Volatile methylsiloxanes through wastewater treatment plants - A review of levels and implications

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.

Personal care products in soil-plant and hydroponic systems: Uptake, translocation, and accumulation

Personal care products (PCPs) are organic compounds that are incorporated in several daily life products, such as shampoos, lotions, perfumes, cleaning products, air fresheners, etc. Due to their massive and continuous use and because they are not routinely monitored in the environment, these compounds are considered emerging contaminants. In fact, residues of PCPs are being discharged into the sewage system, reaching wastewater treatment plants (WWTPs), where most of these compounds are not completely degraded, being partially released into the environment via the final effluents and/or accumulating in the sewage sludges. Environmental sustainability is nowadays one of the main pillars of society and the application of circular economy models, promoting the waste valorisation, is increasingly encouraged. Therefore, irrigation with reclaimed wastewater or soil fertilization with sewage sludge/biosolids are interesting solutions. However, these practices raise concerns due to the potential risks associated to the presence of hazardous compounds, including PCPs. When applied to agricultural soils, PCPs present in these matrices can contaminate the soil or be taken up by crops. Crops can therefore become a route of exposure for humans and pose a risk to public health. However, the extent to which PCPs are taken up and bioaccumulated in crops is highly dependent on the physicochemical properties of the compounds, environmental variables, and the plant species. This issue has attracted the attention of scientists in recent years and the number of publications on this topic has rapidly increased, but a systematic review of these studies is lacking. Therefore, the present paper reviews the uptake, accumulation, and translocation of different classes of PCPs (biocides, parabens, synthetic musks, phthalates, UV-filters) following application of sewage sludge or reclaimed water under field and greenhouse conditions, but also in hydroponic systems. The factors influencing the uptake mechanism in plants were also discussed.

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.

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

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

Volatile Methylsiloxanes in Complex Samples: Recent Updates on Pretreatment and Analysis Methods

Volatile methylsiloxanes (VMSs) are massively produced chemicals having applications in industry and home because of their physical and chemical characteristics. They are used in personal care products such as cosmetics, household coatings, cleaners, skin care products, and others. Resultantly, large number of VMSs are discharged into air where they can be subjected to atmospheric migrations over long distances causing toxic and estrogenic effects, persistence, and bioaccumulations. Many institutions have taken measures to control VMSs. They require accurate, rapid, and sensitive pretreatment and analysis methods for diverse samples. Herein, the pretreatment and determination methods of VMSs as reported in recent years are reviewed and summarized. Pretreatments include commonly methods such as membrane-assisted solvent extraction, liquid-liquid extraction, and others, while novel methods are solid phase extraction, solid phase microextraction, diverse liquid phase microextraction and others. Analyses are made through gas chromatography-based methods. In addition, the advantages, and disadvantages of techniques are compared, and the prospects of pretreatment and analysis methods are discussed.

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

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

Plant uptake potential and soil persistence of volatile methylsiloxanes in sewage sludge amended soils

Volatile methylsiloxanes (VMSs) are organosilicon compounds, ubiquitous in modern life. Due to their high use in consumer products, large amounts of these compounds are released into sewer systems, reaching wastewater treatment plants (WWTPs). Its frequent detection in sewage sludge can be of concern when considering its land application, not only due to potential negative impacts on the environment, but also on human health. In this work, the effects of sewage sludge application on plant development and crop productivity were studied, as well as VMSs persistence in the soil and their plant uptake. This study focused on 7 VMSs (D3, D4, D5, D6, L3, L4 and L5) and consisted of a 12-week greenhouse pot experiment, where sewage sludge-amended soils were used to cultivate Pisum sativum (peas). Sewage sludge application to soils had no negative effects on plant development and was tied to crop productivity improvements. Most of the VMSs were still present in soils at the end of the experiment and plant uptake and translocation of the 4 cyclic VMSs (D3, D4, D5, D6) occurred. VMSs were detected in plant tissues up to 161 ± 27 ng g^-1 dw (samples of stems, leaves and tendrils), but did not exceed 50 ± 19 ng g^-1 dw in peas, which did not translate into a human exposure risk due to ingestion, according to an intake risk assessment. However, soil risk assessments showed that for L5 the hazardous ratios were higher than the threshold value of 1. This means a potential environmental risk despite the low levels of this compound in soils (up to 7.3 ± 0.7 ng g^-1 dw). Considering these results, sewage sludge monitoring plans should be defined for VMSs, namely when its final destination is land application, thus allowing a safer management of this residue, taking advantage of its valorization potential.

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 (K_OW ) values are high, air:water partition coefficient (K_AW ) values are also high and n-octanol/air partition coefficient (K_OA ) values are relatively low. In addition, organic carbon/water partition coefficient (K_OC ) values are substantially lower than expectations based on K_OW . This means that most empirical relationships between K_OC and K_OW 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 K_OC ; (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).

Temporal and spatial variation, input fluxes and risk assessment of cyclic methylsiloxanes in Rivers-Bohai Sea System

In the present study, the total concentrations of three cyclic methylsiloxanes (ΣCMSs), including octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6), in surface water and sediment samples of five main rivers draining into the Bohai Sea were in the range of 1.62-1.39 × 10³ ng/L and 1.92-1.69 × 10³ ng/g dw, respectively. Riverine input had great influence on the coastal distribution of siloxanes in the Bohai Sea. The concentrations of ΣCMSs in coastal sediments farthest away (40-50 Km) from the estuaries were only 4-33% of those close to the estuaries. But surprisingly, compared with those in coastal sediments (1.03-1.44 × 10³ ng/g dw), the concentrations of CMSs (1.56-2.67 × 10³ ng/g dw) in some deep-sea sediments were higher, and certain positive correlation existed between sediment ΣCMSs in this area with the total petroleum hydrocarbons concentration (R² = 0.92, p < 0.05) suggested offshore oil exploitation as one important emission source of siloxanes. Overall, calculated based on their sediment concentrations, D4-D6 had negligible ecological risks to the benthic organisms in river-Bohai Sea system, i.e. HQs < 1. However, sediment-accumulation of siloxanes should be paid attention, especially for some deep-sea sediments nearby drilling platforms, where it will take only less than 1 year for D4 to reach its threshold.

Novel biotechnologies for nitrogen removal and their coupling with gas emissions abatement in wastewater treatment facilities

Wastewaters contaminated with nitrogenous pollutants, derived from anthropogenic activities, have exacerbated our ecosystems sparking environmental problems, such as eutrophication and acidification of water reservoirs, emission of greenhouse gases, death of aquatic organisms, among others. Wastewater treatment facilities (WWTF) combining nitrification and denitrification, and lately partial nitrification coupled to anaerobic ammonium oxidation (anammox), have traditionally been applied for the removal of nitrogen from wastewaters. The present work provides a comprehensive review of the recent biotechnologies developed in which nitrogen-removing processes are relevant for the treatment of both wastewaters and gas emissions. These novel processes include the anammox process with alternative electron acceptors, such as sulfate (sulfammox), ferric iron (feammox), and anodes in microbial electrolysis cells (anodic anammox). New technologies that couple nitrate/nitrite reduction with the oxidation of methane, H₂S, volatile methyl siloxanes, and other volatile organic compounds are also described. The potential of these processes for (i) minimizing greenhouse gas emissions from WWTF, (ii) biogas purification, and (iii) air pollution control is critically discussed considering the factors that might trigger N₂O release during nitrate/nitrite reduction. Moreover, this review provides a discussion on the main challenges to tackle towards the consolidation of these novel biotechnologies.

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.

Microaerobic conditions in anaerobic sludge promote changes in bacterial composition favouring biodegradation of polymeric siloxanes

Volatile organic silicon compounds (VOSiC) are harmful pollutants to the biota and ecological dynamics as well as biogas-based energy conversion systems. However, there is a lack of understanding regarding the source of VOSiCs in biogas, especially arising from the biochemical conversion of siloxane polymers such as polydimethylsiloxanes (PDMS). The biodegradation of PDMS was evaluated under anaerobic/microaerobic conditions (P_O2 = 0, 1, 3, 5%), using wastewater treatment plant (WWTP) sludge as an inoculum and PDMS as a co-substrate (0, 50, 100, 500 ppm). On average, strictly anaerobic treatments produced significantly less methane than the 3 and 5% microaerated ones, which show the highest PMDS biodegradation at 50 ppm. Thauera sp. and Rhodococcus sp. related phylotypes were identified as the most abundant bacterial groups in microaerated treatments, and siloxane-related molecules were identified as remnants of PDMS catabolism. Our study demonstrates that microaeration promotes changes to the native bacterial community which favour the biological degradation of PDMS. This confirms that the presence of VOSiC (e.g., D4-D6) in biogas is not only due to its direct input in wastewaters, but also to the PDMS microbial catabolism. Microaerobic conditions enhance both PDMS and (subsequent) VOSiC degradation in the liquid phase, increasing the concentrations of D4 and D5 in biogas, and the production of less toxic siloxane-based derivatives in the liquid phase. This study suggests that microaeration of the anaerobic sludge can significantly decrease the concentration of PDMSs in the WWTP effluent. However, for WWTPs to become effective barriers for the emission of these ecotoxic contaminants to the environment, such a strategy needs to be coupled with an efficient biodegradation of VOSiCs from the biogas.

Methylsiloxanes in petroleum refinery facility: Their sources, emissions, environmental distributions and occupational exposure

High concentrations (1.08 ng/g-3.61 mg/g) of methylsiloxanes, including cyclic analogs [octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6)], and linear analogs with 3-14 silicon atoms (L3-L14), have been detected in crude oil, additives and petroleum products from one petroleum refinery facility in China. Overall, the total mass load of Σmethylsiloxanes (1320 kg/day) in crude oil and additives was 1.5 times higher than that in petroleum products (857 kg/day), indicating their potential emissions in this facility, which were further confirmed by the find of their obvious emission through exhaust-gas (89.4 kg/day) and wastewater (4.70 kg/day). Σmethylsiloxanes emission from exhaust-gas discharge outlets of deep catalytic cracking units (60.6 kg/day) took up 68% of their total emission from all gas outlets. Overall, Σmethylsiloxanes in air (17.1-743 μg/m³) and soil samples [311 ng/g dw (dry weight) - 34.2 μg/g dw] from this facility were up to four orders of magnitude greater than those from surrounding areas, and plasma concentrations of Σmethylsiloxanes in current workers from this facility (7.4-609 ng/mL) were up to two orders of magnitude larger than those from reference group (<LOQ-21.2 ng/mL). Furthermore, concentration ratios (0.09-0.58) of total cyclic methylsiloxanes to their hepatic metabolites for workers were 2.3-17 times lower than those (1.32-1.56) for reference group, indicating that refinery workers may be exposed to more unknown methylsiloxane analogs than general population.

Using Design of Experiments to Optimize a Screening Analytical Methodology Based on Solid-Phase Microextraction/Gas Chromatography for the Determination of Volatile Methylsiloxanes in Water

Volatile methylsiloxanes (VMSs) constitute a group of compounds used in a great variety of products, particularly personal care products. Due to their massive use, they are continually discharged into wastewater treatment plants and are increasingly being detected in wastewater and in the environment at low concentrations. The aim of this work was to develop and validate a fast and reliable methodology to screen seven VMSs in water samples, by headspace solid-phase microextraction (HS-SPME) followed by gas chromatography with flame ionization detection (GC-FID). The influence of several factors affecting the extraction efficiency was investigated using a design of experiments approach. The main factors were selected (fiber type, sample volume, ionic strength, extraction and desorption time, extraction and desorption temperature) and optimized, employing a central composite design. The optimal conditions were: 65 µm PDMS/Divinylbenzene fiber, 10 mL sample, 19.5% NaCl, 39 min extraction time, 10 min desorption time, and 33 °C and 240 °C as extraction and desorption temperature, respectively. The methodology was successfully validated, showing low detection limits (up to 24 ng/L), good precision (relative standard deviations below 15%), and accuracy ranging from 62% to 104% in wastewater, tap, and river water samples.

Cyclic Phenylmethylsiloxane Oligomers in Municipal Landfills and Their Elimination Mechanisms in Leachate Treatment Processes

This study investigated some sources and elimination mechanisms of phenylmethylsiloxanes in landfill leachates. During a 20-day leaching experiment for electronic wastes collected from one Chinese landfill, significant release (4.9 ng/L to 1.3 μg/L) of cis-/trans-2,4,6-triphenyl-2,4,6-trimethylcyclotrisiloxanes (cis-P3 and trans-P3) and cis-/trans-2,4,6,8-tetraphenyl-2,4,6,8-tetramethylcyclotetrasiloxanes (cis-P4 and trans-P4a,b,c) in simulated leachates was found. From January 2017 to December 2018, P3 and P4 isomers were detected in raw leachates from active cells [<LOQ-990 ng/L, detection frequency (df) = 67-100%] and closed cells (<LOQ-282 ng/L, df = 2.1-98%) of this landfill. Generally, mean mass loads of total phenylmethylsiloxanes in raw leachates were larger in the summer (380 mg/d) and winter (295 mg/d) for active cells, while they decreased from 36.1 mg/d to <LOQ for closed cells during the entire period. During leachate treatment processes, sorption to sludge was responsible for major removal (64-84%) of phenylmethylsiloxanes, while Fenton treatment accounted for 8.5-25% removal. Simulated Fenton experiments indicated that hydroxylation half-lives of P3 (1.3-1.5 h) and P4 (0.65-0.86 h) were 15-91 times faster than their hydrolysis half-lives (22-59 h, pH 3.5). Furthermore, monohydroxylated P4 isomers with a hydroxyphenyl group had larger (3.2-3.9 times) concentrations than those with a hydroxymethyl group, meaning that a phenyl group may be more likely to be hydroxylated than a methyl group.

Development of a solid-phase microextraction method for fast analysis of cyclic volatile methylsiloxanes in water

Cyclic volatile methylsiloxanes (cVMS) are widely used in consumer products and commonly detected in the environment. There are challenges in the analysis of cVMS because of their ubiquitous use which can introduce high background contamination. The current study introduces a sample preparation method based on headspace of solid-phase microextraction (SPME) for monitoring the cVMS in waters. Efforts were made to reduce the background contamination during sample preparation and instrument analysis. A laboratory prepared MIL-101 coating was prepared using polysulfone instead of polydimethylsiloxane as adhesive to avoid the contamination. The extraction performance of the MIL-101 fiber was optimized and evaluated. The optimized extraction time and temperature were 60 min and 40 °C, respectively. The method quantification limits of the MIL-101 fiber for octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecylcyclohexasiloxane (D6) in water were 0.15 ng mL^-1, 0.14 ng mL^-1, and 0.27 ng mL^-1, respectively. The extraction efficiency of the proposed MIL-101 fiber was comparable to the commercial polydimethylsiloxane/divinylbenzene fiber. The developed method was applied to analyze the cVMS in wastewater treatment plant and the concentrations in the barscreen and in the aeration tank ranged from 0.73 to 3.3 ng mL^-1 and 7.74-85.1 ng mL^-1, respectively. The MIL-101 fiber was also applied to study the photodegradation of the cVMS in water under simulated sunlight. Approximately 25%, 20%, and 45% of D4, D5, and D6, respectively, were degraded after 10 h exposure.

Tracing Urban Wastewater Contaminants into the Atlantic Ocean by Nontarget Screening

Oceans are the ultimate sink for many of the over 100 million man-made substances. Until now, monitoring was limited to a reduced number of targeted persistent organic pollutants, reaching open waters mainly via atmospheric deposition. However, the composition and fate of the thousands of pollutants reaching the marine environment though wastewater discharges from coastal sources remain largely unexplored. By combining a newly developed nontarget screening (NTS) workflow and high-resolution mass spectrometry (HRMS), we have identified over 500 sewage-derived contaminants occurring in the ocean. Samples from the NE Atlantic contained this anthropogenic imprint at distances over 50 km from the coastline and >500 m depth, beyond the continental margin. The range of identified compounds spans from pharmaceuticals and personal care products to food additives and industrial chemicals, including several that have never been reported in the environment, as they escaped conventional targeted analytical methods. Predicting the effects of the continuous input of this chemical "cocktail" on marine ecosystems is a formidable challenge, since 40% of the detected compounds lack information regarding their use and ecotoxicity.

Hydroxyl radical oxidation of cyclic methylsiloxanes D4 ∼ D6 in aqueous phase

Cyclic methylsiloxanes (CMS) were listed as candidates of substances of very high concerns in 2018 by the REACH. These compounds can enter environmental waters, and potentially cause harmful effects to aquatic organisms and human beings. Until now, reaction mechanisms of these pollutants with hydroxyl radicals (HO) in aqueous phase were unknown. In this study, reaction mechanisms of three typical CMS (D4 ∼ D6) with HO in aqueous phase were investigated by employing both UV/H₂O₂ experiments and density functional theoretical calculations. Bimolecular reaction rate constants (k_HO·) of D4 ∼ D6 with HO were determined as k_HO·(D4) = 8k_HO·(D5) = 12k_HO·(D6) = 6.6 × 10⁸ L mol^-1 s^-1. Half-lives of HO oxiding D4 ∼ D6 ranged from 12 to 140 days at [HO] = 10^-15 mol L^-1 in sunlit surface water, and were comparable to (D4, D5) or much shorter (D6) than hydrolytic half-lives. The reactivity to HO decreased with the increasing size of siloxane ring in aqueous phase, in an order totally opposite to that in gaseous phase. Calculation results indicated that HO oxidation of the three CMS proceeded spontaneously through an exothermic H-abstraction process at the first step. Water molecules participated into H-abstraction of CMS and caused energy barrier of D5 higher than that of D4. Thus, H-bonds formed by water molecules were responsible for the reverse reactivity of CMS in aqueous phase. This work provided basic evidences suggesting environmental persistence of CMS in aqueous phase completely different from that in gaseous phase.

Estimation of the Contribution Made to Down-the-Drain Emissions of D5 by Personal Care Product Categories in the European Union

Aquatic risk assessment of personal care chemicals requires quantifying the contribution of all product types containing these ingredients to down-the-drain emissions. We developed a probabilistic model framework embracing stochastic variability associated with individual consumers and their behaviors in the European Union, as well as other sources of uncertainty related to losses following applications (e.g., volatilization). The model was applied to decamethylcyclopentasoloxane (D5), an emollient used in wash-off (WO) and leave-on (LO) products. Quantifying contributions from each product category containing D5 to down-the-drain emissions is necessary to inform optimal risk management options. Simulation results for the baseline scenario in 2012 support the argument that LO products make up a minor contribution (7.1%) to down-the-drain emissions of D5, with only 0.20% of the D5 used in LO products being released to wastewater. The most influential model parameters are the release factor from WO products and the time between application and use for various LO product types, stressing the importance of embracing stochastic variability across individuals' behavior when assessing contributions of various product types to environmental emissions. The downward trend in WO use from 2010 to 2016 is reflected in declining concentrations in wastewater influent during the same period. Uncertainty remains about future levels of D5, once phasing out WO products is complete. The probabilistic model in conjunction with high-tier data of consumer habits is a promising high-tier tool for the characterization of complex emission scenarios of personal care ingredients. Integr Environ Assess Manag 2019;00:1-12. © 2019 SETAC.

A review of contamination status, emission sources, and human exposure to volatile methyl siloxanes (VMSs) in indoor environments

Siloxanes are organo-silicon compounds containing Si-O-Si linkages and methyl branches. Depending on the structure, siloxanes can be divided into cyclic and linear compounds. Methyl siloxanes with small and medium molecular weights (molecular weights less than 500 g mol^-1), are volatile under normal conditions, and hence are referred to as volatile methyl siloxanes (VMSs). VMSs are additive ingredients in many products such as plastics, rubber, personal care products, and household items. This review provides information on the distribution of VMSs in consumer products, indoor air and dust, and their implications for human exposure. VMSs have been used in personal care products and household items at concentrations on the order of hundreds to thousands of micrograms per gram which are the main sources of contamination in the indoor environments. VMSs have been found widely in indoor air and dust. A significant correlation existed between VMS concentrations in indoor air and dust. Among typical VMSs, dodecamethylcylcopentasiloxane (D5) is the major compound found in indoor environments. The human exposure doses to VMSs through dermal absorption, dust ingestion, and inhalation were compiled; Inhalation is a dominant pathway of exposure to VMSs, especially in indoor environments of occupational settings like hair salons. The human exposure doses were higher in children than in adults.

Contamination characteristics of siloxanes in coastal sediment collected from industrialized bays in South Korea

Siloxanes have been used as chemical additives in various products since the 1940s. They are known to have potentially toxic effects, to be environmentally persistent, and to be bioaccumulative. Previous studies have reported high levels of siloxanes in various environmental matrices. In this study, 6 cyclic siloxanes (D4-D9) and 13 linear siloxanes (L3-L15) in coastal sediment collected from southeastern bays adjacent to industrial zones in South Korea (Busan, Ulsan, Jinhae, and Gwangyang) were analyzed. The contamination levels and spatial distribution of siloxanes in the coastal sediment samples were investigated, with the hazard quotients (HQs) for siloxanes evaluated using Monte Carlo simulation. Across all samples, the total concentration (Σ₁₉) of siloxanes was in the range of 11.6-3877 (mean: 305; median: 133) ng/g dry weight (dw). The highest average concentration of Σ₁₉ siloxanes was found in Busan (mean: 580; median: 233 ng/g dw), followed by Ulsan (mean: 316; median: 209 ng/g dw), Jinhae (mean: 266; median: 125 ng/g dw), and Gwangyang (mean: 33; median: 27 ng/g dw), all of which are suggested to be affected by both industrial and domestic activities. The highest contributions were from D5 (18%) and D6 (34%), followed by D9 (7.3%) and L11 (5.8%). The HQs for siloxanes were less than 1, indicating that there was no risk to benthic organisms in the study areas; however, further monitoring of various environmental matrices is required to fully assess the potential ecological risks.

Siloxane in baking moulds, emission to indoor air and migration to food during baking with an electric oven

Linear and cyclic volatile methylsiloxanes (l-VMS and c-VMS) are man-made chemicals with no natural source. They have been widely used in cosmetics, personal care products, coatings and many other products. As a consequence of their wide use, VMS can be found in different environmental media, as well as in humans. We bought 14 new silicone baking moulds and 3 metallic moulds from the market and used them in different baking experiments. Four of the silicone baking moulds were produced in Germany, two in Italy, four in China, and for the other moulds were no information available. The metal forms were all produced in Germany. VMS were measured in the indoor air throughout the baking process and at the edge and in the center of the finished cakes using a GC/MS system. Additionally, the particle number concentration (PNC) and particle size distribution were measured in the indoor air. The highest median concentrations of VMS were observed immediately following baking: 301 μg/m³ of D7, 212 μg/m³ of D6, and 130 μg/m³ of D8. The silicone moulds containing the highest concentrations of c-VMS corresponded with distinctly higher concentrations of the compounds in indoor air. Using a mould for more than one baking cycle reduced the indoor air concentrations substantially. Samples collected from the edge of the cake had higher concentrations relative to samples from the center, with a mean initial concentration of 6.6 mg/kg of D15, 3.9 mg/kg of D9, 3.7 mg/kg of D12, and 4.8 mg/kg of D18. D3 to D5 were measured only at very low concentrations. Before starting the experiment, an average PNC of 7300 particles/cm³ was observed in the room's air, while a PNC of 140,000 particles/cm³ was observed around the electric stove while it was baking, but this PNC slowly decreased after the oven was switched off. Baking with 4 of the moulds exceeded the German indoor precaution guide value for c-VMS, but the health hazard guide value was not reached during every experiment. Compared to other exposure routes, c-VMS contamination of cake from silicone moulds seems to be low, as demonstrated by the low concentrations of D4 and D6 measured. For less volatile c-VMS > D6 the results of the study indicate that food might play a more important role for daily intake. As a general rule, silicone moulds should be used only after precleaning and while strictly following the temperature suggestions of the producers.

Chlorinated-Methylsiloxanes in Shengli Oilfield: Their Generation in Oil-Production Wastewater Treatment Plant and Presence in the Surrounding Soils

In two oil-wastewater treatment stations of Shengli Oilfield, cyclic volatile methylsiloxanes (cVMS, D4-D6) in the wastewater stream were found to undergo chlorination during electro-oxidation process for wastewater containing chlorine ions (16.1-42.0 g/L). Their converted fractions were 4.71-28.0% for monochlorinated D4-D6 and 0.22-7.96% for dichlorinated D4, which were ∼2 orders of magnitude higher than those for hydroxylated products. Furthermore, portions of chlorinated methylsiloxanes retained in excess sludge were released to the surrounding soils. In soil samples ( n = 500), chlorinated methylsiloxanes concentrations (<LOD-586 ng/g dw (dry weight), detection frequency (df) = 6.60-45.6%) decreased roughly exponentially with respect to the distance away from these two stations. During 2008-2017, the measured total chlorinated cVMS kept increasing in the dewatered-sludge (from 58.5 to 120 μg/g dw), while their concentrations in the surrounding soils doubled (from 93.4 to 184 ng/g dw) in first 6 years, but decreased since then (48.0 ng/g at 2017). Simulating experiments showed that monochlorinated D4-D6 in soil had 1.1-2.4 times longer hydrolysis (6.92-234 days) and volatilization (4.62-325 days) half-lives than their paired nonchlorinated cVMS. Among isomers of dichlorinated D4, D3D(CHCl₂) had greatest hydrolysis (7.75-33.8 days) and volatilization (135-271 days) rates, followed by D3D(CH₂Cl)₂, D2(D(CH₂Cl))₂ and DD(CH₂Cl)DD(CH₂Cl).

Footprints in the sand - Assessing the seasonal trends of volatile methylsiloxanes and UV-filters

This study focused on the determination of seven volatile methylsiloxanes (VMSs) and eleven UV-filters (UVFs) in beach sand from the Oporto's region (Portugal). A QuEChERS methodology ("Quick, Easy, Cheap, Effective, Rugged, and Safe") was used to extract VMSs from the sand, which has never been employed before. To extract the UVFs, a solid-phase microextraction (SPME) was used. The analyses were performed by gas chromatography-mass spectrometry (GC-MS). Twenty-three beach sand samples were analysed, from two campaigns - summer/winter. VMSs were found in all the samples with concentrations ranging from 0.007 ± 0.001 to 17.8 ± 0.9 ng g^-1_dw, while UVFs in summer samples from 0.030 ± 0.001 to 373 ± 17 ng g^-1_dw. Cyclic VMSs and octocrylene (OC) were detected in higher concentrations. In general, higher levels were detected in summer than winter. Hazard quotients were determined and 3-(4'-methylbenzylidene) camphor (4-MBC), 2-ethylhexyl 4-methoxycinnamate (EMC) and benzophenone-3 (BP3) presented values >1, which may indicate that they may pose an ecotoxicological risk.

Distribution of methylsiloxanes in benthic mollusks from the Chinese Bohai Sea

Methylsiloxanes are a class of silicone compounds that have been widely used in various industrial processes and personal care products for several decades. This study investigated the spatial distribution of three cyclic methylsiloxanes (D4-D6) and twelve linear methylsiloxanes (L5-L16) in mollusks collected from seven cities along the Bohai Sea. D4-D6 (df = 71%-81%) and L8-L16 (df = 32%-40%) were frequently detectable in the mollusk samples, while L5-L7 were not found in any mollusk samples. Cyclic methylsiloxanes (D4-D6) were found in mollusks with the mean concentrations of 15.7 ± 12.3 ng/g ww for D4, 24.6 ± 15.8 ng/g ww for D5 and 34.0 ± 23.0 ng/g ww for D6. Among the seven sampling cities, the cyclic methylsiloxanes were predominant in mollusks, with the total cyclic methylsiloxanes (sum of D4-D6, ∑CMS) accounting for 74.2%-80.7% of the total methylsiloxanes. ∑CMS along the coastline demonstrated a clear gradient, with the highest concentrations in mollusks at the sampling sites located in the western part of the Bohai Sea and the lowest concentrations in mollusks from cities located in the eastern part of the Bohai Sea. The biota-sediment accumulation factors for cyclic methylsiloxanes (D4-D6) and linear methylsiloxanes (L8-L16) were estimated as 0.42 ± 0.06-0.53 ± 0.06 and 0.13 ± 0.03-0.19 ± 0.05, respectively.

Determination of linear and cyclic volatile methyl siloxanes in biogas and biomethane by solid-phase microextraction and gas chromatography-mass spectrometry

A new method based on solid-phase microextraction (SPME) followed by gas chromatography-mass spectrometry (GC-MS) was developed for the analysis of seven linear (L2 - L5) and cyclic (D3 - D5) volatile methyl siloxanes (VMS) in biogas and biomethane, directly collected into Tedlar® bags (Tedlar SPME) from anaerobic digesters and wastewater treatment plants. The method was employed to monitor VMS content in biomethane produced by biogas upgrading with a pilot-plant membrane unit and provided adequate limits of quantification (< 0.05 mg m^-3) to detect trace siloxane impurities. Tedlar SPME was validated against a standard procedure based on indirect sampling of gas streams with sorbent tubes followed by solvent extraction and GC-MS. Method precision (RSD) on total and individual VMS concentrations was lower than 10%, while RSD values of the standard procedure were higher than 20%. Tedlar SPME suitably revealed high VMS levels, expressed as total volatile silicon (> 1 mg_Sim^-3), in wastewater biogas and provided a more efficient sampling of heavier VMS in comparison to the sorbent tubes method. At low values (< 0.1 mg_Sim^-3) typical of wood waste biogas and biomethane, no statistically significant differences were observed between the two methods. Overall, Tedlar SPME simplified the analytical procedure by reducing the procedural steps, avoiding the use of solvents and demonstrated its applicability for testing the quality of biomethane as advanced biofuel.

Sources and Fate of Cyclic Phenylmethylsiloxanes in One Municipal Wastewater Treatment Plant and Biosolids-Amended Soil

cis-/ trans-2,4,6-Triphenyl-2,4,6-trimethylcyclotrisiloxanes ( cis-P3 and trans-P3) and cis-/ trans-2,4,6,8-tetraphenyl-2,4,6,8-tetramethylcyclotetrasiloxanes ( cis-P4 and trans-P4a,b,c) were detected in personal care products [<LOD-54.2 μg/g, detection frequencies (df) = 14.5-15.5%, n = 110] collected from a Chinese city, suggesting their potential release to local municipal wastewater treatment plant (WWTP). In the local WWTP, per capita mass loadings of P3 and P4 were 43.4-340 μg/d in influents, while neither P3 nor P4 was detected in effluents. Due to large solid/water distribution coefficients (apparent Log K_d = 3.42-3.99), sorption to sludge had a dominant contribution (95.6-99.2%) to phenylmethylsiloxanes removal in the WWTP. As amended by biosolids containing phenylmethylsiloxanes [66.2 ng/g to 2.63 μg/g dw (dry weight)] from this WWTP, concentrations (<LOD -255 ng/g dw, df = 27.5-52.5%, n = 120) of six phenylmethylsiloxane isomers in soils from one commercial forest were significantly higher than those (<LOD) in the reference area without biosolids application, but no increasing trend was found at six sampling events during July 2015 to February 2017. Simulated experiments indicated that hydrolysis half-lives of phenylmethylsiloxanes (1.50-6.50 d for P3, 16.5-65.4 d for P4) in soil were 4.74-46.3 times shorter than volatilization half-lives (51.9-120 d for P3, 158-376 d for P4). For both cyclic phenylmethylsiloxanes, their trans-isomers had lower (1.14-1.82 times) degradation rates than their cis-isomers.

Occurrence and profiles of methylsiloxanes and their hydrolysis product in aqueous matrices from the Daqing oilfield in China

In the present study, the occurrence and distribution of methylsiloxanes (D4-D6, L5-L16) in the surface water and sediment collected from the Daqing oilfield were explored. For wastewater samples from an oilfield combination station, the concentrations of total cyclic methylsiloxanes (∑CMS, D4-D6) and total linear methylsiloxanes (∑LMS, L5-L16) ranged from 137-1911ng/L to 49.4-190ng/L, respectively. Cyclic methylsiloxanes were the predominant methylsiloxanes in the analyzed wastewater samples from the oilfield combination station. In addition, methylsiloxanes were detected in the surface water from three sampling areas, and the total concentrations varied from <LOQ-785ng/L (mean=219±277ng/L, median=120ng/L) for the new oilfield area, 15.1-1808ng/L (mean=270±409ng/L, median=105ng/L) for the old oilfield area and 18.0-252ng/L (mean=103±90.4ng/L, median=52.3ng/L) for the reference area. In the sediment, the ∑CMS and ∑LMS values in the samples collected from the old oilfield area were almost four to nine times higher than those in the samples from the new oilfield area. In addition, elevated concentrations of dimethylsilanediol were detected in the three sampling areas, especially in the old oilfield area (mean=85.6±98.3ng/L), which confirmed that hydrolysis occurred.

Predicted persistence and response times of linear and cyclic volatile methylsiloxanes in global and local environments

We investigated the response times of eight volatile methylsiloxanes (VMSs) in environmental systems at different scales from local to global, with a particular focus on overall loss rates after cessation of emissions. In part, this is driven by proposals to restrict the use of some of these compounds in certain products in Europe. The GloboPOP model estimated low absolute Arctic Contamination Potentials for all VMSs and rapid response times in all media except sediment. VMSs are predicted to be distributed predominantly in air where they react with OH radicals, leading to short response times. After cessation of emissions VMSs concentrations in the environment are expected to decrease rapidly from current levels. Response times in specific water and sediment systems were evaluated using a dynamic QWASI model. Response times were sensitive to both physico-chemical properties and environmental characteristics. Degradation was predicted to play the most important role in determining response times in water and sediment. In the case of the lowest molecular weight VMSs such as L2 and D3, response times were essentially independent of environmental characteristics due to fast hydrolysis in water and sediment. However, response times for the other VMSs are system-specific. They are relatively short in shallow water bodies but increase with depth due to the diminishing role of volatilization on concentration change as volume to surface area ratio increases. In sediment, degradation and resuspension rates also contribute most to the response times. The estimated response times for local environments are useful for planning future monitoring programs.

Evolution of consciousness of exposure to siloxanes-review of publications

The purpose of this description is to review scientific literature from 1944 to 2017 as a source of information on the reasons for the increased interest in siloxanes (silicones). Not only the research area, but first, the changes in the tendency of research aims are important issues in the evaluation. On the one hand, the authors emphasize the unique properties of linear and cyclic siloxanes, providing many examples of beneficial applications, and on the other hand, there are some warnings of overcoming of the safety barrier of their presence in human environment. Analyzing the results from the SCOPUS database, it can be argued that the increased interest of scientists and government agencies particularly relates to the analysis of siloxanes in biological and environmental samples. This is caused not only by the widespread use of various siloxanes in the pharmaceutical, medical, cosmetic and food industries, but also by the direct contact of these compounds with tissues, as well as an increased access to knowledge and modern research tools that have developed the awareness of hazards. The development of research methods enables not only constant monitoring of progressively lower siloxanes concentrations in various samples, but because of the specificity of these methods, it also enables an identification of specific siloxane compounds and evaluation of their effects on humans and environment. This paper discusses the issues of the evolution of consciousness of exposure to siloxanes due to their increased synthesis and widespread use in many areas of human life, which contributes to environmental pollution.