Speciation and quantitation of degradation products of silicones (Silane/Siloxane Diols) by gas chromatography—mass spectrometry and stability of dimethylsilanediol

Gas chromatography-mass spectrometry (GC-MS) methodology was developed to speciate and quantitate several degradation products of polydimethylsiloxane (PDMS) in soil. We have demonstrated that the major degradation product,viz., dimethylsilanediol, can be readily analyzed by GC-MS without derivatization as commonly practiced in analyzing such materials. A mixture of linear siloxane diols (n = 1–5, wheren is the number of Me₂SiO units), and cyclic dimethylsiloxanes (n = 4–6) was resolved by GC-MS. We also found that peak identity of various diols required that GC-MS is done in the chemical ionization (CI) mode, since the electron impact (EI) ionization mode produced similar mass fragmentation patterns for diols and cyclics containing the same number of silicon atoms. For siloxane diols, detection limits ranged from 100 pg (forn = 1) to 1 ng (for n = 5). For cyclics, the detection limit was about 1 pg. Dimethylsilanediol, known to be unstable even in the solid state, was shown by NMR techniques to be stable in aqueous solution at <0.1% concentration. A 100-ppm solution was stable for over a year. Purity check for dimethylsilanediol is best carried out by Si-29 solid-state NMR technique.     

Proposed mechanism for bacterial metabolism of polyacrylate

A possible aerobic degradative pathway for polyacrylate was examined with trimer (1,3,5-pentane tricarboxylic acid; PTCA)-utilizing bacteria. A few metabolic products from PTCA accumulated in culture filtrates and reaction mixtures of washed cells. Fraction A was detected as a main metabolite by high-performance liquid chromatography. A small amount of fraction B was concomitant with fraction A. Another fraction, C, was also detected. These compounds were suggested by liquid chromatography-mass spectrometry analyses to be 1,3,5-(1- or 2-pentene)tricarboxylic acid (fraction A or B) and 1,3,5-(2-oxopentane)tricarboxylic acid (fraction C). Fraction A was quickly further metabolized by washed cells, but fraction B was only gradually degraded. From these results, the metabolic pathway for polyacrylate is suggested to be quite similar to-oxidation for saturated fatty acids. The degradation of PTCA by washed cells was slower than that by growing cells and was inhibited by 5 mM NaN₃. This suggests that the metabolism is linked to a respiratory chain or energy-producing system of bacteria which can aerobically assimilate PTCA.Paper presented at the Bio/Environmentally Degradable Polymer Society—Second National Meeting, August 19–21, 1993, Chicago, Illinois.     

Effects of Nitrogen Supply on the Sensitivity to O3 of Growth and Photosynthesis of Japanese Beech (Fagus crenata) Seedlings

To obtain basic information for evaluating critical levels of O₃ under different nitrogen loads for protecting Japanese beech forests, two-year-old seedlings of Fagus crenata Blume were grown in potted andisol supplied with N as NH₄NO₃ solution at 0, 20 or 50 kg ha⁻¹ year⁻¹ and exposed to charcoal-filtered air or O₃ at 1.0, 1.5 and 2.0 times the ambient concentration from 16 April to 22 September 2004. The O₃ induced significant reductions in the whole-plant dry mass, net photosynthetic rate at 380 μmol mol⁻¹ CO₂ (A ₃₈₀), carboxylation efficiency (CE) and concentrations of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and total soluble protein (TSP) in the leaves. The concentrations of Rubisco and TSP were negatively correlated with the concentration of leaf acidic amino acid, suggesting that O₃ enhanced the degradation of protein such as Rubisco. The N supply to the soil did not significantly change the whole-plant dry mass and A ₃₈₀, whereas it significantly increased the CE and concentrations of Rubisco and total amino acid. No significant interactive effects of O₃ and N supply to the soil were detected on the growth, photosynthetic parameters and concentrations of protein and amino acid in the leaves. In conclusion, N supply to the soil at ≤50 kg ha⁻¹ year⁻¹ does not significantly change the sensitivity to O₃ of growth and net photosynthesis of Fagus crenata seedlings.     

Thermocatalytic Degradation of High Density Polyethylene into Liquid Product

Thermocatalytic degradation of high density polyethylene (HDPE) was carried out using acid activated fire clay catalyst in a semi batch reactor. Thermal pyrolysis was performed in the temperature range of 420–500 °C. The liquid and gaseous yields were increased with increase in temperature. The liquid yield was obtained 30.1 wt% with thermal pyrolysis at temperature of 450 °C, which increased to 41.4 wt% with catalytic pyrolysis using acid activated fire clay catalyst at 10 wt% of catalyst loading. The composition of liquid products obtained by thermal and catalytic pyrolysis was analyzed by gas chromatography-mass spectrometry and compounds identified for catalytic pyrolysis were mainly paraffins and olefins with carbon number range of C₆–C₁₈. The boiling point was found in the range of commercial fuels (gasoline, diesel) and the calorific value was calculated to be 42 MJ/kg.     

Alkaline solution neutralization capacity of soil

Alkaline eluate from municipal solid waste (MSW) incineration residue deposited in landfill alkalizes waste and soil layers. From the viewpoint of accelerating stability and preventing heavy metal elution, pH of the landfill layer (waste and daily cover soil) should be controlled. On the other hand, pH of leachate from existing MSW landfill sites is usually approximately neutral. One of the reasons is that daily cover soil can neutralize alkaline solution containing Ca²⁺ as cation. However, in landfill layer where various types of wastes and reactions should be taken into consideration, the ability to neutralize alkaline solutions other than Ca(OH)₂ by soil should be evaluated. In this study, the neutralization capacities of various types of soils were measured using Ca(OH)₂ and NaOH solutions. Each soil used in this study showed approximately the same capacity to neutralize both alkaline solutions of Ca(OH)₂ and NaOH. The cation exchange capacity was less than 30% of the maximum alkali neutralization capacity obtained by the titration test. The mechanism of neutralization by the pH-dependent charge can explain the same neutralization capacities of the soils. Although further investigation on the neutralization capacity of the soils for alkaline substances other than NaOH is required, daily cover soil could serve as a buffer zone for alkaline leachates containing Ca(OH)₂ or other alkaline substances.     

Fate and behavior of metal(loid) contaminants in an organic matter-rich shooting range soil: Implications for remediation

This study investigates the fate and behavior of lead (Pb), copper (Cu), antimony (Sb), and arsenic (As) in a shooting range soil. The soil samples were collected from the surface (0–15 cm) and the subsurface (15–40 cm and 40–55 cm) of a grassy and wood chip covered impact area behind a firing position. Optical microscopy images indicate significant amounts of corroded bullet fragments and organic wood chips in the surface soil. Analysis by X-ray powder diffraction (XRPD) and scanning electron microscopy electron dispersive X-ray spectroscopy (SEM-EDS) showed that metallic Pb was transformed into lead oxides (litharge PbO and massicot PbO) and lead carbonates (hydrocerussite Pb₃(CO₃)₂(OH)₂, cerussite PbCO₃, and plumbonacrite Pb₅(CO₃)₃O(OH)₂). Rietveld quantification indicated the surface soil contained 14.1% metallic Pb, 17.9% hydrocerussite, 5.2% plumbonacrite, 5.9% litharge, and 3.9% massicot on a dry weight basis, or a total of 39.7% Pb, far in excess of lead concentrations typically found in US shooting range soils. Metallic Cu (bullet jacket material) appeared stable as no secondary minerals were detected in the surface soil. As and Sb concentrations were on the order of 1,057 mg/kg and 845 mg/kg respectively. The elevated soil pH coupled with high organic carbon content is thought to have caused downward migration of metals, especially for Pb, since 4,153 mg Pb/kg was observed at a depth of 55 cm. More than 60% of Pb was concentrated in the coarse soil (> 0.425 mm) fraction, suggesting soil clean-up possible by physical soil washing may be viable. The concentrations of Pb, As, and Sb in the toxicity characteristic leaching procedure (TCLP) extracts were 8,869 mg/L, 6.72 mg/L, and 6.42 mg/L respectively, were above the USEPA non-hazardous regulatory limit (As and Pb) of 5 mg/L. The elevated Sb and As concentrations draw concern because there is historically limited information concerning these metals at firing ranges and several values exceeded local soil cleanup criteria. As the high Pb concentrations appeared to be linked to the presence of organic-rich berm cover materials, the use of wood chips as berm cover to prevent soil erosion requires reconsideration as a shooting range management practice.     

Recovery of benzene-rich oil from the degradation of metal- and metal oxide-containing poly(ethylene terephthalate) composites

Pure poly(ethylene terephthalate) (PET) resin and metal-/metal oxide-containing PET composites were thermally decomposed in the presence of Ca(OH)₂ using a tube reactor. The effects of batch and continuous processing, the presence of Ca(OH)₂, and PET size on benzene production were investigated. A maximum benzene yield and purity of 82.9 % and 78.8 wt%, respectively, were obtained at 700 °C in the presence of Ca(OH)₂ when using small PET particles; further, a continuous feed reactor was favored over a batch reactor. Effective contact between PET and Ca(OH)₂ was important in the PET degradation, which promoted hydrolysis of PET and decarboxylation of terephthalic acid, whereas pyrolysis was suppressed. Furthermore, the results of thermal decomposition of PET-based waste—PET-based X-ray films, magnetic tape, and prepaid cards—indicated that the metal and metal oxides contained in the waste had no significant catalytic effect on PET degradation or on the recovery of benzene-rich oil in the presence of Ca(OH)₂.     

Mechanical properties of incineration bottom ash: The influence of composite species

The mechanical properties, including strength, deformational behavior, and wetting softening phenomena of municipal solid waste incinerator (MSWI) bottom ash are one of the major concerns for reuse applications. However, owing to the complex constituents of municipal solid waste, the properties of MSWI bottom ash are often highly variable. A series of artificial specimens with controlled chemical components were tested in this study. The test results show that the artificial bottom ash possesses the following mechanical characteristics: (1) for the strength, the frictional angles of the bottom ash under dry and saturated conditions vary from 34.8° to 51.1° and 26.0° to 37.2°, respectively; (2) for the deformation, the shear stiffness increases with the normal stress arises and degrades upon increased shearing; (3) significant wetting degradation of the strength and stiffness were observed.The multi-variable regression analysis was conducted to evaluate the associated influence of the chemical components on the strength. Among the evaluated components, Fe₂O₃ and Al₂O₃ are key factors; an increase in either results in higher strength at both dry and saturated conditions. The results were used to propose empirical relationships for ?_dry and ?_sat, expressed in terms of Fe₂O₃ and Al₂O₃. Accordingly, a strength classification chart is proposed for engineering purposes.     

Quantification of Polymerisation Processes During The Oxidative Degradation of 14C-Labelled Chlorophenols

In experiments employing the lignocellulose-decaying basidiomycetes Trametes versicolor and Stropharia rugosoannulata degrading uniformly¹⁴C-labelled 2,4-dichlorophenol and pentachlorophenol, acombination of size exclusion chromatography (SEC),fractionation, and -scintillation counting wasapplied to quantify polymerisation products formed duringchlorophenol degradation. Time-dependent mass balances weregenerated by analysis of ¹⁴C in polymerisation products,CO₂, as well as monomer non-polar and polar metabolites.Approximately 30% of the chlorophenols were found to bepolymerised. A major fraction of the polymerised productscorresponded to a molecular weight range from 0.24 – 40 kDa.Only a minor fraction could be attributed to a molecularweight >40 kDa. This method proved to be useful inquantification of polymerisation products and kinetics of thepolymerisation processes, whereas UV/Vis detection ofpolymerisation products separated by SEC led to false positiveresults. The SEC-¹⁴C method could also be applied forother complex processes where polymerisation ordepolymerisation occurs (humification, degradation oflignocellulose, formation of bound residues from xenobioticssuch as polycyclic aromatic hydrocarbons or 2,4,6-trinitrotoluene) and where spectrophotometric determinationsare difficult or impossible.     

Fungal biotransformation of 6:2 fluorotelomer alcohol

Fungal degradation of 6:2 fluorotelomer alcohol (6:2 FTOH, C₆F₁₃CH₂CH₂OH) by two wood‐decaying fungal strains and six fungal isolates from a site contaminated with per‐ and polyfluoroalkyl substances (PFASs) was investigated. 6:2 FTOH is increasingly being used in FTOH‐based products, and previous reports on the microbial fate of 6:2 FTOH have focused on bacteria and environmental microbial consortia. Prior to this study, one report demonstrated that the 6:2 FTOH biotransformation by the wood‐decaying fungus, Phanerochaete chrysosporium, generated more polyfluoroalkyl substances, such as 5:3 acid (F(CF₂)₅CH₂CH₂COOH), and diverted away from producing the highly stable perfluorocarboxylic acids (PFCAs). Most of the fungi (Gloeophyllum trabeum and isolates TW4‐2, TW4‐1, B79, and B76) examined in this study showed similar degradation patterns, further demonstrating that fungi yield more 5:3 acid (up to 51 mol% of initial 6:2 FTOH dosed) relative to other metabolites (up to 12 mol% total PFCAs). However, medium amendments can potentially improve 6:2 FTOH biotransformation rates and product profiles. The six fungal isolates tolerated up to 100 or 1,000 milligrams per liter of perfluorooctanoic acid and perfluorooctane sulfonic acid, and some isolates experienced increased growth with increasing concentrations. This study proposes that fungal pathways must be considered for the biotransformation of potential PFAS precursors, such as 6:2 FTOH, and suggests the basis for selecting proper microorganisms for remediation of fluoroalkyl‐contaminated sites.     

Assessing detoxification and degradation of wood preserving and petroleum wastes in contaminated soil

This study was undertaken to evaluate in-situ soil bioremediation processes, including degradation and detoxification, for two types of wood preserving wastes and two types of petroleum refining wastes at high concentrations in an unacclimated soil. The soil solid phase, water soluble fractions of the soil, and column leachates were evaluated. Two bioassays, a mutagenic potential asay (Ames assay) and an aqueous toxicity assay (Microtox^™ assay) were used to evaluate detoxification; high performance liquid chromatography was used to evaluate chemical concentration and degradation for eight polynuclear aromatic hydrocarbons (PAHs). The group of non-carcinogenic PAHs studied demonstrated greater degradation, ranging from 54–90% of mass added for the four wastes; the carcinogenic group of PAHs studied exhibited degradation ranging from 24–53% of mass added. Although no mutagenicity was observed in waste/soil mixtures after one year of treatment, Microtox^™ toxicity was observed in water soluble fractions and in leachate samples. An integration of information concerning degradation of hazardous constituents with bioassay information represents an approach for designing treatability studies and for evaluating the effectiveness of in-situ bioremediation of contaminated soil/waste systems. When combined with information from waste, site and soil characterization studies, the data generated in treatability studies may be used in predictive mathematical models to: (1) evaluate the effectiveness of use of on-site bioremediation for treatment of wastes in soil systems; (2) develop appropriate containment structures to prevent unacceptable waste transport from the treatment zone; and (3) design performance monitoring strategies.     

Decomposition of dichloromethane and in situ alkali absorption of resulting halogenated products by a packed-bed non-thermal plasma reactor

For an effective decomposition and removal of organic halogenated compounds, a packed-bed non-thermal plasma reactor with in situ absorption of the resulting halogenated products by alkaline sorbent incorporated was proposed. In the plasma reactor, α-Al₂O₃ particles of 1 and 3 mm (mean particle diameter) were packed as solid dielectric medium to enhance the plasma power density in the reactor. Further, alkaline sorbent of Ca(OH)₂ was doped onto the surface of α-Al₂O₃ particles, in order to remove halogenated products by in situ absorption with Ca(OH)₂. A high-voltage and high-frequency pulsed power of −15 to 15 kV and 1 kHz was applied to the wire electrode of the plasma reactor by means of a DC power source. In the present study, as the sample of an organic halogenated compound that is most popularly used, we selected dichloromethane (CH₂Cl₂), and 500 ppm of the initial concentration of CH₂Cl₂ was fed into the reactor accompanied by air at a fixed flow rate of 500 × 10⁻⁶ m³ min⁻¹ at room temperature. As a result, it was recognized that the amount of CH₂Cl₂ decomposed by non-thermal plasma in an α-Al₂O₃ particle bed increased with an increase in plasma input power. The ratio of decomposition of CH₂Cl₂ was almost 100% at 13 kV of electric power and 1 kHz frequency, and CO₂, CH₃Cl, COCl₂, HCl, and Cl₂ were observed as the major reaction products. On the other hand, when CH₂Cl₂ was introduced into the plasma reactor where α-Al₂O₃ particles doped with Ca(OH)₂ were packed, the ratio of decomposition of CH₂Cl₂ became higher, compared to the case that α-Al₂O₃ particles were not doped with Ca(OH)₂. Moreover, there were no halogenated by-product gases detected in the outlet gas from the reactor. As the solid reaction products, CaClOH and Ca(ClO)₂·4H₂O were detected on Ca(OH)₂ by X-ray diffraction. From these findings, it was recognized that CH₂Cl₂ was decomposed more effectively without producing unwanted harmful halogenated by-products in the proposed non-thermal plasma reactor where α-Al₂O₃ particles doped with Ca(OH)₂ sorbent were packed.     

Influence of H<Subscript>2</Subscript> on the decomposition of halides by nonthermal plasma incorporated with in situ alkaline absorption

To control the emission of halides into the environment, an experiment on the nonthermal plasma decomposition of the halides CF₄, CHF₃, C₂HCl₃, and CHClF₂ was conducted in a wire-in-tube corona reactor. It was found that the decomposition of C₂HCl₃ and CHClF₂ was easy compared with the decomposition of CF₄ and CHF₃. With the addition of H₂ in N₂ gas, the decomposition ratio of CF₄, C₂HCl₃, and CHClF₂ increased. In contrast, the decomposition ratio of CHF₃ in a hydrogen-rich atmosphere was lower than that in an N₂ atmosphere. It was demonstrated that the yields of HF and/or HCl formed during halide decomposition clearly increased in the presence of H₂ in N₂ gas. Furthermore, in order to prevent the production of unwanted products from halide decomposition, a combination of plasma decomposition and in situ alkaline absorption was devised by coating a layer of Ca(OH)₂ onto the surface of the grounding electrode. It was demonstrated that the Ca(OH)₂ sorbent played an effective role as a scavenger, participating in halide decomposition by capturing reaction products such as HCl and HF, therefore resulting in increased halide decomposition.     

Laboratory Measurement of Dry Deposition of Ozone onto Northern Chinese Soil Samples

We used laboratory experiments to investigate surface resistance (R _c) to dry deposition of ozone (O₃) on different types of soil samples collected from the arid deserts and the Loess Plateau of northern China. Furthermore, we measured the factors that affected R _c, which depends on the physical and chemical interaction between trace constituents and the deposition surface, and evaluated deposition velocity (V _d). There was little influence of geometric surface area, soil weight, or O₃ concentration on V _d of O₃. The effect of relative humidity (RH) (i.e. moisture content of the soil) on O₃ uptake was in agreement with results reported in the literature: a distinct RH dependence of V _d and little uptake under water-saturated conditions were observed. R _c values for all the soil samples examined were in the range 0.21–3.3 s mm⁻¹ and were exponentially related to the surface area of the particles and the organic carbon content of each soil sample at RH of both <10 and 60%.     

Synthesis of3H- polyethylene and its use for fate studies on degradable plastics

Determining the fate of xenobiotic materials in the environment can be aided by the use of radioactive isotope technology. Previous research on the degradation of polymers such as polyethylene (PE) was aided by the utilization of radiotracers. In order to study the environmental fate of degradable (PE/starch) plastics, we synthesized³H-labeled PE. Results of soil incubation studies indicate that only minimal degradation of the PE component, as indicated by the production of water-soluble metabolites, occurred during 2 years of incubation in soil. Despite the minimal degradation, the³H label did not allow for detection of the degradation products. In addition, the³H-PE was particularly useful for tracing the fate of degradable plastics after consumption by terrestrial isopods. The detection of aqueous-soluble radioactivity in isopod frass was used to indicate degradation of the plastic film.     

Thermal Stability and Degradation of Chitosan Modified by Acetophenone

N-(Methylphenylmethylidenyl) chitosan (MPMC) polymer was synthesized by chemical modification of chitosan. The chemical structure of the modified polymer was characterized by IR, ¹H NMR and elemental analysis. Thermogravimetric reveals that the thermal stability of chitosan polymer is greater than MPMC polymer. The activation energies of thermal degradation of chitosan and MPMC polymers determined using Arrhenius relationship. Thermal degradation of MPMC polymer was studied and the products of degradation were identified by GC–MS technique. It seems that the mechanism of degradation of MPMC polymer is characterized by elimination of low-molecular weight radicals. Combination or recombination of H^· or OH⁻ with these radicals and random scission mechanism along the backbone chain are the main source of the degradation products.     

Calculation of carbon balances for evaluation of the biodegradability of polymers

Establishing carbon balances has been proven to be an applicable and powerful tool in testing biodegradability of polymers. In controlled degradation tests at a 4-L scale with the model polymer poly(-hydroxybutyrate) (PHB), it was shown that the degree of degradation could not be determined with satisfactory accuracy from CO₂ release alone. Instead, the course of degradation was characterized by means of establishing carbon balances for the degradation of PHB withAcidovorax facilis and a mixed culture derived from compost. Different analytical methods for determining the different carbon fractions were adapted to the particular test conditions and compared. Quantitative determination of biomass and residual polymer were the main problems in establishing carbon balances. Amounts of biomass derived from protein measurements depend strongly on assumptions of the protein content of the biomass. Selective oxidation of biomass with hypochlorite was used as alternative, but here problems arose from insoluble metabolic products. Determination of soluble components with the method of chemical oxygen demand (COD) also includes empirical assumptions but seems acceptable if the dissolved carbon fraction is in the range of some 10% total carbon. Results confirm both analytical assays and theoretical approaches, in ending up at values very close to 100%, within an acceptable standard deviation range under test conditions comparable to standard test practice.Paper presented at the Bio/Environmentally Degradable Polymer Society—Third National Meeting, June 6–8, 1994, Boston, Massachusetts.     

High Immobilization of NH4+ in Danish Heath Soil Related to Succession,Soil and Nutrients: Implications for Critical Loads of N

During recent decades heathlands havechanged into grasslands in regions with high atmosphericnitrogen deposition. In regions with intermediatedeposition level (e.g., Denmark) changes have been lesspronounced which may be due to delay or decrease inresponse of the ecosystem. The mor layer (O horizon) mayplay an important role for this delay due to high sinkstrength for N. In this study, the capacity for netNH₄ ⁺ immobilization and mineralization wasstudied during short- and long-term incubations (2–36 days)of mor samples from Danish dry inland heaths. High short-term capacity for net NH₄ ⁺ immobilization wasfound to be a general characteristic of Danish heath morlayers both under heather (Calluna vulgaris) andcrowberry (Empetrum nigrum ssp nigrum), the latterdominating late stages in heathland succession. The netNH₄ ⁺ immobilization was higher under youngcompared to old or dead vegetation, and higher on lessnutrient poor soils than on extremely nutrient poor soils.The addition of N, P and C stimulated CO₂ productionand net NH₄ ⁺ immobilization, but not net Nmineralization. The immobilization of ¹⁵NH₄ ⁺caused release of dissolved organic N, increased N anddecreased C/N ratio in the microbial biomass, and indicatedgrowth of microorganisms with other metabolic abilitiesthan the indigenous population. No evidence was obtained ofstabilization of immobilized ¹⁵NH₄ ⁺ intosoil organic matter during the experiment. On background ofthe results and current knowledge it was concluded that therecognition of the high capacity for net NH₄ ⁺immobilization in mor layers does not allow for a raiseof critical loads for N for northern dry inland heaths.     

Novel Bioactive Chiral Poly(amide–imide)s Containing Different Amino Acids Linkages: Studies on Synthesis, Characterization and Biodegradability

In this paper chiral bioactive poly(amide–imide)s (PAI)s were synthesized from four different diacids containing chiral amino acids with 4,4′-methylene bis(3-chloro 2,6-diethylaniline) as a diamine via direct polycondensation reaction in a system of tetra-n-butylammonium bromide and triphenyl phosphite as a condensing agent. The structures of these polymers were confirmed by FT-IR, ¹H-NMR, specific rotation, elemental and thermogravimetric analysis (TGA) techniques. TGA showed that the 10 % weight loss temperature in a nitrogen atmosphere was more than 378 °C, which indicates that the resulting PAIs have a good thermal stability. The biodegradability of the monomers and prepared polymers was investigated in culture media and soil burial test for assessment of the susceptibility of these compounds to microbial degradation. The results showed that the synthesized monomers and theirs derived polymers are biologically active and nontoxic to microbial growth.     

A Review of the Fate and Effects of Silicones in the Environment

Silicones are well-known useful materials varying in structure, reactivity, and chemical and physical properties, but they all contain a covalent bond between the silicon atom and an organic group. Most common of these polymers are those based on polydimethylsiloxane (PDMS) having a siloxane (Si–O–Si) repeat unit and two methyl groups on each silicon atom. All these polymers are manmade, and the organosilicon linkage is not found in nature. It was therefore erroneously assumed that these polymers do not degrade naturally in the environment. It is the purpose of this review to refute this myth and to describe the degradation processes of PDMS in the environment and any potential ecological impact on the terrestrial, aquatic, and atmospheric compartments. Although it was found that minor degradation takes place by hydrolysis of PDMS to dimethylsilandiol followed by oxidation of the methyl group to aldehyde and ultimately to CO₂ by Arthobacter and Fusarium oxysporium schlechtendahl, the major degradation processes are abiotic. High molecular weight PDMS are initially depolymerized by soil hydrolysis of the siloxane bonds to yield organosilanol terminated oligomers. These organosilanols and low molecular weight linear PDMS and cyclics are evaporated into the atmosphere and are oxidized there by hydroxyl radicals to benign silica, water, and CO₂.