below the chronic reference dose for all exposure routes and all students, the total daily doses of exposure to D4 and D5 via dermal PCP absorption approached the chronic reference dose in four female students. Therefore, the effects of MSs on female students should be further investigated in future studies.

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.

Application of multimedia models for understanding the environmental behavior of volatile methylsiloxanes: Fate, transport, and bioaccumulation

Multimedia fate and transport models (MFTMs) describe how chemicals behave in the environment based on their inherent properties and the characteristics of receiving systems. We critically review the use of MFTMs for understanding the behavior of volatile methylsiloxanes (VMS). MFTMs have been used to predict the fate of VMS in wastewater treatment, rivers, lakes, marine systems, and the atmosphere, and to assess bioaccumulation and trophic transfers. More widely, they have been used to assess the overall persistence, long-range transport potential (LRTP), and the propensity for atmosphere-surface exchange. The application of MFTMs for VMS requires particularly careful selection of model inputs because the properties of VMS differ from those of most organic compounds. For example, although n-octanol/water partition coefficient (KOW ) values are high, air:water partition coefficient (KAW ) values are also high and n-octanol/air partition coefficient (KOA ) values are relatively low. In addition, organic carbon/water partition coefficient (KOC ) values are substantially lower than expectations based on KOW . This means that most empirical relationships between KOC and KOW are not appropriate. Good agreement between modeled and measured concentrations in air, sediment, and biota indicates that our understanding of environmental fate is reasonable. VMS compounds are "fliers" that principally partition to the atmosphere, implying high LRTP, although they have low redeposition potential. They are degraded in air (half-lives 3-10 days) and, thus, have low overall persistence. In water, exposure can be limited by hydrolysis, volatilization, and partitioning to sediments (where degradation half-lives are likely to be high). In food webs, they are influenced by metabolism in biota, which tends to drive trophic dilution (i.e., trophic magnification factors are often but not always <1). Key remaining uncertainties include the following: (i) the strength and direction of the temperature dependence for KOC ; (ii) the fate of atmospheric reaction products; and (iii) the magnitude of emissions to wastewater. Integr Environ Assess Manag 2022;18:599-621. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Assessment of distributional characteristics and ecological risks of cyclic volatile methylsiloxanes in sediments from urban rivers in northern Vietnam

In this report, four cVMSs including hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) were determined in 85 sediment samples collected from three rivers in northern Vietnam during the period from May to November 2020. Total mean concentrations of cVMSs ranged from 75.4 to 15,000 ng/g-dw. The highest levels of cVMS were found in sediment samples collected from the To Lich River (range, 260-15,000 ng/g-dw; median, 2840 ng/g-dw), followed by the Nhue River (range, 188-6800 ng/g-dw; median, 1370 ng/g-dw), and the Day River (range, 75.4-4600 ng/g-dw; median, 666 ng/g-dw). Among cVMSs, decamethylcyclopentasiloxane (D5) was found at the highest levels in all samples and ranged from 9.00 to 11,000 ng/g-dw. Significant correlations exist between the concentrations of D4/D6 and D5/D6 pairs in river sediment samples. Although the calculated ecological risk was not high, the presence of cVMSs in the sediment raises concerns about the impact on aquatic life because of their long-term accumulation capacity.

Occurrence of methylsiloxanes in sediments from a subtropical river-lake system in eastern China and its implication for ecological risks

Distribution of methylsiloxanes in environment is still far from being well studied. Little is known about the concentrations and associated risks of these chemicals in river-lake systems. This study investigated the occurrence of twelve methylsiloxanes (D₄-D₆, L₅-L₁₃) in the sediments from Lake Chaohu and its inflowing rivers, China, and found the total concentrations (ng/g dry weight) were in the range of 47.1-496 and 239-3593, respectively. Linear congeners were dominant, representing a median of 62.8% and 58.7% of the total concentrations found in the lake and its inflowing rivers, respectively. In general, the concentrations of sediment methylsiloxanes in the investigated river-lake system were low to moderate, compared with the results reported previously in other waters. Source assessment indicated that the emissions from industrial activities and the use of silicone-containing products were the main contributors of sediment methylsiloxanes in the investigated waters. D₄ and D₅ in 18.5% and 11.1% of river sediment samples might pose ecological risks to fish. The risks from the linear congeners in sediments in the area were not estimated due to no related benchmarks available. More studies are needed to investigate the occurrence of these chemicals and associated risks in aquatic environment.

Methyl siloxanes in soils from a large silicone-manufacturing site, China: concentrations, distributions and potential human exposure

Methyl siloxanes are widely found in the environment, but little is known about the distributions of these chemicals in soils especially in areas where they are manufactured. We determined the concentrations of four cyclic (D₃-D₆) and 13 linear methyl siloxanes (L₄-L₁₆) in the soils from a siloxane-manufacturing site in China; the total concentrations of these 17 siloxanes (TSi) in the soils were 17.1-3,191 (median, 134) ng/g. We did not find extremely high concentrations of siloxanes in the soils. The median concentrations of total cyclic siloxanes (TCSi) were approximately sevenfold higher than those of total linear congeners. Hexamethylcyclotrisiloxane and octamethylcyclotetrasiloxane contributed a median of 59.7% and 20.3% of the TSi concentrations, respectively. Higher concentrations of soil TCSi were found in the silicone-manufacturing area relative to the other study areas. Source analysis indicated that industrial activities contributed substantially to soil siloxanes, in addition to the contribution of the siloxane emissions from specific consumer products. We calculated that the median values of daily TSi intakes through soil ingestion were 0.021 and 0.138 ng/kg-body weight/day for adults and children, respectively, under high exposure scenarios. Although our estimated daily intakes of the chemicals from soils were low, more research is required to improve our understanding of the health risks posed to humans exposed to siloxanes through other pathways.

Distribution of cyclic volatile methylsiloxanes in drinking water, tap water, surface water, and wastewater in Hanoi, Vietnam

In this study, four cyclic volatile methylsiloxanes (cVMSs) were determined in drinking water, tap water, surface water, and wastewater samples collected from Hanoi metropolitan area, Vietnam, during August to December 2020 (dry season) by using solid phase extraction combined with gas chromatography tandem mass spectrometry. Highest concentrations of cVMSs in the range of 63-7400 ng/L (mean/median: 1840/1310 ng/L) were found in wastewater samples. A significant difference existed in the concentrations of cVMSs between influent and effluent of a wastewater treatment plant. The sum concentrations of four cVMSs in lake water, tap water, and bottled water samples were in the ranges of 67.0-1100 ng/L (mean/median: 350/282 ng/L), 19.8-350 ng/L (12.6/12.3 ng/L), and 2.31-28.1 ng/L (10.3/8.23 ng/L), respectively. Among the four cVMSs, decamethylcyclopentasiloxane (D5) was found at the highest concentrations in all water samples analyzed. The mean exposure doses of cVMSs calculated for adults and children through the consumption of drinking were 0.409 and 0.412 ng/kg-bw/day, respectively. Human exposure to cVMSs calculated through drinking water consumption was significantly lower than that reported for inhalation.

Assessment of internal exposure to methylsiloxanes in children and associated non-dietary exposure risk

Methylsiloxanes (MSs) are a significant source of indoor environmental pollution due to their high production level and widespread application, and pose a potential health risk. Given the special vulnerability of children to environmental contaminants, assessment of indoor MSs exposure in children is quite essential. In this study, we assessed internal exposure doses and external exposure levels of MSs in children from industrial and residential areas in southwestern China. Indoor air, indoor dust, and personal care product (PCP) samples were collected to evaluate indoor non-dietary MSs exposure in children through various pathways. The concentrations of MSs in indoor environments of industrial areas were approximately one to four orders of magnitude higher than those of residential areas. Sun protection products contained the highest concentrations of MSs. Relatively high levels of cyclic methylsiloxanes (CMSs) were found in plasma of children from industrial areas, which were one to two orders of magnitude higher than those in children from residential areas. The highest MSs levels in plasma were detected in infants (0-1 year), with values of 1.4 × 10² ng/mL and 1.3 × 10² ng/mL for CMSs (D4-D6) and linear methylsiloxanes (LMSs) (L5-L16), respectively. The internal exposure dose of infants in residential areas is driven by major unknown sources of MSs. The average daily doses via inhalation and dust ingestion in children from industrial areas were one to three orders of magnitude higher than in those from residential areas, indicating that these children should be considered a highly exposed population. Inhalation and dust ingestion were both major exposure pathways to MSs for children of all age groups in industrial areas, whereas dermal absorption from PCPs was the predominant exposure pathway for children of all age groups in residential areas (except for infants). Although the exposure risk to D4 and D5 was at an acceptable level for all children studied, the total daily exposure doses of these two cyclic compounds via inhalation for infants in the industrial areas was near the chronic reference dose. Meanwhile, MSs may accumulate in infant plasma within a short period of time (<6 months). Therefore, infants should be the focus of greater attention in future research. As indoor environments may pose high risks for infants in industrial areas, they should be the focus of future research.

Review of recent findings on occurrence and fates of siloxanes in environmental compartments

In view of their vast global usage in both consumer products and industrial processes, environmental emission and fates of siloxanes have become concerned issue. This review summarized the research progress, especially in the last decade, on production/consumption data, toxicities, analysis methods, environmental distribution, migration and degradation/transformation of both dimethylsiloxanes and modified siloxanes in atmospheric, aquatic and terrestrial compartments from various areas (especially in China). In spite of their fast degradation (hydrolysis and hydroxylation, etc) in various matrices (except sediment), dimethylsiloxane oligomers have been found in various environmental matrices from many countries due to their constant usage and emission. Moreover, recent literatures have paid attention to behaviors of dimethylsiloxanes in industrial areas, e.g., their higher residual levels compared with residential areas and unique transformed products (such as halogenated products) arose from special industrial production scenarios. Meanwhile, although most prior studies focused on dimethylsiloxanes, identification of modified-siloxanes with other functional groups in environment have been beginning to attract the attention of scientists. Furthermore, related literatures indicated that compared with dimethylsiloxanes, both halogenated-dimethylsiloxanes and modified methylsiloxanes (phenylsiloxanes and trifluoropropylsiloxanes) could have stronger persistence due to their weaker volatilization and degradation, especially in terrestrial matrices.

Methylsiloxane occurrence and distribution in free-range poultry eggs near a rural industrial park: Indicators of potential risks to birds

The ecological harm from methylsiloxanes has drawn worldwide attention. This study investigated three cyclic (D₄-D₆) and four linear siloxanes (L₇-L₁₀) in the eggs of free-range poultry collected near a rural industrial park in China and found total concentrations in the range of 19.2-1204 (median, 268) ng/g dry weight. Higher concentrations of methylsiloxanes were observed in chicken eggs than duck eggs. Cyclic siloxanes represented a median of 62.2% of the total methylsiloxane concentrations. A source assessment indicated that local soils and outdoor dust were more important sources of egg methylsiloxanes than poultry food. The partitioning of methylsiloxanes between egg yolk and egg albumen was investigated, and preferential distributions of the chemicals in the yolk were observed. This study confirmed that methylsiloxanes were highly prevalent in the study poultry eggs. The results suggested that the potential risks to some wild birds inhabiting this area should be of concern, as their physiologies and feeding ecologies are similar to those of the studied poultry, although available ecotoxicological data of the chemicals to birds remains scarce. Additional research is needed to characterize the accumulation of methylsiloxanes in different bird species and its associated adverse effects on their offspring.

Assessment bioaccumulation factor (BAF) of methyl siloxanes in crucian carp (Carassius auratus) around a siloxane production factory

Methyl siloxanes are identified as emerging persistent toxic compounds and the ecological environment risks of these compounds have been caused of great concern worldwide. In this study, the concentrations of methyl siloxanes were reported in dissolved water and crucian carp around a methyl siloxane production factory located in Liaoning Province, Northeast China. D4, D5, D6, D7, L4, L5 and L6 were detectable both in dissolved water and crucian carp. The total concentrations of 7 methyl siloxanes (Σ_7MS) were 14 ± 6.3 ng/L in dissolved water and 43 ± 22 ng/g ww in crucian carp, respectively. D5 has the highest concentration both in dissolved water (5.5 ± 3.5 ng/L) and crucian carp (17 ± 11 ng/g ww). Based on the monitoring values, bioaccumulation factor (BAF) of these compounds were calculated. Significant bioaccumulation potential was observed for D4 (BAF = 5900 ± 3500 L/kg) based on the bioaccumulation criteria suggested by USEPA and EU (BAF > 5000 L/kg). To our understanding, this is the first report of BAF values of methyl siloxane in field study, which will provide important support for further assessment of bioaccumulation of these compounds.

Identification of organosiloxanes in ambient fine particulate matters using an untargeted strategy via gas chromatography and time-of-flight mass spectrometry

Organosilicons are widely used in consumer products and are ubiquitous in living environments. However, there is little systemic information on this group of pollutants in ambient particles. This study proposes a novel untargeted strategy based mainly on the mass difference of three silicon isotopes to screen organosilicon compounds from 2-year PM_2.5 samples of Beijing using gas chromatography and high-resolution time-of-flight mass spectrometry. 61 organosilicons were filtered from 1019 peaks, and 35 ones were identified as organosiloxanes including 17 methylsiloxanes and 18 phenylmethylsiloxanes, of which 6 and 3 species were confirmed using reference standards, respectively. These organosiloxanes could be clustered into three groups: low-silicon-number methylsiloxanes, high-silicon-number methylsiloxanes, and phenylmethylsiloxanes. Low-silicon-number methylsiloxanes showed high abundance in the heating season but low abundance in the non-heating season, whereas high-silicon-number methylsiloxanes showed the opposite seasonal variation. This study provides a promising strategy for screening organosilicon compounds through an untargeted approach and gives insights for further investigation of the sources and health risks of organosiloxanes.

Cross-interface transfer of polycyclic aromatic hydrocarbons (PAHs) in a shallow urban lake in Shanghai, China based on the fugacity model

Shallow urban lakes are important urban ecosystems; however, these systems are subject to severe polycyclic aromatic hydrocarbons (PAHs) contamination. An understanding of the distribution and dynamics of PAHs in lakes is required to restore the functions of lake ecosystems and to ensure the ecological security of urban water sources. The Quantitative Water Air Sediment Interaction (QWASI) model and partition coefficient and fugacity fraction methods were applied to estimate the multimedia transfers of PAHs in Dianshan Lake, a typical shallow lake in Shanghai, China. In addition, some new concepts and methods related to PAH transfers were introduced. The results showed that while the gas-solid partition in the area remained in non-equilibrium, the influence of pollution sources tended to weaken. Atmospheric advection was the main source of PAHs to the lake, and a portion of the net loss of advection was transformed into total flux of cross-interface transfers, in which transport fluxes from air to water and from water to sediment were dominant, with a significant correlation between the two types of transfer. The large resuspension of high molecular weight (HMW)-PAHs occurred, possibly related to frequent hydrodynamic disturbances. Furthermore, this study explored the distribution of PAHs among different compartments and the seasonal variation of multimedia transfers. Sensitivity analysis showed that the model is remarkably sensitive to four parameters including temperature and advection. Monte Carlo uncertainty analysis verified that the simulation results were stable and reliable. The results can provide a theoretical basis for the monitoring and control of shallow lake pollution.

Exploring the Environmental Exposure to Methoxychlor, α-HCH and Endosulfan-sulfate Residues in Lake Naivasha (Kenya) Using a Multimedia Fate Modeling Approach

Distribution of pesticide residues in the environment and their transport to surface water bodies is one of the most important environmental challenges. Fate of pesticides in the complex environments, especially in aquatic phases such as lakes and rivers, is governed by the main properties of the contaminants and the environmental properties. In this study, a multimedia mass modeling approach using the Quantitative Water Air Sediment Interaction (QWASI) model was applied to explore the fate of organochlorine pesticide residues of methoxychlor, α-HCH and endosulfan-sulfate in the lake Naivasha (Kenya). The required physicochemical data of the pesticides such as molar mass, vapor pressure, air-water partitioning coefficient (K_AW), solubility, and the Henry's law constant were provided as the inputs of the model. The environment data also were collected using field measurements and taken from the literature. The sensitivity analysis of the model was applied using One At a Time (OAT) approach and calibrated using measured pesticide residues by passive sampling method. Finally, the calibrated model was used to estimate the fate and distribution of the pesticide residues in different media of the lake. The result of sensitivity analysis showed that the five most sensitive parameters were K_OC, logKow, half-life of the pollutants in water, half-life of the pollutants in sediment, and K_AW. The variations of outputs for the three studied pesticide residues against inputs were noticeably different. For example, the range of changes in the concentration of α-HCH residue was between 96% to 102%, while for methoxychlor and endosulfan-sulfate it was between 65% to 125%. The results of calibration demonstrated that the model was calibrated reasonably with the R² of 0.65 and RMSE of 16.4. It was found that methoxychlor had a mass fraction of almost 70% in water column and almost 30% of mass fraction in the sediment. In contrast, endosulfan-sulfate had highest most fraction in the water column (>99%) and just a negligible percentage in the sediment compartment. α-HCH also had the same situation like endosulfan-sulfate (e.g., 99% and 1% in water and sediment, respectively). Finally, it was concluded that the application of QWASI in combination with passive sampling technique allowed an insight to the fate process of the studied OCPs and helped actual concentration predictions. Therefore, the results of this study can also be used to perform risk assessment and investigate the environmental exposure of pesticide residues.

Assessment of volatile methylsiloxanes in environmental matrices and human plasma

Volatile methylsiloxanes (VMSs) are widely used in various personal-care products and industrial additives and products. This study focused on VMSs exposure in the general population, workers, and the families of workers living in residential and industrial areas of southwestern China. VMSs concentrations in indoor environmental matrices from six industrial facilities were 3.4 × 10² to 9.0 × 10² μg m^-3 in gas-phase samples, 4.7 × 10² to 1.5 × 10⁴ μg g^-1 in PM_2.5 samples, and 2.3 × 10² to 7.2 × 10³ μg g^-1 in dust samples, which were two to four orders of magnitude higher than the concentrations measured in residential areas. Exposure to VMSs was investigated by analysis of plasma samples from workers in residential and industrial areas for the presence of cyclic (D4-D6) and linear (L3-L16) VMSs. VMSs concentrations in plasma samples ranged from 84 to 2.3 × 10² ng ml^-1 in workers, one to two orders of magnitude higher than those in the general population (2.2 ng ml^-1). Daily VMSs indoor exposure via inhalation and ingestion in individuals from residential and industrial areas were estimated and assessed under working-time and leisure-time conditions. This study showed that exposure to VMSs in industrial areas is approximately two to four or one to two orders of magnitude higher than that in residential areas during the working- or leisure-time scenario, respectively. Furthermore, the families of workers (the non-occupational group) experienced higher levels of exposure to VMSs in their homes compared with the general population. The ratios of exposure to linear VMSs via PM_2.5 inhalation to that via the gas phase ranged from 7.8% to 43.1% in industrial areas. This study suggests that intake of linear VMSs via PM_2.5 inhalation should be considered when estimating human exposure to VMSs in areas with high levels of PM_2.5 air pollution.