Masks for the Reduction of Methyl Methacrylate Vapor Inhalation.

Background: Exposure to methyl methacrylate vapor (MMA) presents an occupational risk to orthopedic surgeons and ancillary personnel in the operating room. The purpose of this study was to identify a disposable face mask to reduce MMA organic vapor inhalation in the operative suite. Methods: First, the effectiveness of MMA vapor filtration was determined in the laboratory. A section of activated carbon impregnated filter face mask (Model 8514, 3M Inc.) was exposed to 150 ppm MMA vapor and MMA ppm of filtered air was monitored until MMA vapor was detectable. The face mask was then worn as directed in the operating room during routine cement mixing during total knee arthroplasty to determine the exposure to MMA vapors during the procedure both with and without the activated carbon impregnated filter face mask. Results: The activated carbon impregnated face mask was effective in reducing MMA vapor inhalation to non-detectable levels for up to 40 minutes in the laboratory at steady-state exposure of 150 ppm MMA vapor as well as throughout cement mixing and curing in the operative suite during routine total knee arthroplasty. Conclusions: An activated carbon impregnated face mask offers a solution for the orthopedic surgeon and supporting personnel who wish to limit their exposure to MMA vapors due to health concerns.Level of Evidence: III.

Allergic reactions to lower concentrations of nickel sulfate and formaldehyde often appear later than reactions to higher concentrations.

BACKGROUND: A late-appearing patch test reaction may be a sign of active sensitization or represent a delayed elicitation reaction. OBJECTIVES: To retrospectively study the effect of concentration on the time course of allergic reactions to routine concentration dilution series of formaldehyde and nickel sulfate. METHODS: We tested concentration dilution series of 2%, 1%, 0.32% and 0.1% formaldehyde and 5%, 1.6%, 0.5% and 0.16% nickel sulfate, respectively. The last readings were performed on day 4 to day 6. We included patients with allergic reactions to either of the two lowest concentrations in each dilution series and whose tests had been read three times. RESULTS: Forty-two nickel-allergic and 23 formaldehyde-allergic patients fulfilled the inclusion criteria. In 26 (62%) of the nickel-sensitive patients, reactions to lower concentrations appeared later than reactions to the highest concentration. Of the formaldehyde-sensitive patients, 17 (74%) developed one or two allergic reactions to lower concentrations later than reactions to the highest concentration, and one (4%) patient developed allergic reactions to lower concentrations sooner than a reaction to the highest concentration. The remaining patients showed all allergic reactions at the same reading. CONCLUSIONS: In these selected, relatively strongly sensitized patients, allergic reactions to lower concentrations quite regularly appeared later than reactions to higher concentrations.

Effects of antibacterial coating on monomer exudation and the mechanical properties of denture base resins.

STATEMENT OF PROBLEM: Denture base resin may be exposed to different conditions for long periods, resulting in the loss of monomer by exudation and a decrease in mechanical properties. PURPOSE: The purpose of this in vitro study was to evaluate monomer loss by exudation from denture base resins doped with antibacterial coatings and their mechanical properties after long-term water immersion. MATERIAL AND METHODS: Four kinds of dental base resin materials were used as experimental materials. The specimens of each resin were divided into an experimental group (coated) and a control group (uncoated). Monomer exudation was tested at 7 and 28 days by gas chromatography after materials were immersed in distilled water or a solution of 75% alcohol/distilled water. Flexural strength and elastic modulus were tested with a universal testing machine after immersion for 2 and 180 days. The surface morphology was characterized with atomic force microscopy. The data were analyzed using 3-way ANOVA followed by the Tukey-Kramer honest significant difference test (α=.05). RESULTS: In both of the immersion media, each of the 3 factors (materials, coating, and immersion time) significantly affected the monomer exudation (P<.05). In addition, the interaction between any 2 of those factors or among the 3 factors had a significant interaction effect on the monomer exudation of the denture base (P<.05). The mechanical properties of the tested materials were different, and the immersion time had a significant effect on the flexural properties (P<.05). For flexural strength, a significant interaction effect occurred among the 3 factors (material, coating, and immersion time) (P<.05). The coating has a significant effect on the elastic modulus of denture base resin (P<.05) and on the interaction between the material and immersion time (P<.05). CONCLUSIONS: The silver-loaded mesoporous silica antibacterial coating can effectively reduce monomer exudation and enhance the flexural properties of denture base resin after immersion.

Characterization of emissions from a desktop 3D printer and indoor air measurements in office settings.

Emissions from a desktop 3D printer based on fused deposition modeling (FDM) technology were measured in a test chamber and indoor air was monitored in office settings. Ultrafine aerosol (UFA) emissions were higher while printing a standard object with polylactic acid (PLA) than with acrylonitrile butadiene styrene (ABS) polymer (2.1 × 10(9) vs. 2.4 × 10(8) particles/min). Prolonged use of the printer led to higher emission rates (factor 2 with PLA and 4 with ABS, measured after seven months of occasional use). UFA consisted mainly of volatile droplets, and some small (100-300 nm diameter) iron containing and soot-like particles were found. Emissions of inhalable and respirable dust were below the limit of detection (LOD) when measured gravimetrically, and only slightly higher than background when measured with an aerosol spectrometer. Emissions of volatile organic compounds (VOC) were in the range of 10 µg/min. Styrene accounted for more than 50% of total VOC emitted when printing with ABS; for PLA, methyl methacrylate (MMA, 37% of TVOC) was detected as the predominant compound. Two polycyclic aromatic hydrocarbons (PAH), fluoranthene and pyrene, were observed in very low amounts. All other analyzed PAH, as well as inorganic gases and metal emissions except iron (Fe) and zinc (Zn), were below the LOD or did not differ from background without printing. A single 3D print (165 min) in a large, well-ventilated office did not significantly increase the UFA and VOC concentrations, whereas these were readily detectable in a small, unventilated room, with UFA concentrations increasing by 2,000 particles/cm(3) and MMA reaching a peak of 21 µg/m(3) and still being detectable in the room even 20 hr after printing.

Evaluating a county-based healthy nail salon recognition program.

OBJECTIVES: The City of San Francisco, California established a recognition program for nail salons that use safer nail products and receive worker safety training. This pilot study examined whether participating salons had reduced levels of toluene, methyl methacrylate (MMA), and total volatile organic compounds (TVOC), and improved knowledge and behavior compared to control salons. METHODS: We conducted personal air monitoring and administered surveys assessing knowledge and behaviors of two workers from each of six intervention salons and five control salons. We conducted assessments before and after the worker training. RESULTS: Although non-significant, there was a reduction in toluene (-46% vs. 0%) and TVOC (-19% vs. +47%), but an increase in MMA (+113% and +72%) among intervention salons compared to control salons. Awareness of dibutyl phthalates in nail products increased (+55%) among intervention salons between surveys. CONCLUSIONS: A government-administered nail salon recognition program may reduce chemical exposures and increase work-related knowledge.

Concentrations and stability of methyl methacrylate, glutaraldehyde, formaldehyde and nickel sulfate in commercial patch test allergen preparations.

BACKGROUND: Epicutaneous patch tests are used to reproduce allergy and diagnose allergic contact dermatitis. Reliable allergen test preparations are required. OBJECTIVES: The purpose of the present study was to measure the actual concentrations of nickel(II) sulfate hexahydrate (NiSO4 ), methyl methacrylate, formaldehyde, and glutaraldehyde, and to compare them with the labelled concentrations, in commercial patch test allergen preparations found in dermatology clinics where patch testing is routinely performed. MATERIALS AND METHODS: The commercial in-date and out-of-date patch test allergen preparations concentrations of NiSO4 , methyl methacrylate, formaldehyde and glutaraldehyde from one to three participating clinics were analysed with chromatographic or wet chemical techniques. RESULTS: NiSO4 and formaldehyde concentrations were at or above the labelled concentrations; however, formaldehyde loss occurred with storage. NiSO4 particulate was uniformly distributed throughout the petrolatum. 'In-use' methyl methacrylate reagent syringes all contained ≤ 56% of the 2% label concentration, with no observable relationship with expiration date. Lower methyl methacrylate cocentrations were consistently measured at the syringe tip end, suggesting loss resulting from methyl methacrylate's volatility. The concentrations of glutaraldehyde patch test allergen preparations ranged from 27% to 45% of the labelled (1% in pet.) concentration, independently of expiration date. CONCLUSIONS: Some false-negative methyl methacrylate, formaldehyde or glutaraldehyde patch test results may be attributable to instability of the test preparations.

Vortex-assisted liquid-liquid micro-extraction and high-performance liquid chromatography for a higher sensitivity methyl methacrylate determination in biological matrices.

A vortex-assisted liquid-liquid micro-extraction coupled with high-performance liquid chromatography, with UV-vis, is proposed to pre-concentrate methyl methacrylate and to improve separation in biological matrices. The use of 1-octanol as extracting phase, its volume, the need for a dispersant agent, the agitation conditions and the cooling time before phase separation were evaluated. In optimum conditions, enrichment factors of 20 (±0.5) and enrichment recovery of 99% were obtained. The straightforward association of this extraction process with the HPLC method, previously regulated by the International Organization for Standardization, afforded a detection limit of 122 ng/mL and a quantification limit of 370 ng/mL. The within-batch precision, relative standard deviation, was 3% for a sample with 1.49 µg/mL and 4% for a sample with 13.4 µg/mL. The results showed a between batch-precision of 21% for experiments performed on five different days, for a sample with a concentration of 1.10 µg/mL in methyl methacrylate.

Investigation of the homogeneity of methacrylate allergens in commercially available patch test preparations.

BACKGROUND: The homogeneity of methacrylates in commercial patch test preparations has not yet been investigated. Inhomogeneous patch test preparations may give rise to false-negative or false-positive patch test results in patients suspected of having methacrylate allergy. OBJECTIVES: To investigate the homogeneity of methacrylates in commercial patch test preparations. METHODS: Fresh commercial patch test preparations of methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (2-HEMA) from three test material suppliers in Europe were analysed quantitatively by means of normal-phase high-performance liquid chromatography. RESULTS: The initial concentration of MMA in all six patch test preparations was lower than stated on the label, whereas four of six patch test preparations of 2-HEMA were in accordance with the stated concentrations. The concentration of MMA increased markedly from the top segment close to the tip of the syringe to the bottom segment adjacent to the piston in four syringes (3-6). In contrast, syringes with 2-HEMA maintained a constant concentration throughout the test preparation, apart from two syringes (11 and 12). CONCLUSION: Variations in concentration and heterogeneous distribution of MMA and 2-HEMA in patch test preparations may be an additional cause of variation in patch test results, besides other technical details and reading.

High performance liquid chromatographic determination of residual monomer released from heat-cured acrylic resin. An in vivo study.

PURPOSE: Heat-polymerized acrylic resins are used in dentistry for complete denture fabrication. Despite the polymerization method, conversion of monomer into polymer is often incomplete with free or unreacted residual monomer remaining in the polymerized resin. The aim of this study was to determine the amount of residual monomeric methyl methacrylate (MMA) leaching in the saliva of patients wearing complete dentures in their postinsertion period. MATERIALS AND METHODS: Thirty edentulous participants as first-time complete denture wearers (age 60 to 65 years) were selected. All the prostheses were fabricated using a similar standard technique with a heat-cured acrylic resin denture base material. Saliva samples were collected at time intervals of 1 hour, 1 day, and 3 days postdenture insertion. Participants were asked to discharge saliva every 30 seconds into a pre-weighed screw-capped container for a 5-minute period. MMA levels were measured using high performance liquid chromatography. Data were analyzed by ANOVA and Tukey-HSD. RESULTS: The maximum concentration of monomer released into saliva peaked 1 day after insertion of the complete dentures. The mean (SD) MMA content was 0.04 ± 0.01 (µg/ml) 1 hour after insertion, and 0.3 ± 0.09 (µg/ml), and 0.05 ± 0.01 (µg/ml) on the first and third days postinsertion, respectively. CONCLUSIONS: Although the released monomeric MMA was not at toxic levels, it could potentially sensitize complete denture patients or elicit an allergic reaction. The risk of the residual material as a primary irritant for a sensitizing reaction could be minimized by immersion of the denture in water for 24 hours before insertion.

Avaliação morfológica e por imagem radiográfica da matriz óssea mineralizada heteróloga fragmentada e metilmetacrilato, preservados em glicerina para reparação de falhas ósseas em tíbias de coelhos / Morphological evaluation and radiographic image of fragmented heterolog mineralized bone matrix and methylmethacrylate preserved in glycerin to repair osseous defects in tibias of rabbits

Os traumas que resultam em fraturas ósseas, principalmente as cominutivas, têm uma importância muito grande na rotina clínico-cirúrgica veterinária e humana. Foi realizada falha segmentar de 6mm na região metafisária medial da tíbia esquerda de 12 coelhos, a qual foi preenchida com implante constituído de matriz óssea mineralizada heteróloga fragmentada e metilmetacrilato, preservados em glicerina (98%) para a sua reconstrução. Foi realizada avaliação morfológica e radiológica aos 30, 60, 90 e 120 dias e observou-se a incorporação do implante ao leito receptor, em 100% dos casos, mostrando ser biologicamente compatível, pois promoveu a reparação das falhas ósseas, sem sinais de infecção, migração e/ou rejeição, sendo uma opção de substituto para preencher defeitos ósseos.

The traumas that result in bone fractures, especially comminuted, have high importance in veterinary and human surgical routine. A 6mm of segmental defect was performed at the medial metaphyseal region of the left tibia of 12 rabbits and an association of fragmented heterologue mineralized bone matrix and methylmethacrylate conserved in glycerin (98%) was used as a graft to fill the bone defect. To evaluate the procedure morphological and radiological exams were performed after 30, 60, 90 and 120 days. There was gradual integration of the bone graft in the receptor bed in 100% of the cases showing that the material is biologically compatible as it promotes bone defect reparation without signs of infection, migration and/or rejection and can be considered one more option to be used as a substitute to fill bone defects.

Preconcentration and determination of methyl methacrylate by dispersive liquid-liquid microextraction.

This article describes the preconcentration of methyl methacrylate in produced water by the dispersive liquid-liquid microextraction using extraction solvents lighter than water followed by gas chromatography. In the present experiments, 0.4 mL dispersive solvent (ethanol) containing 15.0 µL extraction solvent (toluene) was rapidly injected into the samples and followed by centrifuging and direct injection into the gas chromatograph equipped with flame ionization detector. The parameters affecting the extraction efficiency were evaluated and optimized including toluene (as extraction solvent), ethanol (as dispersive solvent), 15 µL and 0.4 mL (as the volume of extraction and dispersive solvents, respectively), pH 7, 20% ionic strength, and extraction's temperature and time of 20°C and 10 min, respectively. Under the optimum conditions, the figures of merits were determined to be LOD = 10 µg/L, dynamic range = 20-180 µg/L, RSD = 11% (n = 6). The maximum recovery under the optimized condition was determined to be 79.4%.

Serum levels of methyl methacrylate following inhalational exposure to polymethylmethacrylate bone cement.

UNLABELLED: Teratogenic effects of polymethylmethacrylate cement at levels used during routine orthopaedic procedures have never been reported, however the hypothetical risk remains a major concern among female surgeons. Our aim was to determine if methyl methacrylate is detectible in the serum during routine cement exposure. METHODS: Twenty healthy volunteers were exposed during the mixing of polymethylmethacrylate cement in a simulated operating room environment. Forty serum samples were obtained during the expected peak inhalational exposure and levels of methyl methacrylate were assessed utilizing headspace gas chromatography mass spectrometry. RESULTS: Methyl methacrylate was not detected in any of the forty experimental specimens. CONCLUSIONS: With a detection level of 0.5 ppm, methyl methacrylate is undetectable in the serum during routine mixing of polymethylmethacrylate cement.

Experience with local lymph node assay performance standards using standard radioactivity and nonradioactive cell count measurements.

The local lymph node assay (LLNA) is the preferred test for identification of skin-sensitizing substances by measuring radioactive thymidine incorporation into the lymph node. To facilitate acceptance of nonradioactive variants, validation authorities have published harmonized minimum performance standards (PS) that the alternative endpoint assay must meet. In the present work, these standards were applied to a variant of the LLNA based on lymph node cell counts (LNCC) run in parallel as a control with the standard LLNA with radioactivity measurements, with threshold concentrations (EC3) being determined for the sensitizers. Of the 22 PS chemicals tested in this study, 21 yielded the same results from standard radioactivity and cell count measurements; only 2-mercaptobenzothiazole was positive by LLNA but negative by LNCC. Of the 16 PS positives, 15 were positive by LLNA and 14 by LNCC; methylmethacrylate was not identified as sensitizer by either of the measurements. Two of the six PS negatives tested negative in our study by both LLNA and LNCC. Of the four PS negatives which were positive in our study, chlorobenzene and methyl salicylate were tested at higher concentrations than the published PS, whereas the corresponding concentrations resulted in consistent negative results. Methylmethacrylate and nickel chloride tested positive within the concentration range used for the published PS. The results indicate cell counts and radioactive measurements are in good accordance within the same LLNA using the 22 PS test substances. Comparisons with the published PS results may, however, require balanced analysis rather than a simple checklist approach.

Effect of post-polymerization heat-treatments on degree of conversion, leaching residual MMA and in vitro cytotoxicity of autopolymerizing acrylic repair resin.

OBJECTIVES: This study evaluated the effect of post-polymerization heat-treatments on degree of conversion (DC), residual methyl methacrylate concentration (MMA(r)) and in vitro cytotoxicity of autopolymerizing acrylic repair resin. METHODS: A total of 336 specimens were prepared by bench- and hydroflask-curing and subjected to post-polymerization heat-treatments: a) water immersion at 60°C for 30 min, b) microwaving at 500 W for 3 min, c) combined use of water immersion and microwaving d) no treatment (as control). Specimens were eluted in cell culture medium for 1, 2, 5 and 7 days. DC and MMA(r) in eluates were measured by FTIR spectrometry and HPLC, respectively. In vitro cytotoxicity of eluates on L-929 fibroblasts was determined by XTT assay. Data were statistically analyzed with Dunn's multiple comparison and Pearson correlation tests (p≤0.05). RESULTS: DC was highest (99.9%) in bench- and hydroflask-cured groups which were subjected to water immersion. At all elution periods, MMA(r) was detected in eluates of all treatment groups and were higher in bench-cured groups than hydro-flask cured groups. Cell proliferation values indicated slightly cytotoxic effect throughout 7 days; regardless of the curing method or post-polymerization treatment. The correlation between MMA(r) and cell proliferation was negative after elution of 1, 2, 5 days and was only statistically significant (p<0.05) at 5 days. At elution of 7 days, the correlation was positive with no significance. SIGNIFICANCE: Post-polymerization heat-treatment of autopolymerizing acrylic repair resin by immersion in water at 60°C for 30 min is clinically recommended to improve the DC while reducing the leaching residual MMA.

[Monitoring of methyl methacrylate monomer released from autopolymerized denture base polymers during processing using time-of-flight mass spectrometer].

OBJECTIVE: To analyze the amount and tendency of methyl methacrylate (MMA) released from autopolymerized denture base polymer (self-curing resin) during processing using time-of-flight mass spectrometer (TOF-MS). METHODS: Self-curing resin was mixed in the container using a ratio of 2 g of powder to 1 g of liquid in accordance with the manufacturer's instructions for 40 s as a specimen. The amount of MMA released from the specimen was continuously monitored and simultaneously recorded every minute by TOF-MS since immediately after mixing. A total of five specimens were monitored. RESULTS: The amount of MMA increased dramatically at 11 min [(45.2 ± 3.5) mg/L] after mixing, and reached the highest level at 13 min [(228.9 ± 22.6) mg/L], then become stable at 23 min [(8.8 ± 2.3) mg/L] after mixing. CONCLUSIONS: The releasing tendency of MMA could be analyzed accurately with continuously monitoring during processing. The amount of MMA released from self-curing resin changed rapidly and the processing was complicated and changeful.

Characterizing workplace exposures in Vietnamese women working in California nail salons.

OBJECTIVES: We engaged Vietnamese nail salon workers in a community-based participatory research (CBPR) study to measure personal and area concentrations of solvents in their workplace. METHODS: We measured average work-shift concentrations of toluene, ethyl acetate, and isopropyl acetate among 80 workers from 20 salons using personal air monitors. We also collected area samples from 3 salons using summa canisters. RESULTS: For personal measurements, the arithmetic mean was 0.53 parts per million (range = 0.02-5.50) for ethyl acetate, 0.04 parts per million (range = 0.02-0.15) for isopropyl acetate, and 0.15 parts per million (range = 0.02-1.0) for toluene. Area measurements were lower in comparison, but we detected notable levels of methyl methacrylate, a compound long banned from nail products. Predictors of solvent levels included different forms of ventilation and whether the salon was located in an enclosed building. CONCLUSIONS: Using a CBPR approach that engaged community members in the research process contributed to the successful recruitment of salon workers. Measured levels of toluene, methyl methacrylate, and total volatile organic compounds were higher than recommended guidelines to prevent health symptoms such as headaches, irritations, and breathing problems, which were frequently reported in this workforce.

Effect of denture cleansers on chemical and mechanical behavior of selected soft lining materials.

OBJECTIVES: The aim of this investigation was to determine the effect of storage in disinfectants and artificial saliva on a series of commercial soft lining materials for dentures. Changes in mechanical properties and the nature of chemicals released into these solutions were studied. METHODS: Four soft lining materials were studied (Vertex Soft® and Villacryl Soft®, both of which are plasticized acrylics; Molloplast B® and Mollosil®, both of which are silicone elastomers). All were cured according to manufacturers' instructions, and then cylindrical specimens (6 mm height × 10 mm diameter) prepared. These were stored under various conditions then loaded in uniaxial compression and the stress measured at a strain corresponding to a 10% deformation to determine Young's modulus. Storage involved exposure either to the following disinfectants: 2% aqueous chlorhexidine gluconate, 2% aqueous sodium hypochlorite, Corega Tabs® cleansing tablets or 3% aqueous hydrogen peroxide; or to artificial saliva. For the latter, storage involved either immersion in artificial saliva at 37°C for the whole study, or immersion for 16h a day and dry at room temperature for the next 8h each day. GC/MS was used to determine species leached into these solutions. RESULTS: The acrylic materials Villacryl Soft and Vertex Soft became less elastic on storage for up to 28 days whereas the silicone materials Molloplast B and Mollosil, showed no change in elastic properties. Various compounds were found to be released from these materials, including EGDMA, methyl methacrylate and dibutyl phthalate. Generally, the silicones were more stable than acrylics, releasing smaller amounts of the various eluants. In all cases, amounts eluted were well below permitted exposure limits. SIGNIFICANCE: Practical denture cleansing agents affect the properties of soft lining materials, reducing their elastomeric character, acrylics being more adversely affected than the silicones. These changes are associated with the loss of various chemicals, including plasticizers and monomers, from the soft lining materials.

[Residual monomer content determination in some acrylic denture base materials and possibilities of its reduction].

BACKGROUND/AIM: Polymethyl methacrylate is used for producing a denture basis. It is a material made by the polymerization process of methyl methacrylate. Despite of the polymerization type, there is a certain amount of free methyl methacrylate (residual monomer) incorporated in the denture, which can cause irritation of the oral mucosa. The aim of this study was to determine the amount of residual monomer in four different denture base acrylic resins by liquid chromatography and the possibility of its reduction. METHODS: After the polymerization, a postpolymerization treatment was performed in three different ways: in boiling water for thirty minutes, with 500 W microwaves for three minutes and in steam bath at 22 degrees C for one to thirty days. RESULTS: The obtained results showed that the amount of residual monomer is significantly higher in cold polymerizing acrylates (9.1-11%). The amount of residual monomer after hot polymerization was in the tolerance range (0.59-0.86%). CONCLUSION: The obtained results denote a low content of residual monomer in the samples which have undergone postpolymerization treatment. A lower percent of residual monomer is established in samples undergone a hot polymerization.

Potential dermal exposure to methyl methacrylate among dental technicians; variability and determinants in a field study.

Methyl methacrylate (MMA) is a commonly used chemical in dental work that can cause dermatitis. Nineteen dental technicians participated in a field study in which potential dermal exposure to MMA and exposure determinants, including glove use and MMA vapour in the breathing zone, were repeatedly monitored during three consecutive days. Using patches placed on various parts of their hands we observed that the fingers and palms of the dental technicians were exposed to MMA, and their forefingers were significantly more exposed than their ring fingers; this is based on pooled data for both left and right hands (p = 0.04). The exposure variability was greater between workers than within worker (i.e. day-to-day variability), but the between worker variability was to some extent explained by a model which included the tested determinants. Neither the amount of MMA vapours in the breathing zone nor glove use was consistently correlated with the dermal exposure. Thus, the effects of glove use and the distribution of exposure to MMA on the hands in working environments needs to be further investigated.

Groundwater derived arsenic in high carbonate wetland soils: sources, sinks, and mobility.

Wetlands and organic soils have been recognized as important sinks for arsenic in the environment, yet sources and immobilization mechanisms of As are often unclear. To begin rectifying this deficiency, we investigated As retention and binding mechanisms at a degraded, minerotrophic wetland site in contact with groundwater rich in As and Fe. Arsenic occurred in high dissolved concentrations of up to 467 microg L(-1) in the groundwater, but dropped to values below 10 microg L(-1) towards the surface. The solid phase As content instead was high in the topsoil with up to 3400 mg kg(-1) and decreased with depth to 15 mg kg(-1). A similar pattern was observed with respect to Fe. Amorphous and crystalline iron precipitates were the main sorbents for arsenic in the soil horizons according to results from wet chemical sequential extractions. Arsenic was apparently not associated with inorganic carbon phases, but a substantial portion of up to 31% of As(tot) could be mobilized by dispersion of soil organic matter. Ratios of dissolved As(III)/As(V) decreased from the deeper As(III) dominated groundwater to the As(V) dominated soil porewaters, where As was apparently immobilized in its oxidized form. Concentrations of the organic species DMA and MMA were negligible. According to the results of simple one-dimensional estimates the vertical arsenic transport from the source in the groundwater to the topsoil was slow given an extrapolation of current conditions. These results suggest that As accumulation started before the beginning of drainage in the now degraded peatland soils and the degradation and mass loss of organic matter under oxic conditions caused the very high As concentrations found in the topsoil horizon today.