Cyclic Volatile Methylsiloxanes Research Articles

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−1dw, while UVFs in summer samples from 0.030 ± 0.001 to 373 ± 17 ng g−1dw. 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.

Uncertainty and equifinality in environmental modelling of organic pollutants with specific focus on cyclic volatile methyl siloxanes.

Multi-media fate and transport models (MFTMs) are invaluable tools in understanding and predicting the likely behaviour of organic pollutants in the environment. However, some parameters describing the properties of both the environmental system and the chemical pollutant under consideration are uncertain and or variable in space and time. Furthermore, model performance is often evaluated using sparse data sets on chemical concentrations in different media. This can result in equifinality - the phenomenon in which several different combinations of model parameters can result in similar predictions of environmental concentrations. We explore this idea for MFTMs for the first time using, as examples, three cyclic volatile methyl siloxanes (cVMS: D4, D5 and D6) and the QWASI lake model applied to Tokyo Bay. Monte Carlo simulation was employed with parameters selected from probability distributions representing estimated uncertainty in a large number of iterations. This generated distributions of predicted chemical concentrations in water (CW) and sediment (CS) which represent the aleatory uncertainty envelope but which also demonstrate significant equifinality. For all three compounds, the uncertainty implied in the CW was lower (coefficient of variation, CV, of the order of 20%) than for CS (CV ca. 45%), reflecting the propensity of cVMS compounds to sorb to sediment and the sensitivity of the model to KOC. Confidence intervals were particularly high for the persistence of D5 and D6 in sediment which both ranged between approximately 1.7 years and approximately 26 years for Tokyo Bay. Predicted concentration distributions matched observations well for D5 and D6 not for D4. Equifinality could be reduced by better constraining acceptable parameter sets using additional measured data from different environmental compartments.

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

Cyclic volatile methyl siloxanes (cVMS) used in personal care products are released to aquatic environments through wastewater effluent. cVMS are persistent, toxic, bioaccumulative, and have potential to cause ecological harm. In this study, the environmental behavior of octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6) were evaluated in the largest lake of southwest China, Dian Lake. Air, water and sediment samples were measured for three cVMS compounds in the winter (January) and summer (July) of 2017. In air, D5 exhibited the highest measured mean concentration among the three cVMS, which were 18.4 ± 8.0 ng·m−3 in winter and 5.78 ± 3.61 ng·m−3 in summer. In water and sediment, D6 was the cVMS with the highest measured mean concentration. The mean concentrations in water of D6 were 20.8 ± 5.8 ng·L−1 in winter and 20.4 ± 5.8 ng·L−1 in summer. The mean concentrations in sediment of D6 were 281 ± 45.8 ng·g−1 dw in winter and 270 ± 31.3 ng·g−1 dw in summer. A fugacity-based mass balance chemical fate model for lakes (QWASI) was used for Dian Lake to compare measurements and explore the behavior of cVMS. D6 was predicted to have the highest water column and sediment concentrations. Modeling results showed that most of the D5 and D6 partitioned into sediment and could persist for several years. Persistence was significantly influenced by the high rate of sediment burial. In an analysis of the impact of physicochemical properties and environmental parameters, KOC was identified as a key parameter for predicting cVMS behavior. This study illustrates the importance of cVMS in sediments and the potential aquatic risk that they may pose.

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 mgSim−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 mgSim−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.

Marine vegetation analysis for the determination of volatile methylsiloxanes in coastal areas

Volatile methylsiloxanes (VMSs) are massively produced chemicals that comprise a wide range of industrial and household applications. The presence of cyclic and linear VMSs in several environmental matrices and ecosystems indicates persistence associated with a potential of (bio)accumulation and food web transfer with possible toxicological effects. Due to the high anthropogenic pressure in its vicinities particularly in summer, coastal areas in Southern European countries are potential hotspots for the presence of VMSs. The massive afflux of tourists and consequent increase of the use of personal care products (PCPs) with VMSs in their formulations highlight the importance of VMSs assessment in such areas. In this study, different species of marine vegetation (algae and seaweed) were collected in three different geographical areas, covering the Atlantic Ocean (North coast of Portugal), as well as the Mediterranean Sea (coasts of the Region of Murcia, Spain and of the city of Marseille, France). Samples were analysed for the determination of 4 cyclic (D3, D4, D5, D6) and 3 linear (L3, L4, L5) VMSs employing a QuEChERS extraction methodology, followed by gas chromatography/mass spectrometry (GC/MS) quantification. VMSs were detected in 92% of the 74 samples analysed, with the sum of the concentrations per sample ranging from below the limit of detection (LOD) to 458 ± 26 ng·g−1dw (dry weight). A strong predominance of cyclic VMSs over linear ones was verified in almost all samples studied, with D5 and D6 found at higher concentrations. Seasonal variation was also assessed and despite higher levels of VMSs being identified mostly in summer months, clear seasonal trends were not perceived. It was also noted that generally the higher incidence of VMSs occurred in samples from urban and industrialized areas or in the vicinities of WWTPs, suggesting a direct input from these sources in the levels of siloxanes observed.

Headspace passive dosing of volatile hydrophobic chemicals – Aquatic toxicity testing exactly at the saturation level

It is challenging to conduct aquatic tests with highly hydrophobic and volatile chemicals while avoiding substantial sorptive and evaporative losses. A simple and versatile headspace passive dosing (HS-PD) method was thus developed for such chemicals: The pure liquid test chemical was added to a glass insert, which was then placed with the open end in the headspace of a closed test system containing aqueous test medium. The test chemical served as the dominating partitioning donor for establishing and maintaining maximum exposure levels in the headspace and aqueous solution, without direct contact between the donor and the test medium. The HS-PD method was cross validated against passive dosing with a saturated silicone elastomer, using headspace gas chromatography as analytical instrument and saturated vapors as reference. The HS-PD method was then applied to control the exposure in algal growth inhibition tests with the green algae Raphidocelis subcapitata. The model chemicals were C9-C14 n-alkanes and the cyclic volatile methyl siloxanes octamethyltetracyclosiloxane (D4) and decamethylpentacyclosiloxane (D5). Growth rate inhibition at the solubility limit was 100% for C9-C13 n-alkanes and 53 ± 31% (95% CI) for tetradecane. A moderate inhibition of 11 ± 4% (95% CI) was observed for D4, whereas no inhibition was observed for D5. The present study introduces an effective method for aquatic toxicity testing of a difficult-to-test group of chemicals and provides an improved experimental basis for investigating toxicity cut-offs.

Best Paper Award.

Best Paper Award.

Occurrence and spatial distribution of neutral perfluoroalkyl substances and cyclic volatile methylsiloxanes in the atmosphere of the Tibetan Plateau

Abstract. Due to their properties of bioaccumulation, toxicity, and long-range atmospheric transport, polyfluoroalkyl and perfluoroalkyl substances (PFASs) and cyclic volatile methylsiloxanes (cVMSs) are currently being considered as emerging persistent organic pollutants (POPs) for regulation. To date, there are limited data on PFASs and cVMSs in the atmosphere of the Tibetan Plateau (TP), a remote environment which can provide information on global background conditions. Sorbent-impregnated polyurethane foam (SIP) disc passive air samplers were therefore deployed for 3 months (May to July 2011 and 2013) at 16 locations across the TP. Using previously reported methods for estimating the air volume sampled by SIP discs, the derived atmospheric concentrations ranged as follows: 18–565 ng m−3 for ΣcVMS (including D3, D4, D5, and D6); 65–223 pg m−3 for fluorotelomer alcohols (ΣFTOHs); 1.2–12.8 pg m−3 for fluorinated sulfonamides (ΣFOSA); and 0.29–1.02 pg m−3 for fluorinated sulfonamidoethanols (ΣFOSE). The highest ΣcVMS occurred at Lhasa, the capital city of the TP, indicating the local contribution to the emerging pollutants. Higher levels of ΣFTOHs were observed at sites close to the transport channel of the Yarlung Tsangpo Grand Canyon, indicating possible long-range atmospheric transport (LRAT). Elevated concentrations of shorter-chain volatile PFAS precursors (4 : 2 FTOH and fluorobutane sulfonamidoethanol) were found in most air samples, reflecting the shift in production from long- to short-chain PFASs in Asia. Overall, concentrations of emerging POPs at background sites of the TP were 1–3 orders of magnitude higher than those reported for legacy POPs.

Predicting Indoor Emissions of Cyclic Volatile Methylsiloxanes from the Use of Personal Care Products by University Students.

Characterization of indoor emissions of cyclic volatile methylsiloxanes (cVMS) due to the use of personal care products is important for elucidating indoor air composition and associated health risks. This manuscript describes a mass transfer model to characterize the emission behaviors of decamethylcyclopentasiloxane (D5, the most abundant indoor cVMS) from skin lipids. A C-history method is introduced to determine the key parameters in the model, i.e., the initial concentration and diffusion coefficient of D5 inside the skin lipids. Experiments were conducted in a university classroom to examine the D5 emission behaviors by using a proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS). Data from the first class session of two typical days was applied to obtain the key parameters, which were subsequently used for predicting D5 concentrations in other class sessions. Good agreement between model predictions and experiments demonstrates the effectiveness of the model and parameter determination method. With the model, we found that the reuse of personal care products has a significant impact on the D5 emissions. In addition, the time-dependent emission rate and remaining amount of D5 inside the skin can also be calculated. These results indicate a fast decay pattern during the initial emission period, which is consistent with prior experimental studies.

Fluorotelomer alcohols (FTOHs), brominated flame retardants (BFRs), organophosphorus flame retardants (OPFRs) and cyclic volatile methylsiloxanes (cVMSs) in indoor air from occupational and home environments

Indoor air samples were collected from private homes and various occupational indoor environments using passive air sampler and analysed for fluorotelomer alcohols (FTOHs), brominated flame retardants (BFRs), organophosphorus flame retardants (OPFRs) and cyclic volatile methyl siloxanes (cVMSs). The aim was to investigate their occurrence in indoor air, factors that may affect their presence and human daily exposure dose (DED) via inhalation. In general, levels of cVMSs were 3–4 orders of magnitude greater than the other compound classes. OPFRs concentration was found significantly higher than BFRs in indoor air. The most abundant compounds in each chemical class were 8:2 FTOH, 2,4,6-TBP, TNBP and TCEP and decamethylcyclopentasiloxane (D5). Home samples contained higher level of FTOHs, BFRs and cVMSs than occupational environments, whereas concentration of OPFRs in office samples were higher. BFRs concentrations were significantly correlated with building age and with the number of electronic/electrical devices at the sampling sites. Moreover, significantly lower levels of FTOHs and cVMSs were observed in rooms with forced-ventilation system. Estimated DED via inhalation was significantly higher at home than in office and the total DED was on average 3–5 orders of magnitude lower than the reference value.

Use of multiple lines of evidence to provide a realistic toxic substances control act ecological risk evaluation based on monitoring data: D4 case study

D4 (octamethylcyclotetrasiloxane) is a high-production-volume cyclic volatile methyl siloxane with a wide range of industrial and consumer applications. This study conducted a robust ecological risk evaluation for D4 using exposure data collected under a nation-wide environmental monitoring program facilitated under the Toxic Substances Control Act (TSCA). This ecological risk evaluation was conducted consistent with the principles outlined in the U.S. Environmental Protection Agency's (EPA's) Guidance to Assist Interested Persons in Developing and Submitting Draft Risk Evaluations under TSCA (U.S. EPA 2017a). The evaluation examined multiple lines of evidence (LoEs) to determine the potential risks from D4 to aquatic receptors in rivers and streams in the United States from municipal wastewater treatment plant (WWTP) discharges and discharges from manufacturing, processing, and/or formulating (MPF) facilities after onsite wastewater treatment. The LoEs consisted of comparing D4 concentrations measured in water and sediment to toxicity thresholds derived from laboratory studies; comparing D4 concentrations measured in biota tissue to critical target lipid body burdens (CTLBBs); comparing fugacity-based chemical activities between toxicity thresholds and measured environmental concentrations; and assessing benthic macroinvertebrate community structure and habitat suitability. The approach taken moves beyond a standard deterministic hazard quotient approach to incorporate more advanced methods for risk prediction, using distributions rather than conservative point estimates of exposure to obtain a realistic view of the probability of harm, consistent with EPA's stated intent to “strive to utilize probabilistic approaches for exposure assessments included in a risk evaluation” (U.S. EPA 2017b). The risk evaluation concluded there is negligible risk to water column and sediment receptors from D4 discharged from MPF facilities after onsite wastewater treatment or from municipal WWTPs that may treat a mix of industrial and consumer wastewater.

Diurnal Variability and Emission Pattern of Decamethylcyclopentasiloxane (D5) from the Application of Personal Care Products in Two North American Cities.

Decamethylcyclopentasiloxane (D5) is a cyclic volatile methyl siloxane (cVMS) that is widely used in consumer products and commonly observed in urban air. This study quantifies the ambient mixing ratios of D5 from ground sites in two North American cities (Boulder, CO, USA, and Toronto, ON, CA). From these data, we estimate the diurnal emission profile of D5 in Boulder, CO. Ambient mixing ratios were consistent with those measured at other urban locations; however, the diurnal pattern exhibited similarities with those of traffic-related compounds such as benzene. Mobile measurements and vehicle experiments demonstrate that emissions of D5 from personal care products are coincident in time and place with emissions of benzene from motor vehicles. During peak commuter times, the D5/benzene ratio (w/w) is in excess of 0.3, suggesting that the mass emission rate of D5 from personal care product usage is comparable to that of benzene due to traffic. The diurnal emission pattern of D5 is estimated using the measured D5/benzene ratio and inventory estimates of benzene emission rates in Boulder. The hourly D5 emission rate is observed to peak between 6:00 and 7:00 AM and subsequently follow an exponential decay with a time constant of 9.2 h. This profile could be used by models to constrain temporal emission patterns of personal care products.

Atmospheric concentrations and trends of poly- and perfluoroalkyl substances (PFAS) and volatile methyl siloxanes (VMS) over 7 years of sampling in the Global Atmospheric Passive Sampling (GAPS) network

Poly- and per-fluoroalkyl substances (PFAS) and volatile methyl siloxanes (VMS) were monitored at 21 sites in the Global Atmospheric Passive Sampling (GAPS) Network. Atmospheric concentrations previously reported from 2009 were compared to concentrations measured at these sites in 2013 and 2015, to assess trends over 7 years of monitoring. Concentrations of the fluorotelomer alcohols (FTOHs) and fluorinated sulfonamides and sulfonamidoethanols (FOSAs and FOSEs) were stable at these sites from 2009 to 2015 with no significant difference (p > 0.05) in concentrations. Elevated concentrations of all the neutral PFAS were detected at the urban sites as compared to the polar/background sites. The perfluorosulfonic acids (PFSAs), meanwhile, saw a significant increase (p < 0.001) in concentrations from 2009 to 2015. The perfluorocarboxylic acids (PFCAs) had elevated concentrations in 2015, however, the difference was not statistically significant (p > 0.05). Concentrations of the PFSAs and the PFCAs were similar at all location types, showing the global reach of these persistent compounds. Concentrations of the cyclic VMS (cVMS) were at least an order of magnitude higher than the linear VMS (lVMS) and the PFAS. Octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6) saw a weak significant increase in concentrations from 2009 to 2013 (p < 0.05), however, hexamethylcyclotrisiloxane (D3) had a strong significant decrease in concentrations from 2009 to 2015 (p < 0.01).

Cyclic volatile methylsiloxanes in sediment, soil, and surface water from Dongting Lake, China

Previous reports have shown that some cyclic volatile methylsiloxanes (cVMS) are characterized as persistent, toxic, and potentially harmful to ecology. In the present work, concentrations of three widely used cVMS, namely, octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) were investigated in surface water, sediment, and soil from Dongting Lake in China. Solid-liquid extraction and liquid-liquid extraction were used for solid and aqueous samples. Gas chromatography-mass spectrometry (GC-MS) was used to analyze cVMS concentrations in the samples. The relationship between total organic matter in the samples and cVMS concentrations was also measured. The total concentrations of cVMS ranged from 64.89 to 489.07 ng L−1, < LOD 163.00 ng g−1 dry weight (dw), and 26.63–996.95 ng g−1 dw in surface water, soil, and sediment, respectively. There was a significant correlation between cVMS concentrations and total organic carbon in the sediment samples, suggesting that sediment was the main source of cVMS in the lake area investigated. A very strong geographic gradient in concentrations of total cVMS was found in that sediments from samples collected downstream contained higher concentrations of cVMS than those from upstream. According to the concentrations measured in surface waters, sediments, and soils compared with the criterion for the maximum no observed effected concentrations (NOEC) and LC50 values, cVMS posed low environmental risks to aquatic, sediment-dwelling and terrestrial organisms.

A critical assessment of the environmental fate of linear and cyclic volatile methylsiloxanes using multimedia fugacity models.

We apply multimedia models to systematically evaluate the fate profile of cyclic volatile methyl siloxanes (VMS) D4, D5 and D6, and the linear VMS L4 and L5 using recently reported measurements of their partition ratios between organic carbon and water (KOC), their salting out constants (Ks), and their enthalpy of sorption to organic carbon (ΔHOC). Our assessment follows a multi-stage strategy where the environmental fate of the chemicals is explored in generic regional models with increasing fidelity to the real system and in a region-specific model. Modeled emissions of VMS to air remained in air and were degraded or advected out of the system with overall residence times ranging from 2.4 to 2.5 days, while emissions to water resulted in accumulation in sediment and longer residence times ranging from 29.5 to 1120 days. When emitted to water the modeled residence times of VMS in the sediment exceeded the REACH criterion for persistence in freshwater sediments. Reported KOC measurements for D5 differ by 1 log unit, which results in a 500-day difference in the overall residence times calculated in the generic regional modeling. In the specific-region modeling assessment for Adventfjorden, Svalbard in Norway, the different KOC measurements of D5 resulted in a 200-day difference in overall residence times. Model scenarios that examined combinations of previously published ΔHOC or enthalpy of phase change between octanol and water (ΔHOW) for D5 in combination with the range of the KOC measurements resulted in 1100-days difference in overall residence times. Our results demonstrate that residence times of VMS in aquatic systems are highly sensitive to their degree of sorption to organic carbon, and that residence times of VMS likely exceed several persistence criteria and therefore they cannot be considered as non-persistent.

Bioaccumulation and trophic transfer of cyclic volatile methylsiloxanes (cVMS) in the aquatic marine food webs of the Oslofjord, Norway

The trophic transfer of cyclic methylsiloxanes (cVMS) in aquatic ecosystems is an important criterion for assessing bioaccumulation and ecological risk. Bioaccumulation and trophic transfer of cVMS, specifically octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6), were evaluated for the marine food webs of the Inner and Outer Oslofjord, Norway. The sampled food webs included zooplankton, benthic macroinvertebrates, shellfish, and finfish species. Zooplankton, benthic macroinvertebrates, and shellfish occupied the lowest trophic levels (TL ≈2 to 3); northern shrimp (Pandalus borealis) and Atlantic herring (Clupea harengus) occupied the middle trophic levels (TL ≈3 to 4), and Atlantic cod (Gadus morhua) occupied the highest tropic level (TL>4.0). Trophic dynamics in the Oslofjord were best described as a compressed food web defined by demersal and pelagic components that were confounded by a diversity in prey organisms and feeding relationships. Lipid-normalized concentrations of D4, D5, and D6 were greatest in the lowest trophic levels and significantly decreased up the food web, with the lowest concentrations being observed in the highest trophic level species. Trophic magnification factors (TMF) for D4, D5, and D6 were <1.0 (range 0.3 to 0.9) and were consistent between the Inner and Outer Oslofjord, indicating that exposure did not impact TMF across the marine food web. There was no evidence to suggest biomagnification of cVMS in the Oslofjord. Rather, results indicated that trophic dilution of cVMS, not trophic magnification, occurred across the sampled food webs.

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.

Adsorptive performance of coal-based magnetic activated carbon for cyclic volatile methylsiloxanes from landfill leachate.

Bituminous coal-based magnetic activated carbon (MAC) was prepared, characterized, and used successfully for removal of cyclic volatile methylsiloxanes (cVMSs) from treated landfill leachate. Batch adsorption studies were performed at different adsorption dosages and contact times. With adsorptive dosage of 0.75g/L and contact time of 60min, the removal efficiencies achieved by MAC for octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) are 100, 82.8, and 71.4%, respectively. The specific magnetization coefficients of MAC before and after adsorption are 4.6×10-7 and 5.2×10-7m3/kg, between 1.26×10-7 and 3.8×10-5m3/kg, which suggests that MAC can be recycled by the high-intensity magnetic separators.

Benthic invertebrate exposure and chronic toxicity risk analysis for cyclic volatile methylsiloxanes: Comparison of hazard quotient and probabilistic risk assessment approaches

This study utilized probabilistic risk assessment techniques to compare field sediment concentrations of the cyclic volatile methylsiloxane (cVMS) materials octamethylcyclotetrasiloxane (D4, CAS # 556-67-2), decamethylcyclopentasiloxane (D5, CAS # 541-02-6), and dodecamethylcyclohexasiloxane (D6, CAS # 540-97-6) to effect levels for these compounds determined in laboratory chronic toxicity tests with benthic organisms. The concentration data for D4/D5/D6 in sediment were individually sorted and the 95th centile concentrations determined in sediment on an organic carbon (OC) fugacity basis. These concentrations were then compared to interpolated 5th centile benthic sediment no-observed effect concentration (NOEC) fugacity levels, calculated from a distribution of chronic D4/D5/D6 toxicologic assays per OECD guidelines using a variety of standard benthic species. The benthic invertebrate fugacity biota NOEC values were then compared to field-measured invertebrate biota fugacity levels to see if risk assessment evaluations were similar on a field sediment and field biota basis. No overlap was noted for D4 and D5 95th centile sediment and biota fugacity levels and their respective 5th centile benthic organism NOEC values. For D6, there was a small level of overlap at the exposure 95th centile sediment fugacity and the 5th centile benthic organism NOEC fugacity value; the sediment fugacities indicate that a negligible risk (1%) exists for benthic species exposed to D6. In contrast, there was no indication of risk when the field invertebrate exposure 95th centile biota fugacity and the 5th centile benthic organism NOEC fugacity values were compared.

Elucidating the Behavior of Cyclic Volatile Methylsiloxanes in a Subarctic Freshwater Food Web: A Modeled and Measured Approach

Cyclic volatile methylsiloxanes (cVMS) are used in personal care products and emitted to aquatic environments through wastewater effluents, and their bioaccumulation potential is debated. Here, a new bentho-pelagic version of the ACC-HUMAN model was evaluated for polychlorinated biphenyls (PCBs) and applied to cVMS in combination with measurements to explore their bioaccumulation behavior in a subarctic lake. Predictions agreed better with measured PCB concentrations in Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) when the benthic link was included than in the pelagic-only model. Measured concentrations of decamethylcyclopentasiloxane (D5) were 60 ± 1.2 (Chironomidae larvae), 107 ± 4.5 (pea clams Pisidium sp.), 131 ± 105 (three-spined sticklebacks: Gasterosteus aculeatus), 41 ± 38 (char), and 9.9 ± 5.9 (trout) ng g-1 wet weight. Concentrations were lower for octamethylcyclotetrasiloxane (D4) and dodecamethylcyclohexasiloxane (D6), and none of the cVMS displayed trophic magnification. Predicted cVMS concentrations were lower than measured in benthos, but agreed well with measurements in fish. cVMS removal through ventilation was an important predicted loss mechanism for the benthic-feeding fish. Predictions were highly sensitive to the partition coefficient between organic carbon and water (KOC) and its temperature dependence, as this controlled bioavailability for benthos (the main source of cVMS for fish).