Cyclic Volatile Methylsiloxanes Research Articles

Quantitative structure‐reactivity relationships of hydroxyl radical rate constants for linear and cyclic volatile methylsiloxanes

An accurate understanding of the fate of volatile methylsiloxanes (VMS) in air is crucial for determining their persistence and concentrations in the environment. Although oxidation by atmospheric hydroxyl radicals (•OH) is considered as a major degradation mechanism for airborne VMS, the existing bimolecular rate constants with •OH measured and modeled for any given VMS compound varied greatly, depending on the approaches used to generate the data. The objectives of the present study were to measure •OH reaction rate constants for 4 cyclic and 4 linear VMS based on a relative rate method using a newly designed atmospheric chamber and to establish structure-reactivity relationships for the kinetics. In the past, the reaction rate constants for VMS were generally recognized to increase with the number of the methyl groups per molecule, the only differential factor in the existing models. However, the new measurements indicated that molecular structure should also be considered in the prediction of the reaction rates. Better empirical models were developed by simple and multiple linear regressions of the measured values from the present study and the literature. A high correlation existed for the reaction rates with the number of the methyl group attached at 2 distinct siloxane structures (i.e., linear and cyclic VMS). Even better correlations were obtained with one or 2 molecular descriptors that are directly related to the size of VMS, which, in turn, not only depend on the number of methyl groups, but the linear/cyclic structures as well for permethylsiloxanes. Environ Toxicol Chem 2017;36:3240-3245. © 2017 SETAC.

Determination of cyclic volatile methylsiloxanes in personal care products by gas chromatography.

Organosiloxanes are prevalent in personal care products (PCPs) due to the desired properties they impart in the usage and application of such products. However, the European Chemical Agency (ECHA) has recently published restriction proposals on the amount of two cyclic siloxanes, octamethylcyclotetrasiloxane (D4) and decamethylcyclotetrasiloxane (D5), allowed in wash off products such as shampoos and conditioners which are discharged down the drain during consumer use. This legislation will require that reliable analytical methods are available for manufacturers and government agencies to use in documenting compliance with the restrictions. This article proposes a simple analytical method to enable accurate measurement of these compounds down to the circa 0.1 weight per cent level in PCPs. Although gas chromatography methods are reported in the literature for quantitation of D4 and D5 in several matrices including PCPs, the potential for generation of false positives due to contamination, co-elution and insitu generation of cyclic volatile methylsiloxanes (cVMS) is always present and needs to be controlled. This report demonstrates the applicability of using a combination of emulsion break, liquid-liquid extraction and silylation sample preparation followed by GC-FID analysis as a suitable means of analysing PCPs for specific cVMS. The reliability and limitations of such methodology were demonstrated through several round-robin studies conducted in the laboratories of a consortium of silicone manufacturers. In addition, this report presents examples of false positives encountered during development of the method and presents a comparative analysis between this method and a published QuEChERS sample preparation procedure to illustrate the potential for generation of false positives when an inappropriate approach is applied to determination of cVMS in personal care products. This report demonstrates that an approach to determine cVMS levels in personal care products is to perform an emulsion break on the sample, isolate the non-polar phase from the emulsion break and treat with a silylation reagent to abate potential insitu formation of cyclics during the course of GC-FID analysis. Round-robin studies conducted in laboratories representing multiple siloxane manufacturers demonstrated the reliability of the GC-FID method when measuring cVMS in PCPs down to circa 0.1%.

Comprehensive atmospheric modeling of reactive cyclic siloxanes and their oxidation products.

Cyclic volatile methyl siloxanes (cVMSs) are important components in personal care products that transport and react in the atmosphere. Octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6), and their gas-phase oxidation products have been incorporated into the Community Multiscale Air Quality (CMAQ) model. Gas-phase oxidation products, as the precursor to secondary organic aerosol from this compound class, were included to quantify the maximum potential for aerosol formation from gas-phase reactions with OH. Four 1-month periods were modeled to quantify typical concentrations, seasonal variability, spatial patterns, and vertical profiles. Typical model concentrations showed parent compounds were highly dependent on population density as cities had monthly averaged peak D5 concentrations up to 432ngm−3. Peak oxidized D5 concentrations were significantly less, up to 9ngm−3, and were located downwind of major urban areas. Model results were compared to available measurements and previous simulation results. Seasonal variation was analyzed and differences in seasonal influences were observed between urban and rural locations. Parent compound concentrations in urban and peri-urban locations were sensitive to transport factors, while parent compounds in rural areas and oxidized product concentrations were influenced by large-scale seasonal variability in OH.

Chronic toxicity and oncogenicity of octamethylcyclotetrasiloxane (D4) in the Fischer 344 rat

Octamethylcyclotetrasiloxane (D4) is a cyclic volatile methylsiloxane primarily used in the synthesis of silicon-based materials used in a variety of consumer products. This paper details the chronic toxicity and oncogenicity evaluation of D4 in the Fischer 344 rat. Animals were exposed to 0, 10, 30, 150, or 700ppm D4 vapor for 6h/day, 5days/week for up to 104 weeks in whole-body inhalation chambers. Effects of two year chronic exposure included increased liver, kidney, testes, and uterine weight with correlating microscopic findings of hepatocellular hypertrophy (males only), chronic nephropathy (both sexes), interstitial cell hyperplasia, and cystic endometrial hyperplasia and endometrial adenoma, respectively. Upper respiratory tract irritation and lymphocytic leukocytosis were evident in both sexes. Increased neoplasia was demonstrated only in the uterus. Uterine endometrial adenomas were present in four of sixty animals exposed to 700ppm D4 for 24 months. None were present in the other treatment groups. In contrast, in 700ppm D4 group males the incidence of pituitary and pancreatic neoplasia was reduced as was thyroid c-cell adenoma/carcinoma in 700ppm females. This study has identified that D4 is a mild respiratory irritant and increases liver and kidney weight without inducing neoplasia in these tissues. The increased incidence of uterine adenoma was the only treatment-related neoplastic finding associated with chronic exposure to D4.

Temperature Dependence of the Organic Carbon/Water Partition Ratios (KOC) of Volatile Methylsiloxanes

Knowing the temperature dependence of the organic carbon/water partition ratios (KOC) of volatile methylsiloxanes (VMS) is required to understand their environmental fate. We measured the KOC of two linear VMS (lVMS), three cyclic VMS (cVMS), and six polychlorinated biphenyls (PCBs) at 25, 15, 10, and 5 °C and calculated their enthalpies and entropies of sorption to organic carbon (ΔHOC and ΔSOC, respectively). The ΔHOC of VMS ranged from −79.2 to −45.8 kJ mol–1, while the ΔHOC of the PCBs ranged from −68.7 to −29.3 kJ mol–1. Previously reported measurements of the enthalpy of phase change between octanol and water (ΔHOW) for cVMS (11.3–68.8 kJ mol–1) differed substantially from our ΔHOC measurements, even showing different signs (negative versus positive). Literature data of ΔHOC and ΔHOW for PCBs (−61 to −17 kJ mol–1) are closer to our measured values of ΔHOC for the PCBs showing the same sign (negative) with differences within a factor of 2 in the majority of the cases. Comparison of all available data...

Metabolism and disposition of [14C]-methylcyclosiloxanes in rats

Octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) are low molecular weight cyclic volatile methyl siloxanes (cVMSs) primarily used as intermediates or monomers in the production of high molecular weight silicone polymers. The use of D4 as a direct ingredient in personal care products has declined significantly over the past 20 years, although it may be present as a residual impurity in a variety of consumer products. D5 is still used as an intentional ingredient in cosmetics, consumer products and in dry cleaning. Persons who may be exposed include occupational exposure for workers, and potential inhalation or dermal exposure for consumers and the general public. Because of the diverse use, especially of D5, and the potential for human exposure, a comprehensive program was undertaken to understand the kinetics, metabolism, enzyme induction and toxicity of D4 and D5 in rats following relevant routes of exposure. Physiologically based pharmacokinetic (PBPK) models utilizing these studies have been reported for D4 and D5 in the rat and human following dermal and inhalation exposures, with the oral uptake component of the model being limited in its description. Data from high dose oral studies in corn oil and simethicone vehicles and neat were used in the D4/D5 harmonized PBPK model development. It was uncertain if the inability to adequately describe the oral uptake was due to unrealistic high doses or unique aspects of the chemistry of D4/D5. Low dose studies were used to provide data to refine the description of oral uptake in the model by exploring the dose dependency and the impact of a more realistic food-like vehicle. Absorption, distribution, metabolism and elimination (ADME) of D4 and D5 was determined following a single low oral gavage dose of 14C-D4 and 14C-D5 at 30 and 100mg/kg body weight (bw), respectively, in a rodent liquid diet.Comparison of the low vs. high dose oral gavage administration of D4 and D5 demonstrated dose-dependent kinetic behavior. Data and modeling results suggest differences in metabolism between low and high dose administration indicating high dose administration results in or approaches non-linear saturated metabolism. These low dose data sets were used to refine the D4/D5 multi-route harmonized PBPK model to allow for a better description of the disposition and toxicokinetics of D4/D5 following oral exposure. With a refined oral uptake description, the model could be used in risk assessment to better define the internal dose of D4 and D5 following exposure to D4 and D5 via multiple routes.

Development of collection, storage and analysis procedures for the quantification of cyclic volatile methylsiloxanes in wastewater treatment plant effluent and influent

A reliable and accurate method for collection and analysis of octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) in wastewater treatment plant influent, effluent and surface waters was developed. Due to the use of cyclic volatile methylsiloxanes (cVMS) in industrial and consumer products including some personal care products, the wastewater stream represents a potential post-use disposal route and cVMS may subsequently enter the environment through wastewater treatment plant effluents. cVMS in the environment has come under increased regulatory scrutiny with regard to their potential for persistence, bioaccumulation and toxicity indicating a need for monitoring programs with reliable analytical methods. The developed method is unique in that it utilizes low density polyethylene (LDPE) to inhibit loss of cVMS during sampling and transport to the laboratory. The samples are then processed with a simple solvent extraction and analyzed by gas chromatography mass spectrometry with stable isotope internal standard calibration. This method utilizes readily available laboratory supplies and requires minimal field processing, reducing contamination potential. Method detection limits of 17 ng/L, 57 ng/L, and 20 ng/L were obtained for D4, D5, and D6, respectively. Additionally a robust quality control program was employed to ensure sample integrity. The method described herein can readily be adopted for use in monitoring studies where the amount of cVMS in water samples will be quantified.

Aerosol Formation from OH Oxidation of the Volatile Cyclic Methyl Siloxane (cVMS) Decamethylcyclopentasiloxane.

Aerosol formation from OH oxidation of decamethylcyclopentasiloxane (D5, C10H30O5Si5), a cyclic volatile methyl siloxane (cVMS) found in consumer products, was studied in a flow-through photo-oxidation chamber with and without the presence of ammonium sulfate seed aerosol. For the unseeded experiments, chemical characterization with high-performance mass spectrometry showed that the molecular composition changed substantially with aerosol mass loading in the 1-12 μg/m3 range. Monomers (5 Si atoms/molecule) and dimers (10 Si atoms/molecule) dominated the mass spectra of aerosols at higher mass loadings, while ring-opened species (neither 5 nor 10 Si atoms/molecule) dominated the mass spectra of aerosols at lower mass loadings. Molecular signal intensity dependencies upon the aerosol volume/surface area ratio suggest that non-volatile ring-opened species are formed in the gas phase and assist particle formation through condensation, while dimers are formed by accretion reactions within the particle phase as the particles grow. These conclusions are supported by experiments in the presence of seed aerosol with a similar siloxane aerosol mass loading but higher volume/surface area ratio, where ring-opened species are much less prevalent than monomers or dimers and the aerosol yield is higher. Because of the importance of accretion chemistry, the aerosol yield from D5 oxidation is likely to be strongly dependent upon the particle size and morphology.

Distribution characteristics of volatile methylsiloxanes in Tokyo Bay watershed in Japan: Analysis of surface waters by purge and trap method

Surface waters including river water and effluent from sewage treatment plants (STPs) were collected from Tokyo Bay watershed, Japan, and analyzed for seven cyclic and linear volatile methylsiloxanes (VMSs), i.e., D3, D4, D5, D6, L3, L4, and L5 by an optimized purge and trap extraction method. The total concentrations of seven VMSs (ΣVMS) in river water ranged from <4.9 to 1700ng/L (mean: 220ng/L). The individual mean concentrations of cyclic VMSs in surface waters were; 10ng/L for D3, 13ng/L for D4, 180ng/L for D5, and 18ng/L for D6. The concentrations of ΣVMS determined in STP effluents varied widely from 99 to 2500ng/L and the individual mean concentrations were 21ng/L for D3, 27ng/L for D4, 540ng/L for D5, and 45ng/L for D6. D5, which is widely used in personal-care products, was found to be the most abundant compound in both river water and STP effluent. Linear VMSs were detected at much lower frequency and concentrations than those of cyclic VMSs. The measured concentrations of D4 were below the no-observed effect concentration (NOEC). The annual emission of ΣVMS through STPs into Tokyo Bay watershed was estimated at 2300kg. Our results indicate widespread distribution of VMSs in Tokyo Bay watershed and the influence of domestic wastewater discharges as a source of VMSs in the aquatic environment.

Volatile methyl siloxanes (VMS) concentrations in outdoor air of several Catalan urban areas

Volatile methyl siloxanes (VMS) were evaluated in ten Catalan urban areas with different industrial impacts, such as petrochemical industry, electrical and mechanical equipment, metallurgical and chemical industries, municipal solid waste treatment plant and cement and food industries, during 2013–2015. 24 h samples were taken with LCMA-UPC pump samplers specially designed in our laboratory, with a flow range of 70 ml min−1. A sorbent-based sampling method, successfully developed to collect a wide-range of VOC, was used. The analysis was performed by automatic thermal desorption coupled with capillary gas chromatography/mass spectrometry detector. The presented methodology allows the evaluation of VMS together with a wide range of other VOC, increasing the number of compounds that can be determined in outdoor air quality assessment of urban areas. This aspect is especially relevant as a restriction of several VMS (D4 and D5) in consumer products has been made by the European Chemicals Agency and US EPA is evaluating to include D4 in the Toxic Substances Control Act, regarding the concern of the possible effects of these compounds in human health and the environment. ΣVMS concentrations (L2-L5, D3-D6 and trimethylsilanol) varied between 0.3 ± 0.2 μg m−3 and 18 ± 12 μg m−3, determined in a hotspot area. Observed VMS concentrations were generally of the same order of magnitude than the previously determined in Barcelona, Chicago and Zurich urban areas, but higher than the published from suburban sites and Arctic locations. Cyclic siloxanes concentrations were up to two-three orders of magnitude higher than those of linear siloxanes, accounting for average contributions to the total concentrations of 97 ± 6% for all samples except for the hotspot area, where cyclic VMS accounted for 99.9 ± 0.1%. D5 was the most abundant siloxane in 5 sampling points; however, differing from the generally observed in previous studies, D3 was the most abundant compound in the other 5 sampling points.

Understanding of Cyclic Volatile Methyl Siloxane Fate in a High Latitude Lake Is Constrained by Uncertainty in Organic Carbon-Water Partitioning.

Cyclic volatile methyl siloxanes (cVMS) are emitted to aquatic environments with wastewater effluents. Here, we evaluate the environmental behavior of three cVMS compounds (octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6)) in a high latitude lake (Storvannet, 70°N 23°E), experiencing intermittent wastewater emissions and high latitude environmental conditions (low temperatures and seasonal ice cover). Measured cVMS concentrations in lake water were below detection limits in both March and June 2014. However, mean concentrations in sediments were 207 ± 30, 3775 ± 973 and 848 ± 211 ng g-1 organic carbon for D4, D5 and D6, respectively. To rationalize measurements, a fugacity-based model for lakes (QWASI) was parametrized for Storvannet. The key removal process for cVMS from the lake was predicted to be advection due to the low hydraulic retention time of the lake, followed by volatilization. Predicted cVMS behavior was highly sensitive to the partition coefficient between organic carbon and water (KOC) and its temperature dependence. Predictions indicated lower overall persistence with decreasing temperature due to enhanced partitioning from sediments to water. Inverse modeling to predict steady-state emissions from cVMS concentrations in sediment provided unrealistically high emissions, when evaluated against measured concentrations in sewage. However, high concentrations of cVMS in sediment and low concentrations in water could be explained via a hypothetical dynamic emission scenario consistent with combined sewer overflows. The study illustrates the importance of considering compound-specific behavior of emerging contaminants that may differ from legacy organic contaminants.

An approach to the environmental prioritisation of volatile methylsiloxanes in several matrices.

Siloxane-based compounds are widely used in personal care, pharmaceutical and household products as well as in industrial applications. Among the wide variety of these chemicals, special attention has been given to volatile methylsiloxanes (VMSs). These compounds have been extensively detected in several environmental compartments, as they are not effectively removed from wastewater and may migrate through different matrices and being lipophilic, bioaccumulate and biomagnify in living organisms. In this work, a prioritisation methodology for several VMSs in different environmental matrices was applied, estimating a hazard quotient by combining exposure evaluation through measured or predicted environmental concentrations (MEC or PEC) and effects using ecotoxicity data to establish no effect concentrations (PNEC). VMSs show quite different hazard potentials in the environment: for linear VMSs it is not considerable, while for cyclic VMSs the hazard is disperse. D4 and D5 may have adverse effects in water, as well as D5 and D6 in sediments. This first multi-matrix approach for the prioritisation of VMSs sets the ground for more accurate studies in the future, provided that more field-based data are reported.

Trophic dilution of cyclic volatile methylsiloxanes (cVMS) in the pelagic marine food web of Tokyo Bay, Japan

Bioaccumulation and trophic transfer of cyclic volatile methylsiloxanes (cVMS), specifically octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6), were evaluated in the pelagic marine food web of Tokyo Bay, Japan. Polychlorinated biphenyl (PCB) congeners that are “legacy” chemicals known to bioaccumulate in aquatic organisms and biomagnify across aquatic food webs were used as a benchmark chemical (CB-180) to calibrate the sampled food web and as a reference chemical (CB-153) to validate the results. Trophic magnification factors (TMFs) were calculated from slopes of ordinary least-squares (OLS) regression models and slopes of bootstrap regression models, which were used as robust alternatives to the OLS models. Various regression models were developed that incorporated benchmarking to control bias associated with experimental design, food web dynamics, and trophic level structure. There was no evidence from any of the regression models to suggest biomagnification of cVMS in Tokyo Bay. Rather, the regression models indicated that trophic dilution of cVMS, not trophic magnification, occurred across the sampled food web. Comparison of results for Tokyo Bay to results from other studies indicated that bioaccumulation of cVMS was not related to type of food web (pelagic vs demersal), environment (marine vs freshwater), species composition, or location. Rather, results suggested that differences between study areas was likely related to food web dynamics and variable conditions of exposure resulting from non-uniform patterns of organism movement across spatial concentration gradients.

Removal of cyclic volatile methylsiloxanes in effluents from treated landfill leachate by electrochemical oxidation

An electrochemical oxidation reactor was used for advanced treatment of cyclic volatile methylsiloxanes using stainless steel plates as anode and cathode electrode. Several key factors were studied to optimize the electrochemical oxidation process. During the electrochemical oxidation process, the removal efficiencies of D5 (decamethylcyclopentasiloxane) increased with the reaction time and applied current densities. At the optimal operating parameters including plate distance of 1.0 cm, electrode plate amounts of 4 pairs, current density of 20 mA/cm2 and reaction time of 30 min, the removal efficiencies of D4 (octamethylcyclotetrasiloxane), D5 (decamethylcyclopentasiloxane), and D6 (dodecamethylcyclohexasiloxane) can reach 100, 82.1, and 72.5 %, respectively.

Assessing the Aquatic Risks of the Cyclic Volatile Methyl Siloxane D4

Assessing the ecological risks of the widely used cyclic volatile methyl siloxane D4 (octamethylcyclotetrasiloxane, CAS Registry Number 556-67-2) to aquatic systems is difficult because of its high volatility and low water solubility, but the potential for long distance atmospheric transport and persistence in the sediments has placed D4 under intense regulatory scrutiny. This paper explores the difficulties inherent in determining the toxicity of D4 to aquatic species and reveals the increased sensitivity of aquatic species tested within artificially closed systems compared to that of similar tests conducted in open systems that allow natural volatilization to occur. The concepts of narcosis mode of action and chemical activity explain the apparent lack of toxicity of D4 to aquatic species under environmentally realistic conditions. Discharge levels for the past 30 years during which D4 has been in use have produced field-measured concentrations that pose negligible risk to aquatic organisms.

Determination of linear and cyclic volatile methylsiloxanes in blood of turtles, cormorants, and seals from Canada

We measured the concentrations of linear and cyclic volatile methylsiloxanes (VMS) concentrations in the blood plasma of turtles, cormorants, and seals collected from Canadian freshwater and marine ecosystems. A modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) method was developed to quantify the levels of linear and cyclic VMS in the plasma samples. The cyclic VMS of hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) were present in the plasma of all three species. Linear VMS compounds were observed only in seal plasma from one contaminated site. There was no statistically significant difference among species and locations for D3, D4, and D6 concentrations. Average D5 concentrations ranged from 0.143 to 7.39ngg−1; these concentrations appeared to be associated with diffuse/urban sources. Snapping turtles, cormorants, and seals all exhibited elevated D5 concentrations in contaminated sites relative to the reference sites. Our data indicate that local urban sources of VMS contributed significantly to the observed D5 concentrations in free-ranging wildlife. The presence of cyclic VMS in the plasma of the three species from Canada demonstrates that these chemicals are ubiquitous in aquatic biological systems. This finding raises concerns regarding their persistence in freshwater and marine environments. To the best of our knowledge, this study reports the first measurements of VMS compounds in the plasma of reptiles, birds, and mammals.

Exposure to cyclic volatile methylsiloxanes (cVMS) causes anchorage-independent growth and reduction of BRCA1 in non-transformed human breast epithelial cells.

Dermal absorption of components of personal care products (PCPs) may contribute to breast cancer development. Cyclic volatile methylsiloxanes (cVMS) are used widely in the formulation of PCPs, and their presence has been recently detected in human blood. The objectives of this study were to investigate any genotoxic effects after short- (1 week) or longer-term (30 weeks) exposure to hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4) or decamethylcyclopentasiloxane (D5) in MCF-10 A and MCF-10F immortalized non-transformed human breast epithelial cells. Genotoxic effects were assessed by an ability of cells to grow in suspension culture, from DNA damage measured by comet assays, and from a reduction in levels of DNA repair proteins measured by RT-PCR and western immunoblotting. Dose-dependent anchorage-independent growth in methocel culture was observed after exposure to D3 (10-13 M-10-5 M) and D4/D5 (10-9 M-10-5 M). DNA damage was measured by the comet assay after 1-h exposure to D3 (10-6 M-10-5 M) and D4 (10-5 M). BRCA1 mRNA and BRCA1 protein levels were reduced after 30-week exposure to 10-5 M D4 and D5 in both cell lines. Reduced levels of mRNAs for other DNA repair proteins (BRCA2, ATM, ATR, CHK1 and CHK2) were also observed after exposure to 10-5 M D5 in both cell lines, and some reductions after exposure to D3 and D4. If cVMS can not only enable anchorage-independent growth of non-transformed breast epithelial cells and damage DNA, but also compromise DNA repair systems, then there is the potential for them to impact on breast carcinogenesis. Further risk assessment now requires information concerning the extent to which cVMS may be present in human breast tissues. Copyright © 2016 John Wiley & Sons, Ltd.

Measurement of volatile organic compounds (VOCs) in libraries and archives in Florence (Italy)

Indoor air samples from libraries and archives in Florence, Italy, were collected and analysed for a variety of volatile organic compounds. The aim was to perform a characterisation of the indoor air quality, and try to elucidate if there are VOCs that may cause or result from the determination of the cultural heritage institutions.All compounds of interest were regularly detected, with BTEXs (Benzene, Toluene, Ethylbenzene, Xylenes) being the most abundant and followed by cyclic volatile methylsiloxanes, aldehydes, terpenes and organic acids. The prevalence and qualitative characteristics, such as concentrations, profiles and indoor/outdoor ratios of BTEXs underline the important influence of the outdoor air infiltrations on the indoor air concentrations. Acetic acid that is a substance that can oxidise books and other exposed objects was detected at concentrations ranging between 1.04 and 18.9μgm−3, while furfural, that is a known marker of paper degradation, was constantly present at concentrations that ranged between 5.26 and 32.6μgm−3.This work shows the importance that indoor air quality monitoring campaigns can have in order to give early warning to cultural heritage institution managers about the impact that indoor air quality can have on exposed and/or preserved objects.

Emission of poly and perfluoroalkyl substances, UV-filters and siloxanes to air from wastewater treatment plants

The potential of wastewater treatment plants (WWTPs) to act as sources of poly and perfluoroalkyl substances (PFASs), volatile methyl siloxanes (VMSs) and organic UV-filters to the atmosphere was investigated. Target compounds included: PFASs (fluorotelomer alcohols (FTOHs), perfluorooctane sulfonamides/sulfonamidoethanols (FOSAs/FOSEs), perfluroalkyl sulfonic acids (PFSAs) and perfluroalkyl carboxylic acids (PFCAs)), cyclic VMSs (D3 to D6), linear VMSs (L3 to L5) and eight UV-filters. Emissions to air were assessed at eight WWTPs using paired sorbent-impregnated polyurethane foam passive air samplers, deployed during summer 2013 and winter 2014. Samplers were deployed on-site above the active tank and off-site as a reference. Several types of WWTPs were investigated: secondary activated sludge in urban areas (UR-AS), secondary extended aeration in towns (TW-EA) and facultative lagoons in rural areas (RU-LG). The concentrations of target compounds in air were ∼1.7–35 times higher on-site compared to the corresponding off-site location. Highest concentrations in air were observed at UR-AS sites while the lowest were at RU-LG. Higher air concentrations (∼2–9 times) were observed on-site during summer compared to winter, possibly reflecting enhanced volatilization due to higher wastewater temperatures or differences in influent wastewater concentrations. A significant positive correlation was obtained between concentrations in air and WWTP characteristics (influent flow rate and population in the catchment of the WWTP); whereas a weak negative correlation was obtained with hydraulic retention time. Emissions to air were estimated using a simplified dispersion model. Highest emissions to air were seen at the UR-AS locations. Emissions to air (g/year/tank) were highest for VMSs (5000–112,000) followed by UV-filters (16–2000) then ΣPFASs (10–110).

Evaluating the Salting-Out Effect on the Organic Carbon/Water Partition Ratios (KOC and KDOC) of Linear and Cyclic Volatile Methylsiloxanes: Measurements and Polyparameter Linear Free Energy Relationships

Dissolved inorganic salts influence the partitioning of organic chemicals between water and sorbents. We present new measurements of the salting-out constants (Ks) for partition ratios between water and organic carbon (KOC) and between water and dissolved organic carbon (KDOC) of three cyclic volatile methylsiloxanes (cVMS), two linear volatile methylsiloxanes (lVMS), three polychlorinated biphenyls (PCBs), and α-hexachlorocyclohexane (α-HCH). Ks, KOC, and KDOC were derived from volatilization rates of the chemicals from mixtures of water and organic carbon with varying concentrations of sodium chloride in a purge-and-trap system. KOC and KDOC values at different salinities were determined by fitting their values to reproduce observed volatilization rates using a fugacity-based multimedia model and assuming first-order kinetics for volatilization. The Ks values of cVMS and lVMS ranged from 0.16–0.76. The log KOC of cVMS and lVMS in fresh water interpolated from our measurements ranged from 5.20 to 7.36 an...