Degradation of polydimethylsiloxane fluids in the environment--a review

Lifetime-configurable soft robots via photodegradable silicone elastomer composites

Developing soft robots that can control their own life cycle and degrade on-demand while maintaining hyperelasticity is a notable research challenge. On-demand degradable soft robots, which conserve their original functionality during operation and rapidly degrade under specific external stimulation, present the opportunity to self-direct the disappearance of temporary robots. This study proposes soft robots and materials that exhibit excellent mechanical stretchability and can degrade under ultraviolet light by mixing a fluoride-generating diphenyliodonium hexafluorophosphate with a silicone resin. Spectroscopic analysis revealed the mechanism of Si─O─Si backbone cleavage using fluoride ion (F-) and thermal analysis indicated accelerated decomposition at elevated temperatures. In addition, we demonstrated a robotics application by fabricating electronics integrated gaiting robot and a fully closed-loop trigger disintegration robot for autonomous, application-oriented functionalities. This study provides a simple yet novel strategy for designing life cycle mimicking soft robotics that can be applied to reduce soft robotics waste, explore hazardous areas, and ensure hardware security with on-demand destructive material platforms.

United atom and coarse grained models for crosslinked polydimethylsiloxane with applications to the rheology of silicone fluids

Siloxane systems consisting primarily of polydimethylsiloxane (PDMS) are versatile, multifaceted materials that play a key role in diverse applications. However, open questions exist regarding the correlation between their varied atomic-level properties and observed macroscale features. To this effect, we have created a systematic workflow to determine coarse-grained simulation models for crosslinked PDMS in order to further elucidate the effects of network changes on the system's rheological properties below the gel point. Our approach leverages a fine-grained united atom model for linear PDMS, which we extend to include crosslinking terms, and applies iterative Boltzmann inversion to obtain a coarse-grain "bead-spring-type" model. We then perform extensive molecular dynamics simulations to explore the effect of crosslinking on the rheology of silicone fluids, where we compute systematic increases in both density and shear viscosity that compare favorably to experiments that we conduct here. The kinematic viscosity of partially crosslinked fluids follows an empirical linear relationship that is surprisingly consistent with Rouse theory, which was originally derived for systems comprised of a uniform distribution of linear chains. The models developed here serve to enable quantitative bottom-up predictions for curing- and age-induced effects on macroscale rheological properties, allowing for accurate prediction of material properties based on fundamental chemical data.

High-temperature decomposition chemistry of trimethylsiloxane surfactants, a potential Fluorine-Free replacement for fire suppression

Per- and polyfluoroalkyl substances (PFAS) have become global environmental contaminants due to being notoriously difficult to degrade, and it has become increasingly important to employ suitable PFAS alternatives, especially in aqueous film-forming foams (AFFF). Trimethylsiloxane (TriSil) surfactants are potential fluorine-free replacements for PFAS in fire suppression technologies. Yet because these compounds may be more susceptible to high-temperature decomposition, it is necessary to assess the potential environmental impact of their thermal degradation products. Our study analyzes the high-temperature degradation of a truncated trimethylsiloxane (TriSil-1n) surfactant based on quantum mechanical methods. The degradation chemistry of TriSil-1n was studied through radical formation and propagation initiated from two prominent pathways (unimolecular and bimolecular reactions) at both 298 K and 1200 K, a relevant temperature in flames and thermal incinerators. Regardless of the pathway taken and temperature, all radical intermediates stemmed from the polyethylene glycol chain and primarily formed stable polydimethylsiloxanes (PDMS) and small organics such as ethylene, formaldehyde, and acetaldehyde, among other products. The major degradation products of TriSil-1n resulting from high-temperature thermal degradation as predicted by this study would be relatively less harmful to the environment compared to PFAS incineration/combustion products from previous research, supporting the replacement of PFAS with TriSil surfactants.

Chemical Recycling of High-Molecular-Weight Organosilicon Compounds in Supercritical Fluids

The main known patterns of thermal and/or catalytic destruction of high-molecular-weight organosilicon compounds are considered from the viewpoint of the prospects for processing their wastes. The advantages of using supercritical fluids in plastic recycling are outlined. They are related to a high diffusion rate, efficient extraction of degradation products, the dependence of solvent properties on pressure and temperature, etc. A promising area for further research is described concerning the application of supercritical fluids for processing the wastes of organosilicon macromolecular compounds.

Integrating Microfluidics and Electronics in Point-of-Care Diagnostics: Current and Future Challenges

Point-of-Care (POC) diagnostics have gained increasing attention in recent years due to its numerous advantages over conventional diagnostic approaches. As proven during the recent COVID-19 pandemic, the rapidity and portability of POC testing improves the efficiency of healthcare services and reduces the burden on healthcare providers. There are hundreds of thousands of different applications for POC diagnostics, however, the ultimate requirement for the test is the same: sample-in and result-out. Many technologies have been implemented, such as microfluidics, semiconductors, and nanostructure, to achieve this end. The development of even more powerful POC systems was also enabled by merging multiple technologies into the same system. One successful example is the integration of microfluidics and electronics in POC diagnostics, which has simplified the sample handling process, reduced sample usage, and reduced the cost of the test. This review will analyze the current development of the POC diagnostic systems with the integration of microfluidics and electronics and discuss the future challenges and perspectives that researchers might have.

Vinylmethylsiloxanes in Municipal Wastewater Treatment Plant and Biosolid-Amended Soils: Their Distribution and Backbone/Vinyl Branch Degradation

This study is the first to investigate the emission and environmental fate of one type of modified methylsiloxane with double-bond (vinyl) groups. During 2018-2020, 2,4,6-trimethyl-2,4,6-trivinylcyclotrisiloxane (V3), 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4), and 2,4,6,8,10-pentavinyl-2,4,6,8,10-pentamethylcyclopentasiloxane (V5) were found in aqueous (<LOD-72.9 ng/L) and solid [13.0-371 ng/g dw (dry weight)] phases of wastewater samples from one Chinese municipal wastewater treatment plant (WWTP) as well as the corresponding biosolid-amended soils [<LOD-36.9 ng/g dw, df (detection frequency) = 37.5-41.7%, n = 48]. Based on the measure of environmental samples, simulated experiment, and product analysis by ESI-FT-ICR-MS, it was found that (1) in addition to sorption to sludge, abiotic degradation of vinylmethylsiloxanes (especially V3, t_1/2 = 0.5-1.9 h at pH = 5.2-9.2) should have an important contribution to their sufficient removal in WWTP; (2) different from siloxane analogues with saturated branches and aromatic branches, abiotic degradation pathways of vinylmethylsiloxane might include both the hydrolysis of Si-O backbone and the oxidation/addition reactions of vinyl branches; (3) although vinylmethylsiloxanes in wastewater could be transferred to soil by biosolids application, these compounds had no accumulation in soil, which should arise from their fast elimination, such as volatilization (t_1/2 = 3.2 h-20.9 days) and degradation (t_1/2 =9.1 h-96.3 days); and (4) degradation of the Si-O backbone and vinyl branches had slowing trends with the increase in the soil organic matter.

On the mechanism of marine fouling-prevention performance of oil-containing silicone elastomers

For many decades, silicone elastomers with oil incorporated have served as fouling-release coating for marine applications. In a comprehensive study involving a series of laboratory-based marine fouling assays and extensive global field studies of up to 2-year duration, we compare polydimethylsiloxane (PDMS) coatings of the same composition loaded with oil via two different methods. One method used a traditional, one-pot pre-cure oil addition approach (o-PDMS) and another method used a newer post-cure infusion approach (i-PDMS). The latter displays a substantial improvement in biofouling prevention performance that exceeds established commercial silicone-based fouling-release coating standards. We interpret the differences in performance between one-pot and infused PDMS by developing a mechanistic model based on the Flory–Rehner theory of swollen polymer networks. Using this model, we propose that the chemical potential of the incorporated oil is a key consideration for the design of future fouling-release coatings, as the improved performance is driven by the formation and stabilization of an anti-adhesion oil overlayer on the polymer surface.

Polymer degradation through chemical change: a quantum-based test of inferred reactions in irradiated polydimethylsiloxane

Chemical reaction schemes are key conceptual tools for interpreting the results of experiments and simulations, but often carry implicit assumptions that remain largely unverified for complicated systems. Established schemes for chemical damage through crosslinking in irradiated silicone polymers comprised of polydimethylsiloxane (PDMS) date to the 1950's and correlate small-molecule off-gassing with specific crosslink features. In this regard, we use a somewhat reductionist model to develop a general conditional probability and correlation analysis approach that tests these types of causal connections between proposed experimental observables to reexamine this chemistry through quantum-based molecular dynamics (QMD) simulations. Analysis of the QMD simulations suggests that the established reaction schemes are qualitatively reasonable, but lack strong causal connections under a broad set of conditions that would enable making direct quantitative connections between off-gassing and crosslinking. Further assessment of the QMD data uncovers a strong (but nonideal) quantitative connection between exceptionally hard-to-measure chain scission events and the formation of silanol (Si-OH) groups. Our analysis indicates that conventional notions of radiation damage to PDMS should be further qualified and not necessarily used ad hoc. In addition, our efforts enable independent quantum-based tests that can inform confidence in assumed connections between experimental observables without the burden of fully elucidating entire reaction networks.

Methylsiloxanes in street dust from Hefei, China: Distribution, sources, and human exposure

Methylsiloxanes are widely found in the environment and have been of increasing concern because of their strong resistance to degradation and potential toxicity to organisms. However, little is known about the distributions of these chemicals in street dust and the associated human health risks. This study investigated three cyclic (D₄-D₆) and nine linear methylsiloxanes (L₅-L₁₃) in street dust from Hefei, China and found total concentrations in the range of 183-1030 (median, 527) ng/g dry weight. The linear congeners were dominant and represented a median of 85.3% of the total methylsiloxanes. D₅ contributed 90.0% of the total concentrations of cyclic methylsiloxanes. In this study, higher concentrations of dust methylsiloxanes were found in the industrial area relative to the other functional areas. A source assessment indicated that the linear and cyclic methylsiloxanes in the street dust were mainly from the industrial and traffic activities, respectively, in addition to important sources of the use of siloxanes-containing products. The estimated median daily intakes of total methylsiloxanes through street dust were 0.037 and 0.476 ng/kg-bw/d for adults and children, respectively, under high-exposure scenarios. More research is needed to characterize the occurrence of methylsiloxane in various exposure sources and the associated adverse effects on human health.

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

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

Methyl siloxanes in road dust from a large silicone manufacturing site in China: implications of human exposure

Methyl siloxanes are becoming increasingly prevalent in the environment because of their extensive use in various consumer products. Little is known about the distribution of these chemicals around factories or their presence in road dust. We conducted a survey of four cyclic (D₃-D₆) and 13 linear (L₄-L₁₆) siloxanes in road dusts around a manufacturing site and found a total siloxane concentration range of 47.3-3.16 × 10³ ng/g (median 372). The predominant siloxanes in the road dust samples were D₃, D₄, D₅, and D₆, with median contributions of 65.3%, 17.9%, 6.36%, and 2.16% of the total siloxane concentrations, respectively. Our reported concentrations were comparable to those found in household dusts in previous studies. No high concentrations of siloxanes were observed in the road dust samples from the manufacturing site, which suggests that siloxanes in outdoor dusts are likely affected by many factors. Under a high exposure scenario, the daily intakes of total siloxanes via road dust ingestion at the 95th percentile were 2.13 and 0.313 ng/kg-bw/day for children and adults, respectively. Although the estimated exposure to siloxanes in outdoor dust for humans was low, more studies on the distributions and risks of siloxanes released from manufacturing sites are needed.

Methylsiloxanes and Their Brominated Products in One e-Waste Recycling Area in China: Emission, Environmental Distribution, and Elimination

The present study investigated the sources and fates of methylsiloxanes and their brominated products in one e-waste recycling area of China. During thermal (30-1000 °C) recycling experiments for printed wiring boards (PWBs), besides volatile methylsiloxanes (D4, D5, and D6), their monobrominated products, that is, D3D(CH₂Br), D4D(CH₂Br), and D5D(CH₂Br), were also found by quadrupole time-of-flight gas chromatography-mass spectrometry to have 2-3 orders of magnitude lower emissions (0.31-1.3 μg/g) than those (18.1-866 μg/g) of parent methylsiloxanes. Overall, the fastest emissions of methylsiloxanes and bromo-methylsiloxanes occurred at 300-400 and 400-500 °C, respectively, accounting for 35.3-51.0 and 39.4-82.1% of their total emission. In the e-waste recycling area, concentrations of D4-D6 were 1.1-75.0 μg/g dw [detection frequency (df) = 100%] in 31 dusts from PWB treatment workshops, while limits of detection (LOD) < 683 ng/g dw (df = 69-100%) in 48 surrounding soils were up to 3 orders of magnitudes higher than those in reference areas. Meanwhile, D3D(CH₂Br)-D5D(CH₂Br) were detected in both dusts (<LOD-1.2 μg/g dw, df = 48-52%) and soils (<LOD-70.3 ng/g dw, df = 23-77%) from the e-waste recycling area, but they were not present in reference samples. Simulating experiments showed that hydrolysis (9.07-378 d) and volatilization (8.55-1007 d) half-lives of monobrominated D4-D6 in soils were 1.6-5.0 times longer than those of their parent methylsiloxanes.

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).

A review on removal of siloxanes from biogas: with a special focus on volatile methylsiloxanes

The occurrence of siloxanes is a major barrier to use of biogas as renewable energy source, and removal of siloxanes from biogas before combustion is needed. The siloxane can be transformed into silicon dioxide (SiO₂) through the combustion process in engine, which will be deposited on the spark plug, cylinder, and impeller to form the silica layer, causing the wear and damage of the engine parts, and shorten the life of the engine and affect the utilization efficiency of the biogas. This paper reviewed some methods and technologies for siloxanes removal from biogas. There are three commercial available technologies to remove siloxanes: adsorption, absorption, and cryocondensation. Other newer technologies with better prospects for development also have made a research progress, including membrane, catalysts, biotrickling filters. This work introduces the source and characterization of siloxanes in biogas, reviews the scientific progress of siloxanes removal, and discusses the development direction and further research of removal siloxanes.

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.

Concentration/time-dependent dissipation, partitioning and plant accumulation of hazardous current-used pesticides and 2-hydroxyatrazine in sand and soil

The dissipation, partitioning dynamics and biouptake was measured for selected hazardous current-used pesticides (conazole fungicides: epoxiconazole, flusilazole, tebuconazole; prochloraz, chlorpyrifos, pendimethalin) and for a transformation product (2-hydroxyatrazine) in agricultural soil and quartz sand as representatives of a real and a worst-case scenario. Dissipation, uptake to Lactuca sativa and the freely dissolved concentration along with the organic carbon-normalized sorption coefficients (Koc) were determined on days 12, 40, and 90 following the application of compounds at three fortification levels (0.1-1.0-10 mg/kg). Conazole fungicides showed similar dissipation patterns and were more persistent in soil than prochloraz, chlorpyrifos and pendimethalin. 2-Hydroxyatrazine showed a concentration-depended decrease in persistency in soil. Lettuce roots were shown to accumulate higher amounts than shoots where the extent of root uptake was driven by compound partitioning. This was evidenced by the ability of freely dissolved concentration (Cfree) to reliably (r2 = 0.94) predict root uptake. Concentration in leaves did not exceed the maximum residue levels (MRLs) for lettuce, which was likely given by the low root-to-shoot translocation factors (TFs) of the tested compounds varying between 0.007 and 0.14. Koc values were in the range of literature values. Sorption to soil was higher than to sand for all compounds, yet following the Koc dynamics compounds did not appear to be sequestered in soil with increasing residence time. From these results, it follows that the tested compounds may persist in soil but since they did not accumulate in lettuce above MRLs, contamination of the food web is unlikely.

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.

Reaction kinetics and mechanisms of organosilicon fungicide flusilazole with sulfate and hydroxyl radicals

Flusilazole is an organosilane fungicide used for treatments in agriculture and horticulture for control of diseases. The reaction kinetics and mechanism of flusilazole with sulfate and hydroxyl radicals were studied. The rate constant of the radicals with the fungicide were determined by laser flash photolysis of peroxodisulfate and hydrogen peroxide. The results were 2.0 × 10⁹ s^-1M^-1 for the reaction of the fungicide with HO and 4.6 × 10⁸ s^-1 M^-1 for the same reaction with SO₄^- radicals. The absorption spectra of organic intermediates detected by laser flash photolysis of S₂O₈^2- with flusilazole, were identified as α-aminoalkyl and siloxyl radicals and agree very well with those estimated employing the time-dependent density functional theory with explicit account for bulk solvent effects. In the continuous photolysis experiments, performed by photo-Fenton reaction of the fungicide, the main degradation products were: (bis(4-fluorophenyl)-hydroxy-methylsilane) and the non-toxic silicic acid, diethyl bis(trimethylsilyl) ester, in ten and twenty minutes of reaction, respectively.

Physical influence on larvicidal and pupicidal activity of the silicone-based monomolecular film

Although silicone-based monomolecular film (MMF) has been accepted as larvicide in several countries, its mosquito control potential has never been investigated in Thailand. Laboratory assessment in this study was conducted to determine the MMF efficacy against Aedes aegypti. At the recommended dosage (1mL/m(2) of water surface), mortality of pupae (99.17±0.83%) was significantly greater than mortality of old and young larvae (73.33±9.13, 11.67±3.47%; respectively). Pupicidal activity was rapidly exhibited within hours while larvicidal activity took at least one day. Interestingly, among the survived mosquitoes after MMF exposure, larval length (3.6±0.18mm), pupation (0%) and adult emergence (0%) were significantly less than the control group. Gravid females also avoided laying eggs in MMF-treated oviposition cups. There was no influence of physical factors on MMF efficacy and no toxic effects on fish and plants. These results indicated the MMF is promising to provide not only larvicidal and pupicidal activity but also inhibition of larval development as indicated by both larval length and stage transformation.

Volatile dimethylsiloxanes in market seafood and freshwater fish from the Xúquer River, Spain

Volatile dimethylsiloxanes are a family of synthetic organosilicon-compounds, which have received rising attention because of their widespread use and occurrence in the environment. In the present work, an analytical method based on ultrasound-assisted solid-liquid extraction (USAE) followed by gas chromatography coupled to tandem mass spectrometry (GC-MS/MS) has been optimized and applied to assess the presence of eight volatile dimethyl siloxanes (VMS) (hexamethylcyclotrisiloxane (D3), octamethylcyclotetra-siloxane (D4), decamethylcyclopentasiloxane (D5), dodecamethylcyclohexasiloxane (D6), octamethyltrisiloxane (MDM), decamethyltetrasiloxane (MD2M) and dodecamethylpentasiloxane (MD3M) and tetradecamethylhexasiloxane (MD4M)) in fish. The optimized method presented limits of quantification between 0.1 and 1.3 pg/g for linear volatile dimethylsiloxanes (lVMS) and between 13 and 39 pg/g for cyclic volatile dimethylsiloxanes (cVMS) and intraday relative standard deviation (between 1.9 and 7.0%). Recovery yields were between 71 and 92%. 40 fish samples collected in different markets in Barcelona, (Spain), and 16 samples of fish directly collected at the Xúquer River were analysed. cVMS were detected in almost all the river fish samples at concentrations between pg/g and ng/g, with a significant correlation between the fat content and VMS concentrations in fish. In addition, significant higher concentrations were found in market samples, suggesting sources of contamination from their manipulation and storage in indoor environments. Multivariate analyses were applied to the results and the siloxane profiles and analyte correlations are discussed.

Distribution, Elimination, and Rearrangement of Cyclic Volatile Methylsiloxanes in Oil-Contaminated Soil of the Shengli Oilfield, China

Cyclic methylsiloxane standards (D4, D5, and D6) and linear methylsiloxanes (L3 through L16) were detected with high total concentrations (from 5.20 × 10(4) to 1.07 × 10(6) ng/g dw) in 18 oil sludge samples collected from the Shengli oilfield during 2008-2013. In 306 soil samples from this oilfield, the mean concentrations (43.4-125 ng/g dw) and the detection frequencies (65-76%) of D4-D6 were 10.9-11.9 and 2.05-2.24 times higher than those in reference soil samples, respectively. The concentrations of total cyclic siloxanes (ΣCyclic) had positive correlations (R(2) = 0.79, p < 0.05) with the total petroleum hydrocarbons concentration (TPH) in soil, indicating that oil production could release cyclic siloxanes to the environment. During 2008-2013, an increasing tendency (mean of 13.4% per annum) of ΣCyclic was found in soil with high TPH (>5000 mg/kg) but was not found in soil with lower TPH. Elimination experiments showed that petroleum hydrocarbons could reduce the degradation and volatilization rates of D4, D5, and D6 in impacted oilfield soil. The half-lives of D4, D5, and D6 in the opened and capped soil systems with TPH = 400-40 000 mg/kg were 1.19-22.2 and 1.03-7.43 times larger than those in common soil (TPH = 80 mg/kg), respectively. Furthermore, the petroleum hydrocarbons could affect the rearrangement-reaction rates of D5 and D6 in soil.

Modeling of spherical silver nanoparticles in silicone-based nanocomposites for marine antifouling

A non-toxic foul-release model of silicone/spherical AgNP hybrid nanocomposites with enhanced hydrophobicity, self-cleaning, and marine fouling release performance.

Cosmetics as a potential source of environmental contamination in the UK

Chemicals of emerging concern (CECs) are frequently used in cosmetic formulations and can potentially reach the environment at concentrations that may cause harm. A methodology was developed to assess over 120 chemicals assembled from product ingredient listings to identify and validate potential CECs in cosmetics, based on Annex XIII of REACH legislation. Ten potential CECs were identified: polydimethylsiloxane, butylated hydroxylanisole (BHA), butylated hydroxytoluene, triclosan, nano titanium dioxide, nano zinc oxide, butylparaben, diethyl phthalate, octinoxate methoxycinnamate and benzophenone. These chemicals were quantified based on their consumption and concentrations in cosmetics and percentage market penetration. The initial predicted environmental concentrations (PEC initial) were estimated to determine their exposure to the environment. With the exception of BHA, the PEC initial highlighted levels of exposure to the environment that triggered the need for further investigation of the chemicals. These chemicals were linked to cosmetics to highlight products with the potential to cause environmental harm. Skin care products had the highest quantities of CECs, with titanium dioxide and zinc oxide nanomaterials being dominant potential contaminants. Further research is required to assess the exposure pathways and fate of these chemicals to determine environmental risks associated with their use and disposal.

Review of 'emerging' organic contaminants in biosolids and assessment of international research priorities for the agricultural use of biosolids

A broad spectrum of organic chemicals is essential to modern society. Once discharged from industrial, domestic and urban sources into the urban wastewater collection system they may transfer to the residual solids during wastewater treatment and assessment of their significance and implications for beneficial recycling of the treated sewage sludge biosolids is required. Research on organic contaminants (OCs) in biosolids has been undertaken for over thirty years and the increasing body of evidence demonstrates that the majority of compounds studied do not place human health at risk when biosolids are recycled to farmland. However, there are 143,000 chemicals registered in the European Union for industrial use and all could be potentially found in biosolids. Therefore, a literature review of 'emerging' OCs in biosolids has been conducted for a selection of chemicals of potential concern for land application based upon human toxicity, evidence of adverse effects on the environment and endocrine disruption. To identify monitoring and research priorities the selected chemicals were ranked using an assessment matrix approach. Compounds were evaluated based upon environmental persistence, human toxicity, evidence of bioaccumulation in humans and the environment, evidence of ecotoxicity and the number and quality of studies focussed on the contaminant internationally. The identified chemicals of concern were ranked in decreasing order of priority: perfluorinated chemicals (PFOS, PFOA); polychlorinated alkanes (PCAs), polychlorinated naphthalenes (PCNs); organotins (OTs), polybrominated diphenyl ethers (PBDEs), triclosan (TCS), triclocarban (TCC); benzothiazoles; antibiotics and pharmaceuticals; synthetic musks; bisphenol A, quaternary ammonium compounds (QACs), steroids; phthalate acid esters (PAEs) and polydimethylsiloxanes (PDMSs). A number of issues were identified and recommendations for the prioritisation of further research and monitoring of 'emerging' OCs for the agricultural use of biosolids are provided. In particular, a number of 'emerging' OCs (PFOS, PFOA and PCAs) were identified for priority attention that are environmentally persistent and potentially toxic with unique chemical properties, or are present in large concentrations in sludge, that make it theoretically possible for them to enter human and ecological food-chains from biosolids-amended soil.